Sato, Ikken; Yoshikawa, Shinji; Yamashita, Takuya; Shimomura, Kenta; Cibula, M.*; Mizokami, Shinya*
Nuclear Engineering and Design, 414, p.112574_1 - 112574_20, 2023/12
Yamashita, Takuya; Honda, Takeshi*; Mizokami, Masato*; Nozaki, Kenichiro*; Suzuki, Hiroyuki*; Pellegrini, M.*; Sakai, Takeshi*; Sato, Ikken; Mizokami, Shinya*
Nuclear Technology, 209(6), p.902 - 927, 2023/06
Miwa, Shuhei; Karasawa, Hidetoshi; Nakajima, Kunihisa; Kino, Chiaki*; Suzuki, Eriko; Imoto, Jumpei
JAEA-Data/Code 2021-022, 32 Pages, 2023/01
The improved model for cesium (Cs) chemisorption onto stainless steel (SS) in the fission product (FP) chemistry database named ECUME was incorporated into the severe accident (SA) analysis code SAMPSON for the more accurate estimation of Cs distribution within nuclear reactor vessels in the TEPCO's Fukushima Daiichi Nuclear Power Station (1F). The SAMPSON with the improved model was verified based on the analysis results reproducing the experimental results which were subjected to the modeling of Cs chemisorption behavior. Then, the experiment in the facility with the temperature gradient tube to simulate SA conditions such as temperature decrease and aerosol formation was analyzed to confirm availability of the improved model to the analysis of Cs chemisorption onto SS. The SAMPSON with the improved model successfully reproduced the experimental results, which indicates that the improved model and the analytical method such as setting a method of node-junction, models of aerosol formation and the calculation method of saturated CsOH vapor pressure can be applicable to the analysis of Cs chemisorption behavior. As the information on water-solubility of Cs deposits was also prerequisite to estimate the Cs distribution in the 1F because Cs can be transported through aqueous phase after the SA, the water-solubility of chemisorbed Cs compounds was investigated. The chemisorbed compounds on SS304 have been identified to CsFeO at 873 K to 973 K with higher water-solubility, CsFeSiO at 973 K to 1273 K and CsSiO at 1073 K to 1273 K with lower water-solubility. From these results, the water-solubility of chemisorbed Cs compounds can be estimated according to the SA analysis conditions such as temperature in the reactor and the CsOH concentration affecting the amount of chemisorbed Cs.
Li, N.*; Sun, Y.*; Nakajima, Kunihisa; Kurosaki, Ken*
Journal of Nuclear Science and Technology, 11 Pages, 2023/00
During the Fukushima Daiichi nuclear power plant (1F) accident, an overwhelming amount of the cesium remaining in the pressure vessel could have been deposited onto 304 stainless steel (SS304) steam separators and dryers, both with large surface areas. During 1F's decommissioning, the deposited cesium is a safety hazard as it can generate radioactive dust. However, the cohesive and adhesive strengths of CsOH-chemisorbed oxide scales are yet to be defined. In this study, we investigated how CsOH-chemisorption affects the cohesive and adhesive strengths between oxide scales and SS304 substrates with a scratch tester. The scratch test results revealed that the cohesive strengths of the oxide scales decreased after CsOH-chemisorption, while adhesive failure could not be reached.
Nakamura, Hideo; Bentaib, A.*; Herranz, L. E.*; Ruyer, P.*; Mascari, F.*; Jacquemain, D.*; Adorni, M.*
Proceedings of International Conference on Topical Issues in Nuclear Installation Safety; Strengthening Safety of Evolutionary and Innovative Reactor Designs (TIC 2022) (Internet), 10 Pages, 2022/10
Yamashita, Takuya; Sato, Takumi; Madokoro, Hiroshi; Nagae, Yuji
Annals of Nuclear Energy, 173, p.109129_1 - 109129_15, 2022/08
Kimura, Fumihito*; Yamamura, Sota*; Fujiwara, Kota*; Yoshida, Hiroyuki; Saito, Shimpei*; Kaneko, Akiko*; Abe, Yutaka*
Nuclear Engineering and Design, 389, p.111660_1 - 111660_11, 2022/04
Osaka, Masahiko; Goullo, M.*; Nakajima, Kunihisa
Journal of Nuclear Science and Technology, 59(3), p.292 - 305, 2022/03
Research on the fission product chemistry made after the severe accident of the Fukushima Daiichi Nuclear Power Station were reviewed with focus on the Cesium chemistry in terms of two regimes, namely the accidental source term and the long-term source term via aqueous phase towards the decommissioning. For the accidental source term, Cs chemical interaction with Mo, B and Si were reviewed. Regarding the unique issue of long-term source term via aqueous phase, Cs penetration into concrete and fuel debris leaching were mentioned as the main sources of FPs. Efforts on the preparation of thermodynamic data for the Cs complex oxides were described. All these Cs chemical behaviors should be modelled and validated/verified through the analysis and evaluation of the actual samples including fuel debris that would be taken from the Fukushima Daiichi Nuclear Power Station in near future.
Yoshida, Naoki; Ono, Takuya; Yoshida, Ryoichiro; Amano, Yuki; Abe, Hitoshi
JAEA-Research 2021-011, 12 Pages, 2022/01
In boiling and drying accidents involving high-level liquid waste in fuel reprocessing plants, emphasis is placed on the behavior of ruthenium (Ru). Ru would form volatile species, such as ruthenium tetroxide (RuO), and could be released to the environment with coexisting gases, including nitric acid, water, or nitrogen oxides. In this study, to contribute toward safety evaluations of these types of accidents, the migration behavior of gaseous Ru into the liquid phase has been experimentally measured by simulating the condensate during an accident. The gas absorption of RuO was enhanced by increasing the nitrous acid (HNO) concentration in the liquid phase, indicating the occurrence of chemical absorption. In control experiments without HNO, the lower the temperature, the greater was the Ru recovery ratio in the liquid phase. Conversely, in experiments with HNO, the higher the temperature, the higher the recovery ratio, suggesting that the reaction involved in chemical absorption was activated at higher temperatures.
Rizaal, M.; Miwa, Shuhei; Suzuki, Eriko; Imoto, Jumpei; Osaka, Masahiko; Goullo, M.*
ACS Omega (Internet), 6(48), p.32695 - 32708, 2021/12
Sahboun, N. F.; Matsumoto, Toshinori; Iwasawa, Yuzuru; Sugiyama, Tomoyuki
Proceedings of Asian Symposium on Risk Assessment and Management 2021 (ASRAM 2021) (Internet), 15 Pages, 2021/10
Sato, Ikken; Arai, Yuta*; Yoshikawa, Shinji
Journal of Nuclear Science and Technology, 58(4), p.434 - 460, 2021/04
Wang, Z.; Duan, G.*; Koshizuka, Seiichi*; Yamaji, Akifumi*
Nuclear Power Plant Design and Analysis Codes, p.439 - 461, 2021/00
Yoshida, Naoki; Amano, Yuki; Ono, Takuya; Yoshida, Ryoichiro; Abe, Hitoshi
JAEA-Research 2020-014, 33 Pages, 2020/12
Considering the boiling and drying accident of high-level liquid waste in fuel reprocessing plant, Ruthenium (Ru) is an important element. It is because Ru would form volatile compounds such as ruthenium tetroxide (RuO) and could be released into the environment with other coexisting gasses such as nitric oxides (NOx) such as nitric oxide (NO) and nitrogen dioxide (NO). To contribute to the safety evaluation of this accident, we experimentally evaluated the effect of NOx on the decomposition and chemical change behavior of the gaseous RuO (RuO(g)). As a result, the RuO(g) decomposed over time under the atmospheric gasses with NO or NO, however, the decomposition rate was slower than the results of experiments without NOx. These results showed that the NOx stabilized RuO(g).
Miyahara, Naoya; Miwa, Shuhei; Goullo, M.*; Imoto, Jumpei; Horiguchi, Naoki; Sato, Isamu*; Osaka, Masahiko
Journal of Nuclear Science and Technology, 57(12), p.1287 - 1296, 2020/12
In order to clarify the cesium iodide (CsI) transport behavior with a focus on the mechanisms of gaseous iodine formation in the reactor coolant system of LWR under a severe accident condition, a reproductive experiment of CsI transport behavior was conducted using a facility equipped with a thermal gradient tube. Various analyses on deposits and airborne materials during transportation could elucidate two mechanisms for the gaseous iodine formation. One was the gaseous phase chemical reaction in Cs-I-O-H system at relatively high-temperature region, which led to gaseous iodine transport to the lower temperature region without any further changes in gas species due to the kinetics limitation effects. The other one was the chemical reactions related to condensed phase of CsI, namely those of CsI deposits on walls with surface of stainless steel to form CsCrO compound and CsI aerosol particles with steam, which were newly found in this study.
Herranz, L. E.*; Pellegrini, M.*; Lind, T.*; Sonnenkalb, M.*; Godin-Jacqmin, L.*; Lpez, C.*; Dolganov, K.*; Cousin, F.*; Tamaki, Hitoshi; Kim, T. W.*; et al.
Nuclear Engineering and Design, 369, p.110849_1 - 110849_7, 2020/12
Phase 2 of the OECD/NEA Project "Benchmark Study of the Accident at the Fukushima Daiichi Nuclear Power Plant (BSAF)" was established in mid-2015. The objectives have been similar to Phase 1 of the project but with an extended analysis period of 3 weeks, a major focus on FP behaviour and releases to the environment and the comparison to various data and results of backwards calculations of the source term. Nine organizations of six countries submitted results of their calculated severe accident scenarios for Unit 1 at the 1F site using different severe accident codes. This paper describes the findings of the comparison of the participants results for Unit1 against each other and against plant data, the evaluation of the accident progression and the final status inside the reactors. Special focus is on RPV status, melt release and FP behaviour and release. Unit specific aspects will be highlighted and points of consensus as well as remaining uncertainties and data needs will be summarised.
Sonnenkalb, M.*; Pellegrini, M.*; Herranz, L. E.*; Lind, T.*; Morreale, A. C.*; Kanda, Kenichi*; Tamaki, Hitoshi; Kim, S. I.*; Cousin, F.*; Fernandez Moguel, L.*; et al.
Nuclear Engineering and Design, 369, p.110840_1 - 110840_10, 2020/12
This is the second paper in a series of 3 in which results of severe accident analyses for Unit 2 of Fukushima Daiichi are presented, gained in Phase 2 of the OECD/NEA project "Benchmark Study of the Accident at the Fukushima Daiichi Nuclear Power Plant (BSAF)". Nine organizations of six countries submitted results of their calculated severe accident scenarios for Unit 2 of Fukushima Daiichi using different severe accident codes. The present paper describes the findings of the comparison of the participants' results for Unit 2 against each other and against plant data, the evaluation of the accident progression and the final status inside the reactors. Special focus is on reactor pressure vessel status, melt release and fission product behavior and release. Unit 2 specific aspects will be highlighted and points of consensus as well as remaining uncertainties and data needs will be summarized.
Ikeuchi, Hirotomo; Yano, Kimihiko; Washiya, Tadahiro
Journal of Nuclear Science and Technology, 57(6), p.704 - 718, 2020/06
To suggest efficient process of the fuel debris treatment after the retrieval from the Fukushima Daiichi Nuclear Power Plant (1F), thorough investigation is indispensable on potential source of U in the fuel debris. Estimation on the fuel debris accumulated in the reactor pressure vessel is specifically important due to its limited accessibility. The present study aims to estimate the chemical forms of U in the in-vessel fuel debris, especially in the minor phases such as metallic phases, by performing the thermodynamic calculation considering the material relocation and changing environment during the accident progression in the 1F Unit 2. Input conditions for the thermodynamic calculation such as composition, temperature, and oxygen amount were assumed mainly based on the results of severe accident analysis. The chemical form of U varied depending on the local amount of Fe and O. In regions of low steel content, the U-containing metallic phase was dominated by -(Zr,U)(O), while regions of high steel content were dominated by Fe(Zr,U) (Laves phase). A few percent of U was transferred to the metallic phases under reducing conditions, raising challenging issues on the chemical removal of nuclear material from fuel debris.
Development Group for LWR Advanced Technology
JAEA-Data/Code 2019-017, 59 Pages, 2020/03
ECUME (ffective hemistry database of fission products nder ultiphase raction) is the database for the analyses of FP chemistry which strongly affects all the FP behaviors in a severe accident (SA) of nuclear facility like LWR. ECUME consists of three kinds of datasets: CRK (dataset for hemical eaction inetics), EM (lemental odel set) and TD (hermoynamic dataset). The present version of ECUME is prepared especially for the more accurate evaluation of cesium and iodine distribution in a reactor and release amount into an environment which should be of crucial importance towards the decommissioning of Fukushima Daiichi Nuclear Power Station of Tokyo Electric Power Company Holdings (1F) and the enhancement of LWR safety after the 1F SA.