Low temperature primary circuit decontamination technology

Low temperature primary circuit decontamination technology | 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 Low temperature primary circuit decontamination technology Kateřina Čubová, Jan Houzar, Mojmír Němec This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8394280/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 Recently, a low-temperature recyclable decontamination medium was developed and patented at Department of Nuclear Chemistry, FNSPE, CTU in Prague for the purposes of decontamination for decommissioning. Due to the presence of silver ions used as a catalyst in the original technology, the medium is not suitable for use in operational decontamination. Current research focuses on modifications in its chemistry to make it applicable for operational decontamination of primary circuit components in specific conditions of Czech nuclear power plants. Summary of the first part of the work aimed at finding a suitable replacement for silver ions. Testing of its effectiveness on model substrates is described in this paper. Decontamination corrosion layer primary circuit Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Introduction In the Czech Republic, there are two nuclear power plants (NPPs), both of them with pressurized water reactor of Russian type VVER. A total of four VVER 440 model V 213 pressurized water reactors, with an electrical output of 512 MWe each, are installed at the Dukovany Nuclear Power Plant, while Temelín Nuclear Power Plant uses two pressurized water reactors VVER 1000 type V 320, what currently generates 2 x 1125 MWe. The primary circuit (PC) components are expected to have a minimum service life of 40 years. Currently, the operation of both Czech nuclear power plants is expected to be extended to 60 years [ 1 ]. Under these circumstances, the maintenance of PC technology and its chemical regime play a crucial role. The components of the Temelín (ETE) and Dukovany (EDU) nuclear power plants (with the exception of the main circulation piping of the EDU) are made of 22K carbon steel, 15Ch2MFA or 15Ch2NMFA low-alloy steel [ 2 , 3 ]. In order to achieve high corrosion resistance, a layer of austenitic stainless-steel type 08Ch19N10G2B (EDU pressure vessel), 04Ch20N10G2B (ETE pressure vessel) or 08Ch18N10T (other components) [ 2 , 3 ] is welded onto inner walls. The main circulation piping of the EDU, as well as the collectors and heat exchange surfaces of the steam generators (SG) of both NPPs, are also made of 08Ch18N10T steel. The composition of the above-mentioned steels is shown in Table 1 . Table 1 Composition of selected austenitic stainless steels (in mass %) [ 4 , 5 , 6 ] Steel C Mn Si P S Cr Ni Mo Nb Ti 08Ch19N10G2B max. 0,08 1,80– 2,20 0,20– 0,45 max. 0,025 max. 0,018 18,5– 20,5 9,50–10,50 max. 0,25 0,90– 1,30 - 04Ch20N10G2B max. 0,03 1,80– 2,20 0,20– 0,45 max. 0,015 max. 0,01 18,5– 22 9,5– 10,5 - 0,9–1,1 - 08Ch18N10T max. 0,08 1,0–2,0 max. 0,8 max. 0,035 max. 0,02 17–19 9–11 - - 5xC– 0,7 High chromium and nickel content gives the steels high corrosion resistance. However, stainless steels are completely inert in coolant and despite the strict chemical regime of primary circuit operating conditions, corrosion layer with different compositions is formed on the inner walls of individual components during operation. The exact composition of the corrosion layers depends primarily on the composition of the base material, the chemical regime of the primary circuit and operational history of the reactors [ 7 ]. The decontamination method in radioactivity management is a procedure aimed at reducing the activity of monitored radionuclides of the contaminated subject, facility or equipment below the level detectable by conventional methods, or below the level set by the limits in the relevant legislation. The level of decontamination defined in the previous definition is, in practice, an ideal state that is desirable to achieve, but this is often not possible, and decontamination is carried out to a reasonably achievable level in terms of minimizing radioactivity of the subject, time needed for decontamination, costs, and the amount of resulting secondary waste. Chemical decontamination processes involve controlled dissolution of contaminated corrosion layers using chemical agents. Individual methods differ in the type of reagents used, their concentration, and the method and conditions of application [ 1 , 2 , 8 , 9 ]. Chemical decontamination is performed either by immersing the decontaminated object in a decontamination solution or by circulating the decontamination solution through a closed system that includes the contaminated surface. The advantage of chemical methods used in nuclear power plants for decontamination of steam generators and main circulation pump, etc. is high versatility, possibility of application to geometrically complex surfaces and relatively high decontamination factors. The disadvantages are generation of large amounts of secondary waste, aggressiveness of the agents and often time-consuming nature of the process [ 1 , 2 , 8 , 9 ]. For successful decontamination of the PC and adjacent technologies, the entire corrosion layer must usually be removed. Regarding the purpose of use, there are two basic approaches to decontamination. Decontamination for decommissioning aims at reduction of the activity of radionuclides below release levels so that the materials can be further treated as non-active and released or re-used. For this purpose, it is usually necessary to remove not only corrosion layer, but also a layer of underlying steel of varying thickness. Therefore, in most cases, more aggressive methods (with higher concentration of reagents) are used, that reach higher efficiency at the cost of greater surface damage. Operational decontamination, on the other hand, is carried out to ensure safe operation for staff and requires minimization of damage to the decontaminated surface. The methods used usually belong to the category of soft methods (lower concentration of reagents), which achieve lower efficiency but also less damage to the material. During operational decontamination, which is performed during regular shutdowns, changes occur in the structure and chemical composition of the corrosion layers [ 10 ]. The composition and thickness of the individual layers depend on the specific conditions in the power plant (operating time, frequency and type of operational decontamination, and changes in the chemical regimes of the coolant in the primary circuit) and are characteristic to individual reactors. However, in all cases, the large volume of secondary waste is generated and must be treated. Based on literary review and practical experience, problematic and difficult-to-dissolve components of corrosion layers were identified – magnetite, chromium oxide, and spinel materials with a higher chromium content [ 7 , 8 , 9 ]. From a chemical point of view, magnetite is an iron-iron spinel with sorption capabilities and considerable stability in common decontamination solutions. Replacing iron atoms with Ni and Cr atoms produces various types of other resistant spinels. Chromium-based spinels (based on chromium oxide) are very stable substances with very limited solubility in common chemicals. Most methods for dissolving highly resistant structures containing chromium utilize the oxidation of trivalent chromium Cr(III) to hexavalent Cr(VI). The resulting chromates are readily soluble. Similarly, it is possible to disrupt the spinel structure of magnetite by oxidizing or reducing one of the iron atoms. Therefore, a two-stage process is usually used for the decontamination of stainless steel, in which the actual dissolution of the corrosion layer is preceded by its oxidation. Given that oxidation is followed by one rinse and dissolution by 2–3 rinses with clean condensate, this type of decontamination produces a quantity of radioactive waste equal to 5–6 times the volume of the decontaminated part [ 8 , 11 ]. In the field of the development of new advanced decontamination methods, in accordance with current trends, great emphasis is placed on maximizing the recycling/regeneration of used decontamination agents and overall process cost savings. In this context, there is a strong demand from nuclear facility operators for new solutions that would replace or improve the currently used technologies. Important and positively evaluated parameters of the procedures under consideration are: the overall economics of the process, its environmental impact, and the load on the radioactive waste repository. The development of new advanced processes for decontamination is therefore desirable and requires targeted industrial applications of scientific knowledge. Following the above-mentioned requirements, recyclable decontamination medium for decommissioning nuclear facilities was developed at the Department of Nuclear Chemistry, FNSPE, CTU in Prague in the frame of project MPO TRIO (see Acknowledgement). The research was focused on finding a suitable chemical system that would effectively disrupt and dissolve the specific corrosion layer formed on the inner surface of the primary circuit material in VVER-type power plants (EDU and ETE) covered with corrosion-resistant austenitic steel 08Ch18N10T. The aim was therefore to find a system for circuit decontamination, in which the decontamination solution would effectively dissolve corrosion layers and be easily recyclable, i.e., reusable after purification and restoration of key chemical components. The solution was aimed primarily to pre-dismantling decontamination as part of the decommissioning of a nuclear power plant, which meets the requirement to minimize secondary radioactive waste. It has been found that the only system that reliably dissolves all of the tested substrates is potassium peroxydisulfate (PDS) in an acidic environment catalysed by silver ions. Peroxydisulfate is a very strong oxidizing agent with an oxidation potential around 2.0 [ 12 , 13 ], but at normal temperatures the reaction proceeds relatively slowly. Therefore, so-called activators are used to increase the reaction rate. It has been found that in sulfuric acid environment, dissolution did not occur without the presence of catalysing ions, and only Ag + ions showed an observable effect. The resulting medium, which was patented in 2021 [ 14 ], consisted of 0.1M potassium peroxydisulfate (K 2 S 2 O 8 ) and 0.8mM AgNO 3 in 5% H 2 SO 4 . This medium efficiently dissolved model substrates from the group of oxides and spinels as analogues and building materials of real corrosion layers. The most significant advantage of this medium was highest efficiency for dissolving model substrates at 50°C, which means significant cost savings compared to commonly used methods that require an operating temperature of around 90°C. [ 15 ]. Given its effectiveness at low temperatures, it would be strongly desirable to use the developed medium not only for decontamination during decommissioning, but also for regular operational decontamination. Unfortunately, even the medium meets requirements for decommissioning purposes, its application in operational decontamination is complicated by the presence of silver ions, which are an undesirable contaminant in primary circuit due to their neutron activation – nuclides with longer lifetimes and significant gamma emissions are produced such as 110m Ag (249.83 days), and 108m Ag (437.27 y). Therefore, research described in this paper focused on modifications in its chemistry to make it applicable for operational decontamination of primary circuit components in specific conditions of Czech NPPs. Successful application would enable decontamination at significantly lower temperatures, reduction of the volume of secondary waste and overall improvement of the economy of the decontamination process. Theory As stated above, corrosion layers formed on stainless steels used in primary circuit consist of insoluble spinel-type mixed oxides of Fe(II/III), Cr(III) and Ni(II). Due to high content of Cr, the corrosion layers need to be oxidized to form more soluble compounds. To oxidize Cr(III) to Cr(VI), a strong oxidation agent with redox potential of at least 1.38 V vs. SHE is necessary [ 16 ]. Table 2 summarizes redox potentials of selected chemical species capable of oxidizing Cr(III). Several decontamination methods for stainless steel materials are based on the use of strong oxidizing agents, e.g. KMnO 4 , O 3 or Ce(IV) [ 17 ]. However, most conventional chemical decontamination methods achieve required decontamination factors only at high temperatures (around 90°C). Therefore, novel chemical agents are sought, that could work at lower temperatures, similar to the patented peroxydisulfate-based medium, which showed maximum efficiency for Cr 2 O 3 dissolution at 50°C; hence this paper is focused on identifying low-temperature oxidation agent to be applicable for operational use as a part of decontamination medium. Table 2 Redox potentials of selected pairs [ 16 , 18 ] Redox pair Cr(VI) Ce(IV) MnO 4 - O 3 (g) BrO 3 - Pb(IV) S 2 O 8 2- Ag(II) Cr(III) Ce(III) Mn(IV) O 2 (g) Br - Pb 2+ SO 4 2- Ag + E [V vs. SHE] 1.38 1.72 1.68 2.08 1.42 1.46 2.01 1.98 Peroxydisulfate (PDS), used in the previously developed medium (see introduction), is a strong oxidation agent capable of Cr(III) oxidation. However, under normal conditions, direct oxidation by PDS is slow. Therefore, a suitable activation method is necessary. During activation, secondary, highly oxidizing species (e.g. SO 4 • - , OH• or Ag(II)) are produced, that oxidize the substrate [ 19 , 20 ]. Methods for activation of peroxydisulfate include alkali, heat, UV irradiation, ultrasound, activated carbon and transition metal ions [ 21 ]. PDS activated by transition metals is being intensively studied for degradation of organic pollutants. Metal ions that have been reported to work as activators for PDS are Ag(I), Fe(II/III), Cu(II), Co(II), Ce(III), Mn(II), Ni(II) or Ru(III) [ 20 , 22 , 23 , 24 , 25 , 26 ]. Reports on PDS use for decontamination purposes are very scarce. In the current research, alternatives to silver ions activated PDS were sought. Based on available literature assessment, bromate was chosen as another oxidation agent for testing in this study due to its sufficient redox potential for oxidation of Cr(III), short-lived activation products and possible electrolytic regeneration, similar to persulfate. Oxidation of Cr(III) to Cr(VI) by BrO 3 - has been experimentally verified by different authors [ 27 , 28 , 29 ]. However, to the best knowledge of the authors, bromate has not yet been tested as a part of decontamination solution. Depending on pH, oxidation by bromate can proceed via different reaction paths. In acidic environment, reactions (1) or (2) take place with standard redox potential 1.48 V vs. SHE and 1.42 V vs. SHE, respectively [ 18 ]. In basic environment, oxidation proceeds through reaction (3) with standard redox potential 0.61 V vs. SHE [ 18 ]. BrO 3 - + 6 H + + 5 e - ↔ ½ Br 2 + 3 H 2 O (1) BrO 3 - + 6 H + + 6 e - ↔ Br - + 3 H 2 O (2) BrO 3 - + 3 H 2 O + 6 e - ↔ Br - + 6 OH - (3) This paper summarizes preliminary testing aimed at finding a suitable replacement for silver ions and/or peroxydisulfate in decontamination media. The effectiveness of potential activators and/or oxidizing agents was tested on commercially available model substrates, specifically Fe 3 O 4 , Cr 2 O 3 , Fe 2 NiO 4 . Experimental Chemicals Potassium bromate (KBrO 3 ; ≥ 99.8%) and nitric acid (HNO 3 ; 68%) were obtained from VWR Chemicals. Potassium peroxydisulfate (K 2 S 2 O 8 ; ≥ 99%) was purchased from Carl Roth. Chromium(III) oxide (Cr 2 O 3 ; p.a.), lead(IV) oxide (PbO 2 ; p.a.), phosphoric acid (H 3 PO 4 ; 85%) and sulphuric acid (H 2 SO 4 ; 93%) were procured from Lachema. Iron nickel oxide (Fe 2 NiO 4 ; ≥ 98%) and ruthenium(III) nitrosyl nitrate solution in dilute nitric acid (Ru(NO)(NO 3 ) x (OH) y ) were obtained from Sigma Aldrich. Iron (II, III) oxide (Fe 3 O 4 ; 97%) and silver nitrate (AgNO 3 ; p.a.) were purchased from Alfa-Aesar and Penta Chemicals, respectively. Methods Dissolution experiments were carried out in plastic 15 ml vials. Stock solutions of K 2 S 2 O 8 (0.15 mol L -1 ) or KBrO 3 (0.35 mol L -1 ) were prepared daily by dissolving the appropriate amount of solid in demineralized (demi) water. Stock solutions of peroxodisulfate activators were prepared at concentrations of 0.1 or 0.01 mol L -1 in demi water. The amount of 25 ± 2 mg of the selected substrate (Cr 2 O 3 ; Fe 3 O 4 or Fe 2 NiO 4 ) was put in the vial and appropriate volumes of K 2 S 2 O 8 or KBrO 3 stock solution, activator stock solution (only for PDS) and acid were added, and the vial was filled up to 10 ml using demi water (V/m = 400 mL g -1 ). Content of the vial was shaken gently and put in a thermoreactor (Spectroquant TR 420, Merck) preheated to set temperature. Unless stated otherwise, final conditions were: 0.1M K 2 S 2 O 8 /KBrO 3 + 0.8mM activator (PDS only) + 5% H 2 SO 4 at 50°C. During experiments, the vials were shaken gently in fixed intervals (15 min; 30 min; 1 h; 2 h; 3 h; 4 h and 5 h). After 5 h (excluding kinetics experiments), the vials were taken out of the reactor and centrifugated at 1500 RCF for 1 minute. Aliquots from each vial were taken and diluted in 1% HNO 3 (prepared from 67–69% stock solution; for trace metal analysis, NORMATOM ® , VWR Chemicals). Concentrations of Cr were determined by AAS (Varian AA240FS, Varian) and concentrations of Fe and Ni by ICP-MS (Agilent 7500 ICP-MS, Agilent Technologies). The uncertainties of percentages of dissolved metals were quantified as a combined uncertainty of the statistics of the measurement and pipetting. In experiments, where less than 5% of a substrate was dissolved, the absolute uncertainties were lower than 0.4%. In most experiments, where dissolution was higher than 5%, the relative uncertainties were lower than 5%. Results and discussion Decontamination medium based on peroxydisulfate Based on previously published result of the authors [ 15 ], experiments with peroxydisulfate were conducted. As a strong oxidation agent, peroxydisulfate anion has high enough redox potential to oxidize Cr 2 O 3 into CrO 4 2- . However, as seen from Fig. 1 , no Cr 2 O 3 dissolved in a solution containing 0.1 mol L -1 PDS in 5% acid at 50°C. A number of potential alternatives to Ag + was tested for activation of PDS. Selected chemical compounds include Cu 2+ , VO 2+ , Fe 3+ , Ce 3+ , Cr 3+ , Bi 3+ , Br - , ReO 4 - , MnO 4 - , CrO 4 2- , Ru(NO)(NO 3 ) x (OH) y , PbO 2 and 4-hydroxy-TEMPO. It was found that both Fe 3 O 4 and Fe 2 NiO 4 dissolve efficiently in 0.1M PDS in 5% H 2 SO 4 , even without the presence of any activator. On the other hand, in the presence of vast majority of the tested activators, less than 0.1% of Cr 2 O 3 was dissolved. The only exceptions, apart from silver ions, were lead(IV) oxide and ruthenium in the form of nitrosyl nitrate (Fig. 1 ). Highest percentage of dissolved Cr was achieved using silver ions-activated PDS in sulfuric acid. Dissolution efficiency in the presence of Ru(NO)(NO 3 ) x (OH) y (hereafter abbreviated as RuN) and PbO 2 was much lower. Also, PbO 2 was identified as a primary oxidation agent, capable of Cr 2 O 3 dissolution even in absence of PDS. Unfortunately, neither PbO 2 nor Ag + are suitable for use in operational decontamination. Therefore, only RuN was selected as an activator for more detailed experiments. Dependence of percentage of dissolved chromium by 0.1M PDS in 5% H 2 SO 4 on temperature and concentration of RuN is shown in Fig. 2 . Dissolution efficiency increases with both - temperature and concentration of the activator. Without the presence of RuN, no Cr 2 O 3 dissolution was observed up to 50°C after 5 h, and even at 80°C, less than 0.5% of Cr 2 O 3 amount dissolved. On the other hand, more than 5% was dissolved by PDS activated with 1.2mM RuN at 80°C. Similar trend in temperature dependence can be seen in Fig. 3 , which shows the effect of H 2 SO 4 concentration with 0.1M PDS and 0.8mM RuN. For all three concentrations of sulfuric acid (1, 5 and 10%), amount of dissolved Cr increased with temperature. However, no clear trends could be observed regarding the effect of H 2 SO 4 concentration across the whole temperature range. Even though Ru(NO)(NO 3 ) x (OH) y can act as an activator for PDS for Cr 2 O 3 dissolution, the efficiency was much lower compared to silver ions in previously patented medium. From activation point of view, 103 Ru (β - , 39.2 days) would be the main produced radionuclide, which should not be critical for general radioactive waste management. Moreover, a black film was observed forming on walls of the vials; its intensity increased with temperature a Ru concentration. The film formation was presumably caused by sorption of the ruthenium compound. This effect would have a negative influence on heat exchange properties of steam generator tubes, when used for operational decontamination of primary circuit, therefore Ru(NO)(NO 3 ) x (OH) y is not suitable for this purpose. Since no suitable decontamination solution based on peroxydisulfate was found, further research focused on finding a different oxidation agent as a replacement for PDS. Decontamination medium based on bromate Based on available literature search, bromate was chosen as an alternative to PDS. From activation point of view, the longest activation product 82 Br (β - , 35.28 h) does not constitute a problem for general radioactive waste management. The next chapter covers the dependence of Cr 2 O 3 , Fe 3 O 4 and Fe 2 NiO 4 dissolution by KBrO 3 solution on the most important parameters of the system. These parameters include acidity of the solution, temperature and concentration of KBrO 3 . Furthermore, the kinetics of Cr 2 O 3 dissolution was studied. Influence of acidity Unlike PDS, bromate can oxidize Cr 2 O 3 , as well as other insoluble compounds found in corrosion layers, in acidic environment without the need of any activator. Percentage of dissolved Cr 2 O 3 , Fe 3 O 4 and Fe 2 NiO 4 using 0.1M KBrO 3 solution in different acids (H 2 SO 4 , HNO 3 and H 3 PO 4 ; fixed concentration 5%) is shown in Fig. 4 . In presence of KBrO 3 , Cr 2 O 3 dissolved efficiently in HNO 3 and H 2 SO 4 , but not in H 3 PO 4 . On the other hand, Fe 3 O 4 was dissolved easily in H 3 PO 4 and H 2 SO 4 , but not in HNO 3 . Fe 2 NiO 4 was found to dissolve readily in all three acids with H 2 SO 4 showing highest efficiency. Based on these results, solution of bromate in H 2 SO 4 was selected for further testing, as it showed reasonable efficiency for all three model substrates and sulfuric acid or sulphates are also well accepted in radioactive waste solidification processes. Efficiency of Cr 2 O 3 , Fe 3 O 4 and Fe 2 NiO 4 dissolution is affected not only by the nature of the acid, but also by its concentration. None of the substrates was dissolved by bromate in neutral or basic environment. As seen in Fig. 5 , both Cr 2 O 3 and Fe 3 O 4 were dissolved only if concentration of H 2 SO 4 was higher than ca. 0.5%. Dissolution of Fe from Fe 2 NiO 4 took place at concentrations higher than 0.1% and release of Ni from Fe 2 NiO 4 was observed even in 0.005% H 2 SO 4 . It is worth mentioning that in all experiments with Fe 2 NiO 4 , percentage of dissolved nickel was higher than dissolved iron. Dissolution efficiency of all selected substrates increased with increasing concentration of H 2 SO 4 . It should be noted that Fe 3 O 4 and Fe 2 NiO 4 were dissolved with similar efficiency even without the presence of KBrO 3 . The observed increased dissolution rate with H 2 SO 4 concentration can therefore be attributed to the acid itself. On the other hand, in the case of Cr 2 O 3 , which did not dissolve in H 2 SO 4 alone, the same effect probably has a different cause. In acidic environment, bromate reduction can proceed through reactions (1) or (2), while in basic environment, only reaction (3) takes place (see the Theory section). Redox potential of reaction (3) is not sufficient for Cr 2 O 3 oxidation. Therefore, Cr 2 O 3 can only be oxidized by KBrO 3 when concentration of H + is high enough for reaction (1) or (2) to proceed. Increasing acid concentration favours Cr 2 O 3 oxidation and enhances dissolution efficiency. Influence of bromate concentration and temperature Efficiency of the substrates’ dissolution is also affected by temperature of the solution and concentration of KBrO 3 . As seen from Fig. 6 , efficiency of Cr 2 O 3 dissolution increased with both temperature and KBrO 3 concentration. In 0.01M KBrO 3 , percentage of dissolved Cr was negligible (< 1%) at 30 and 40°C, and even at 70°C, the efficiency reached only ca. 7%. On the other hand, in 0.3M KBrO 3 , more than 18% of Cr 2 O 3 was dissolved at 30°C, and at 60 and 70°C, the dissolution reached almost 100%. Achieving sufficient decontamination factors is a crucial part in development of a low-temperature decontamination medium. In the bromate-based medium, decreased efficiency of Cr 2 O 3 -based corrosion layers’ dissolution due to lower temperature could be compensated by increasing bromate concentration. Dissolution rate of Fe 3 O 4 also increased with reaction temperature (Fig. 7 ), although in this case, no significant effect of bromate concentration was observed. At 30°C, the percentage of dissolved Fe was very low (~ 2%), for all four KBrO 3 concentrations. At higher temperatures, the efficiency increases significantly, reaching ca. 13% and 40% at 50°C and 70°C, respectively. The independence of Fe 3 O 4 dissolution rate on concentration of KBrO 3 indicates that, in this case, the dissolution is not coupled with oxidation and proceeds directly in acidic environment without bromate contribution. However, the efficiency can still be increased by increasing H 2 SO 4 concentration (Fig. 5 ). In the case of Fe 2 NiO 4 , even less distinctive trends compared to Fe 3 O 4 in the dependence on temperature and bromate concentration were observed. Percentage of dissolved Fe and Ni are shown in Figs. 8 and 9 , respectively. In all experiments, under the same conditions, the amount of dissolved Fe corresponded to the amount of dissolved Ni, with Ni dissolution efficiency reaching higher values. Of the selected oxides, Fe 2 NiO 4 was the easiest to dissolve. Even at 30°C, ca. 30% of Fe and 52% of Ni were dissolved, independently on KBrO 3 concentration. At higher temperatures, the efficiency increased up to 74% of Fe and 94% of Ni. However, no clear trend was observed in temperature dependence. Similarly to Fe 3 O 4 , Fe 2 NiO 4 was readily dissolved even without the presence of KBrO 3 as the dissolution is probably not accompanied by oxidation. Dissolution kinetics Another important aspect of decontamination media is kinetics of the dissolution. To achieve sufficient decontamination factors, the decontamination media are usually employed for several hours (or even days) and must keep its efficiency over the whole period. A dependence of amount of Cr dissolved from Cr 2 O 3 by the proposed medium on reaction time at different conditions is shown in Fig. 10 . In all experiments, percentage of dissolved Cr increased with reaction time. At milder conditions (c(KBrO 3 ≤ 0.1 mol L -1 ); T ≤ 50°C), amount of dissolved Cr 2 O 3 in time increased linearly, indicating that the solution preserves its efficiency even after 5 h of contact. Under harsher conditions (0.3M KBrO 3 , 50°C and 0.1M KBrO 3 , 70°C), the curve deviated from linearity as most of the substrate dissolved, reducing contact area between the solution and the solid. The results show that proposed bromate-based decontamination medium can efficiently dissolve model substrates representing real corrosion layers, including highly stable Cr 2 O 3 , even at temperatures around 50°C. Its efficiency is comparable to the previously patented peroxydisulfate-based medium (at 50°C, 5% H 2 SO 4 and 0.1M PDS/KBrO 3 , around 20% of Cr 2 O 3 were dissolved in both systems). However, unlike the previously patented medium, bromate-based medium seems to be suitable for the use in operational decontamination. With the verification of functionality on model substrates finished, the medium was deemed suitable for testing on real samples. In parallel, recycling and regeneration possibilities of the medium are being investigated, together with dissolution mechanisms. Conclusions The research summarized in this paper was focused on development of low-temperature decontamination medium for operational decontamination of VVER-type pressurized reactors. It was based on a patented medium featuring peroxydisulfate as oxidation agent with Ag as activator. Number of chemical species were tested as alternatives to silver ions in the original medium. From number of the potential activators tested, all three selected model substrates (Cr 2 O 3 , Fe 3 O 4 and Fe 2 NiO 4 ) were dissolved only in the presence of lead(IV) oxide and ruthenium nitrosyl nitrate. However, both of these compounds were deemed unsuitable for operational decontamination of primary circuit. Instead of the originally used peroxydisulfate, bromate was chosen as a primary oxidation agent. Potassium bromate solution in a sulfuric acid environment achieved comparable dissolution efficiencies for model substrates including highly stable Cr 2 O 3 as the original medium under the same conditions. Dissolution efficiency increased with temperature, KBrO 3 concentration and acidity, and the solution does not lose its efficiency even after 5 hours of exposure. After optimization of the composition and verification of the functionality (including its influence on corrosion resistance of the decontaminated material), the bromate-based medium could be suitable for use in operational decontamination. Declarations Author Contribution Authors contributed equally to the manuscript Acknowledgements This work was supported by Ministry of Trade and Industry of the Czech Republic under grant TRIO No: FV10023 and Center for Advanced Nuclear Technology II (CANUT II) – TN02000012; Technology Agency of the Czech Republic and by CTU grant no. SGS24/148/OHK4/3T/14. Data Availability Conflict of Interest Statement:There is no conflict of interest (financial or non-financial).Data availability statement:All data associated with the paper are available from the authors of the manuscripts on request. References Trtílek R et al (2020) Study for the update of the Concept for the Management of Radioactive Waste and Spent Fuel in the Czech Republic. Technical report 528/2020. SÚRAO. In Czech Kysela J, Zmítko M, Yurmanov VA, Tiapkov VF (1996) Primary coolant chemistry in VVER units. Nucl Eng Des 160(1):185–192 Katona T (2011) Long-Term Operation of VVER Power Plants Keim E, Lidbury D (2012) Review Of Assessment Methods Used In Nuclear Plant Life Management. European Commission EC. NULIFE No. (12)5 Galkin MP, Elanskii GN, Chirkov AA, Savchenko BI (2011) Effect of the High-Temperature Steel Composition on the Ferrite Phase Content, Russian Metallurgy (Metally), Vol. 2011, No. 6, pp. 565–567, ISSN 00360295 Assessment and management of ageing of major nuclear power plant components important to safety Primary piping in PWRs, IAEA-TECDOC-1361, 2013, ISBN 92-0-108003–4 Zmitko M, Kysela J (2005) Coolant technology and experience in VVER units. Power Plant Chem 7(3):133–141 Szabó A et al (2006) Effect of a chemical decontamination procedure on the corrosion state of the heat exchanger tubes of steam generators. Online Corros Sci 48(9):2727–2749. https://doi.org/10.1016/j.corsci.2005.09.008 Varga K et al (2006) Comprehensive investigation of the corrosion state of the heat exchanger tubes of steam generators. Part I. General corrosion state and morphology. Online. Journal of Nuclear Materials. 348, č. 1–2, 181–190. ISSN 00223115. https://doi.org/10.1016/j.jnucmat.2005.09.012 Nagy A et al (2006) Effect of a chemical decontamination procedure on the corrosion state of the heat exchanger tubes of steam generators. Corros Sci 48:2727–2749. 10.1016/j.corsci.2005.09.008 Grygar T, Zmitko M (2002) Corrosion products behaviour under VVER primary coolant conditions. Chemistr. International conference on water chemistry in nuclear reactors systems - operation optimisation and new developments, France Solutions FMCE (2010) Activated persulfate chemistry: Combined Oxidation and Reduction Mechanisms, Peroxygen Talk Peroxygen Talk #1 (2006) Choosing the Right Activator for Klozur Persulfate Czech Technical university in Prague, Prague 6, Dejvice CZ, ÚJV Řež as, Husinec, Řež CZ, CHEMCOMEX, a.s., Prague 5, Zbraslav, CZ. Method of decontamination of internal surfaces of the primary circuit of a nuclear power plant and decontamination solution. Inventors: Němec M, Čubová K et al Czech Republic. Patent CZ308870. 2021-07-15 Čubová K, Němec M, Šobová T, Drtinová B (2024) Development of low-temperature decontamination medium for decommissioning. J Radioanal Nucl Chem 333(7):3621–3629. 10.1007/s10967-024-09361-5 Sun Y-C, Lin CY, Wu S-F, Chung Y, ‐Y (2006) Evaluation of on-line desalter-inductively coupled plasma-mass spectrometry system for determination of Cr(III), Cr(VI), and total chromium concentrations in natural water and urine samples. Spectrochimica Acta Part B At Spectrosc 61(2):230–234. 10.1016/j.sab.2006.01.007 Ngulimi MF, Kim S, Asghar K, Seo BK, Roh C (2025) Nuclear Decommissioning and Sustainable Environment: Insights on Decontamination Processes. Adv Energy Sustain Res 6(1). 10.1002/aesr.202400243 David R, Lide (2005) CRC Handbook of Chemistry and Physics, Internet Version 2005. http://www.hbcpnetbase.com , CRC Press, Boca Raton, FL Chen N, Lee D, Kang H, Cha D, Lee J, Lee C (2022) Catalytic persulfate activation for oxidation of organic pollutants: A critical review on mechanisms and controversies. J Environ Chem Eng 10(3):107654–107654. 10.1016/j.jece.2022.107654 Mandal S, Bera T, Dubey G, Saha J, Joydev K, Laha (2018) Uses of Ksub2/subSsub2/subOsub8/sub in Metal-Catalyzed and Metal-Free Oxidative Transformations. ACS Catal 8(6):5085–5144. 10.1021/acscatal.8b00743 Wang B, Wang Y (2022) A comprehensive review on persulfate activation treatment of wastewater. Sci Total Environ 831:154906. 10.1016/j.scitotenv.2022.154906 George P, Anipsitakis DD, Dionysiou (2004) Radical Generation by the Interaction of Transition Metals with Common Oxidants. Environ Sci Technol 38(13):3705–3712. 10.1021/es035121o Balazs G, Bryan; Cooper JF, Lewis PR, Adamson, Martyn G (2002) Transition Metal Catalysts for the Ambient Temperature Destruction of Organic Wastes Using peroxydisulfate. Online. In: Tedder, D. William a Pohland, Frederick G. Emerging Technologies in Hazardous Waste Management 8. Boston: Kluwer Academic Publishers, 229–239. ISBN 0-306-46362-8. 10.1007/0-306-46921-9_20 Fang G, Wu W, Deng Y, Zhou D (2017) Homogenous activation of persulfate by different species of vanadium ions for PCBs degradation. Chem Eng J 323:84–95. 10.1016/j.cej.2017.04.092 Krot NN, Shilov VP, Fedoseev AM et al (1999) Development of Alkaline Oxidative Dissolution Methods for Chromium(III) Compounds Present in Hanford Site Tank Sludges. Pacific Northwest National Lab Zhang B-T, Zhang Y, Teng Y, Fan M (2014) Sulfate Radical and Its Application in Decontamination Technologies. Crit Rev Environ Sci Technol 45(16):1756–1800. 10.1080/10643389.2014.970681 Shoba US, Udupa MR (1994) The thermal decomposition of potassium bromate in the presence of chromium(III) oxide. Thermochimica acta 242:215–221. 10.1016/0040-6031(94)85023-2 Sun H, Zhang L, Wang Y, Zhang J, Dong D, Guo Z (2024) Bromate-induced oxidation of carbamazepine and toxicity assessment of transformation products in the freezing-sunlight process: Effects of trivalent chromium. Environ Res 262(Pt 1):119815–119815. 10.1016/j.envres.2024.119815 Kim DWM, Kim K, Lee B-M, Choi G, W (2020) Cr(VI) Formation via Oxyhalide-Induced Oxidative Dissolution of Chromium Oxide/Hydroxide in Aqueous and Frozen Solution. Environ Sci Technol 54(22):14413–14421. 10.1021/acs.est.0c04851 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. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-8394280","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":569397104,"identity":"6dfc9f56-7139-4b80-bc45-72c65e4886ef","order_by":0,"name":"Kateřina Čubová","email":"data:image/png;base64,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","orcid":"","institution":"Czech technical University in Prague","correspondingAuthor":true,"prefix":"","firstName":"Kateřina","middleName":"","lastName":"Čubová","suffix":""},{"id":569397107,"identity":"61dee7c3-a5ab-4578-a76c-59d78c098fde","order_by":1,"name":"Jan Houzar","email":"","orcid":"","institution":"Czech technical University in Prague","correspondingAuthor":false,"prefix":"","firstName":"Jan","middleName":"","lastName":"Houzar","suffix":""},{"id":569397110,"identity":"b77fd337-2fb5-4586-9c33-769c62d7b93a","order_by":2,"name":"Mojmír Němec","email":"","orcid":"","institution":"Czech technical University in Prague","correspondingAuthor":false,"prefix":"","firstName":"Mojmír","middleName":"","lastName":"Němec","suffix":""}],"badges":[],"createdAt":"2025-12-18 10:23:56","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8394280/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8394280/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":104597132,"identity":"fbdf83f5-2fed-41ec-bafc-c790f4cbf48f","added_by":"auto","created_at":"2026-03-13 18:45:27","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":808076,"visible":true,"origin":"","legend":"\u003cp\u003ePercentage of dissolved Cr from Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e after 5 h at 50 °C in 0.1M PDS + 5% acid + 0.8mM activator, V/m = 400 mL g\u003csup\u003e-1\u003c/sup\u003e\u003c/p\u003e","description":"","filename":"Fig1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8394280/v1/79e516c0d52194b2bcd139c8.jpg"},{"id":104781200,"identity":"062535b3-4781-4cad-8505-50f0bc4c5213","added_by":"auto","created_at":"2026-03-17 07:55:07","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1113016,"visible":true,"origin":"","legend":"\u003cp\u003ePercentage of dissolved Cr from Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e after 5 h at different temperatures in 0.1M PDS + 5% H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e + Ru(NO)(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003ex\u003c/sub\u003e(OH)\u003csub\u003ey\u003c/sub\u003e, V/m = 400 mL g\u003csup\u003e-1\u003c/sup\u003e\u003c/p\u003e","description":"","filename":"Fig2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8394280/v1/a78781539fc7e2deba147d65.jpg"},{"id":104781568,"identity":"0babd8ce-287c-455f-9978-4e215c6fbc9f","added_by":"auto","created_at":"2026-03-17 07:55:56","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":904913,"visible":true,"origin":"","legend":"\u003cp\u003ePercentage of dissolved Cr from Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e after 5 h at different temperatures in 0.1M PDS + H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e + 0.8mM Ru(NO)(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003ex\u003c/sub\u003e(OH)\u003csub\u003ey\u003c/sub\u003e, V/m = 400 mL g\u003csup\u003e-1\u003c/sup\u003e\u003c/p\u003e","description":"","filename":"Fig3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8394280/v1/0e6be3d11de51f1fbb849780.jpg"},{"id":104597139,"identity":"7f7dc8d8-eb4c-4808-8899-03de1e21eb15","added_by":"auto","created_at":"2026-03-13 18:45:27","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":944029,"visible":true,"origin":"","legend":"\u003cp\u003ePercentage of dissolved metals from their respective oxides after 5 h at 50 °C in 0.1M KBrO\u003csub\u003e3\u003c/sub\u003e + 5% acid, V/m = 400 mL g\u003csup\u003e-1\u003c/sup\u003e\u003c/p\u003e","description":"","filename":"Fig4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8394280/v1/854ee4bd5f5f021a60376d2a.jpg"},{"id":104781550,"identity":"8aa93c16-ca80-4e0c-9476-5afa58186991","added_by":"auto","created_at":"2026-03-17 07:55:54","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":687224,"visible":true,"origin":"","legend":"\u003cp\u003ePercentage of dissolved metals from their respective oxides after 5 h at 50 °C in 0.1M KBrO\u003csub\u003e3\u003c/sub\u003e + H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, V/m = 400 mL g\u003csup\u003e-1\u003c/sup\u003e\u003c/p\u003e","description":"","filename":"Fig5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8394280/v1/5ae15881969528087197fb61.jpg"},{"id":104597134,"identity":"07823152-5d4e-4e0f-9dac-d9b87a3c6303","added_by":"auto","created_at":"2026-03-13 18:45:27","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1019619,"visible":true,"origin":"","legend":"\u003cp\u003ePercentage of dissolved Cr from Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e after 5 h at different temperatures in KBrO\u003csub\u003e3\u003c/sub\u003e solution in 5% H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, V/m = 400 mL g\u003csup\u003e-1\u003c/sup\u003e\u003c/p\u003e","description":"","filename":"Fig6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8394280/v1/5dae07597fe2e01163b1213e.jpg"},{"id":104781424,"identity":"6a9eaa5c-9d79-45f6-9b5f-bc822670d786","added_by":"auto","created_at":"2026-03-17 07:55:39","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":1039274,"visible":true,"origin":"","legend":"\u003cp\u003ePercentage of dissolved Fe from Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e after 5 h at different temperatures in KBrO\u003csub\u003e3\u003c/sub\u003e solution in 5% H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, V/m = 400 mL g\u003csup\u003e-1\u003c/sup\u003e\u003c/p\u003e","description":"","filename":"Fig7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8394280/v1/037d3671b185e9d912910595.jpg"},{"id":104597137,"identity":"edafe5ac-a83e-41ad-834f-de1a1b62f7fc","added_by":"auto","created_at":"2026-03-13 18:45:27","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":932430,"visible":true,"origin":"","legend":"\u003cp\u003ePercentage of dissolved Fe from Fe\u003csub\u003e2\u003c/sub\u003eNiO\u003csub\u003e4\u003c/sub\u003e after 5 h at different temperatures in KBrO\u003csub\u003e3\u003c/sub\u003e solution in 5% H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, V/m = 400 mL g\u003csup\u003e-1\u003c/sup\u003e\u003c/p\u003e","description":"","filename":"Fig8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8394280/v1/be298ac2b5c74b93916197c3.jpg"},{"id":104781216,"identity":"291d5ff5-3dbd-42e4-b248-d19215e72e4d","added_by":"auto","created_at":"2026-03-17 07:55:09","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":930863,"visible":true,"origin":"","legend":"\u003cp\u003ePercentage of dissolved Ni from Fe\u003csub\u003e2\u003c/sub\u003eNiO\u003csub\u003e4\u003c/sub\u003e after 5 h at different temperatures in KBrO\u003csub\u003e3\u003c/sub\u003e solution in 5% H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, V/m = 400 mL g\u003csup\u003e-1\u003c/sup\u003e\u003c/p\u003e","description":"","filename":"Fig9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8394280/v1/763c04c587d24ed9150bc4dd.jpg"},{"id":104781407,"identity":"bd005939-8d38-4ea5-92c3-88623e47d635","added_by":"auto","created_at":"2026-03-17 07:55:37","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":804604,"visible":true,"origin":"","legend":"\u003cp\u003eKinetics of Cr dissolution from Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e in KBrO\u003csub\u003e3\u003c/sub\u003e solution in 5% H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e at different temperatures, V/m = 400 mL g\u003csup\u003e-1\u003c/sup\u003e\u003c/p\u003e","description":"","filename":"Fig10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-8394280/v1/3ea9b2e2141c090454c9fb4b.jpg"},{"id":104784734,"identity":"9c7bf4ab-0834-4f80-88ee-6e4f14d92a4b","added_by":"auto","created_at":"2026-03-17 08:08:47","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":9943945,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8394280/v1/ef0cbbe2-a5d7-4ec2-a40a-2ede8c27f807.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Low temperature primary circuit decontamination technology","fulltext":[{"header":"Introduction","content":"\u003cp\u003eIn the Czech Republic, there are two nuclear power plants (NPPs), both of them with pressurized water reactor of Russian type VVER. A total of four VVER 440 model V 213 pressurized water reactors, with an electrical output of 512 MWe each, are installed at the Dukovany Nuclear Power Plant, while Temelín Nuclear Power Plant uses two pressurized water reactors VVER 1000 type V 320, what currently generates 2 x 1125 MWe.\u003c/p\u003e \u003cp\u003eThe primary circuit (PC) components are expected to have a minimum service life of 40 years. Currently, the operation of both Czech nuclear power plants is expected to be extended to 60 years [\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e]. Under these circumstances, the maintenance of PC technology and its chemical regime play a crucial role.\u003c/p\u003e \u003cp\u003eThe components of the Temelín (ETE) and Dukovany (EDU) nuclear power plants (with the exception of the main circulation piping of the EDU) are made of 22K carbon steel, 15Ch2MFA or 15Ch2NMFA low-alloy steel [\u003cspan class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e3\u003c/span\u003e]. In order to achieve high corrosion resistance, a layer of austenitic stainless-steel type 08Ch19N10G2B (EDU pressure vessel), 04Ch20N10G2B (ETE pressure vessel) or 08Ch18N10T (other components) [\u003cspan class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e3\u003c/span\u003e] is welded onto inner walls. The main circulation piping of the EDU, as well as the collectors and heat exchange surfaces of the steam generators (SG) of both NPPs, are also made of 08Ch18N10T steel. The composition of the above-mentioned steels is shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\u003cdiv class=\"gridtable\"\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003ctable id=\"Tab1\" border=\"1\"\u003e \u003ccaption\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComposition of selected austenitic stainless steels (in mass %) [\u003cspan class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e6\u003c/span\u003e]\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"11\"\u003e \u003c/colgroup\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\"\u003e \u003cp\u003eSteel\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eC\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eMn\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eSi\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eP\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eS\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eCr\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eNi\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eMo\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eNb\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eTi\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e\u003cb\u003e08Ch19N10G2B\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003emax. 0,08\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e1,80– 2,20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e0,20– 0,45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003emax. 0,025\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003emax. 0,018\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e18,5– 20,5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e9,50–10,50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003emax. 0,25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e0,90– 1,30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e\u003cb\u003e04Ch20N10G2B\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003emax. 0,03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e1,80– 2,20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e0,20– 0,45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003emax. 0,015\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003emax. 0,01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e18,5– 22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e9,5– 10,5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e0,9–1,1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e\u003cb\u003e08Ch18N10T\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003emax. 0,08\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e1,0–2,0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003emax. 0,8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003emax. 0,035\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003emax. 0,02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e17–19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e9–11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\"\u003e \u003cp\u003e5xC– 0,7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/table\u003e\u003c/div\u003e \u003cp\u003e\u003c/p\u003e \u003cp\u003eHigh chromium and nickel content gives the steels high corrosion resistance. However, stainless steels are completely inert in coolant and despite the strict chemical regime of primary circuit operating conditions, corrosion layer with different compositions is formed on the inner walls of individual components during operation. The exact composition of the corrosion layers depends primarily on the composition of the base material, the chemical regime of the primary circuit and operational history of the reactors [\u003cspan class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe decontamination method in radioactivity management is a procedure aimed at reducing the activity of monitored radionuclides of the contaminated subject, facility or equipment below the level detectable by conventional methods, or below the level set by the limits in the relevant legislation. The level of decontamination defined in the previous definition is, in practice, an ideal state that is desirable to achieve, but this is often not possible, and decontamination is carried out to a reasonably achievable level in terms of minimizing radioactivity of the subject, time needed for decontamination, costs, and the amount of resulting secondary waste.\u003c/p\u003e \u003cp\u003eChemical decontamination processes involve controlled dissolution of contaminated corrosion layers using chemical agents. Individual methods differ in the type of reagents used, their concentration, and the method and conditions of application [\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e9\u003c/span\u003e]. Chemical decontamination is performed either by immersing the decontaminated object in a decontamination solution or by circulating the decontamination solution through a closed system that includes the contaminated surface. The advantage of chemical methods used in nuclear power plants for decontamination of steam generators and main circulation pump, etc. is high versatility, possibility of application to geometrically complex surfaces and relatively high decontamination factors. The disadvantages are generation of large amounts of secondary waste, aggressiveness of the agents and often time-consuming nature of the process [\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e9\u003c/span\u003e]. For successful decontamination of the PC and adjacent technologies, the entire corrosion layer must usually be removed.\u003c/p\u003e \u003cp\u003eRegarding the purpose of use, there are two basic approaches to decontamination. Decontamination for decommissioning aims at reduction of the activity of radionuclides below release levels so that the materials can be further treated as non-active and released or re-used. For this purpose, it is usually necessary to remove not only corrosion layer, but also a layer of underlying steel of varying thickness. Therefore, in most cases, more aggressive methods (with higher concentration of reagents) are used, that reach higher efficiency at the cost of greater surface damage. Operational decontamination, on the other hand, is carried out to ensure safe operation for staff and requires minimization of damage to the decontaminated surface. The methods used usually belong to the category of soft methods (lower concentration of reagents), which achieve lower efficiency but also less damage to the material. During operational decontamination, which is performed during regular shutdowns, changes occur in the structure and chemical composition of the corrosion layers [\u003cspan class=\"CitationRef\"\u003e10\u003c/span\u003e]. The composition and thickness of the individual layers depend on the specific conditions in the power plant (operating time, frequency and type of operational decontamination, and changes in the chemical regimes of the coolant in the primary circuit) and are characteristic to individual reactors. However, in all cases, the large volume of secondary waste is generated and must be treated.\u003c/p\u003e \u003cp\u003eBased on literary review and practical experience, problematic and difficult-to-dissolve components of corrosion layers were identified – magnetite, chromium oxide, and spinel materials with a higher chromium content [\u003cspan class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e9\u003c/span\u003e]. From a chemical point of view, magnetite is an iron-iron spinel with sorption capabilities and considerable stability in common decontamination solutions. Replacing iron atoms with Ni and Cr atoms produces various types of other resistant spinels. Chromium-based spinels (based on chromium oxide) are very stable substances with very limited solubility in common chemicals. Most methods for dissolving highly resistant structures containing chromium utilize the oxidation of trivalent chromium Cr(III) to hexavalent Cr(VI). The resulting chromates are readily soluble. Similarly, it is possible to disrupt the spinel structure of magnetite by oxidizing or reducing one of the iron atoms. Therefore, a two-stage process is usually used for the decontamination of stainless steel, in which the actual dissolution of the corrosion layer is preceded by its oxidation. Given that oxidation is followed by one rinse and dissolution by 2–3 rinses with clean condensate, this type of decontamination produces a quantity of radioactive waste equal to 5–6 times the volume of the decontaminated part [\u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn the field of the development of new advanced decontamination methods, in accordance with current trends, great emphasis is placed on maximizing the recycling/regeneration of used decontamination agents and overall process cost savings. In this context, there is a strong demand from nuclear facility operators for new solutions that would replace or improve the currently used technologies. Important and positively evaluated parameters of the procedures under consideration are: the overall economics of the process, its environmental impact, and the load on the radioactive waste repository. The development of new advanced processes for decontamination is therefore desirable and requires targeted industrial applications of scientific knowledge.\u003c/p\u003e \u003cp\u003eFollowing the above-mentioned requirements, recyclable decontamination medium for decommissioning nuclear facilities was developed at the Department of Nuclear Chemistry, FNSPE, CTU in Prague in the frame of project MPO TRIO (see Acknowledgement). The research was focused on finding a suitable chemical system that would effectively disrupt and dissolve the specific corrosion layer formed on the inner surface of the primary circuit material in VVER-type power plants (EDU and ETE) covered with corrosion-resistant austenitic steel 08Ch18N10T. The aim was therefore to find a system for circuit decontamination, in which the decontamination solution would effectively dissolve corrosion layers and be easily recyclable, i.e., reusable after purification and restoration of key chemical components. The solution was aimed primarily to pre-dismantling decontamination as part of the decommissioning of a nuclear power plant, which meets the requirement to minimize secondary radioactive waste. It has been found that the only system that reliably dissolves all of the tested substrates is potassium peroxydisulfate (PDS) in an acidic environment catalysed by silver ions. Peroxydisulfate is a very strong oxidizing agent with an oxidation potential around 2.0 [\u003cspan class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e13\u003c/span\u003e], but at normal temperatures the reaction proceeds relatively slowly. Therefore, so-called activators are used to increase the reaction rate. It has been found that in sulfuric acid environment, dissolution did not occur without the presence of catalysing ions, and only Ag\u003csup\u003e+\u003c/sup\u003e ions showed an observable effect. The resulting medium, which was patented in 2021 [\u003cspan class=\"CitationRef\"\u003e14\u003c/span\u003e], consisted of 0.1M potassium peroxydisulfate (K\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e) and 0.8mM AgNO\u003csub\u003e3\u003c/sub\u003e in 5% H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e. This medium efficiently dissolved model substrates from the group of oxides and spinels as analogues and building materials of real corrosion layers. The most significant advantage of this medium was highest efficiency for dissolving model substrates at 50°C, which means significant cost savings compared to commonly used methods that require an operating temperature of around 90°C. [\u003cspan class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eGiven its effectiveness at low temperatures, it would be strongly desirable to use the developed medium not only for decontamination during decommissioning, but also for regular operational decontamination. Unfortunately, even the medium meets requirements for decommissioning purposes, its application in operational decontamination is complicated by the presence of silver ions, which are an undesirable contaminant in primary circuit due to their neutron activation – nuclides with longer lifetimes and significant gamma emissions are produced such as \u003csup\u003e110m\u003c/sup\u003eAg (249.83 days), and \u003csup\u003e108m\u003c/sup\u003eAg (437.27 y). Therefore, research described in this paper focused on modifications in its chemistry to make it applicable for operational decontamination of primary circuit components in specific conditions of Czech NPPs. Successful application would enable decontamination at significantly lower temperatures, reduction of the volume of secondary waste and overall improvement of the economy of the decontamination process.\u003c/p\u003e\n\u003ch3\u003eTheory\u003c/h3\u003e\n\u003cp\u003eAs stated above, corrosion layers formed on stainless steels used in primary circuit consist of insoluble spinel-type mixed oxides of Fe(II/III), Cr(III) and Ni(II). Due to high content of Cr, the corrosion layers need to be oxidized to form more soluble compounds. To oxidize Cr(III) to Cr(VI), a strong oxidation agent with redox potential of at least 1.38 V vs. SHE is necessary [\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e]. Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e summarizes redox potentials of selected chemical species capable of oxidizing Cr(III). Several decontamination methods for stainless steel materials are based on the use of strong oxidizing agents, e.g. KMnO\u003csub\u003e4\u003c/sub\u003e, O\u003csub\u003e3\u003c/sub\u003e or Ce(IV) [\u003cspan class=\"CitationRef\"\u003e17\u003c/span\u003e]. However, most conventional chemical decontamination methods achieve required decontamination factors only at high temperatures (around 90°C). Therefore, novel chemical agents are sought, that could work at lower temperatures, similar to the patented peroxydisulfate-based medium, which showed maximum efficiency for Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e dissolution at 50°C; hence this paper is focused on identifying low-temperature oxidation agent to be applicable for operational use as a part of decontamination medium.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\u003cdiv class=\"gridtable\"\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\"\u003e\u003c/div\u003e\u003ctable id=\"Tab2\" border=\"1\"\u003e \u003ccaption\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eRedox potentials of selected pairs [\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003c/colgroup\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" rowspan=\"2\"\u003e \u003cp\u003eRedox pair\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eCr(VI)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eCe(IV)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eMnO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eO\u003csub\u003e3\u003c/sub\u003e(g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eBrO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003ePb(IV)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eAg(II)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\"\u003e \u003cp\u003eCr(III)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eCe(III)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eMn(IV)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eO\u003csub\u003e2\u003c/sub\u003e(g)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eBr\u003csup\u003e-\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003ePb\u003csup\u003e2+\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eSO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\"\u003e \u003cp\u003eAg\u003csup\u003e+\u003c/sup\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\"\u003e \u003cp\u003eE [V vs. SHE]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e1.38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e1.72\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e1.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e2.08\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e1.42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e1.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e2.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\"\u003e \u003cp\u003e1.98\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/table\u003e\u003c/div\u003e \u003cp\u003e\u003c/p\u003e \u003cp\u003ePeroxydisulfate (PDS), used in the previously developed medium (see introduction), is a strong oxidation agent capable of Cr(III) oxidation. However, under normal conditions, direct oxidation by PDS is slow. Therefore, a suitable activation method is necessary. During activation, secondary, highly oxidizing species (e.g. SO\u003csub\u003e4\u003c/sub\u003e•\u003csup\u003e-\u003c/sup\u003e, OH• or Ag(II)) are produced, that oxidize the substrate [\u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e]. Methods for activation of peroxydisulfate include alkali, heat, UV irradiation, ultrasound, activated carbon and transition metal ions [\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e]. PDS activated by transition metals is being intensively studied for degradation of organic pollutants. Metal ions that have been reported to work as activators for PDS are Ag(I), Fe(II/III), Cu(II), Co(II), Ce(III), Mn(II), Ni(II) or Ru(III) [\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e]. Reports on PDS use for decontamination purposes are very scarce.\u003c/p\u003e \u003cp\u003eIn the current research, alternatives to silver ions activated PDS were sought. Based on available literature assessment, bromate was chosen as another oxidation agent for testing in this study due to its sufficient redox potential for oxidation of Cr(III), short-lived activation products and possible electrolytic regeneration, similar to persulfate. Oxidation of Cr(III) to Cr(VI) by BrO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e has been experimentally verified by different authors [\u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e]. However, to the best knowledge of the authors, bromate has not yet been tested as a part of decontamination solution. Depending on pH, oxidation by bromate can proceed via different reaction paths. In acidic environment, reactions (1) or (2) take place with standard redox potential 1.48 V vs. SHE and 1.42 V vs. SHE, respectively [\u003cspan class=\"CitationRef\"\u003e18\u003c/span\u003e]. In basic environment, oxidation proceeds through reaction (3) with standard redox potential 0.61 V vs. SHE [\u003cspan class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eBrO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e + 6 H\u003csup\u003e+\u003c/sup\u003e + 5 e\u003csup\u003e-\u003c/sup\u003e ↔ ½ Br\u003csub\u003e2\u003c/sub\u003e + 3 H\u003csub\u003e2\u003c/sub\u003eO (1)\u003c/p\u003e \u003cp\u003eBrO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e + 6 H\u003csup\u003e+\u003c/sup\u003e + 6 e\u003csup\u003e-\u003c/sup\u003e ↔ Br\u003csup\u003e-\u003c/sup\u003e + 3 H\u003csub\u003e2\u003c/sub\u003eO (2)\u003c/p\u003e \u003cp\u003eBrO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e + 3 H\u003csub\u003e2\u003c/sub\u003eO + 6 e\u003csup\u003e-\u003c/sup\u003e ↔ Br\u003csup\u003e-\u003c/sup\u003e + 6 OH\u003csup\u003e-\u003c/sup\u003e (3)\u003c/p\u003e \u003cp\u003eThis paper summarizes preliminary testing aimed at finding a suitable replacement for silver ions and/or peroxydisulfate in decontamination media. The effectiveness of potential activators and/or oxidizing agents was tested on commercially available model substrates, specifically Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, Fe\u003csub\u003e2\u003c/sub\u003eNiO\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003cdiv id=\"Sec4\" class=\"Section3\"\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Experimental","content":"\u003ch2\u003eChemicals\u003c/h2\u003e\u003cp\u003ePotassium bromate (KBrO\u003csub\u003e3\u003c/sub\u003e; ≥ 99.8%) and nitric acid (HNO\u003csub\u003e3\u003c/sub\u003e; 68%) were obtained from VWR Chemicals. Potassium peroxydisulfate (K\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e; ≥ 99%) was purchased from Carl Roth. Chromium(III) oxide (Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e; p.a.), lead(IV) oxide (PbO\u003csub\u003e2\u003c/sub\u003e; p.a.), phosphoric acid (H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e; 85%) and sulphuric acid (H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e; 93%) were procured from Lachema. Iron nickel oxide (Fe\u003csub\u003e2\u003c/sub\u003eNiO\u003csub\u003e4\u003c/sub\u003e; ≥ 98%) and ruthenium(III) nitrosyl nitrate solution in dilute nitric acid (Ru(NO)(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003ex\u003c/sub\u003e(OH)\u003csub\u003ey\u003c/sub\u003e) were obtained from Sigma Aldrich. Iron (II, III) oxide (Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e; 97%) and silver nitrate (AgNO\u003csub\u003e3\u003c/sub\u003e; p.a.) were purchased from Alfa-Aesar and Penta Chemicals, respectively.\u003c/p\u003e\n\u003ch3\u003eMethods\u003c/h3\u003e\n\u003cp\u003eDissolution experiments were carried out in plastic 15 ml vials. Stock solutions of K\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e (0.15 mol L\u003csup\u003e-1\u003c/sup\u003e) or KBrO\u003csub\u003e3\u003c/sub\u003e (0.35 mol L\u003csup\u003e-1\u003c/sup\u003e) were prepared daily by dissolving the appropriate amount of solid in demineralized (demi) water. Stock solutions of peroxodisulfate activators were prepared at concentrations of 0.1 or 0.01 mol L\u003csup\u003e-1\u003c/sup\u003e in demi water. The amount of 25\u0026thinsp;\u0026plusmn;\u0026thinsp;2 mg of the selected substrate (Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e; Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e or Fe\u003csub\u003e2\u003c/sub\u003eNiO\u003csub\u003e4\u003c/sub\u003e) was put in the vial and appropriate volumes of K\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e or KBrO\u003csub\u003e3\u003c/sub\u003e stock solution, activator stock solution (only for PDS) and acid were added, and the vial was filled up to 10 ml using demi water (V/m\u0026thinsp;=\u0026thinsp;400 mL g\u003csup\u003e-1\u003c/sup\u003e). Content of the vial was shaken gently and put in a thermoreactor (Spectroquant TR 420, Merck) preheated to set temperature. Unless stated otherwise, final conditions were: 0.1M K\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e/KBrO\u003csub\u003e3\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;0.8mM activator (PDS only)\u0026thinsp;+\u0026thinsp;5% H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e at 50\u0026deg;C. During experiments, the vials were shaken gently in fixed intervals (15 min; 30 min; 1 h; 2 h; 3 h; 4 h and 5 h).\u003c/p\u003e \u003cp\u003eAfter 5 h (excluding kinetics experiments), the vials were taken out of the reactor and centrifugated at 1500 RCF for 1 minute. Aliquots from each vial were taken and diluted in 1% HNO\u003csub\u003e3\u003c/sub\u003e (prepared from 67\u0026ndash;69% stock solution; for trace metal analysis, NORMATOM\u003csup\u003e\u0026reg;\u003c/sup\u003e, VWR Chemicals). Concentrations of Cr were determined by AAS (Varian AA240FS, Varian) and concentrations of Fe and Ni by ICP-MS (Agilent 7500 ICP-MS, Agilent Technologies). The uncertainties of percentages of dissolved metals were quantified as a combined uncertainty of the statistics of the measurement and pipetting. In experiments, where less than 5% of a substrate was dissolved, the absolute uncertainties were lower than 0.4%. In most experiments, where dissolution was higher than 5%, the relative uncertainties were lower than 5%.\u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eDecontamination medium based on peroxydisulfate\u003c/h2\u003e \u003cp\u003eBased on previously published result of the authors [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], experiments with peroxydisulfate were conducted. As a strong oxidation agent, peroxydisulfate anion has high enough redox potential to oxidize Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e into CrO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e. However, as seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, no Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e dissolved in a solution containing 0.1 mol L\u003csup\u003e-1\u003c/sup\u003e PDS in 5% acid at 50\u0026deg;C. A number of potential alternatives to Ag\u003csup\u003e+\u003c/sup\u003e was tested for activation of PDS. Selected chemical compounds include Cu\u003csup\u003e2+\u003c/sup\u003e, VO\u003csup\u003e2+\u003c/sup\u003e, Fe\u003csup\u003e3+\u003c/sup\u003e, Ce\u003csup\u003e3+\u003c/sup\u003e, Cr\u003csup\u003e3+\u003c/sup\u003e, Bi\u003csup\u003e3+\u003c/sup\u003e, Br\u003csup\u003e-\u003c/sup\u003e, ReO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e, MnO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e, CrO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2-\u003c/sup\u003e, Ru(NO)(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003ex\u003c/sub\u003e(OH)\u003csub\u003ey\u003c/sub\u003e, PbO\u003csub\u003e2\u003c/sub\u003e and 4-hydroxy-TEMPO. It was found that both Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and Fe\u003csub\u003e2\u003c/sub\u003eNiO\u003csub\u003e4\u003c/sub\u003e dissolve efficiently in 0.1M PDS in 5% H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, even without the presence of any activator. On the other hand, in the presence of vast majority of the tested activators, less than 0.1% of Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e was dissolved. The only exceptions, apart from silver ions, were lead(IV) oxide and ruthenium in the form of nitrosyl nitrate (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Highest percentage of dissolved Cr was achieved using silver ions-activated PDS in sulfuric acid. Dissolution efficiency in the presence of Ru(NO)(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003ex\u003c/sub\u003e(OH)\u003csub\u003ey\u003c/sub\u003e (hereafter abbreviated as RuN) and PbO\u003csub\u003e2\u003c/sub\u003e was much lower. Also, PbO\u003csub\u003e2\u003c/sub\u003e was identified as a primary oxidation agent, capable of Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e dissolution even in absence of PDS. Unfortunately, neither PbO\u003csub\u003e2\u003c/sub\u003e nor Ag\u003csup\u003e+\u003c/sup\u003e are suitable for use in operational decontamination. Therefore, only RuN was selected as an activator for more detailed experiments.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eDependence of percentage of dissolved chromium by 0.1M PDS in 5% H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e on temperature and concentration of RuN is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Dissolution efficiency increases with both - temperature and concentration of the activator. Without the presence of RuN, no Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e dissolution was observed up to 50\u0026deg;C after 5 h, and even at 80\u0026deg;C, less than 0.5% of Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e amount dissolved. On the other hand, more than 5% was dissolved by PDS activated with 1.2mM RuN at 80\u0026deg;C. Similar trend in temperature dependence can be seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, which shows the effect of H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e concentration with 0.1M PDS and 0.8mM RuN. For all three concentrations of sulfuric acid (1, 5 and 10%), amount of dissolved Cr increased with temperature. However, no clear trends could be observed regarding the effect of H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e concentration across the whole temperature range.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eEven though Ru(NO)(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003ex\u003c/sub\u003e(OH)\u003csub\u003ey\u003c/sub\u003e can act as an activator for PDS for Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e dissolution, the efficiency was much lower compared to silver ions in previously patented medium. From activation point of view, \u003csup\u003e103\u003c/sup\u003eRu (β\u003csup\u003e-\u003c/sup\u003e, 39.2 days) would be the main produced radionuclide, which should not be critical for general radioactive waste management. Moreover, a black film was observed forming on walls of the vials; its intensity increased with temperature a Ru concentration. The film formation was presumably caused by sorption of the ruthenium compound. This effect would have a negative influence on heat exchange properties of steam generator tubes, when used for operational decontamination of primary circuit, therefore Ru(NO)(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003ex\u003c/sub\u003e(OH)\u003csub\u003ey\u003c/sub\u003e is not suitable for this purpose. Since no suitable decontamination solution based on peroxydisulfate was found, further research focused on finding a different oxidation agent as a replacement for PDS.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eDecontamination medium based on bromate\u003c/h2\u003e \u003cp\u003eBased on available literature search, bromate was chosen as an alternative to PDS. From activation point of view, the longest activation product \u003csup\u003e82\u003c/sup\u003eBr (β\u003csup\u003e-\u003c/sup\u003e, 35.28 h) does not constitute a problem for general radioactive waste management. The next chapter covers the dependence of Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and Fe\u003csub\u003e2\u003c/sub\u003eNiO\u003csub\u003e4\u003c/sub\u003e dissolution by KBrO\u003csub\u003e3\u003c/sub\u003e solution on the most important parameters of the system. These parameters include acidity of the solution, temperature and concentration of KBrO\u003csub\u003e3\u003c/sub\u003e. Furthermore, the kinetics of Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e dissolution was studied.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eInfluence of acidity\u003c/h3\u003e\n\u003cp\u003eUnlike PDS, bromate can oxidize Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, as well as other insoluble compounds found in corrosion layers, in acidic environment without the need of any activator. Percentage of dissolved Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and Fe\u003csub\u003e2\u003c/sub\u003eNiO\u003csub\u003e4\u003c/sub\u003e using 0.1M KBrO\u003csub\u003e3\u003c/sub\u003e solution in different acids (H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, HNO\u003csub\u003e3\u003c/sub\u003e and H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e; fixed concentration 5%) is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. In presence of KBrO\u003csub\u003e3\u003c/sub\u003e, Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e dissolved efficiently in HNO\u003csub\u003e3\u003c/sub\u003e and H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, but not in H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e. On the other hand, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e was dissolved easily in H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e and H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, but not in HNO\u003csub\u003e3\u003c/sub\u003e. Fe\u003csub\u003e2\u003c/sub\u003eNiO\u003csub\u003e4\u003c/sub\u003e was found to dissolve readily in all three acids with H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e showing highest efficiency. Based on these results, solution of bromate in H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e was selected for further testing, as it showed reasonable efficiency for all three model substrates and sulfuric acid or sulphates are also well accepted in radioactive waste solidification processes.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eEfficiency of Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and Fe\u003csub\u003e2\u003c/sub\u003eNiO\u003csub\u003e4\u003c/sub\u003e dissolution is affected not only by the nature of the acid, but also by its concentration. None of the substrates was dissolved by bromate in neutral or basic environment. As seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, both Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e were dissolved only if concentration of H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e was higher than ca. 0.5%. Dissolution of Fe from Fe\u003csub\u003e2\u003c/sub\u003eNiO\u003csub\u003e4\u003c/sub\u003e took place at concentrations higher than 0.1% and release of Ni from Fe\u003csub\u003e2\u003c/sub\u003eNiO\u003csub\u003e4\u003c/sub\u003e was observed even in 0.005% H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e. It is worth mentioning that in all experiments with Fe\u003csub\u003e2\u003c/sub\u003eNiO\u003csub\u003e4\u003c/sub\u003e, percentage of dissolved nickel was higher than dissolved iron. Dissolution efficiency of all selected substrates increased with increasing concentration of H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e. It should be noted that Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and Fe\u003csub\u003e2\u003c/sub\u003eNiO\u003csub\u003e4\u003c/sub\u003e were dissolved with similar efficiency even without the presence of KBrO\u003csub\u003e3\u003c/sub\u003e. The observed increased dissolution rate with H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e concentration can therefore be attributed to the acid itself. On the other hand, in the case of Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, which did not dissolve in H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e alone, the same effect probably has a different cause. In acidic environment, bromate reduction can proceed through reactions (1) or (2), while in basic environment, only reaction (3) takes place (see the Theory section). Redox potential of reaction (3) is not sufficient for Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e oxidation. Therefore, Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e can only be oxidized by KBrO\u003csub\u003e3\u003c/sub\u003e when concentration of H\u003csup\u003e+\u003c/sup\u003e is high enough for reaction (1) or (2) to proceed. Increasing acid concentration favours Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e oxidation and enhances dissolution efficiency.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eInfluence of bromate concentration and temperature\u003c/h3\u003e\n\u003cp\u003eEfficiency of the substrates\u0026rsquo; dissolution is also affected by temperature of the solution and concentration of KBrO\u003csub\u003e3\u003c/sub\u003e. As seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, efficiency of Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e dissolution increased with both temperature and KBrO\u003csub\u003e3\u003c/sub\u003e concentration. In 0.01M KBrO\u003csub\u003e3\u003c/sub\u003e, percentage of dissolved Cr was negligible (\u0026lt;\u0026thinsp;1%) at 30 and 40\u0026deg;C, and even at 70\u0026deg;C, the efficiency reached only ca. 7%. On the other hand, in 0.3M KBrO\u003csub\u003e3\u003c/sub\u003e, more than 18% of Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e was dissolved at 30\u0026deg;C, and at 60 and 70\u0026deg;C, the dissolution reached almost 100%. Achieving sufficient decontamination factors is a crucial part in development of a low-temperature decontamination medium. In the bromate-based medium, decreased efficiency of Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-based corrosion layers\u0026rsquo; dissolution due to lower temperature could be compensated by increasing bromate concentration.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eDissolution rate of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e also increased with reaction temperature (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e), although in this case, no significant effect of bromate concentration was observed. At 30\u0026deg;C, the percentage of dissolved Fe was very low (~\u0026thinsp;2%), for all four KBrO\u003csub\u003e3\u003c/sub\u003e concentrations. At higher temperatures, the efficiency increases significantly, reaching ca. 13% and 40% at 50\u0026deg;C and 70\u0026deg;C, respectively. The independence of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e dissolution rate on concentration of KBrO\u003csub\u003e3\u003c/sub\u003e indicates that, in this case, the dissolution is not coupled with oxidation and proceeds directly in acidic environment without bromate contribution. However, the efficiency can still be increased by increasing H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e concentration (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the case of Fe\u003csub\u003e2\u003c/sub\u003eNiO\u003csub\u003e4\u003c/sub\u003e, even less distinctive trends compared to Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e in the dependence on temperature and bromate concentration were observed. Percentage of dissolved Fe and Ni are shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e and \u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e, respectively. In all experiments, under the same conditions, the amount of dissolved Fe corresponded to the amount of dissolved Ni, with Ni dissolution efficiency reaching higher values. Of the selected oxides, Fe\u003csub\u003e2\u003c/sub\u003eNiO\u003csub\u003e4\u003c/sub\u003e was the easiest to dissolve. Even at 30\u0026deg;C, ca. 30% of Fe and 52% of Ni were dissolved, independently on KBrO\u003csub\u003e3\u003c/sub\u003e concentration. At higher temperatures, the efficiency increased up to 74% of Fe and 94% of Ni. However, no clear trend was observed in temperature dependence. Similarly to Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, Fe\u003csub\u003e2\u003c/sub\u003eNiO\u003csub\u003e4\u003c/sub\u003e was readily dissolved even without the presence of KBrO\u003csub\u003e3\u003c/sub\u003e as the dissolution is probably not accompanied by oxidation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eDissolution kinetics\u003c/h2\u003e \u003cp\u003eAnother important aspect of decontamination media is kinetics of the dissolution. To achieve sufficient decontamination factors, the decontamination media are usually employed for several hours (or even days) and must keep its efficiency over the whole period. A dependence of amount of Cr dissolved from Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e by the proposed medium on reaction time at different conditions is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e. In all experiments, percentage of dissolved Cr increased with reaction time. At milder conditions (c(KBrO\u003csub\u003e3\u003c/sub\u003e\u0026thinsp;\u0026le;\u0026thinsp;0.1 mol L\u003csup\u003e-1\u003c/sup\u003e); T\u0026thinsp;\u0026le;\u0026thinsp;50\u0026deg;C), amount of dissolved Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e in time increased linearly, indicating that the solution preserves its efficiency even after 5 h of contact. Under harsher conditions (0.3M KBrO\u003csub\u003e3\u003c/sub\u003e, 50\u0026deg;C and 0.1M KBrO\u003csub\u003e3\u003c/sub\u003e, 70\u0026deg;C), the curve deviated from linearity as most of the substrate dissolved, reducing contact area between the solution and the solid.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe results show that proposed bromate-based decontamination medium can efficiently dissolve model substrates representing real corrosion layers, including highly stable Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, even at temperatures around 50\u0026deg;C. Its efficiency is comparable to the previously patented peroxydisulfate-based medium (at 50\u0026deg;C, 5% H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e and 0.1M PDS/KBrO\u003csub\u003e3\u003c/sub\u003e, around 20% of Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e were dissolved in both systems). However, unlike the previously patented medium, bromate-based medium seems to be suitable for the use in operational decontamination. With the verification of functionality on model substrates finished, the medium was deemed suitable for testing on real samples. In parallel, recycling and regeneration possibilities of the medium are being investigated, together with dissolution mechanisms.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThe research summarized in this paper was focused on development of low-temperature decontamination medium for operational decontamination of VVER-type pressurized reactors. It was based on a patented medium featuring peroxydisulfate as oxidation agent with Ag as activator. Number of chemical species were tested as alternatives to silver ions in the original medium. From number of the potential activators tested, all three selected model substrates (Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and Fe\u003csub\u003e2\u003c/sub\u003eNiO\u003csub\u003e4\u003c/sub\u003e) were dissolved only in the presence of lead(IV) oxide and ruthenium nitrosyl nitrate. However, both of these compounds were deemed unsuitable for operational decontamination of primary circuit.\u003c/p\u003e \u003cp\u003eInstead of the originally used peroxydisulfate, bromate was chosen as a primary oxidation agent. Potassium bromate solution in a sulfuric acid environment achieved comparable dissolution efficiencies for model substrates including highly stable Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e as the original medium under the same conditions. Dissolution efficiency increased with temperature, KBrO\u003csub\u003e3\u003c/sub\u003e concentration and acidity, and the solution does not lose its efficiency even after 5 hours of exposure. After optimization of the composition and verification of the functionality (including its influence on corrosion resistance of the decontaminated material), the bromate-based medium could be suitable for use in operational decontamination.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAuthors contributed equally to the manuscript\u003c/p\u003e\u003cp\u003eAcknowledgements\u003c/p\u003e\n\u003cp\u003eThis work was supported by Ministry of Trade and Industry of the Czech Republic under grant TRIO No: FV10023 and Center for Advanced Nuclear Technology II (CANUT II) \u0026ndash; TN02000012; Technology Agency of the Czech Republic and by CTU grant no. SGS24/148/OHK4/3T/14.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eConflict of Interest Statement:There is no conflict of interest (financial or non-financial).Data availability statement:All data associated with the paper are available from the authors of the manuscripts on request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eTrt\u0026iacute;lek R et al (2020) Study for the update of the Concept for the Management of Radioactive Waste and Spent Fuel in the Czech Republic. Technical report 528/2020. S\u0026Uacute;RAO. In Czech\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKysela J, Zm\u0026iacute;tko M, Yurmanov VA, Tiapkov VF (1996) Primary coolant chemistry in VVER units. Nucl Eng Des 160(1):185\u0026ndash;192\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKatona T (2011) Long-Term Operation of VVER Power Plants\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKeim E, Lidbury D (2012) Review Of Assessment Methods Used In Nuclear Plant Life Management. European Commission EC. NULIFE No. (12)5\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGalkin MP, Elanskii GN, Chirkov AA, Savchenko BI (2011) Effect of the High-Temperature Steel Composition on the Ferrite Phase Content, Russian Metallurgy (Metally), Vol. 2011, No. 6, pp. 565\u0026ndash;567, ISSN 00360295\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAssessment and management of ageing of major nuclear power plant components important to safety Primary piping in PWRs, IAEA-TECDOC-1361, 2013, ISBN 92-0-108003\u0026ndash;4\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZmitko M, Kysela J (2005) Coolant technology and experience in VVER units. Power Plant Chem 7(3):133\u0026ndash;141\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSzab\u0026oacute; A et al (2006) Effect of a chemical decontamination procedure on the corrosion state of the heat exchanger tubes of steam generators. Online Corros Sci 48(9):2727\u0026ndash;2749. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.corsci.2005.09.008\u003c/span\u003e\u003cspan address=\"10.1016/j.corsci.2005.09.008\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVarga K et al (2006) Comprehensive investigation of the corrosion state of the heat exchanger tubes of steam generators. Part I. General corrosion state and morphology. Online. Journal of Nuclear Materials. 348, č. 1\u0026ndash;2, 181\u0026ndash;190. ISSN 00223115. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jnucmat.2005.09.012\u003c/span\u003e\u003cspan address=\"10.1016/j.jnucmat.2005.09.012\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNagy A et al (2006) Effect of a chemical decontamination procedure on the corrosion state of the heat exchanger tubes of steam generators. Corros Sci 48:2727\u0026ndash;2749. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.corsci.2005.09.008\u003c/span\u003e\u003cspan address=\"10.1016/j.corsci.2005.09.008\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGrygar T, Zmitko M (2002) Corrosion products behaviour under VVER primary coolant conditions. Chemistr. International conference on water chemistry in nuclear reactors systems - operation optimisation and new developments, France\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSolutions FMCE (2010) Activated persulfate chemistry: Combined Oxidation and Reduction Mechanisms, Peroxygen Talk\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePeroxygen Talk #1 (2006) Choosing the Right Activator for Klozur Persulfate\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCzech Technical university in Prague, Prague 6, Dejvice CZ, \u0026Uacute;JV Řež as, Husinec, Řež CZ, CHEMCOMEX, a.s., Prague 5, Zbraslav, CZ. Method of decontamination of internal surfaces of the primary circuit of a nuclear power plant and decontamination solution. Inventors: Němec M, Čubov\u0026aacute; K et al Czech Republic. Patent CZ308870. 2021-07-15\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eČubov\u0026aacute; K, Němec M, Šobov\u0026aacute; T, Drtinov\u0026aacute; B (2024) Development of low-temperature decontamination medium for decommissioning. J Radioanal Nucl Chem 333(7):3621\u0026ndash;3629. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/s10967-024-09361-5\u003c/span\u003e\u003cspan address=\"10.1007/s10967-024-09361-5\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSun Y-C, Lin CY, Wu S-F, Chung Y, ‐Y (2006) Evaluation of on-line desalter-inductively coupled plasma-mass spectrometry system for determination of Cr(III), Cr(VI), and total chromium concentrations in natural water and urine samples. Spectrochimica Acta Part B At Spectrosc 61(2):230\u0026ndash;234. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.sab.2006.01.007\u003c/span\u003e\u003cspan address=\"10.1016/j.sab.2006.01.007\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNgulimi MF, Kim S, Asghar K, Seo BK, Roh C (2025) Nuclear Decommissioning and Sustainable Environment: Insights on Decontamination Processes. Adv Energy Sustain Res 6(1). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/aesr.202400243\u003c/span\u003e\u003cspan address=\"10.1002/aesr.202400243\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDavid R, Lide (2005) CRC Handbook of Chemistry and Physics, Internet Version 2005. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://www.hbcpnetbase.com\u003c/span\u003e\u003cspan address=\"http://www.hbcpnetbase.com\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e, CRC Press, Boca Raton, FL\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen N, Lee D, Kang H, Cha D, Lee J, Lee C (2022) Catalytic persulfate activation for oxidation of organic pollutants: A critical review on mechanisms and controversies. J Environ Chem Eng 10(3):107654\u0026ndash;107654. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.jece.2022.107654\u003c/span\u003e\u003cspan address=\"10.1016/j.jece.2022.107654\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMandal S, Bera T, Dubey G, Saha J, Joydev K, Laha (2018) Uses of Ksub2/subSsub2/subOsub8/sub in Metal-Catalyzed and Metal-Free Oxidative Transformations. ACS Catal 8(6):5085\u0026ndash;5144. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1021/acscatal.8b00743\u003c/span\u003e\u003cspan address=\"10.1021/acscatal.8b00743\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang B, Wang Y (2022) A comprehensive review on persulfate activation treatment of wastewater. Sci Total Environ 831:154906. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.scitotenv.2022.154906\u003c/span\u003e\u003cspan address=\"10.1016/j.scitotenv.2022.154906\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGeorge P, Anipsitakis DD, Dionysiou (2004) Radical Generation by the Interaction of Transition Metals with Common Oxidants. Environ Sci Technol 38(13):3705\u0026ndash;3712. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1021/es035121o\u003c/span\u003e\u003cspan address=\"10.1021/es035121o\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBalazs G, Bryan; Cooper JF, Lewis PR, Adamson, Martyn G (2002) Transition Metal Catalysts for the Ambient Temperature Destruction of Organic Wastes Using peroxydisulfate. Online. In: Tedder, D. William a Pohland, Frederick G. Emerging Technologies in Hazardous Waste Management 8. Boston: Kluwer Academic Publishers, 229\u0026ndash;239. ISBN 0-306-46362-8. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/0-306-46921-9_20\u003c/span\u003e\u003cspan address=\"10.1007/0-306-46921-9_20\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFang G, Wu W, Deng Y, Zhou D (2017) Homogenous activation of persulfate by different species of vanadium ions for PCBs degradation. Chem Eng J 323:84\u0026ndash;95. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.cej.2017.04.092\u003c/span\u003e\u003cspan address=\"10.1016/j.cej.2017.04.092\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKrot NN, Shilov VP, Fedoseev AM et al (1999) Development of Alkaline Oxidative Dissolution Methods for Chromium(III) Compounds Present in Hanford Site Tank Sludges. Pacific Northwest National Lab\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang B-T, Zhang Y, Teng Y, Fan M (2014) Sulfate Radical and Its Application in Decontamination Technologies. Crit Rev Environ Sci Technol 45(16):1756\u0026ndash;1800. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1080/10643389.2014.970681\u003c/span\u003e\u003cspan address=\"10.1080/10643389.2014.970681\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShoba US, Udupa MR (1994) The thermal decomposition of potassium bromate in the presence of chromium(III) oxide. Thermochimica acta 242:215\u0026ndash;221. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/0040-6031(94)85023-2\u003c/span\u003e\u003cspan address=\"10.1016/0040-6031(94)85023-2\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSun H, Zhang L, Wang Y, Zhang J, Dong D, Guo Z (2024) Bromate-induced oxidation of carbamazepine and toxicity assessment of transformation products in the freezing-sunlight process: Effects of trivalent chromium. Environ Res 262(Pt 1):119815\u0026ndash;119815. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.envres.2024.119815\u003c/span\u003e\u003cspan address=\"10.1016/j.envres.2024.119815\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKim DWM, Kim K, Lee B-M, Choi G, W (2020) Cr(VI) Formation via Oxyhalide-Induced Oxidative Dissolution of Chromium Oxide/Hydroxide in Aqueous and Frozen Solution. Environ Sci Technol 54(22):14413\u0026ndash;14421. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1021/acs.est.0c04851\u003c/span\u003e\u003cspan address=\"10.1021/acs.est.0c04851\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\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":"Decontamination, corrosion layer, primary circuit","lastPublishedDoi":"10.21203/rs.3.rs-8394280/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8394280/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eRecently, a low-temperature recyclable decontamination medium was developed and patented at Department of Nuclear Chemistry, FNSPE, CTU in Prague for the purposes of decontamination for decommissioning. Due to the presence of silver ions used as a catalyst in the original technology, the medium is not suitable for use in operational decontamination. Current research focuses on modifications in its chemistry to make it applicable for operational decontamination of primary circuit components in specific conditions of Czech nuclear power plants. Summary of the first part of the work aimed at finding a suitable replacement for silver ions. Testing of its effectiveness on model substrates is described in this paper.\u003c/p\u003e","manuscriptTitle":"Low temperature primary circuit decontamination technology","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-13 18:45:22","doi":"10.21203/rs.3.rs-8394280/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":"5872ecb4-0f14-4290-8cfb-eae8b2253a94","owner":[],"postedDate":"March 13th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-03-26T13:28:37+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-13 18:45:22","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8394280","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8394280","identity":"rs-8394280","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}