Experimental Study on Nuclear Power Plant Operators’ Performance during a Major Earthquake with Aftershocks

Experimental Study on Nuclear Power Plant Operators’ Performance during a Major Earthquake with Aftershocks | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Experimental Study on Nuclear Power Plant Operators’ Performance during a Major Earthquake with Aftershocks Ayako Hirose, Kohei Nonose, Daisuke Takeda This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4221596/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Experiments were conducted to clarify the effects of seismic motion and aftershocks on the performance and physiological and psychological states of nuclear power plant operators. Nine reactor operators (average experience: 5.2 years) responded to various events associated with a great earthquake using a virtual reality simulator that simulated the main control room and plant behavior and a chair-type earthquake simulator. The experimental conditions were the presence and absence of vibrations. For each condition, the differences in the following indices were analyzed: The errors and utterances made during plant response were performance indices; cardiac sympathetic index, cardiac vagal index, and skin conductance level were physiological indices; and responses to a questionnaire on stress were psychological indices. Results revealed that operators experienced transient physiological stress at the time of the main shock, and felt the seismic motion’s effects on plant operations, such as “delay in initial response” and “disruption of priorities,” which did not seem threatening. They did not perceive any impact on performance. For aftershocks, it was found that the motion of the aftershocks themselves had almost no effect on the operators, but that the presence of aftershocks increased omission errors for events occurring immediately before the aftershocks, and that “work interruption” and “changes in plant conditions” due to aftershocks had affected them. Adding a seismic vibration experience using a simulated environment to regular training will contribute to the collection of performance data for operators and improve operators’ preparedness for earthquakes. Earthquake Main shock Aftershock Nuclear power plant Virtual reality Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1 Introduction Major earthquakes significantly affect nuclear power plants (NPPs), as evidenced by the accident at the Fukushima Daiichi Nuclear Power Station of Tokyo Electric Power Company (Fukushima accident) caused by the Great East Japan Earthquake in March 11, 2011. Since Japan is an earthquake-prone country, it is anticipated it will continue to experience major earthquakes that could cause significant damage (Hok et al. 2011 ; Hyodo et al. 2016 ). When major earthquakes occur, nuclear reactors generally shut down automatically. However, operators must possess steady judgment to handle the malfunctions and defects resulting from earthquakes and to safely bring the reactor to cold shutdown (Shibata and Takada 1995 ; Yokobayashi et al. 2002 ). To prevent erroneous judgments that aggravate disaster situations, as happened previously at Three Mile Island (Jang et al. 2016 ) and Chernobyl (Salge and Milling 2006 ), operators regularly train using training simulators to respond steadily and appropriately during major earthquakes. However, since the earthquake response training is reproduced only by the interruption of operations for a certain period, it is not possible to reproduce the earthquakes’ characteristics, such as sudden shaking. Therefore, it remains uncertain whether all operators, particularly those who have never previously experienced a major earthquake, can respond in the same way to a real earthquake as they respond in training. In the Fukushima accident, despite the occurrence of an unprecedentedly strong main shock and repeated aftershocks, there was no evidence of operator error or significantly delayed operator actions in the main control room (MCR) during the first 40 minutes before the tsunami hit (Electric Power Research Institute 2016 ). However, because major earthquakes, such as the Great East Japan Earthquake, occur rarely, it is difficult to exhaustively extract human performance–related problems during an earthquake from a single disaster (Park et al. 2015 ). If trends in human performance during earthquakes can be ascertained from the data obtained by simulating earthquake environments, we can identify new problems that cannot be extracted from routine trainings or a small number of cases. Reflecting these data in education and training, procedural revisions, and facility improvements will increase operator reliability during earthquakes. Several studies have investigated the impact of earthquakes on operator performance by setting up a simple simulated operation panel on a shaking table (Shibata 1987 ; Kitada et al. 1994 ; Park et al. 2018 ; Kim et al. 2019 ; Yokobayashi et al. 2002 ). Shibata ( 1987 ) set up a cathode ray tube (CRT) and keyboard on a shaking table and conducted an experiment in which subjects typed in the letters appearing on the CRT during vibration. Although the error rate increased above 0.4 G (390 Gal), their cognition and judgment, such as mental arithmetic and judging the magnitude of numbers, were hardly affected by the seismic motion’s magnitude. Similarly, Kitada et al. ( 1994 ) established a simulated console and CRT on a shaking table for NPP operators to respond to earthquake events. Results indicated that the seismic motion’s magnitude had almost no influence on the operators’ performance. However, these experiments were conducted while varying the seismic motion’s magnitude and, hence, were criticized for not simulating the psychological difficulties arising from the “suddenness” characteristic of earthquakes (Shibata and Takada 1995 ). Subsequently, Park et al. ( 2018 ) and Kim et al. ( 2019 ) conducted experiments with students by simulating accident response at an NPP using a shaking table. To maintain the suddenness of the event, the students were not informed of seismic motion occurrence. In these experiments, no differences were found in the accuracy or speed of accident diagnosis or in relevant physiological and psychological indices depending on the seismic motion’s magnitude. The shaking table experiments suggest that the seismic motion itself may not significantly affect operators’ performance. However, the aforementioned studies focus solely on operators’ performance during or immediately after the so-called main shock and do not consider the response to simultaneous equipment failure caused by the earthquake’s occurrence, or repeated aftershocks. Only a few studies have experimentally examined aftershocks’ effects on operator performance. Contrastingly, a number of literatures highlight the effects of aftershocks (Human-Machine Systems Research Subcommittee in Atomic Energy Society of Japan et al. 2015; IAEA 2015; Liu and Hwang 2014 ; Shibata and Takada 1995 ; The National Diet of Japan 2012 ; Yokobayashi et al. 2002 ; Yamaguchi 2021 ). In addition, every accident investigation report on the Fukushima accident described the adverse effects of aftershocks and accompanying interruption of operations, as follows: “Recovery tasks were further interrupted as workers reacted to the intermittent and significant aftershocks and tsunami” (The National Diet of Japan 2012 , p. 14); “Aftershock was still continuing, prompting evacuation each time, and preventing the preparation from progressing” (Yamaguchi 2021 , p. 110); “Until 15:25, before the second tsunami wave hit, six aftershocks with a seismic intensity of 4 or more were recorded in succession. It can be inferred that the psychological tension and anxiety of the operators were great” (Human-Machine Systems Research Subcommittee in Atomic Energy Society of Japan et al. 2015, p. 10–11). To obtain data on operators’ performance during earthquakes, it is necessary to reproduce situations that may occur during a major earthquake, such as sudden occurrence, simultaneous equipment failures, and repeated aftershocks. However, arranging a control panel’s mockup on a shaking table is expensive and fraught with challenges, such as ensuring participants’ safety and preventing vibration-related damage to the control panel. Therefore, in the current study, virtual reality (VR) technology was adopted to create an MCR. Today, VR is widely adopted in various industries for training and other purposes because it enables people to safely and realistically experience disasters and emergencies (Bergroth et al. 2018 ; Engelbrecht et al. 2019 ; Patle et al. 2019 ; Xu et al. 2018 ). Many VRs have been developed to simulate earthquakes (Fenz et al. 2020; Lovreglio et al. 2018 ; Sinha et al. 2012 ; Ting 2017 ). However, since the main purpose of using VRs to simulate earthquakes is disaster prevention, most of them enable users to experience seismic motions visually and audibly with the tipping over of bookshelves and cupboards, without creating actual vibrations (Fenz et al. 2020; Sinha et al. 2012 ; Ting 2017 ). However, in this study, since the targeted MCR was designed so that nothing tipped over, it was not sufficient to use only the audiovisual sensory experiences of earthquakes. Accordingly, this study used a safe chair-type earthquake simulator (Adachi 2010; Kuroda et al. 2012 ; Lovreglio et al. 2018 ). In an earlier study using non-professionals, Hirose et al. ( 2021 ) conducted an experimental study using a VR-simulated NPP MCR and the above earthquake simulator. This study clarifies the effects of seismic motion and aftershocks on operators’ physiological and psychological states and performance based on the aforementioned experiment conducted by Hirose et al. ( 2021 ). 2. Methods 2.1 Equipment To ensure participants’ safety in this study, we used the “Jishin The Vuton” (Adachi 2010: Kuroda et al. 2012 ), a chair-type earthquake simulator developed by Hakusan Corporation (Fuchu, Japan). The simulator can reproduce past seismic motions, except vertical motion and allow adjustment of the earthquakes’ magnitude and duration. In addition, the MCR was simulated by a VR plant simulator system developed by Hitachi GE Nuclear Energy, Ltd. (Hitachi, Japan). The system comprised an MCR of an advanced boiling water reactor (ABWR) in a virtual environment (Fig. 1 ) and a simulator to simulate several emergency events, such as alarms and parameters, similar to the ones in a real plant. Additionally, the simulator reflected an operator’s actions. The MCR in the virtual environment simulated a large display panel, an operator’s desk, a shift manager’s desk, and some main control boards with an operation console. However, due to the limitations of the head-mounted display (HMD) technology, the operation was performed by the experimenter using a personal computer (PC), and participants only called out the operation they wanted to perform (e.g., “Startup RHR Pump B”). Unlike in the actual plant, the PC’s specifications did not allow the display to change as it would if the participant was using the operation control panel on the main control board; therefore, nine parameter display screens were prepared in advance. Among them, four were displayed on the main board in advance and could be changed at the participants’ request. 2.2 Participants In our experiment, nine healthy ABWR-type reactor operators (all qualified personnel) from a single NPP participated. All were men, with a mean age of 34.7 years (age range: 26–42 years). Their average years of experience as reactor operators was 5.2 years (from < 1 year to 16 years). All the participants were volunteers and had never experienced an earthquake of more than a seismic intensity of 6. This study was approved by the Nuclear Risk Research Center’s Research Ethics Review Committee in the Central Research Institute of Electric Power Industry (O2022003). All participants provided informed consent. 2.3 Experimental conditions Two conditions were specified: In one condition, the occurrence of an earthquake >[1] was notified verbally (i.e., the no vibration condition) and, in the other, notification was provided by vibrating the earthquake simulator (i.e., the with vibration condition). These conditions were tested on all participants. Considering that the increase in heart rate caused by vibration would subside at different rates, all the participants experienced the no vibration condition first and then the with vibration condition. 2.4 Experimental scenario While working as reactor operators, participants took appropriate actions for each event according to the experimental scenario, as presented in Table 1 . Specifically, they examined the numerical values of the large display panel or main board, declared what operations were needed, made requests to other operators, and reported the results of their responses to the sub-shift manager who oversaw plant operation. Although the operations were performed by a team, the VR plant simulator had the limitation that only one person could experience the environment at a time. Hence, to compensate, and create an immersive experience, two experienced but nonparticipating NPP operators played the roles of the sub-shift manager and other operators by giving instructions to the participants regarding instrument checks and operations and responding to the participants’ requests. They followed the relevant scripts that had been prepared in advance according to Table 1 . However, the participants’ unscripted comments were managed in a more flexible manner. The scenario was devised with the cooperation of four NPP operators and a plant manufacturer. It comprised three major phases: the main shock, first aftershock, and second aftershock. Each phase started with the sounding of an earthquake early warning, and new events were generated sequentially with the seismic motion. Although the two experimental conditions indicated the same scenario, the high reactor internal pump (RIP) motor vibration in the main shock phase (event no. 2 in Table 1 ) was used only in the with vibration condition, to prevent participants from recognizing they were the same scenario from the beginning. Table 1 Experimental Scenario Phase Event no. Contents of events Required response Main shock 1 Main shock 1) Check & report: plant parameters 2 High RIP motor vibration 1) Report: RIP alarm 2) Report: level of RIP motor vibration First aftershock 3 First aftershock Loss of off-site power Failure of reactor scram 1) Report: failure of reactor scram 2) Operations: treatments of ATWS(Reactor mode switch shutdown, manual ARI operation, manual scram operation) 3) Check & report: plant parameters 4) Check & report: RCIC startup 4 High turbine vibration 1) Operation: close MSIV 2) Operation: RHR startup(S/C cooling) 5 Flooding of fuel pool 1) Request: check the ITV # 2) Report: result of the ITV check # 3) Check & report: FPC pump operating status # 6 Injured person 1) Response: paging from injured person 2) Report: occurrence of injury to person # Second aftershock 7 Second aftershock RCIC trip 1) Check & report: plant parameters 2) Report: tripping of RCIC 3) Operation: HPCF(B) startup 8 Opening of blowout panel 1) Check & report: SGTS(R/B negative pressure) abnormality Event no. 2 was conducted only under the with vibration condition. # These responses were conducted in the second aftershock phase. RIP reactor internal pump, ATWS anticipated transient without scram, ARI alternate rod insertion, RCIC reactor core isolation cooling system, MSIV main steam isolation valve, RHR residual heat removal system, S/C suppression chamber, ITV industrial television, FPC fuel pool cooling and filtering system, HPCF high-pressure core flooder system, SGTS stand-by gas treatment system, R/B reactor building For the main shock and first aftershock phases, the earthquake early warning was sounded at the following time points, and one phase shifted to the next. In the second aftershock phase, each condition was terminated at the following time points: Main shock phase: Immediately after the sub-shift manager instructed the participants about the reactor scram (2 min after the experiment’s initiation in the no vibration condition) First aftershock phase: Immediately after the other operator (injured person) called for assistance Second aftershock phase: Participants reported their response to event no. 8 (Table 1 ) 2.5 Seismic motions In addition to the main shock, two aftershocks were interspersed at short intervals with reference to the report from the Great East Japan Earthquake that “a total of three aftershocks including two of seismic intensity 4 occurred in the 10 minutes immediately after the main shock” (Human-Machine Systems Research Subcommittee in Atomic Energy Society of Japan et al. 2015, p. 17). The duration of each seismic motion was 30 s. The first 10 s produced only the earthquake early warning sound, whereas the remaining 20 s produced vibrations. In the no vibration condition, the earthquake early warning sound alone was generated for 30 s. In the experiment, seismic motions were reproduced from past earthquakes. After consulting an earthquake expert, the following earthquake motions were selected as ones that could be clearly experienced, even when wearing HMDs. Main shock Place of occurrence: Mashiki Town (Kumamoto Prefecture) Date and time of occurrence: 04/14/2016 at 21:26 Seismic intensity: 7 (magnitude: 6.5) Maximum acceleration: 708 Gal First aftershock Place of occurrence: Mashiki Town (Kumamoto Prefecture) Date of occurrence: 04/16/2016 at 01:25 Seismic intensity: 7 (magnitude: 7.3) Maximum acceleration: 730 Gal Second aftershock Place of occurrence: Nishihara Village (Kumamoto Prefecture) Date of occurrence: 04/16/2016 at 01:25 Seismic intensity: 7 (magnitude: 7.3) Maximum acceleration: 755 Gal Participants were instructed in advance of the possibility that seismic motion occurring and were requested to fasten their seatbelts when seated and to keep their hands on the bar next to their chairs during the experiment. Further, they were told that, in both conditions, the sub-shift manager would give the command “Earthquake, ensuring safety” in the event of an earthquake and prohibit all operations to ensure the participants’ personal safety. 2.6 Procedure After being briefed on the experiment and providing consent to participate in the study, participants were seated on “Jishin The Vuton” and fitted with physiological index sensors. For baseline measurement, they remained in a resting state with their eyes open for 3 min. Subsequently, they were fitted with an HMD (HP Reverb) and asked to perform plant operations as the reactor’s operator, as described in Section 2.4 . To familiarize the participants with responding in VR, a trial comprising events for which they had been well trained was conducted. Further, as described in Section 2.3 , the participants responded to the plant without and with vibrations, in that order. At the end of each condition, the participants removed their HMDs and responded to psychological indices, as described in Section 2.7.3 . Following the completion of all experimental conditions, the participants were interviewed about the experiment. To prevent VR sickness, the participants were not allowed to move around in the simulated environment. A speaker placed in front of the participants output the earthquake early warning sound and various other warning sounds generated by the plant. Additionally, a screen set up at the front of the laboratory enabled experimenters to see the images experienced by participants. Further, two video cameras were placed with the participants’ permission to measure their responses to the scenarios. Figure 2 depicts the experiment’s arrangement. 2.7 Measures To assess participants’ responses to the scenario, we measured the presence or absence of responses to each event against the “required response,” as described in Table 1 . The participants’ utterances were captured verbatim using video recordings. Additionally, physiological and psychological data were captured to evaluate the stress levels caused by the seismic motion. 2.7.1 Performance measures (1) Number of errors In this study, errors were specifically defined as failures to respond to “required responses,” which included omissions of checks, reports, or operations, and responses involving unnecessary operations. Further, the following were calculated: a) the number of errors associated with each event and b) The cumulative number of errors across all events. However, the analysis did not include event no. 2 in Table 1 because it was conducted exclusively under the with vibration condition. (2) Number of utterances The study captured utterances other than the required responses assumed in Table 1 . Therefore, participants’ verbatim utterances were classified into the following three categories: a) Normal utterances “Required responses (such as check, operation, etc.)” and other responses (e.g., checking of various parameters associated with the reactor scram, such as drywell temperature, pressure, and reactor containment isolation system status, etc.). b) Spontaneous utterances Spontaneous operations by participants prior to instructions from the sub-shift manager or spontaneous requests to other operators not made through the sub-shift manager (e.g., requests regarding ATWS treatments made to an auxiliary equipment operator to check an ITV, etc., including necessary responses). c) Repetitions The repetition of instructions or announcements by the sub-shift manager or other operators using three-way communication (e.g., “Close the MSIV valve, right?”). The total number of utterances and repetitions of a) to c) were calculated by event and for all events. 2.7.2 Physiological measures The heart rate (R-R interval) and skin conductance level (SCL), which is a slow stimulation-induced variation of the skin’s electrical activity, were measured as physiological indices of tension and stress during plant operations. Wearable biometric signal measurement platforms (Biosignalsplux by Plux) were used to measure physiological indices. The output waveforms were AD-converted by the sensor box (sampling frequency: 500 Hz; resolution: 16 bit), sent to the data measurement application software (OpenSignals by Plux) in real time through Bluetooth, and recorded on a PC. Lorenz plots were used for the R-R interval (Toichi et al. 1997 ; Toichi et al. 1998 ; Nose et al. 2022 ) since they measure tension and stress without requiring controlled respiration and can be analyzed in the short term. After removing obvious outliers, such as R-R intervals less than 400 ms or greater than 2000 ms or values greater than 20% of the mean of the preceding and following 20 beats, Lorenz plots were generated per unit time, as described below. The cardiac sympathetic index (CSI), an index of sympathetic activity, and the cardiac vagal index (CVI), an index of parasympathetic activity, were calculated (Toichi et al. 1997 ; Toichi et al. 1998 ; Sato et al. 2020 ). The CSI value is known to be higher in tense/stressful situations, whereas that of CVI is higher in relaxed states (Toichi et al. 1997 ; Toichi et al. 1998 ; Nose et al. 2022 ). To measure SCL, the average value per unit time was calculated. To remove individual differences, the mean and standard deviation (SD) of each participant’s baseline data were used and standardized such that mean = 0 and variance = 1. To further examine the physiological effects of vibration during the scenario, the aforementioned values were calculated for each phase. Since it was assumed that physiological states would differ across significant events, such as ATWS, and individuals would respond to the events at different speeds, the data were divided into two or three parts within the same phase as the events progressed, as follows: Main shock phase: (1) From the beginning to the end of the main shock. (2) At the end of (1) to the start of the first aftershock. First aftershock phase: (1) From the beginning to the end of the first aftershock. (2) From the end of (1) until the sub-shift manager repeats participants’ report on the insertion of all control rods (completion of the ATWS treatment). (3) From the end of (2) to the start of the second aftershock. Second aftershock phase: (1) From the beginning to the end of the second aftershock. (2) From the end of (1) until the sub-shift manager repeats participants’ report on injuries and High-Pressure Core Flooder System startup. (3) From the end of (2) to the end of the phase. 2.7.3 Psychological measures To measure the transient tension and anxiety resulting from an earthquake, 14 items from the Phasic Stress Scale (HQL 2000; Suzuki et al. 1999 ), including the five factors Languor,” “Comfort,” “Anxiety/Uneasiness,” “Tension,” and “Overall Stress Level,” were used as psychological indices. Additionally, participants were asked about “experiencing hesitation in judgment” and “degree of difficulty” during plant operation. At the end of each condition, the participants had to assess their mood using a visual analog scale by marking a point on the number line between “not at all” (0 point, left end) and “very much” (100 points, right end). Further, the line’s length from the left end to the mark was measured. After each item was rated, they were scored against the average rating of the items belonging to each factor (HQL 2000). 2.8 Statistical analysis Data analysis was performed using SPSS software version 27.0. A significance level of less than 5% was considered significant. To assess the impact of seismic motion all analyses included inter-condition comparisons. 2.8.1 Performance indices For each index listed in Section 2.7.1 , the following inter-conditional comparisons were conducted. Since the data for these indices (i.e., errors, normal utterances, spontaneous utterances, and repetitions) did not follow a normal distribution for each event, Wilcoxon’s signed-rank test was applied to each index. Further, once the normality of data distribution for each index for all events was confirmed, a corresponding t-test was conducted. 2.8.2 Physiological indices For each physiological index, repeated-measures analyses of variance (ANOVAs) for two factors (condition × elapsed time within a phase) were performed to compare the conditions for each phase. Before performing ANOVAs, Mauchly's sphericity test was conducted. If the assumption of sphericity did not hold, the ANOVAs degrees of freedom were adjusted using Huynh–Feldt’s ε. If a significant main effect was identified, Bonferroni’s multiple comparisons were performed. For SCL, one participant with incomplete data was excluded from the analysis. 2.8.3 Psychological indices Psychological indices also had outliers and the data did not satisfy the normality assumption for the indices. Hence, a Wilcoxon signed-rank test was conducted for each index. 3. Results 3.1 Performance indices 3.1.1 Number of errors Table 2 depicts the contents and numbers of observed errors. The analysis revealed that for all events, the number of errors did not differ according to the presence or absence of vibrations (Table 2 ). Further, no significant differences were observed in the total number of errors (Table 3 ). Regardless of the presence or absence of vibration, the largest number of errors occurred during event no. 5, the “flooding of the fuel pool” (Table 2 ). Table 2 Numbers and descriptions of errors by event Event no. Number of errors Z p Contents of errors No vibration With vibration 1 0 2 -1.410 0.500 No report of plant parameters 3 1 2 -1.000 1.000 No report of plant parameters 4 0 0 - - - 5 9 10 -0.136 1.000 No request for checking the ITV No report of result of the ITV check No report of FPC pump operating status 6 1 1 0.000 1.000 No report of occurrence of injured person 7 5 3 -1.410 0.500 No report of plant parameters No report of RCIC trip & HPCF(B) startup 8 4 2 -1.410 0.500 No report of SGTS abnormality Incorrect shutdown of a SGTS Sum 22 22 See Table 1 for abbreviations (e.g. ITV, FPC, etc.) Table 3 Average values of the total number for each performance index Total number No vibration With vibration t p Mean SD Mean SD Errors 2.560 1.878 2.560 2.242 0.000 1.000 Normal utterances 21.444 5.199 20.444 3.395 1.095 0.305 Spontaneous utterances 4.667 2.550 6.444 2.186 -4.097 0.003 Repetitions 5.556 0.882 5.889 2.088 -0.603 0.563 3.1.2 Number of utterances Table 4 depicts the median and interquartile range of the observed number of normal utterances, spontaneous utterances, and repetitions by event. Analysis revealed no difference in the number of utterances or repetitions in all events with or without the presence of vibration (Table 4). However, the analysis revealed that the total number of spontaneous utterances was significant and that it increased with the vibration condition (Table 3). Table 4 Median and interquartile ranges of the number of utterances by event Event no. Normal utterances Spontaneous utterances Repetitions No vibration With vibration Z p No vibration With vibration Z p No vibration With vibration Z p 1 2 (2–3) 2 (1–2) 0.952 0.438 0 (0–0) 0 (0–0) - - 1 (0–2) 0 (0–1) 1.633 0.250 3 10 (8–15) 10 (9–11) 0.530 0.719 2 (0–3) 3 (2–4) -2.060 0.063 1 (1–1) 1 (1–2) -1.414 0.313 4 3 (2–3) 2 (1–3) -1.857 0.125 1 (1–3) 2 (1–3) 1.732 0.250 0 (0–1) 0 (0–2) 0.816 0.750 5 2 (1–3) 1 (1–3) -0.531 0.688 0 (0–0) 0 (0–1) 1.414 0.500 1 (0–2) 1 (0–1) -0.378 1.000 6 1 (1–1) 1 (1–2) 1.732 0.250 0 (0–0) 0 (0–0) - - 1 (0–1) 1 (1–1) 1.414 0.500 7 3 (1–4) 3 (2–5) 2.121 0.063 1 (1–1) 1 (1–1) 0.000 1.000 2 (1–2) 2 (1–3) 0.816 0.688 8 1 (0–2) 1 (0–3) 0.276 1.000 0 (0–1) 0 (0–1) -0.577 1.000 0 (0–1) 0 (0–0) -1.414 0.500 The data in parentheses indicate the interquartile range 3.2 Physiological indices 3.2.1 Skin conductance level Figure 3 depicts the trends with elapsed times for the SCL. Analysis revealed that the main effect of a condition was significant in the main shock phase ( F (1, 7) = 11.551, p < .05, ηp 2 = .623). Further, the main effect of elapsed time was significant in all phases (the main shock phase: F (1, 7) = 6.525, p < .05, ηp 2 = .482, the first aftershock phase: F (2, 12) = 9.872, p < .01, ηp 2 = .622, the second aftershock phase: F (1.211, 8.475) = 4.936, p no vibration ( p (2) (before the first aftershock) ( p (3) (before the second aftershock) ( p < .05) in the first aftershock phase. The results for the second aftershock phase were not statistically significant. In the main shock phase, SCL was higher in the with vibration condition than the no vibration condition; however, there was no difference in SCL between the two conditions after the first aftershock. Regarding elapsed time, SCL was low at the end of the main shock and first aftershock phases. No interactions were observed in any of the phases. 3.2.2 Cardiac sympathetic index Figure 4 depicts the trends with elapsed time for the CSI. Analysis revealed that elapsed time’s main effect on CSI, a measure of the sympathetic nervous system, was significant in the first aftershock phase ( F (2, 16) = 7.515, p < .01, ηp 2 = .484). Multiple comparisons showed higher values ( p < .01) for (2) (until all the control rods were inserted) than (1) (at the onset of the first aftershock). That was, CSI increased at the time of ATWS response after the first aftershock, regardless of the presence or absence of vibration. 3.2.3 Cardiac vagal index Figure 5 depicts the CVI trends with elapsed time. Analysis revealed no statistical difference in CVI, a measure of the parasympathetic nervous system, in any phase. 3.3 Psychological indices The analysis revealed no difference between the presence and absence of vibration in any factor, including hesitation in judgment and degree of difficulty (Table 5 ). Table 5 Median and interquartile range of each psychological index Factor No vibration With vibration Z p Languor 29 ( 2–59) 37 ( 5–58) -0.178 0.910 Comfort 13 ( 1–49) 4 ( 1–41) 0.840 0.461 Anxiety/Uneasiness 13 ( 0–48) 16 ( 0–48) -0.889 0.406 Tension 55 (27–67) 68 (17–83) -1.126 0.289 Overall stress level 29 (11–68) 63 (15–66) -0.772 0.500 Hesitation in judgment 20 (10–59) 30 ( 1–71) -1.245 0.238 Degree of difficulty 32 (17–54) 37 (21–57) -0.777 0.469 The data in parentheses indicate the interquartile range 3.4 Interviews Subsections describe participants’ interviews after the experiment. 3.4.1 Sense of reality and immersion Eight of the nine participants mentioned experiencing a sense of reality in the VR environment. When asked whether they could immerse themselves in the plant’s response, five answered they could, two felt that they could do so fairly well, and two expressed being unable to do so well. The respondents’ reasons for not able to do so well were “it was stressful not being able to see the display screen I wanted to see” and “I couldn’t feel the tension because it was a one-person training.” 3.4.2 Seismic motion’s impact on plant response Five of the nine participants clarified seismic motion’s impact on plant response. Further, six participants indicated that carrying out the plant responses with seismic motion (like this time) was more difficult than the usual earthquake response using a training simulator. The following were cited as the specific effects of the occurrence of vibration: - In the case of no vibration, I was able to organize my thoughts regarding plant response while ensuring personal safety during earthquake; but it was not possible in the case of vibration. So, I was not able to clarify what I should do thereafter. - Could not operate it while it was vibrating; so, what I wanted to do was delayed. - It took time to grasp the situation and detect anomalies and the first response was delayed, because the viewpoint was not fixed due to the vibration and all the parameters had changed when I looked up. - The earthquake cause confusion about how to prioritize. - I got nervous when it shook. I could not think straight when I had to worry about various things, such as parameters. - There was no difference in the plant’s response; but I felt psychologically uneasy when it shook (two people answered similarly). - The one with vibration was more realistic. I felt that I needed to check a wider range of parameters. These results indicate that participants experienced “disorganized thinking,” “delayed actions,” “disorganized priorities,” and “tension/anxiety” following seismic motion. Some participants felt a strong sense of reality due to feeling the vibration. However, only three participants answered that they felt threatened by the seismic motion. 3.4.3 Effects of aftershocks on plant response Six of the nine participants answered that aftershocks had an impact on plant response. They cited the following specific effects of aftershocks: - It was stressful that the aftershocks occurred when I was trying to do something. - The time gap indicated that the priorities given by the sub-shift manager were not being followed. - It was difficult to decide whether to give priority to dealing with injuries that occurred just before the aftershock or to dealing with the plant (two people answered similarly). - I had to hold my hands until the shaking subsided; so, I forgot what I was supposed to do. - The burden of plant reconfirmation was heavy because the main parameters changed due to the aftershocks. - I felt that I would forget the parameters I had checked and the operations I had planned, because they would be reset by the vibration. - I thought that the aftershocks would confuse my thoughts. - I was worried about the aftershocks affecting the water level and the places that held water (water intake tanks, etc.). These results indicate that participants experienced work interruption due to the aftershocks, resulting in concerns about forgetting what was handled and “burden and confusion due to changes in the plant situation.” 3.4.4 Differences in the effects of main shock and aftershocks Participants’ responses to whether the main shock or aftershocks had a greater impact on plant response and psychological aspects were divided nearly by half. The reasons for each answer were as follows: Main shock (answered by four participants) - The impact on psychological aspect was significant because we did not know when it would occur. - Because it occurred when the plant was running (two persons answered similarly). - It was difficult to move (if there was a real aftershock, I would operate the plant even if it was shaking). Aftershock (answered by five participants) - As in this case, when an event progressed due to aftershocks (or a new event started), it was incredibly stressful (two people answered similarly). - While rechecking values, it was necessary to carefully find any differences. - The main shock was considered a loss of off-site power and reactor scram; but, in aftershocks, it was difficult to detect anomalies without following the system, which was unpleasant. - Since I was already in the process of dealing with the plant, there was a great deal of psychological distress. Participants who responded it was the main shock cited concerns about the suddenness of earthquake occurrence and the fact that the plant was in operation. However, those who responded that it was the aftershocks were concerned about changes in plant conditions (the development of events and occurrence of new events). 4. Discussion 4.1 Effects of seismic motion on operators’ states and performance This study examined the effects of seismic motion on NPP operators’ physiological and psychological states and performance. Results revealed that vibration resulted in almost no differences in performance and psychological indices, such as the number of errors and utterances. However, among physiological indices, SCL was higher in the main shock phase than in the no vibration condition, indicating that seismic motion affected operators’ states only in the main shock phase. However, there was no difference in heart rate between the conditions. Approximately half of the post-experiment interview participants mentioned seismic motion’s impact on plant response. However, only three participants felt threatened by it. The study revealed that seismic motion had physiological effects on operators at the time of the main shock; it caused disorganized thinking and priorities, delayed reactions, tension and anxiety, but was not felt as threatening. Similar to earlier studies (Shibata 1987; Kitada et al. 1994; Park et al. 2018; Kim et al. 2019), the current study found that seismic motion by itself did not affect performance, for instance, by causing an increase in errors. In the current study, participants responded to multiple events that could occur during a major earthquake; hence, this study was more challenging than earlier studies that used shaking table experiments (Shibata 1987; Kitada et al. 1994; Park et al. 2018; Kim et al. 2019). Furthermore, the seismic intensity considered in the current study’s experiment was 7, which is the same as that of great earthquakes that have occurred in Japan. In other words, the seismic motion by itself had almost no effect on operators’ performance, even when the earthquake’s magnitude and the task’s difficulty were increased. Further, the Electric Power Research Institute (2016), which reviewed operating experience during earthquakes in nuclear and non-nuclear industries, concluded that although there were only a limited number of examples, operator behavior generally remained reliable regardless of earthquakes’ magnitude. Regarding the effect of seismic motion on operator performance, only SCL increased during the main shock (Fig. 3) when emotional stress or arousal level was high (Hassett 1978; Andreassi 1980). The increase in SCL during the main shock phase may be attributed to an increase in arousal level and emotional stress caused by the unexpected occurrence of seismic motion resulting in surprise and anxiety. However, in the latter half of the phase, SCL decreased, suggesting that the vibration’s physiological effect was transient. This is consistent with the perspective that the effect of vibration (acceleration) is short term (Amico et al. 2011) and with the findings of Hirose et al. (2021). Furthermore, no condition-based differences were observed after the first aftershock phase, which suggests that the surprise and arousal related to aftershocks were weaker than those related to the main shock. However, the main effect of elapsed time on the CSI was observed in the first aftershock. Further, regardless of the presence or absence of vibration, the CSI was higher after, rather than at the onset of, the first aftershock (Fig. 4). Although the values were not significantly different, the CSI tended to be higher after, rather than at the time of the earthquake (Fig. 4), regardless of the conditions or phase. The CSI has been shown to increase during a mental arithmetic task that required active coping (Allen et al. 2007; Shiraiwa et al. 2020). This study included a reactor scram failure event, in which some control rods did not enter the reactor, following the occurrence of the first aftershock. Normally, the operator performs plant operation under the sub-shift manager’s instruction. However, this was a critical event that required the power plant operator to respond immediately without waiting for instructions from the sub-shift manager. Various events, including a reactor scram failure event that requires active and immediate response, occurred simultaneously with the loss of off-site power, which might have increased the CSI from after the first aftershock to the insertion of all control rods. These results indicate that the emotional stresses that are added during seismic motion are switched to other stresses during post-earthquake response, that is, the need to solve problems with significant effort. However, since this study examined the effects of vibration, it used identical scenarios. Therefore, participants probably became accustomed to the scenario, and no differences in performance or psychological indices were observed between the two conditions. This is indicated by the increase in the total number of spontaneous utterances that preceded the sub-shift manager’s instructions to the operators, as well as the fact that approximately half of the participants reported that the second response was easier. Nevertheless, physiologically, the effect of earthquake shaking is not zero; rather, the effect is present but transient. More than half of the participants answered that plant response was affected by vibration, it was more difficult than normal training, and two participants forgot to report the reactor parameters in the main shock phase under the with vibration condition (Table 2). These results indicate the influence of vibration. Unexpected events may occur during a major earthquake, and events may not always occur in the order that has been trained for. As a future issue for this study, it is necessary to use a first-time scenario while collecting data during earthquake. In addition, each of the events included in this study’s scenario had already been conducted during previous daily training. Here, the effects of an event that have never been experienced by operators before have not been clarified experimentally. In the future, researchers should continue studying the effects of unexpected earthquake-related events on operators. 4.2 Effects of aftershocks As described in Section 4.1, the effects of frequent aftershocks on operators, in terms of vibration, are inferred to be small because no differences were observed in any of the indices between the presence and absence of vibration. In other words, the vibrations of aftershocks are unlikely to cause physical and mental stress. However, Table 2 indicates that the number of errors related to event no. 5, “Flooding of Fuel Pool,” was higher than that of other events regardless of the presence or absence of vibration. Further, in their interviews, six participants clarified that plant response was affected by aftershocks. Accordingly, the existence of aftershock effects other than vibrations was confirmed. Hirose et al. (2021) reported an increase in human errors during aftershocks, which was also supported by the current study. The interviews findings suggested that “work interruption” and “changes in plant conditions” caused by aftershocks had an impact on the participants. One significant effect observed in this study was the disruption of work caused by the aftershocks. In event no. 5, which led to the highest number of errors, the sub-shift manager had instructed participants carry out three responses, as detailed in Table 1, before the occurrence of the second aftershock. However, in addition to event no. 6 (injured person), the second aftershock and its associated event no. 7 (RCIC Trip) occurred before the response, so the actual response could not be made until after the second aftershock’s occurrence. Notably, all the errors recorded for event no. 5 were omission errors—failures to perform checks or make reports. Although it is possible that event no. 6 which occurred just before the second aftershock influenced the results, some interview comments were concerned about work interruption and oblivion (e.g., “The earthquake occurred when I was trying to do something,” “I could not follow the sub-shift manager’s instructions because of the pause,” and “I forgot what to do”) and about the time required to reconfirm the plant (e.g., “The major parameters changed due to the aftershock so it was burdensome to reconfirm,” and “I had to reconfirm again”) were obtained. The adverse effects of aftershocks were described in the introduction; however, this study clarifies that the “forced interruption (halt) of response” and “interruption of plant reconfirmation work due to aftershocks” can easily induce omission errors. Another aftershock effect is the stress on changes in plant conditions, particularly new abnormalities, caused by aftershocks. This study could not determine the aftershocks’ impact on physiological and psychological indices. However, as mentioned earlier, several interview comments on the time and effort required to reconfirm the plant were obtained. In addition, comments such as “It was difficult to detect abnormalities in aftershocks without following the system,” “I had to be very careful to find differences,” and “It was very stressful when an event progressed (or a new event started) due to aftershocks” suggested that the start or progress of events due to aftershocks and the need to detect them was stressful for the operators. The Electric Power Research Institute (2016) describes aftershocks as important distractors. Further, other literature (The National Diet of Japan 2012; Human-Machine Systems Research Subcommittee in Atomic Energy Society of Japan et al. 2015) highlights the impact of aftershocks’ using earlier cases, as noted in the introduction. This study also clarified this type of effect. Further, the effects of aftershocks are as important as those of the main shock when considering operators’ performance during earthquakes. 4.3 Limitations Limitations of this study are as follows. (1) Real disasters cannot be completely reproduced. Participants were aware that the earthquakes in this study were simulated and merely vibrations. Although they were not explicitly informed of the time of occurrence of the seismic motion, they were instructed in advance that the motion might occur. Therefore, we could not completely reproduce the psychological difficulties caused by the suddenness (Shibata and Takada 1995) unique to earthquake occurrence. Furthermore, there was no danger, such as any uncertainty regarding the safety of family members or an increase in radiation levels in the MCR, as was the case in the Fukushima accident. Therefore, it is impossible to completely reproduce the situation of a major earthquake in a simulated environment. However, as indicated by Hirose et al. (2021), it is possible to obtain data on operator performance during an earthquake and identify problems by focusing only on certain parts of the simulated environment, such as the response immediately after an earthquake, and, by making some modifications to ensure a high sense of realism, such as seismic motion, and the communication among other operators. Although the study did not completely simulate the earthquake, most participants felt a sense of reality in the VR environment and could immerse themselves in plant response, indicating that they had a sense of realism and were able to respond to the situation. In addition, changes in physiological indices and an increase in the number of errors during aftershocks were confirmed. Furthermore, the interviews conducted after the experiment provided information on the problems caused by vibration that were not clarified in normal training, such as disorganized thinking, delayed movements, and disorganized prioritization. In addition to collating the lessons obtained from major earthquake cases, future studies should collect data under simulated environments for different scenarios and operator attributes (age, position, etc.) to implement measures to improve safety from a broad perspective. (2) Large differences from actual operation Another limitation of this study includes the following differences from real-world operations : 1) All checks and operations are performed based on the operation manual. 2) The operators themselves perform detailed checks of alarms and operations. 3) Responses are performed by a team. These issues were caused by the performance limitations of devices such as PCs and HMDs. Since the simulated operations were different from actual ones, unnecessary stress might have been added unintentionally. If the operation manual had been available and the operation had been handled by a team, recovery actions, such as the pointing out of errors by other operators, could have occurred, and the number of errors could have been significantly reduced. Furthermore, since all the operations were performed by the experimenter, this study could not provide any indication of operational errors. Moreover, it was not possible to investigate how the sub-shift manager, who was giving instructions, was affected by exposure to seismic motion. In the future, researchers should address these issues using technologically advanced PCs and HMDs. 5. Conclusions The results of this study revealed the following effects on operators of seismic motion by itself: First, the occurrence of transient physiological stress during the main shock and second, feeling the effects on plant response, such as “disorganized thinking,” “delayed actions,” “disorganized priorities,” and “tension/anxiety,” but not so strongly as to feel threatened and with almost no effect on actual performance. However, regarding the aftershocks’ effects on operators, results revealed that first, the motion caused by the aftershocks by itself had almost no effect; second, the presence of aftershocks increased event-related omission errors immediately before the shock occurrence; and third, the effects of aftershocks felt by the operators were work interruption, resulting in concern about forgetting what had been handled and the “effort to recheck the plant,” and “burden and confusion due to changes in the plant situation, particularly the occurrence of new events.” Although the simulated environment is a limitation, it was possible to obtain data on the psychological effects of seismic motion that could not be obtained during normal training. Adding a seismic vibration experience using a simulated environment, as in this study, to regular training will not only help operators develop safety countermeasures based on data collected on operators’ performance, but it will also improve their earthquake preparedness. In the future, we plan to try to discover new findings by changing the scenarios and the attributes of the participants in the experiments. Declarations Funding: The authors did not receive support from any organization for the submitted work. Conflict of interest: The authors have no relevant financial or non-financial interests to declare. Ethics approval: This study was approved by the Nuclear Risk Research Center’s Research Ethics Review Committee in Central Research Institute of Electric Power Industry. Author Contribution All authors contributed to the study’s conception, design, and data collection. Ayako Hirose conducted the analyses and wrote the paper. Finally, all authors commented and approved the paper. Acknowledgement We express our gratitude to the staff of Hamaoka Nuclear Power Station and Mr. Shingo Kuroda for their significant contribution to this research. We would also like to thank the staff of Hitachi GE Nuclear Energy, Ltd., and Hakusan Corporation for their technical assistance with the experiments. Finally, we would like to thank Editage (www.editage.jp) for English language editing. Data availability The data that support the findings of this study are not openly available due to reasons of individuals’ privacy and are available from the corresponding author upon reasonable request. References Adachi S, Matsudaira M, Hirayama Y, Yoshida M, Midorikawa S, Hirose S (2010) Development of Earthquake Experience System Using Ground Motion Simulator “Jishin The Vuton”. Joint Conference Proceedings of the 7th International Conference on Urban Earthquake Engineering (7CUEE) and 5th International Conference on Earthquake Engineering (5ICEE), Tokyo, Japan: 317-320. 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(in Japanese). https://doi.org/10.3327/taesj2002.1.95 Footnotes In this study, the vibrations simulated by the apparatus to replicate earthquake conditions are designated in specific terms: the first simulated vibration is termed the main shock and subsequent vibrations are referred to as aftershocks. Together, these terms called an earthquake or a seismic motion in this study. Further, even when no vibration is generated under experimental conditions, the terms main shock and aftershock are used in the same manner. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4221596","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":288439330,"identity":"4af9ff86-4ea4-4baa-ad27-2ec3d5624bba","order_by":0,"name":"Ayako Hirose","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABFklEQVRIie3RsWqDQBjA8U+EZrno+gnFvMLJQduhD6MEzJIHcLLXxS51N89RKI4nQlyunbOlXTplqGOGQu9ShBSuCd0CuT/ofSg/Dj0Am+0kIyD04qtLDajv7vAuPkgC/h+yi4rhwR4x5vNx02ZZHrLu5V309Q14XdnSvobwmsPHm4Gg8OJGypZdyRltFhIhkK/TZCGBXQqYUdM26w1t7guRPK8uoB0XCHQ1Z2qApAJI0SAmgmiS3z1Vinxpst4wNfxN6A9xY4qKOLtdCJs6B0ikCZdtVMkUmlIiCeScRWWBDF3zt4SCsJ5n+cR/WLqf2zoPvU4y3Ba3IY4eU9Mf+53Dh2PSZ+qS9KjQZL/R8jix2Wy2M+gbihBkTdiZTOEAAAAASUVORK5CYII=","orcid":"","institution":"Central Research Institute of Electric Power Industry","correspondingAuthor":true,"prefix":"","firstName":"Ayako","middleName":"","lastName":"Hirose","suffix":""},{"id":288439331,"identity":"4c2c88b3-df52-4b88-adcc-5834249fa010","order_by":1,"name":"Kohei Nonose","email":"","orcid":"","institution":"Central Research Institute of Electric Power Industry","correspondingAuthor":false,"prefix":"","firstName":"Kohei","middleName":"","lastName":"Nonose","suffix":""},{"id":288439332,"identity":"432162ac-d854-4b5d-9827-2aa49443b874","order_by":2,"name":"Daisuke Takeda","email":"","orcid":"","institution":"Central Research Institute of Electric Power Industry","correspondingAuthor":false,"prefix":"","firstName":"Daisuke","middleName":"","lastName":"Takeda","suffix":""}],"badges":[],"createdAt":"2024-04-05 08:24:18","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4221596/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4221596/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":54517396,"identity":"94dfb0ae-43a1-4716-9917-f3c95ec2df76","added_by":"auto","created_at":"2024-04-11 16:59:29","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":33394,"visible":true,"origin":"","legend":"\u003cp\u003eVirtual reality plant simulator system (Hitachi GE Nuclear Energy, Ltd. Web.)\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4221596/v1/4b2a6b3bb2c7e61a223fba1f.jpg"},{"id":54517171,"identity":"3b522f0d-c7c1-4904-824c-d9cc8330f18c","added_by":"auto","created_at":"2024-04-11 16:51:29","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":47066,"visible":true,"origin":"","legend":"\u003cp\u003eLayout of the experiment\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4221596/v1/dbd990130086634f81673013.jpg"},{"id":54517169,"identity":"41afdfc1-3f4e-401a-8fb4-71da807c8cac","added_by":"auto","created_at":"2024-04-11 16:51:29","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":40664,"visible":true,"origin":"","legend":"\u003cp\u003eTransition in skin conductance level (SCL) as whole phases\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4221596/v1/f1fd94b118d7f9ef0722557d.jpg"},{"id":54516784,"identity":"d17391e3-ba70-4c55-ac70-e4600eb3faa6","added_by":"auto","created_at":"2024-04-11 16:43:29","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":39310,"visible":true,"origin":"","legend":"\u003cp\u003eTransition in cardiac sympathetic index (CSI) as whole phases\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4221596/v1/ed736c3d3013d9aa3a4b5412.jpg"},{"id":54516786,"identity":"91345849-d051-4ec5-9817-a37a1340c388","added_by":"auto","created_at":"2024-04-11 16:43:29","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":34038,"visible":true,"origin":"","legend":"\u003cp\u003eTransition in the cardiac vagal index (CVI) as whole phases\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4221596/v1/aaccf1e275f4b39689c3f54e.jpg"},{"id":106656425,"identity":"4d7ceffa-4bc9-4abe-af91-7ef25f290bac","added_by":"auto","created_at":"2026-04-11 03:25:08","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1402681,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4221596/v1/f4d5492b-b9ed-4811-b019-6bbd29d419da.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Experimental Study on Nuclear Power Plant Operators’ Performance during a Major Earthquake with Aftershocks","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eMajor earthquakes significantly affect nuclear power plants (NPPs), as evidenced by the accident at the Fukushima Daiichi Nuclear Power Station of Tokyo Electric Power Company (Fukushima accident) caused by the Great East Japan Earthquake in March 11, 2011. Since Japan is an earthquake-prone country, it is anticipated it will continue to experience major earthquakes that could cause significant damage (Hok et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Hyodo et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eWhen major earthquakes occur, nuclear reactors generally shut down automatically. However, operators must possess steady judgment to handle the malfunctions and defects resulting from earthquakes and to safely bring the reactor to cold shutdown (Shibata and Takada \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; Yokobayashi et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). To prevent erroneous judgments that aggravate disaster situations, as happened previously at Three Mile Island (Jang et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) and Chernobyl (Salge and Milling \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2006\u003c/span\u003e), operators regularly train using training simulators to respond steadily and appropriately during major earthquakes.\u003c/p\u003e \u003cp\u003eHowever, since the earthquake response training is reproduced only by the interruption of operations for a certain period, it is not possible to reproduce the earthquakes\u0026rsquo; characteristics, such as sudden shaking. Therefore, it remains uncertain whether all operators, particularly those who have never previously experienced a major earthquake, can respond in the same way to a real earthquake as they respond in training. In the Fukushima accident, despite the occurrence of an unprecedentedly strong main shock and repeated aftershocks, there was no evidence of operator error or significantly delayed operator actions in the main control room (MCR) during the first 40 minutes before the tsunami hit (Electric Power Research Institute \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). However, because major earthquakes, such as the Great East Japan Earthquake, occur rarely, it is difficult to exhaustively extract human performance\u0026ndash;related problems during an earthquake from a single disaster (Park et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). If trends in human performance during earthquakes can be ascertained from the data obtained by simulating earthquake environments, we can identify new problems that cannot be extracted from routine trainings or a small number of cases. Reflecting these data in education and training, procedural revisions, and facility improvements will increase operator reliability during earthquakes.\u003c/p\u003e \u003cp\u003eSeveral studies have investigated the impact of earthquakes on operator performance by setting up a simple simulated operation panel on a shaking table (Shibata \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e1987\u003c/span\u003e; Kitada et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e1994\u003c/span\u003e; Park et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Kim et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Yokobayashi et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). Shibata (\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e1987\u003c/span\u003e) set up a cathode ray tube (CRT) and keyboard on a shaking table and conducted an experiment in which subjects typed in the letters appearing on the CRT during vibration. Although the error rate increased above 0.4 G (390 Gal), their cognition and judgment, such as mental arithmetic and judging the magnitude of numbers, were hardly affected by the seismic motion\u0026rsquo;s magnitude. Similarly, Kitada et al. (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e1994\u003c/span\u003e) established a simulated console and CRT on a shaking table for NPP operators to respond to earthquake events. Results indicated that the seismic motion\u0026rsquo;s magnitude had almost no influence on the operators\u0026rsquo; performance. However, these experiments were conducted while varying the seismic motion\u0026rsquo;s magnitude and, hence, were criticized for not simulating the psychological difficulties arising from the \u0026ldquo;suddenness\u0026rdquo; characteristic of earthquakes (Shibata and Takada \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e1995\u003c/span\u003e). Subsequently, Park et al. (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) and Kim et al. (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) conducted experiments with students by simulating accident response at an NPP using a shaking table. To maintain the suddenness of the event, the students were not informed of seismic motion occurrence. In these experiments, no differences were found in the accuracy or speed of accident diagnosis or in relevant physiological and psychological indices depending on the seismic motion\u0026rsquo;s magnitude.\u003c/p\u003e \u003cp\u003eThe shaking table experiments suggest that the seismic motion itself may not significantly affect operators\u0026rsquo; performance. However, the aforementioned studies focus solely on operators\u0026rsquo; performance during or immediately after the so-called main shock and do not consider the response to simultaneous equipment failure caused by the earthquake\u0026rsquo;s occurrence, or repeated aftershocks.\u003c/p\u003e \u003cp\u003eOnly a few studies have experimentally examined aftershocks\u0026rsquo; effects on operator performance. Contrastingly, a number of literatures highlight the effects of aftershocks (Human-Machine Systems Research Subcommittee in Atomic Energy Society of Japan et al. 2015; IAEA 2015; Liu and Hwang \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Shibata and Takada \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; The National Diet of Japan \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Yokobayashi et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Yamaguchi \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In addition, every accident investigation report on the Fukushima accident described the adverse effects of aftershocks and accompanying interruption of operations, as follows: \u0026ldquo;Recovery tasks were further interrupted as workers reacted to the intermittent and significant aftershocks and tsunami\u0026rdquo; (The National Diet of Japan \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2012\u003c/span\u003e, p. 14); \u0026ldquo;Aftershock was still continuing, prompting evacuation each time, and preventing the preparation from progressing\u0026rdquo; (Yamaguchi \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2021\u003c/span\u003e, p. 110); \u0026ldquo;Until 15:25, before the second tsunami wave hit, six aftershocks with a seismic intensity of 4 or more were recorded in succession. It can be inferred that the psychological tension and anxiety of the operators were great\u0026rdquo; (Human-Machine Systems Research Subcommittee in Atomic Energy Society of Japan et al. 2015, p. 10\u0026ndash;11).\u003c/p\u003e \u003cp\u003eTo obtain data on operators\u0026rsquo; performance during earthquakes, it is necessary to reproduce situations that may occur during a major earthquake, such as sudden occurrence, simultaneous equipment failures, and repeated aftershocks. However, arranging a control panel\u0026rsquo;s mockup on a shaking table is expensive and fraught with challenges, such as ensuring participants\u0026rsquo; safety and preventing vibration-related damage to the control panel.\u003c/p\u003e \u003cp\u003eTherefore, in the current study, virtual reality (VR) technology was adopted to create an MCR. Today, VR is widely adopted in various industries for training and other purposes because it enables people to safely and realistically experience disasters and emergencies (Bergroth et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Engelbrecht et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Patle et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Xu et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Many VRs have been developed to simulate earthquakes (Fenz et al. 2020; Lovreglio et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Sinha et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Ting \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). However, since the main purpose of using VRs to simulate earthquakes is disaster prevention, most of them enable users to experience seismic motions visually and audibly with the tipping over of bookshelves and cupboards, without creating actual vibrations (Fenz et al. 2020; Sinha et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Ting \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). However, in this study, since the targeted MCR was designed so that nothing tipped over, it was not sufficient to use only the audiovisual sensory experiences of earthquakes. Accordingly, this study used a safe chair-type earthquake simulator (Adachi 2010; Kuroda et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Lovreglio et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). In an earlier study using non-professionals, Hirose et al. (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) conducted an experimental study using a VR-simulated NPP MCR and the above earthquake simulator.\u003c/p\u003e \u003cp\u003eThis study clarifies the effects of seismic motion and aftershocks on operators\u0026rsquo; physiological and psychological states and performance based on the aforementioned experiment conducted by Hirose et al. (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e"},{"header":"2. Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Equipment\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo ensure participants\u0026rsquo; safety in this study, we used the \u0026ldquo;Jishin The Vuton\u0026rdquo; (Adachi 2010: Kuroda et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2012\u003c/span\u003e), a chair-type earthquake simulator developed by Hakusan Corporation (Fuchu, Japan). The simulator can reproduce past seismic motions, except vertical motion and allow adjustment of the earthquakes\u0026rsquo; magnitude and duration. In addition, the MCR was simulated by a VR plant simulator system developed by Hitachi GE Nuclear Energy, Ltd. (Hitachi, Japan). The system comprised an MCR of an advanced boiling water reactor (ABWR) in a virtual environment (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) and a simulator to simulate several emergency events, such as alarms and parameters, similar to the ones in a real plant. Additionally, the simulator reflected an operator\u0026rsquo;s actions. The MCR in the virtual environment simulated a large display panel, an operator\u0026rsquo;s desk, a shift manager\u0026rsquo;s desk, and some main control boards with an operation console. However, due to the limitations of the head-mounted display (HMD) technology, the operation was performed by the experimenter using a personal computer (PC), and participants only called out the operation they wanted to perform (e.g., \u0026ldquo;Startup RHR Pump B\u0026rdquo;). Unlike in the actual plant, the PC\u0026rsquo;s specifications did not allow the display to change as it would if the participant was using the operation control panel on the main control board; therefore, nine parameter display screens were prepared in advance. Among them, four were displayed on the main board in advance and could be changed at the participants\u0026rsquo; request.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Participants\u003c/h2\u003e \u003cp\u003eIn our experiment, nine healthy ABWR-type reactor operators (all qualified personnel) from a single NPP participated. All were men, with a mean age of 34.7 years (age range: 26\u0026ndash;42 years). Their average years of experience as reactor operators was 5.2 years (from \u0026lt;\u0026thinsp;1 year to 16 years). All the participants were volunteers and had never experienced an earthquake of more than a seismic intensity of 6. This study was approved by the Nuclear Risk Research Center\u0026rsquo;s Research Ethics Review Committee in the Central Research Institute of Electric Power Industry (O2022003). All participants provided informed consent.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Experimental conditions\u003c/h2\u003e \u003cp\u003eTwo conditions were specified: In one condition, the occurrence of an earthquake\u003csup\u003e\u003e[1]\u003c/sup\u003e was notified verbally (i.e., the no vibration condition) and, in the other, notification was provided by vibrating the earthquake simulator (i.e., the with vibration condition). These conditions were tested on all participants. Considering that the increase in heart rate caused by vibration would subside at different rates, all the participants experienced the no vibration condition first and then the with vibration condition.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Experimental scenario\u003c/h2\u003e \u003cp\u003eWhile working as reactor operators, participants took appropriate actions for each event according to the experimental scenario, as presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Specifically, they examined the numerical values of the large display panel or main board, declared what operations were needed, made requests to other operators, and reported the results of their responses to the sub-shift manager who oversaw plant operation.\u003c/p\u003e \u003cp\u003eAlthough the operations were performed by a team, the VR plant simulator had the limitation that only one person could experience the environment at a time. Hence, to compensate, and create an immersive experience, two experienced but nonparticipating NPP operators played the roles of the sub-shift manager and other operators by giving instructions to the participants regarding instrument checks and operations and responding to the participants\u0026rsquo; requests. They followed the relevant scripts that had been prepared in advance according to Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. However, the participants\u0026rsquo; unscripted comments were managed in a more flexible manner.\u003c/p\u003e \u003cp\u003eThe scenario was devised with the cooperation of four NPP operators and a plant manufacturer. It comprised three major phases: the main shock, first aftershock, and second aftershock. Each phase started with the sounding of an earthquake early warning, and new events were generated sequentially with the seismic motion. Although the two experimental conditions indicated the same scenario, the high reactor internal pump (RIP) motor vibration in the main shock phase (event no. 2 in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) was used only in the with vibration condition, to prevent participants from recognizing they were the same scenario from the beginning.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eExperimental Scenario\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePhase\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEvent no.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eContents of events\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRequired response\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eMain shock\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMain shock\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1) Check \u0026amp; report: plant parameters\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHigh RIP motor vibration\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1) Report: RIP alarm\u003c/p\u003e \u003cp\u003e2) Report: level of RIP motor vibration\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eFirst aftershock\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFirst aftershock\u003c/p\u003e \u003cp\u003eLoss of off-site power\u003c/p\u003e \u003cp\u003eFailure of reactor scram\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1) Report: failure of reactor scram\u003c/p\u003e \u003cp\u003e2) Operations: treatments of ATWS(Reactor mode switch shutdown, manual ARI operation, manual scram operation)\u003c/p\u003e \u003cp\u003e3) Check \u0026amp; report: plant parameters\u003c/p\u003e \u003cp\u003e4) Check \u0026amp; report: RCIC startup\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHigh turbine vibration\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1) Operation: close MSIV\u003c/p\u003e \u003cp\u003e2) Operation: RHR startup(S/C cooling)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFlooding of fuel pool\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1) Request: check the ITV #\u003c/p\u003e \u003cp\u003e2) Report: result of the ITV check #\u003c/p\u003e \u003cp\u003e3) Check \u0026amp; report: FPC pump operating status #\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eInjured person\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1) Response: paging from injured person\u003c/p\u003e \u003cp\u003e2) Report: occurrence of injury to person #\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSecond aftershock\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSecond aftershock\u003c/p\u003e \u003cp\u003eRCIC trip\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1) Check \u0026amp; report: plant parameters\u003c/p\u003e \u003cp\u003e2) Report: tripping of RCIC\u003c/p\u003e \u003cp\u003e3) Operation: HPCF(B) startup\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eOpening of blowout panel\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1) Check \u0026amp; report: SGTS(R/B negative pressure) abnormality\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eEvent no. 2 was conducted only under the with vibration condition.\u003c/p\u003e \u003cp\u003e \u003cem\u003e#\u003c/em\u003e These responses were conducted in the second aftershock phase. \u003cem\u003eRIP\u003c/em\u003e reactor internal pump, \u003cem\u003eATWS\u003c/em\u003e anticipated transient without scram, \u003cem\u003eARI\u003c/em\u003e alternate rod insertion, \u003cem\u003eRCIC\u003c/em\u003e reactor core isolation cooling system, \u003cem\u003eMSIV\u003c/em\u003e main steam isolation valve, \u003cem\u003eRHR\u003c/em\u003e residual heat removal system, \u003cem\u003eS/C\u003c/em\u003e suppression chamber, \u003cem\u003eITV\u003c/em\u003e industrial television, \u003cem\u003eFPC\u003c/em\u003e fuel pool cooling and filtering system, \u003cem\u003eHPCF\u003c/em\u003e high-pressure core flooder system, \u003cem\u003eSGTS\u003c/em\u003e stand-by gas treatment system, \u003cem\u003eR/B\u003c/em\u003e reactor building\u003c/p\u003e \u003cp\u003eFor the main shock and first aftershock phases, the earthquake early warning was sounded at the following time points, and one phase shifted to the next. In the second aftershock phase, each condition was terminated at the following time points:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eMain shock phase: Immediately after the sub-shift manager instructed the participants about the reactor scram (2 min after the experiment\u0026rsquo;s initiation in the no vibration condition)\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eFirst aftershock phase: Immediately after the other operator (injured person) called for assistance\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eSecond aftershock phase: Participants reported their response to event no. 8 (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e)\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Seismic motions\u003c/h2\u003e \u003cp\u003eIn addition to the main shock, two aftershocks were interspersed at short intervals with reference to the report from the Great East Japan Earthquake that \u0026ldquo;a total of three aftershocks including two of seismic intensity 4 occurred in the 10 minutes immediately after the main shock\u0026rdquo; (Human-Machine Systems Research Subcommittee in Atomic Energy Society of Japan et al. 2015, p. 17). The duration of each seismic motion was 30 s. The first 10 s produced only the earthquake early warning sound, whereas the remaining 20 s produced vibrations. In the no vibration condition, the earthquake early warning sound alone was generated for 30 s.\u003c/p\u003e \u003cp\u003eIn the experiment, seismic motions were reproduced from past earthquakes. After consulting an earthquake expert, the following earthquake motions were selected as ones that could be clearly experienced, even when wearing HMDs.\u003c/p\u003e \u003cp\u003eMain shock\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003ePlace of occurrence: Mashiki Town (Kumamoto Prefecture)\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eDate and time of occurrence: 04/14/2016 at 21:26\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eSeismic intensity: 7 (magnitude: 6.5)\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eMaximum acceleration: 708 Gal\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eFirst aftershock\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003ePlace of occurrence: Mashiki Town (Kumamoto Prefecture)\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eDate of occurrence: 04/16/2016 at 01:25\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eSeismic intensity: 7 (magnitude: 7.3)\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eMaximum acceleration: 730 Gal\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eSecond aftershock\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003ePlace of occurrence: Nishihara Village (Kumamoto Prefecture)\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eDate of occurrence: 04/16/2016 at 01:25\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eSeismic intensity: 7 (magnitude: 7.3)\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eMaximum acceleration: 755 Gal\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eParticipants were instructed in advance of the possibility that seismic motion occurring and were requested to fasten their seatbelts when seated and to keep their hands on the bar next to their chairs during the experiment. Further, they were told that, in both conditions, the sub-shift manager would give the command \u0026ldquo;Earthquake, ensuring safety\u0026rdquo; in the event of an earthquake and prohibit all operations to ensure the participants\u0026rsquo; personal safety.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.6 Procedure\u003c/h2\u003e \u003cp\u003e After being briefed on the experiment and providing consent to participate in the study, participants were seated on \u0026ldquo;Jishin The Vuton\u0026rdquo; and fitted with physiological index sensors. For baseline measurement, they remained in a resting state with their eyes open for 3 min. Subsequently, they were fitted with an HMD (HP Reverb) and asked to perform plant operations as the reactor\u0026rsquo;s operator, as described in Section \u003cspan refid=\"Sec6\" class=\"InternalRef\"\u003e2.4\u003c/span\u003e. To familiarize the participants with responding in VR, a trial comprising events for which they had been well trained was conducted. Further, as described in Section \u003cspan refid=\"Sec5\" class=\"InternalRef\"\u003e2.3\u003c/span\u003e, the participants responded to the plant without and with vibrations, in that order.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAt the end of each condition, the participants removed their HMDs and responded to psychological indices, as described in Section \u003cspan refid=\"Sec12\" class=\"InternalRef\"\u003e2.7.3\u003c/span\u003e. Following the completion of all experimental conditions, the participants were interviewed about the experiment. To prevent VR sickness, the participants were not allowed to move around in the simulated environment. A speaker placed in front of the participants output the earthquake early warning sound and various other warning sounds generated by the plant. Additionally, a screen set up at the front of the laboratory enabled experimenters to see the images experienced by participants. Further, two video cameras were placed with the participants\u0026rsquo; permission to measure their responses to the scenarios. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e depicts the experiment\u0026rsquo;s arrangement.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e2.7 Measures\u003c/h2\u003e \u003cp\u003eTo assess participants\u0026rsquo; responses to the scenario, we measured the presence or absence of responses to each event against the \u0026ldquo;required response,\u0026rdquo; as described in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The participants\u0026rsquo; utterances were captured verbatim using video recordings. Additionally, physiological and psychological data were captured to evaluate the stress levels caused by the seismic motion.\u003c/p\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e2.7.1 Performance measures\u003c/h2\u003e \u003cp\u003e \u003cb\u003e(1) Number of errors\u003c/b\u003e \u003c/p\u003e \u003cp\u003eIn this study, errors were specifically defined as failures to respond to \u0026ldquo;required responses,\u0026rdquo; which included omissions of checks, reports, or operations, and responses involving unnecessary operations. Further, the following were calculated: a) the number of errors associated with each event and b) The cumulative number of errors across all events. However, the analysis did not include event no. 2 in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e because it was conducted exclusively under the with vibration condition.\u003c/p\u003e \u003cp\u003e \u003cb\u003e(2) Number of utterances\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe study captured utterances other than the required responses assumed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Therefore, participants\u0026rsquo; verbatim utterances were classified into the following three categories:\u003c/p\u003e \u003cp\u003ea) Normal utterances\u003c/p\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003e\u0026ldquo;Required responses (such as check, operation, etc.)\u0026rdquo; and other responses (e.g., checking of various parameters associated with the reactor scram, such as drywell temperature, pressure, and reactor containment isolation system status, etc.).\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003eb) Spontaneous utterances\u003c/p\u003e \u003cp\u003eSpontaneous operations by participants prior to instructions from the sub-shift manager or spontaneous requests to other operators not made through the sub-shift manager (e.g., requests regarding ATWS treatments made to an auxiliary equipment operator to check an ITV, etc., including necessary responses).\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003ec) Repetitions\u003c/p\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe repetition of instructions or announcements by the sub-shift manager or other operators using three-way communication (e.g., \u0026ldquo;Close the MSIV valve, right?\u0026rdquo;).\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe total number of utterances and repetitions of a) to c) were calculated by event and for all events.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e2.7.2 Physiological measures\u003c/h2\u003e \u003cp\u003eThe heart rate (R-R interval) and skin conductance level (SCL), which is a slow stimulation-induced variation of the skin\u0026rsquo;s electrical activity, were measured as physiological indices of tension and stress during plant operations. Wearable biometric signal measurement platforms (Biosignalsplux by Plux) were used to measure physiological indices. The output waveforms were AD-converted by the sensor box (sampling frequency: 500 Hz; resolution: 16 bit), sent to the data measurement application software (OpenSignals by Plux) in real time through Bluetooth, and recorded on a PC.\u003c/p\u003e \u003cp\u003eLorenz plots were used for the R-R interval (Toichi et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Toichi et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e1998\u003c/span\u003e; Nose et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) since they measure tension and stress without requiring controlled respiration and can be analyzed in the short term. After removing obvious outliers, such as R-R intervals less than 400 ms or greater than 2000 ms or values greater than 20% of the mean of the preceding and following 20 beats, Lorenz plots were generated per unit time, as described below. The cardiac sympathetic index (CSI), an index of sympathetic activity, and the cardiac vagal index (CVI), an index of parasympathetic activity, were calculated (Toichi et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Toichi et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e1998\u003c/span\u003e; Sato et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The CSI value is known to be higher in tense/stressful situations, whereas that of CVI is higher in relaxed states (Toichi et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Toichi et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e1998\u003c/span\u003e; Nose et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTo measure SCL, the average value per unit time was calculated. To remove individual differences, the mean and standard deviation (SD) of each participant\u0026rsquo;s baseline data were used and standardized such that mean\u0026thinsp;=\u0026thinsp;0 and variance\u0026thinsp;=\u0026thinsp;1.\u003c/p\u003e \u003cp\u003eTo further examine the physiological effects of vibration during the scenario, the aforementioned values were calculated for each phase. Since it was assumed that physiological states would differ across significant events, such as ATWS, and individuals would respond to the events at different speeds, the data were divided into two or three parts within the same phase as the events progressed, as follows:\u003c/p\u003e \u003cp\u003eMain shock phase:\u003c/p\u003e \u003cp\u003e(1) From the beginning to the end of the main shock.\u003c/p\u003e \u003cp\u003e(2) At the end of (1) to the start of the first aftershock.\u003c/p\u003e \u003cp\u003eFirst aftershock phase:\u003c/p\u003e \u003cp\u003e(1) From the beginning to the end of the first aftershock.\u003c/p\u003e \u003cp\u003e(2) From the end of (1) until the sub-shift manager repeats participants\u0026rsquo; report on the insertion of all control rods (completion of the ATWS treatment).\u003c/p\u003e \u003cp\u003e(3) From the end of (2) to the start of the second aftershock.\u003c/p\u003e \u003cp\u003eSecond aftershock phase:\u003c/p\u003e \u003cp\u003e(1) From the beginning to the end of the second aftershock.\u003c/p\u003e \u003cp\u003e(2) From the end of (1) until the sub-shift manager repeats participants\u0026rsquo; report on injuries and High-Pressure Core Flooder System startup.\u003c/p\u003e \u003cp\u003e(3) From the end of (2) to the end of the phase.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e2.7.3 Psychological measures\u003c/h2\u003e \u003cp\u003eTo measure the transient tension and anxiety resulting from an earthquake, 14 items from the Phasic Stress Scale (HQL 2000; Suzuki et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e1999\u003c/span\u003e), including the five factors Languor,\u0026rdquo; \u0026ldquo;Comfort,\u0026rdquo; \u0026ldquo;Anxiety/Uneasiness,\u0026rdquo; \u0026ldquo;Tension,\u0026rdquo; and \u0026ldquo;Overall Stress Level,\u0026rdquo; were used as psychological indices. Additionally, participants were asked about \u0026ldquo;experiencing hesitation in judgment\u0026rdquo; and \u0026ldquo;degree of difficulty\u0026rdquo; during plant operation.\u003c/p\u003e \u003cp\u003eAt the end of each condition, the participants had to assess their mood using a visual analog scale by marking a point on the number line between \u0026ldquo;not at all\u0026rdquo; (0 point, left end) and \u0026ldquo;very much\u0026rdquo; (100 points, right end). Further, the line\u0026rsquo;s length from the left end to the mark was measured. After each item was rated, they were scored against the average rating of the items belonging to each factor (HQL 2000).\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e2.8 Statistical analysis\u003c/h2\u003e \u003cp\u003eData analysis was performed using SPSS software version 27.0. A significance level of less than 5% was considered significant. To assess the impact of seismic motion all analyses included inter-condition comparisons.\u003c/p\u003e \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e \u003ch2\u003e2.8.1 Performance indices\u003c/h2\u003e \u003cp\u003eFor each index listed in Section \u003cspan refid=\"Sec10\" class=\"InternalRef\"\u003e2.7.1\u003c/span\u003e, the following inter-conditional comparisons were conducted. Since the data for these indices (i.e., errors, normal utterances, spontaneous utterances, and repetitions) did not follow a normal distribution for each event, Wilcoxon\u0026rsquo;s signed-rank test was applied to each index. Further, once the normality of data distribution for each index for all events was confirmed, a corresponding t-test was conducted.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e \u003ch2\u003e2.8.2 Physiological indices\u003c/h2\u003e \u003cp\u003eFor each physiological index, repeated-measures analyses of variance (ANOVAs) for two factors (condition \u0026times; elapsed time within a phase) were performed to compare the conditions for each phase. Before performing ANOVAs, Mauchly's sphericity test was conducted. If the assumption of sphericity did not hold, the ANOVAs degrees of freedom were adjusted using Huynh\u0026ndash;Feldt\u0026rsquo;s ε. If a significant main effect was identified, Bonferroni\u0026rsquo;s multiple comparisons were performed. For SCL, one participant with incomplete data was excluded from the analysis.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e \u003ch2\u003e2.8.3 Psychological indices\u003c/h2\u003e \u003cp\u003ePsychological indices also had outliers and the data did not satisfy the normality assumption for the indices. Hence, a Wilcoxon signed-rank test was conducted for each index.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1 Performance indices\u003c/h2\u003e\n \u003cdiv id=\"Sec19\" class=\"Section3\"\u003e\n \u003ch2\u003e3.1.1 Number of errors\u003c/h2\u003e\n \u003cp\u003eTable \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e depicts the contents and numbers of observed errors. The analysis revealed that for all events, the number of errors did not differ according to the presence or absence of vibrations (Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). Further, no significant differences were observed in the total number of errors (Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). Regardless of the presence or absence of vibration, the largest number of errors occurred during event no. 5, the \u0026ldquo;flooding of the fuel pool\u0026rdquo; (Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eNumbers and descriptions of errors by event\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eEvent no.\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eNumber of errors\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e\u003cem\u003eZ\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e\u003cem\u003ep\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eContents of errors\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNo vibration\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eWith vibration\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-1.410\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.500\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNo report of plant parameters\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-1.000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNo report of plant parameters\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-0.136\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNo request for checking the ITV\u003c/p\u003e\n \u003cp\u003eNo report of result of the ITV check\u003c/p\u003e\n \u003cp\u003eNo report of FPC pump operating status\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNo report of occurrence of injured person\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-1.410\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.500\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNo report of plant parameters\u003c/p\u003e\n \u003cp\u003eNo report of RCIC trip \u0026amp; HPCF(B) startup\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-1.410\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.500\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNo report of SGTS abnormality\u003c/p\u003e\n \u003cp\u003eIncorrect shutdown of a SGTS\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSum\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003eSee Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e for abbreviations (e.g. ITV, FPC, etc.)\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003cdiv align=\"char\" class=\"colspec\"\u003e\u003cbr\u003e\u003c/div\u003e\u0026nbsp;\u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eAverage values of the total number for each performance index\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eTotal number\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eNo vibration\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eWith vibration\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e\u003cem\u003et\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e\u003cem\u003ep\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSD\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMean\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSD\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eErrors\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.560\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.878\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.560\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.242\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.000\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNormal utterances\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e21.444\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.199\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20.444\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.395\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.095\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.305\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSpontaneous utterances\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.667\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.550\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.444\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.186\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-4.097\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.003\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRepetitions\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.556\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.882\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.889\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.088\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-0.603\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.563\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec20\" class=\"Section3\"\u003e\n \u003ch2\u003e3.1.2 Number of utterances\u003c/h2\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003cp\u003eTable 4 depicts the median and interquartile range\u0026nbsp;of the observed number of normal utterances, spontaneous utterances, and\u0026nbsp;repetitions by event. Analysis revealed no difference in the number of utterances or repetitions in all events\u0026nbsp;with or without the presence of vibration (Table 4).\u003c/p\u003e\n \u003cp\u003eHowever, the analysis revealed that the total number of spontaneous utterances was significant and that it increased with the vibration condition (Table 3).\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eTable 4\u0026nbsp;\u003c/strong\u003eMedian and interquartile ranges of the number of utterances by event\u003c/p\u003e\n \u003ctable id=\"Tab4\" border=\"1\"\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eEvent no.\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"4\"\u003e\n \u003cp\u003eNormal utterances\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"4\"\u003e\n \u003cp\u003eSpontaneous utterances\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"4\"\u003e\n \u003cp\u003eRepetitions\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNo vibration\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eWith vibration\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eZ\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003ep\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNo vibration\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eWith vibration\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eZ\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003ep\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNo vibration\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eWith vibration\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eZ\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003ep\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2 (2\u0026ndash;3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2 (1\u0026ndash;2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.952\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.438\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0 (0\u0026ndash;0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0 (0\u0026ndash;0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1 (0\u0026ndash;2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0 (0\u0026ndash;1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.633\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.250\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10 (8\u0026ndash;15)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10 (9\u0026ndash;11)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.530\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.719\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2 (0\u0026ndash;3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3 (2\u0026ndash;4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-2.060\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.063\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1 (1\u0026ndash;1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1 (1\u0026ndash;2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-1.414\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.313\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3 (2\u0026ndash;3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2 (1\u0026ndash;3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-1.857\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.125\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1 (1\u0026ndash;3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2 (1\u0026ndash;3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.732\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.250\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0 (0\u0026ndash;1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0 (0\u0026ndash;2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.816\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.750\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2 (1\u0026ndash;3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1 (1\u0026ndash;3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-0.531\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.688\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0 (0\u0026ndash;0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0 (0\u0026ndash;1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.414\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.500\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1 (0\u0026ndash;2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1 (0\u0026ndash;1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-0.378\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.000\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1 (1\u0026ndash;1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1 (1\u0026ndash;2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.732\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.250\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0 (0\u0026ndash;0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0 (0\u0026ndash;0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1 (0\u0026ndash;1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1 (1\u0026ndash;1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.414\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.500\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3 (1\u0026ndash;4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3 (2\u0026ndash;5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.121\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.063\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1 (1\u0026ndash;1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1 (1\u0026ndash;1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2 (1\u0026ndash;2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2 (1\u0026ndash;3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.816\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.688\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1 (0\u0026ndash;2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1 (0\u0026ndash;3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.276\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0 (0\u0026ndash;1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0 (0\u0026ndash;1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-0.577\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0 (0\u0026ndash;1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0 (0\u0026ndash;0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-1.414\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.500\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eThe data in parentheses indicate the interquartile range\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec21\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2 Physiological indices\u003c/h2\u003e\n \u003ch3\u003e3.2.1 Skin conductance level\u003c/h3\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e depicts the trends with elapsed times for the SCL. Analysis revealed that the main effect of a condition was significant in the main shock phase (\u003cem\u003eF\u003c/em\u003e (1, 7)\u0026thinsp;=\u0026thinsp;11.551, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;.05, \u003cem\u003e\u0026eta;p\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;.623). Further, the main effect of elapsed time was significant in all phases (the main shock phase: \u003cem\u003eF\u003c/em\u003e (1, 7)\u0026thinsp;=\u0026thinsp;6.525, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;.05, \u003cem\u003e\u0026eta;p\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;.482, the first aftershock phase: \u003cem\u003eF\u003c/em\u003e (2, 12)\u0026thinsp;=\u0026thinsp;9.872, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;.01, \u003cem\u003e\u0026eta;p\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;.622, the second aftershock phase: \u003cem\u003eF\u003c/em\u003e (1.211, 8.475)\u0026thinsp;=\u0026thinsp;4.936, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;.05, \u003cem\u003e\u0026eta;p\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;.414). Multiple comparisons of the main effect were performed. The condition in the main shock phase was with vibration\u0026thinsp;\u0026gt;\u0026thinsp;no vibration (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;.05). In addition, the elapsed time for each phase was (1) (at the onset of the main shock) \u0026gt; (2) (before the first aftershock) (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;.01) in the main shock phase and (2) (until all control rods were inserted) \u0026gt; (3) (before the second aftershock) (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;.05) in the first aftershock phase. The results for the second aftershock phase were not statistically significant. In the main shock phase, SCL was higher in the with vibration condition than the no vibration condition; however, there was no difference in SCL between the two conditions after the first aftershock. Regarding elapsed time, SCL was low at the end of the main shock and first aftershock phases. No interactions were observed in any of the phases.\u003c/p\u003e\n \u003ch3\u003e3.2.2 Cardiac sympathetic index\u003c/h3\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e depicts the trends with elapsed time for the CSI. Analysis revealed that elapsed time\u0026rsquo;s main effect on CSI, a measure of the sympathetic nervous system, was significant in the first aftershock phase (\u003cem\u003eF\u003c/em\u003e (2, 16)\u0026thinsp;=\u0026thinsp;7.515, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;.01, \u003cem\u003e\u0026eta;p\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;.484). Multiple comparisons showed higher values (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;.01) for (2) (until all the control rods were inserted) than (1) (at the onset of the first aftershock). That was, CSI increased at the time of ATWS response after the first aftershock, regardless of the presence or absence of vibration.\u003c/p\u003e\n \u003cdiv id=\"Sec22\" class=\"Section3\"\u003e\n \u003ch2\u003e3.2.3 Cardiac vagal index\u003c/h2\u003e\n \u003cp\u003eFigure 5 depicts the CVI trends with elapsed time. Analysis revealed no statistical difference in CVI, a measure of the parasympathetic nervous system, in any phase.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec23\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3 Psychological indices\u003c/h2\u003e\n \u003cp\u003eThe analysis revealed no difference between the presence and absence of vibration in any factor, including hesitation in judgment and degree of difficulty (Table \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003ctable id=\"Tab5\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eMedian and interquartile range of each psychological index\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFactor\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNo vibration\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eWith vibration\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eZ\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003ep\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLanguor\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e29 ( 2\u0026ndash;59)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e37 ( 5\u0026ndash;58)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-0.178\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.910\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eComfort\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e13 ( 1\u0026ndash;49)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4 ( 1\u0026ndash;41)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.840\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.461\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAnxiety/Uneasiness\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e13 ( 0\u0026ndash;48)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e16 ( 0\u0026ndash;48)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-0.889\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.406\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTension\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e55 (27\u0026ndash;67)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e68 (17\u0026ndash;83)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-1.126\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.289\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eOverall stress level\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e29 (11\u0026ndash;68)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e63 (15\u0026ndash;66)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-0.772\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.500\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHesitation in judgment\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e20 (10\u0026ndash;59)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e30 ( 1\u0026ndash;71)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-1.245\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.238\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDegree of difficulty\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e32 (17\u0026ndash;54)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e37 (21\u0026ndash;57)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-0.777\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.469\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003cp\u003eThe data in parentheses indicate the interquartile range\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec24\" class=\"Section2\"\u003e\n \u003ch2\u003e3.4 Interviews\u003c/h2\u003e\n \u003cp\u003eSubsections describe participants\u0026rsquo; interviews after the experiment.\u003c/p\u003e\n \u003cdiv id=\"Sec25\" class=\"Section3\"\u003e\n \u003ch2\u003e3.4.1 Sense of reality and immersion\u003c/h2\u003e\n \u003cp\u003eEight of the nine participants mentioned experiencing a sense of reality in the VR environment. When asked whether they could immerse themselves in the plant\u0026rsquo;s response, five answered they could, two felt that they could do so fairly well, and two expressed being unable to do so well. The respondents\u0026rsquo; reasons for not able to do so well were \u0026ldquo;it was stressful not being able to see the display screen I wanted to see\u0026rdquo; and \u0026ldquo;I couldn\u0026rsquo;t feel the tension because it was a one-person training.\u0026rdquo;\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec26\" class=\"Section3\"\u003e\n \u003ch2\u003e3.4.2 Seismic motion\u0026rsquo;s impact on plant response\u003c/h2\u003e\n \u003cp\u003eFive of the nine participants clarified seismic motion\u0026rsquo;s impact on plant response. Further, six participants indicated that carrying out the plant responses with seismic motion (like this time) was more difficult than the usual earthquake response using a training simulator. The following were cited as the specific effects of the occurrence of vibration:\u003c/p\u003e\n \u003cp\u003e- In the case of no vibration, I was able to organize my thoughts regarding plant response while ensuring personal safety during earthquake; but it was not possible in the case of vibration. So, I was not able to clarify what I should do thereafter.\u003c/p\u003e\n \u003cp\u003e- Could not operate it while it was vibrating; so, what I wanted to do was delayed.\u003c/p\u003e\n \u003cp\u003e- It took time to grasp the situation and detect anomalies and the first response was delayed, because the viewpoint was not fixed due to the vibration and all the parameters had changed when I looked up.\u003c/p\u003e\n \u003cp\u003e- The earthquake cause confusion about how to prioritize.\u003c/p\u003e\n \u003cp\u003e- I got nervous when it shook. I could not think straight when I had to worry about various things, such as parameters.\u003c/p\u003e\n \u003cp\u003e- There was no difference in the plant\u0026rsquo;s response; but I felt psychologically uneasy when it shook (two people answered similarly).\u003c/p\u003e\n \u003cp\u003e- The one with vibration was more realistic. I felt that I needed to check a wider range of parameters.\u003c/p\u003e\n \u003cp\u003eThese results indicate that participants experienced \u0026ldquo;disorganized thinking,\u0026rdquo; \u0026ldquo;delayed actions,\u0026rdquo; \u0026ldquo;disorganized priorities,\u0026rdquo; and \u0026ldquo;tension/anxiety\u0026rdquo; following seismic motion. Some participants felt a strong sense of reality due to feeling the vibration. However, only three participants answered that they felt threatened by the seismic motion.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec27\" class=\"Section3\"\u003e\n \u003ch2\u003e3.4.3 Effects of aftershocks on plant response\u003c/h2\u003e\n \u003cp\u003eSix of the nine participants answered that aftershocks had an impact on plant response. They cited the following specific effects of aftershocks:\u003c/p\u003e\n \u003cp\u003e- It was stressful that the aftershocks occurred when I was trying to do something.\u003c/p\u003e\n \u003cp\u003e- The time gap indicated that the priorities given by the sub-shift manager were not being followed.\u003c/p\u003e\n \u003cp\u003e- It was difficult to decide whether to give priority to dealing with injuries that occurred just before the aftershock or to dealing with the plant (two people answered similarly).\u003c/p\u003e\n \u003cp\u003e- I had to hold my hands until the shaking subsided; so, I forgot what I was supposed to do.\u003c/p\u003e\n \u003cp\u003e- The burden of plant reconfirmation was heavy because the main parameters changed due to the aftershocks.\u003c/p\u003e\n \u003cp\u003e- I felt that I would forget the parameters I had checked and the operations I had planned, because they would be reset by the vibration.\u003c/p\u003e\n \u003cp\u003e- I thought that the aftershocks would confuse my thoughts.\u003c/p\u003e\n \u003cp\u003e- I was worried about the aftershocks affecting the water level and the places that held water (water intake tanks, etc.).\u003c/p\u003e\n \u003cp\u003eThese results indicate that participants experienced work interruption due to the aftershocks, resulting in concerns about forgetting what was handled and \u0026ldquo;burden and confusion due to changes in the plant situation.\u0026rdquo;\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec28\" class=\"Section3\"\u003e\n \u003ch2\u003e3.4.4 Differences in the effects of main shock and aftershocks\u003c/h2\u003e\n \u003cp\u003eParticipants\u0026rsquo; responses to whether the main shock or aftershocks had a greater impact on plant response and psychological aspects were divided nearly by half. The reasons for each answer were as follows:\u003c/p\u003e\n \u003cp\u003eMain shock (answered by four participants)\u003c/p\u003e\n \u003cp\u003e- The impact on psychological aspect was significant because we did not know when it would occur.\u003c/p\u003e\n \u003cp\u003e- Because it occurred when the plant was running (two persons answered similarly).\u003c/p\u003e\n \u003cp\u003e- It was difficult to move (if there was a real aftershock, I would operate the plant even if it was shaking).\u003c/p\u003e\n \u003cp\u003eAftershock (answered by five participants)\u003c/p\u003e\n \u003cp\u003e- As in this case, when an event progressed due to aftershocks (or a new event started), it was incredibly stressful (two people answered similarly).\u003c/p\u003e\n \u003cp\u003e- While rechecking values, it was necessary to carefully find any differences.\u003c/p\u003e\n \u003cp\u003e- The main shock was considered a loss of off-site power and reactor scram; but, in aftershocks, it was difficult to detect anomalies without following the system, which was unpleasant.\u003c/p\u003e\n \u003cp\u003e- Since I was already in the process of dealing with the plant, there was a great deal of psychological distress.\u003c/p\u003e\n \u003cp\u003eParticipants who responded it was the main shock cited concerns about the suddenness of earthquake occurrence and the fact that the plant was in operation. However, those who responded that it was the aftershocks were concerned about changes in plant conditions (the development of events and occurrence of new events).\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cdiv id=\"Sec30\"\u003e\n \u003ch2\u003e4.1 Effects of seismic motion on operators\u0026rsquo; states and performance\u003c/h2\u003e\n \u003cp\u003eThis study examined the effects of seismic motion on NPP operators\u0026rsquo; physiological and psychological states and performance. Results revealed that vibration resulted in almost no differences in performance and psychological indices, such as the number of errors and utterances. However, among physiological indices, SCL was higher in the main shock phase than in the no vibration condition, indicating that seismic motion affected operators\u0026rsquo; states only in the main shock phase. However, there was no difference in heart rate between the conditions. Approximately half of the post-experiment interview participants mentioned seismic motion\u0026rsquo;s impact on plant response. However, only three participants felt threatened by it.\u003c/p\u003e\n \u003cp\u003eThe study revealed that seismic motion had physiological effects on operators at the time of the main shock; it caused disorganized thinking and priorities, delayed reactions, tension and anxiety, but was not felt as threatening. Similar to earlier studies (Shibata 1987; Kitada et al. 1994; Park et al. 2018; Kim et al. 2019), the current study found that seismic motion by itself did not affect performance, for instance, by causing an increase in errors. In the current study, participants responded to multiple events that could occur during a major earthquake; hence, this study was more challenging than earlier studies that used shaking table experiments (Shibata 1987; Kitada et al. 1994; Park et al. 2018; Kim et al. 2019). Furthermore, the seismic intensity considered in the current study\u0026rsquo;s experiment was 7, which is the same as that of great earthquakes that have occurred in Japan. In other words, the seismic motion by itself had almost no effect on operators\u0026rsquo; performance, even when the earthquake\u0026rsquo;s magnitude and the task\u0026rsquo;s difficulty were increased. Further, the Electric Power Research Institute (2016), which reviewed operating experience during earthquakes in nuclear and non-nuclear industries, concluded that although there were only a limited number of examples, operator behavior generally remained reliable regardless of earthquakes\u0026rsquo; magnitude.\u003c/p\u003e\n \u003cp\u003eRegarding the effect of seismic motion on operator performance, only SCL increased during the main shock (Fig.\u0026nbsp;3) when emotional stress or arousal level was high (Hassett 1978; Andreassi 1980). The increase in SCL during the main shock phase may be attributed to an increase in arousal level and emotional stress caused by the unexpected occurrence of seismic motion resulting in surprise and anxiety. However, in the latter half of the phase, SCL decreased, suggesting that the vibration\u0026rsquo;s physiological effect was transient. This is consistent with the perspective that the effect of vibration (acceleration) is short term (Amico et al. 2011) and with the findings of Hirose et al. (2021). Furthermore, no condition-based differences were observed after the first aftershock phase, which suggests that the surprise and arousal related to aftershocks were weaker than those related to the main shock.\u003c/p\u003e\n \u003cp\u003eHowever, the main effect of elapsed time on the CSI was observed in the first aftershock. Further, regardless of the presence or absence of vibration, the CSI was higher after, rather than at the onset of, the first aftershock (Fig.\u0026nbsp;4). Although the values were not significantly different, the CSI tended to be higher after, rather than at the time of the earthquake (Fig.\u0026nbsp;4), regardless of the conditions or phase. The CSI has been shown to increase during a mental arithmetic task that required active coping (Allen et al. 2007; Shiraiwa et al. 2020). This study included a reactor scram failure event, in which some control rods did not enter the reactor, following the occurrence of the first aftershock. Normally, the operator performs plant operation under the sub-shift manager\u0026rsquo;s instruction. However, this was a critical event that required the power plant operator to respond immediately without waiting for instructions from the sub-shift manager. Various events, including a reactor scram failure event that requires active and immediate response, occurred simultaneously with the loss of off-site power, which might have increased the CSI from after the first aftershock to the insertion of all control rods. These results indicate that the emotional stresses that are added during seismic motion are switched to other stresses during post-earthquake response, that is, the need to solve problems with significant effort.\u003c/p\u003e\n \u003cp\u003eHowever, since this study examined the effects of vibration, it used identical scenarios. Therefore, participants probably became accustomed to the scenario, and no differences in performance or psychological indices were observed between the two conditions. This is indicated by the increase in the total number of spontaneous utterances that preceded the sub-shift manager\u0026rsquo;s instructions to the operators, as well as the fact that approximately half of the participants reported that the second response was easier.\u003c/p\u003e\n \u003cp\u003eNevertheless, physiologically, the effect of earthquake shaking is not zero; rather, the effect is present but transient. More than half of the participants answered that plant response was affected by vibration, it was more difficult than normal training, and two participants forgot to report the reactor parameters in the main shock phase under the with vibration condition (Table\u0026nbsp;2). These results indicate the influence of vibration. Unexpected events may occur during a major earthquake, and events may not always occur in the order that has been trained for. As a future issue for this study, it is necessary to use a first-time scenario while collecting data during earthquake. In addition, each of the events included in this study\u0026rsquo;s scenario had already been conducted during previous daily training. Here, the effects of an event that have never been experienced by operators before have not been clarified experimentally. In the future, researchers should continue studying the effects of unexpected earthquake-related events on operators.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec31\"\u003e\n \u003ch2\u003e4.2 Effects of aftershocks\u003c/h2\u003e\n \u003cp\u003eAs described in Section 4.1, the effects of frequent aftershocks on operators, in terms of vibration, are inferred to be small because no differences were observed in any of the indices between the presence and absence of vibration. In other words, the vibrations of aftershocks are unlikely to cause physical and mental stress. However, Table\u0026nbsp;2 indicates that the number of errors related to event no. 5, \u0026ldquo;Flooding of Fuel Pool,\u0026rdquo; was higher than that of other events regardless of the presence or absence of vibration. Further, in their interviews, six participants clarified that plant response was affected by aftershocks. Accordingly, the existence of aftershock effects other than vibrations was confirmed. Hirose et al. (2021) reported an increase in human errors during aftershocks, which was also supported by the current study. The interviews findings suggested that \u0026ldquo;work interruption\u0026rdquo; and \u0026ldquo;changes in plant conditions\u0026rdquo; caused by aftershocks had an impact on the participants.\u003c/p\u003e\n \u003cp\u003eOne significant effect observed in this study was the disruption of work caused by the aftershocks. In event no. 5, which led to the highest number of errors, the sub-shift manager had instructed participants carry out three responses, as detailed in Table\u0026nbsp;1, before the occurrence of the second aftershock. However, in addition to event no. 6 (injured person), the second aftershock and its associated event no. 7 (RCIC Trip) occurred before the response, so the actual response could not be made until after the second aftershock\u0026rsquo;s occurrence. Notably, all the errors recorded for event no. 5 were omission errors\u0026mdash;failures to perform checks or make reports. Although it is possible that event no. 6 which occurred just before the second aftershock influenced the results, some interview comments were concerned about work interruption and oblivion (e.g., \u0026ldquo;The earthquake occurred when I was trying to do something,\u0026rdquo; \u0026ldquo;I could not follow the sub-shift manager\u0026rsquo;s instructions because of the pause,\u0026rdquo; and \u0026ldquo;I forgot what to do\u0026rdquo;) and about the time required to reconfirm the plant (e.g., \u0026ldquo;The major parameters changed due to the aftershock so it was burdensome to reconfirm,\u0026rdquo; and \u0026ldquo;I had to reconfirm again\u0026rdquo;) were obtained. The adverse effects of aftershocks were described in the introduction; however, this study clarifies that the \u0026ldquo;forced interruption (halt) of response\u0026rdquo; and \u0026ldquo;interruption of plant reconfirmation work due to aftershocks\u0026rdquo; can easily induce omission errors.\u003c/p\u003e\n \u003cp\u003eAnother aftershock effect is the stress on changes in plant conditions, particularly new abnormalities, caused by aftershocks. This study could not determine the aftershocks\u0026rsquo; impact on physiological and psychological indices. However, as mentioned earlier, several interview comments on the time and effort required to reconfirm the plant were obtained. In addition, comments such as \u0026ldquo;It was difficult to detect abnormalities in aftershocks without following the system,\u0026rdquo; \u0026ldquo;I had to be very careful to find differences,\u0026rdquo; and \u0026ldquo;It was very stressful when an event progressed (or a new event started) due to aftershocks\u0026rdquo; suggested that the start or progress of events due to aftershocks and the need to detect them was stressful for the operators.\u003c/p\u003e\n \u003cp\u003eThe Electric Power Research Institute (2016) describes aftershocks as important distractors. Further, other literature (The National Diet of Japan 2012; Human-Machine Systems Research Subcommittee in Atomic Energy Society of Japan et al. 2015) highlights the impact of aftershocks\u0026rsquo; using earlier cases, as noted in the introduction. This study also clarified this type of effect. Further, the effects of aftershocks are as important as those of the main shock when considering operators\u0026rsquo; performance during earthquakes.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec32\"\u003e\n \u003ch2\u003e4.3 Limitations\u003c/h2\u003e\n \u003cp\u003eLimitations of this study are as follows.\u003c/p\u003e\n \u003cdiv\u003e\n \u003cp\u003e(1) Real disasters cannot be completely reproduced.\u003c/p\u003e\n \u003cp\u003eParticipants were aware that the earthquakes in this study were simulated and merely vibrations. Although they were not explicitly informed of the time of occurrence of the seismic motion, they were instructed in advance that the motion might occur. Therefore, we could not completely reproduce the psychological difficulties caused by the suddenness (Shibata and Takada 1995) unique to earthquake occurrence. Furthermore, there was no danger, such as any uncertainty regarding the safety of family members or an increase in radiation levels in the MCR, as was the case in the Fukushima accident. Therefore, it is impossible to completely reproduce the situation of a major earthquake in a simulated environment.\u003c/p\u003e\n \u003c/div\u003e\n \u003cp\u003eHowever, as indicated by Hirose et al. (2021), it is possible to obtain data on operator performance during an earthquake and identify problems by focusing only on certain parts of the simulated environment, such as the response immediately after an earthquake, and, by making some modifications to ensure a high sense of realism, such as seismic motion, and the communication among other operators. Although the study did not completely simulate the earthquake, most participants felt a sense of reality in the VR environment and could immerse themselves in plant response, indicating that they had a sense of realism and were able to respond to the situation. In addition, changes in physiological indices and an increase in the number of errors during aftershocks were confirmed. Furthermore, the interviews conducted after the experiment provided information on the problems caused by vibration that were not clarified in normal training, such as disorganized thinking, delayed movements, and disorganized prioritization. In addition to collating the lessons obtained from major earthquake cases, future studies should collect data under simulated environments for different scenarios and operator attributes (age, position, etc.) to implement measures to improve safety from a broad perspective.\u003c/p\u003e\n \u003cp\u003e(2) Large differences from actual operation\u003c/p\u003e\n \u003cp\u003eAnother limitation of this study includes the following differences from real-world operations :\u003c/p\u003e\n\u003c/div\u003e\n\u003cp\u003e1) All checks and operations are performed based on the operation manual.\u003c/p\u003e\n\u003cp\u003e2) The operators themselves perform detailed checks of alarms and operations.\u003c/p\u003e\n\u003cp\u003e3) Responses are performed by a team.\u003c/p\u003e\n\u003cp\u003eThese issues were caused by the performance limitations of devices such as PCs and HMDs. Since the simulated operations were different from actual ones, unnecessary stress might have been added unintentionally. If the operation manual had been available and the operation had been handled by a team, recovery actions, such as the pointing out of errors by other operators, could have occurred, and the number of errors could have been significantly reduced. Furthermore, since all the operations were performed by the experimenter, this study could not provide any indication of operational errors. Moreover, it was not possible to investigate how the sub-shift manager, who was giving instructions, was affected by exposure to seismic motion. In the future, researchers should address these issues using technologically advanced PCs and HMDs.\u003c/p\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003eThe results of this study revealed the following effects on operators of seismic motion by itself: First, the occurrence of transient physiological stress during the main shock and second, feeling the effects on plant response, such as \u0026ldquo;disorganized thinking,\u0026rdquo; \u0026ldquo;delayed actions,\u0026rdquo; \u0026ldquo;disorganized priorities,\u0026rdquo; and \u0026ldquo;tension/anxiety,\u0026rdquo; but not so strongly as to feel threatened and with almost no effect on actual performance. However, regarding the aftershocks\u0026rsquo; effects on operators, results revealed that first, the motion caused by the aftershocks by itself had almost no effect; second, the presence of aftershocks increased event-related omission errors immediately before the shock occurrence; and third, the effects of aftershocks felt by the operators were work interruption, resulting in concern about forgetting what had been handled and the \u0026ldquo;effort to recheck the plant,\u0026rdquo; and \u0026ldquo;burden and confusion due to changes in the plant situation, particularly the occurrence of new events.\u0026rdquo; Although the simulated environment is a limitation, it was possible to obtain data on the psychological effects of seismic motion that could not be obtained during normal training. Adding a seismic vibration experience using a simulated environment, as in this study, to regular training will not only help operators develop safety countermeasures based on data collected on operators\u0026rsquo; performance, but it will also improve their earthquake preparedness. In the future, we plan to try to discover new findings by changing the scenarios and the attributes of the participants in the experiments.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eFunding:\u003c/h2\u003e \u003cp\u003eThe authors did not receive support from any organization for the submitted work.\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eConflict of interest:\u003c/strong\u003e \u003cp\u003eThe authors have no relevant financial or non-financial interests to declare.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eEthics approval:\u003c/strong\u003e \u003cp\u003e This study was approved by the Nuclear Risk Research Center\u0026rsquo;s Research Ethics Review Committee in Central Research Institute of Electric Power Industry.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAll authors contributed to the study\u0026rsquo;s conception, design, and data collection. Ayako Hirose conducted the analyses and wrote the paper. Finally, all authors commented and approved the paper.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eWe express our gratitude to the staff of Hamaoka Nuclear Power Station and Mr. Shingo Kuroda for their significant contribution to this research. We would also like to thank the staff of Hitachi GE Nuclear Energy, Ltd., and Hakusan Corporation for their technical assistance with the experiments. Finally, we would like to thank Editage (www.editage.jp) for English language editing.\u003c/p\u003e\u003ch2\u003eData availability\u003c/h2\u003e \u003cp\u003eThe data that support the findings of this study are not openly available due to reasons of individuals\u0026rsquo; privacy and are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAdachi S, Matsudaira M, Hirayama Y, Yoshida M, Midorikawa S, Hirose S (2010) Development of Earthquake Experience System Using Ground Motion Simulator \u0026ldquo;Jishin The Vuton\u0026rdquo;. Joint Conference Proceedings of the 7th International Conference on Urban Earthquake Engineering (7CUEE) and 5th International Conference on Earthquake Engineering (5ICEE), Tokyo, Japan: 317-320.\u003c/li\u003e\n\u003cli\u003eAllen JJB, Chambers AS, Towers DN (2007) The many metrics of cardiac chronotropy: a pragmatic primer and a brief comparison of metrics. 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HAI Bulletin 10(1): 84-99. https://doi.org/10.1079/hai.2022.0004\u003c/li\u003e\n\u003cli\u003ePark G, Sim J, Kim J (2018) Experiment Design for Investigating Human Performances in Diagnostic Task Under Seismic Situation. Transactions 119(1): 338-341.\u003c/li\u003e\n\u003cli\u003ePark J, Kim Y, Kim JH, Jung W, Jang SC (2015) Estimating the response times of human operators working in the main control room of nuclear power plants based on the context of a seismic event - A case study. Ann Nucl Energ 85: 36-46. https://doi.org/10.1016/j.anucene.2015.03.053\u003c/li\u003e\n\u003cli\u003ePatle DS, Manca D, Nazir S, Sharma S (2019) Operator training simulators in virtual reality environment for process operators: a review. 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Lisbon, Portugal: 17790-17799. https://www.iitk.ac.in/nicee/wcee/article/WCEE2012_3044.pdf\u003c/li\u003e\n\u003cli\u003eSuzuki M, Terashita H, Oda Y, Yagi A (1999) On the items and usage of a questionnaire for evaluation of stress caused by phasic task demand. The Japanese Journal of Ergonomics 35(4): 259-270. (in Japanese). https://doi.org/10.5100/jje.35.259\u003c/li\u003e\n\u003cli\u003eThe National Diet of Japan (2012) The official report of The Fukushima Nuclear Accident Independent Investigation Commission Executive summary. https://www.cas.go.jp/jp/seisaku/icanps/eng/final-report.html. Accessed 25 Dec. 2023.\u003c/li\u003e\n\u003cli\u003eTing L (2017) Virtual Reality of Earthquake Ground Motions for Emergency Response. In: Proceedings of the 6th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering. Rhodes Island, Greece, COMPDYN2017 (1): 2089-2094. https://epublications.marquette.edu/civengin_fac/184/\u003c/li\u003e\n\u003cli\u003eToichi M, Sugiura T, Murai T, Sengoku A (1997) A new method of assessing cardiac autonomic function and its comparison with spectral analysis and coefficient of variation of R-R interval. J Autonom Nerv Syst 62 (1-2):79-84. https://doi.org/10.1016/s0165-1838(96)00112-9\u003c/li\u003e\n\u003cli\u003eToichi M, Kamio Y, Murai T, Kubota R, Inakuma T, Sengoku A (1998) Changes of Cardiac Autonomic Function in Association with Psychotic Symptoms in Schizophrenia. Seishin Igaku 40(1): 37-42. (in Japanese). https://doi.org/10.11477/mf.1405904466\u003c/li\u003e\n\u003cli\u003eXu J, Tang Z, Yuan X, Nie Y, Ma Z, Wei X, Zhang J (2018) A VR-based the emergency rescue training system of railway accident. Entertain Comput27: 23-31. https://doi.org/10.1016/j.entcom.2018.03.002\u003c/li\u003e\n\u003cli\u003eYamaguchi A (2021) Close Look at the Accident in Fukushima Dai-ichi Nuclear Power Plant and What-if. In: Atomic Energy Society of JAPAN Insights concerning the Fukushima daiichi nuclear accident 1: 106-118.\u003c/li\u003e\n\u003cli\u003eYokobayashi M, Oikawa T, Muramatsu K (2002) Modeling of human error for a seismic PSA. Transactions of the Atomic Energy Society of Japan 1(1): 95\u0026ndash;105. (in Japanese). https://doi.org/10.3327/taesj2002.1.95\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Footnotes","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003e In this study, the vibrations simulated by the apparatus to replicate earthquake conditions are designated in specific terms: the first simulated vibration is termed the main shock and subsequent vibrations are referred to as aftershocks. Together, these terms called an earthquake or a seismic motion in this study. Further, even when no vibration is generated under experimental conditions, the terms main shock and aftershock are used in the same manner.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Earthquake, Main shock, Aftershock, Nuclear power plant, Virtual reality","lastPublishedDoi":"10.21203/rs.3.rs-4221596/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4221596/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eExperiments were conducted to clarify the effects of seismic motion and aftershocks on the performance and physiological and psychological states of nuclear power plant operators. Nine reactor operators (average experience: 5.2 years) responded to various events associated with a great earthquake using a virtual reality simulator that simulated the main control room and plant behavior and a chair-type earthquake simulator. The experimental conditions were the presence and absence of vibrations. For each condition, the differences in the following indices were analyzed: The errors and utterances made during plant response were performance indices; cardiac sympathetic index, cardiac vagal index, and skin conductance level were physiological indices; and responses to a questionnaire on stress were psychological indices. Results revealed that operators experienced transient physiological stress at the time of the main shock, and felt the seismic motion\u0026rsquo;s effects on plant operations, such as \u0026ldquo;delay in initial response\u0026rdquo; and \u0026ldquo;disruption of priorities,\u0026rdquo; which did not seem threatening. They did not perceive any impact on performance. For aftershocks, it was found that the motion of the aftershocks themselves had almost no effect on the operators, but that the presence of aftershocks increased omission errors for events occurring immediately before the aftershocks, and that \u0026ldquo;work interruption\u0026rdquo; and \u0026ldquo;changes in plant conditions\u0026rdquo; due to aftershocks had affected them. Adding a seismic vibration experience using a simulated environment to regular training will contribute to the collection of performance data for operators and improve operators\u0026rsquo; preparedness for earthquakes.\u003c/p\u003e","manuscriptTitle":"Experimental Study on Nuclear Power Plant Operators’ Performance during a Major Earthquake with Aftershocks","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-11 16:43:25","doi":"10.21203/rs.3.rs-4221596/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"201db7d7-9d20-4e1e-b57f-60367ac75ee6","owner":[],"postedDate":"April 11th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-11T03:24:35+00:00","versionOfRecord":[],"versionCreatedAt":"2024-04-11 16:43:25","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4221596","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4221596","identity":"rs-4221596","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}