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Journal Articles

Radiation-induced dissolution of uranium oxide materials in water

Kumagai, Yuta

Hoshasen Kagaku (Internet), (115), p.43 - 49, 2023/04

Oxidation and dissolution of uranium oxide materials has been a subject of numerous studies as a basis of the geological disposal technology for spent nuclear fuel. The understandings obtained by these studies provide useful suggestions for research and development regarding the retrieval and storage of nuclear fuel debris generated by a nuclear severe accident. Here, these research backgrounds of oxidative dissolution of uranium oxides are briefly reviewed and some studies relating to radiation-induced reactions will be introduced.

Journal Articles

Uranium dissolution and uranyl peroxide formation by immersion of simulated fuel debris in aqueous H $_{2}$ O $_{2}$ solution

Kumagai, Yuta; Kusaka, Ryoji; Nakada, Masami; Watanabe, Masayuki; Akiyama, Daisuke*; Kirishima, Akira*; Sato, Nobuaki*; Sasaki, Takayuki*

Journal of Nuclear Science and Technology, 59(8), p.961 - 971, 2022/08

https://doi.org/10.1080/00223131.2021.2023055

Times Cited Count：2 Percentile：53.91(Nuclear Science & Technology)

We investigated potential degradation of fuel debris caused by H $_{2}$ O $_{2}$ , which is the oxidant of major impact from water radiolysis. We performed leaching experiments on different kinds of simulated debris comprising U, Fe, Cr, Ni, and Zr in an aqueous H $_{2}$ O $_{2}$ solution. Chemical analysis of the leaching solution showed that U dissolution was induced by H $_{2}$ O $_{2}$ . Raman analysis after the leaching revealed that uranyl peroxides were formed on the surface of the simulated debris. These results demonstrate that uranyl peroxides are possible alteration products of fuel debris from H $_{2}$ O $_{2}$ reaction. However, the sample in which the main uranium-containing phase was a U-Zr oxide solid solution showed much less uranium dissolution and no Raman signal of uranyl peroxides. Comparison of these results indicates that formation of an oxide solid solution of Zr with UO $_{2}$ improves the stability of fuel debris against H $_{2}$ O $_{2}$ reaction.

Journal Articles

A Study of H $_{2}$ O $_{2}$ -induced oxidative degradation of simulated fuel debris

Kumagai, Yuta; Kusaka, Ryoji; Nakada, Masami; Watanabe, Masayuki; Akiyama, Daisuke*; Kirishima, Akira*; Sato, Nobuaki*; Sasaki, Takayuki*

Hoshasen Kagaku (Internet), (113), p.61 - 64, 2022/04

The severe accident at TEPCO's Fukushima Daiichi Nuclear Power Station resulted in generation of fuel debris. The fuel debris is in contact with water and the radiolysis of water can accelerate degradation of the debris. The analysis of particles sampled from inside or near the damaged reactors indicates the complicated compositions of the fuel debris. It is challenging to estimate the effect of water radiolysis on such a complicated material. Therefore, in this study, we investigated the potential degradation process by leaching experiments of simulated fuel debris in aqueous H $_{2}$ O $_{2}$ solution. The results show that the reaction of H $_{2}$ O $_{2}$ induced uranium dissolution from most of the samples and then formation of uranyl peroxides. In contrast, a sample that had U-Zr oxide solid solution as the major phase exhibited remarkable resistance to H $_{2}$ O $_{2}$ . These findings revealed that the degradation of the simulated debris reflects the reactivity and stability of the uranium phase in the matrices.

Journal Articles

Radiolysis effects, which should be taken into account for safe decommissioning of Fukushima-Daiichi Nuclear Power Station

Hata, Kuniki

Zairyo To Kankyo, 70(12), p.468 - 473, 2021/12

https://doi.org/10.3323/jcorr.70.468

In order to estimate corrosive environment in the contaminated water at Fukushima Daiichi Nuclear Power Station, effects of oxidants, such as H $_{2}$ O $_{2}$ , which were generated from water radiolysis, should be taken into account due to the irradiation field in the reactor building. The process of water radiolysis and the amounts of these oxidants can change depending on the conditions of water and types of radiation. After the accident, a variety of factors, which can affect water radiolysis, such as seawater constituents, surface of oxides, and -radionuclides, had been discussed. In this paper, these effects on radiolysis are reviewed for the better understanding of the corrosive environment in the contaminated water.

Journal Articles

Effect of H $_{2}$ O $_{2}$ concentration on oxidative dissolution of U $_{2}$ O

Kumagai, Yuta

Hoshasen Kagaku (Internet), (107), p.77 - 78, 2019/04

Reaction of hydrogen peroxide (H $_{2}$ O $_{2}$ ) with uranium dioxide (UO $_{2}$ ) oxidizes U(IV) to water-soluble U(VI). In the concept of direct geological disposal of spent nuclear fuel, this reaction is expected to induce dissolution of UO $_{2}$ matrix of the spent fuel. This study investigate effect of H $_{2}$ O $_{2}$ concentration on the kinetics and the yield of U(VI) dissolution of this reaction. A series of experiments of the reaction of H $_{2}$ O $_{2}$ with UO $_{2}$ powder dispersed in water has been carried out. The experimental results reveal that increase in the H $_{2}$ O $_{2}$ concentration slows down the reaction and decreases the yield of U(VI) dissolution. This observation suggests that a reaction intermediate is generated in the course of the H $_{2}$ O $_{2}$ reaction on the surface of UO $_{2}$ .

Journal Articles

Impact of stoichiometry on the mechanism and kinetics of oxidative dissolution of UO $_{2}$ induced by H $_{2}$ O $_{2}$ and -irradiation

Kumagai, Yuta; Fidalgo, A. B.*; Jonsson, M.*

Journal of Physical Chemistry C, 123(15), p.9919 - 9925, 2019/04

https://doi.org/10.1021/acs.jpcc.9b00862

Times Cited Count：19 Percentile：62.54(Chemistry, Physical)

Radiation-induced oxidative dissolution of uranium dioxide (UO $_{2}$ ) is one of the most important chemical processes of U driven by redox reactions. We have examined the effect of UO $_{2}$ stoichiometry on the oxidative dissolution of UO $_{2}$ induced by hydrogen peroxide (H $_{2}$ O $_{2}$ ) and -ray irradiation. By comparing the reaction kinetics of H $_{2}$ O $_{2}$ between stoichiometric UO $_{2.0}$ and hyper-stoichiometric UO $_{2.3}$ , we observed a significant difference in reaction speed and U dissolution kinetics. The stoichiometric UO $_{2.0}$ reacted with H $_{2}$ O $_{2}$ much faster than the hyper-stoichiometric UO $_{2.3}$ . The U dissolution from UO $_{2.0}$ was initially much lower than that from UO $_{2.3}$ , but gradually increased as the oxidation by H $_{2}$ O $_{2}$ proceeded. The -ray irradiation induced the U dissolution that is analogous to the kinetics by the exposure to a low concentration (0.2 mM) of H $_{2}$ O $_{2}$ . The exposure to higher H $_{2}$ O $_{2}$ concentrations caused lower U dissolution and resulted in deviation from the U dissolution behavior by -ray irradiation.

Journal Articles

The Role of surface-bound hydroxyl radicals in the reaction between H $_{2}$ O $_{2}$ and UO $_{2}$

Fidalgo, A. B.*; Kumagai, Yuta; Jonsson, M.*

Journal of Coordination Chemistry, 71(11-13), p.1799 - 1807, 2018/07

https://doi.org/10.1080/00958972.2018.1466287

Times Cited Count：29 Percentile：88.5(Chemistry, Inorganic & Nuclear)

In this work, we have studied the reaction between H $_{2}$ O $_{2}$ and UO $_{2}$ with particular focus on the nature of the hydroxyl radical formed as an intermediate. Experiments were performed to study the kinetics of the reaction at different initial H $_{2}$ O $_{2}$ concentrations. The results show that the consumption rates at a given H $_{2}$ O $_{2}$ concentration are different depending on the initial H $_{2}$ O $_{2}$ concentration. This is attributed to an alteration of the reactive interface, likely caused by blocking of surface sites by oxidized U/surface-bound hydroxyl radicals. The U dissolution yield decreases with increasing initial H $_{2}$ O $_{2}$ concentration. This is expected from the mechanism of catalytic decomposition of H $_{2}$ O $_{2}$ on oxide surfaces. As the experiments were performed in solutions containing 10 mM and a strong concentration dependence was observed in the 0.2 - 2.0 mM H $_{2}$ O $_{2}$ concentration range, we conclude that the intermediate hydroxyl radical is surface bound rather than free.

Journal Articles

Reaction of hydrogen peroxide with uranium zirconium oxide solid solution; Zirconium hinders oxidative uranium dissolution

Kumagai, Yuta; Takano, Masahide; Watanabe, Masayuki

Journal of Nuclear Materials, 497, p.54 - 59, 2017/12

https://doi.org/10.1016/j.jnucmat.2017.10.050

Times Cited Count：13 Percentile：78.05(Materials Science, Multidisciplinary)

We studied oxidative dissolution of uranium and zirconium oxide [(U,Zr)O $_{2}$ ] in aqueous H $_{2}$ O $_{2}$ solution. The interfacial reaction is essential for anticipating how a (U,Zr)O $_{2}$ -based molten fuel may chemically degrade after a severe accident under influence of ionizing radiation. We conducted our experiments with (U,Zr)O $_{2}$ powder and quantitated the H $_{2}$ O $_{2}$ reaction via dissolved U and H $_{2}$ O $_{2}$ concentrations. The dissolution yield relative to H $_{2}$ O $_{2}$ consumption was far less for (U,Zr)O $_{2}$ compared to that of UO $_{2}$ . The reaction kinetics indicates that most of the H $_{2}$ O $_{2}$ catalytically decomposed to O $_{2}$ at the surface of (U,Zr)O $_{2}$ . We confirmed the H $_{2}$ O $_{2}$ catalytic decomposition via O $_{2}$ production (quantitative stoichiometric agreement). In addition, post-reaction Raman scattering spectra of the undissolved (U,Zr)O $_{2}$ showed no additional peaks (indicating a lack of secondary phase formation). The (U,Zr)O $_{2}$ matrix is much more stable than UO $_{2}$ against H $_{2}$ O $_{2}$ -induced oxidative dissolution.

Journal Articles

Effect of chloride concentration on corrosion behavior of carbon steel under -ray irradiation

Motooka, Takafumi; Ueno, Fumiyoshi

Zairyo To Kankyo, 64(6), p.220 - 223, 2015/06

http://doi.org/10.3323/jcorr.64.220

Corrosion behavior of carbon steel in chloride aqueous solutions under a low dose rate was investigated by corrosion test using chloride aqueous solutions with different chloride concentration at a dose rate of 500 Gy/h. The corrosion rate of carbon steel increased by the irradiation, and the corrosion rate had the maximum value at a certain chloride concentration. The oxidants produced by radiolysis of chloride aqueous solution enhanced the corrosion of carbon steel. The main oxidants were oxygen and hydrogen peroxide, and the diffusion process of oxidants controlled the corrosion of carbon steel under irradiation. There was a positive correlation between the dependence of corrosion rate and chloride concentration and the dependence of oxidant concentration and chloride concentration.

Journal Articles

Effect of zeolites on the corrosion potential of type 316L stainless steel in diluted artificial sea water under gamma-ray irradiation

Kato, Chiaki; Sato, Tomonori; Ueno, Fumiyoshi; Yamagishi, Isao; Yamamoto, Masahiro

Zairyo To Kankyo 2015 Koenshu (CD-ROM), p.83 - 86, 2015/05

In relation to the consideration for long-term storage of spent Cs adsorption vessels containing zeolites in the Fukushima Daiichi Nuclear Power Station, corrosion of the vessel material in the spent Cs adsorption vessel is one of important issues. We performed electrochemical tests of stainless steel (SUS 316L) in the zeolites containing artificial seawater under gamma-ray irradiation. The spontaneous potential (ESP) and critical pitting potential (VC), of SUS316L were measured to understand the corrosion resistance of the stainless steel in this study. The rest potential of the stainless steel increased with increasing time after gamma-ray irradiation. The ESP, defined as the steady rest potential, increased with increasing dose rate, while increasing ESP was suppressed by contact with the zeolites. Concentration of H $_{2}$ O $_{2}$ in bulk water increased with increasing dose rate. The concentration increasing was suppressed by contact with the zeolites due to decomposition of H $_{2}$ O $_{2}$ . There was good relationship between ESP and the concentration of H $_{2}$ O $_{2}$ . The VC of SUS316L contacted with the zeolites decreased with increasing Cl $^{-}$ ion concentration and is slightly smaller than the VC in the bulk water. The contact with the zeolites causes the suppressant of increasing ESP under the irradiation. The contact with the zeolites can reduce probability in the localized corrosion for SUS316L.

Journal Articles

In-situ measurement of corrosion environment in high temperature water without electrolyte utilizing electrochemical impedance spectroscopy

Sato, Tomonori; Yamamoto, Masahiro; Tsukada, Takashi; Kato, Chiaki

Zairyo To Kankyo, 64(3), p.91 - 97, 2015/03

https://doi.org/10.3323/jcorr.64.91

In the boiling water reactors (BWRs), reactor cooling water is maintained in high purity condition by controlling of a deionizing and deaerating apparatus, however H $_{2}$ O $_{2}$ contains by water radiolysis. In order to determine the corrosive condition in high-temperature pure water containing H $_{2}$ O $_{2}$ , the electrochemical impedance spectroscopy was performed in this study. To simulate BWR condition precisely, the measurements were performed without any electrolyte. The obtained impedance responses were changed with the H $_{2}$ O $_{2}$ concentration. The solution resistance and polarization resistance were determined by the equivalent circuit analyses. The conductivity was determined by the obtained solution resistance and the calculation of the current flow between the working electrode and the counter electrode by the 3-demensional finite element method. The value, 4.410 $^{-6}$ S/cm, was obtained as the conductivity of the pure water at 288 $^{circ}$ C. The reciprocal of the obtained polarization resistance increased in proportion with H $_{2}$ O $_{2}$ concentration. This indicates that the corrosion current density was determined by the diffusion limiting current density of H $_{2}$ O $_{2}$ . The diffusion coefficient of H $_{2}$ O $_{2}$ at 288 $^{circ}$ C was determined using the relationship between the reciprocal of the polarization resistance and H $_{2}$ O $_{2}$ concentration. The obtained diffusion coefficient was 1.510 $^{-4}$ cm $^{2}$ /s. This is about twice larger than that of the reported value of O $_{2}$ .

Journal Articles

Effect of -ray irradiation on corrosion of low alloy steel in neutral water

Yamamoto, Masahiro; Nakano, Junichi; Komatsu, Atsushi; Sato, Tomonori; Tsukada, Takashi

Proceedings of 19th International Corrosion Congress (19th ICC) (CD-ROM), 6 Pages, 2014/11

Corrosion protection of RPV and PCV is an important issue for the long term maintenance until the end of the decommissioning procedures. One of the uncertain factors for the issue is an effect of radioactivity on corrosion of LAS and CS. Corrosion tests using LAS and CS were conducted in -rays irradiated condition. Oxygen and hydrogen peroxide concentrations in the water were measured after the tests. Corrosion test results indicated that the amounts of corrosion increased by -rays irradiation both air and nitrogen atmosphere. And also corrosion amounts increased with -ray dose rates. Electrochemical analyses indicated that cathodic reaction of Hydrogen peroxide was controlled by diffusion process. The measured diffusion constant of H $_{2}$ O $_{2}$ was about 0.75 times to that of oxygen. From these results, it is estimated that corrosion of LAS and CS in -ray irradiated condition was evaluated by the cathodic reduction reaction of oxidant.

Journal Articles

Consideration of radiolytic behavior in diluted and concentrated systems of seawater for computational simulation of hydrogen generation

Nagaishi, Ryuji; Inoue, Masao; Hino, Ryutaro; Ogawa, Toru

Proceedings of 2014 Nuclear Plant Chemistry Conference (NPC 2014) (USB Flash Drive), 9 Pages, 2014/10

Since seawater has been used as a coolant for reactors and spent fuel pools in broken reactor buildings at Fukushima Daiichi NPS accident, radioactive contaminated water emitted following the accident has contained salt content of seawater at high concentrations, different from that at TMI-2 accident. Radiolysis of seawater leading to hydrogen generation and corrosion has been simulated and reported by several groups. However, the proposed radiolysis models cannot be always applied to water radiolysis at the wide range of salt concentrations present in the NPS, mainly because primary yields of radiolysis products of water and radiation-induced reactions are dependent on the salt concentration. In this study, the radiolytic behavior in diluted and concentrated systems of seawater was considered on the basis of results in steady state and pulse radiolysis experiments, in which the above salt effects were demonstrated from the obtained results.

JAEA Reports

Technology for cleaning of Pb-Bi adhering to steel, 1; Basic tests

Saito, Shigeru; Sasa, Toshinobu; Umeno, Makoto*; Kurata, Yuji; Kikuchi, Kenji; Futakawa, Masatoshi

JAERI-Tech 2004-074, 41 Pages, 2004/12

JAERI-Tech-2004-074.pdf:24.5MB

The accelerator driven system (ADS) is proposed to transmute minor actinides (MA) in high-level waste from spent fuels of nuclear power reactors. Liquid Pb-Bi alloy is a candidate material for spallation target and coolant of ADS. Pb-Bi cleaning technology is required to reduce radiation exposure during maintenance service and to decontaminate replaced components. In this study, three cleaning methods were tested; silicon oil cleaning at 170 $^{circ}$ C, mixture of acetic acid and nitric acid cleaning. Specimens were prepared by immersion in melted Pb-Bi. After silicon oil tests, most of Pb-Bi remained on the surface of the specimens. It was found that blushing was needed to remove Pb-Bi effectively. On the other hands, Pb-Bi was easily dissolved and almost removed in the mixed acid and nitric acid. Silicon oil cleaning did not affect on base metals. The surface of base metals was slightly blacked after mixed acid cleaning. F82H base metals were corroded by nitric acid.

JAEA Reports

Study of assessing aqueous reprocessing process for the pipeless reprocessing plant

*; *; Fumoto, Hiromichi*; *; *

JNC TJ9400 2000-001, 112 Pages, 2000/02

JNC-TJ9400-2000-001.pdf:6.67MB

The purpose of this study is to investigate the possibility of new reprocessing process for the purpose of introducing pipeless plant concept, where aqueous separation methods other than solvent extraction method are adopted in order to develop more economical FBR fuel (MOX fuel) reprocessing process. At it's first stage, literature survey on precipitation method, crystallization method and ion-exchange method was performed. Based on the results, following processes were candidated for pipeless reprocessing plant. (1)The process adopting crystallization method and peroxide precipitation method (2)The process adopting oxalate precipitation method (3)The process under mild aqueous conditions (crystallization method and precipitation method) (4)The process adopting crystallization method and ion-exchange method (5)The process adopting crystallization method and solvent extraction method The processes (1)(5) were compared with each others in terms of competitiveness to the conventional reference process, and merits and demerits were evaluated from the viewpoint of applicability to pipeless reprocessing plant, safety, economy, Efficiencies in consumption of Resources, non-proliferation, and, Operation and Maintenance. As a result, (1)The process adopting crystallization method and peroxide precipitation method was selected as the most reasonable process to pipeless plant. Preliminary criticality safety analyses, main process chemical flowsheet, main equipment list and layout of mobile vessels and stations were reported for the (1) process.