Chemical interaction of CsOH vapor with UO and Fe-Zr melt

Nakajima, Kunihisa; Takano, Masahide

Journal of Nuclear Science and Technology, 62(1), p.78 - 85, 2025/01

https://doi.org/10.1080/00223131.2024.2389153

At TEPCO's Fukushima Daiichi Nuclear Power Station, it is estimated that considerable amounts of cesium still remain in the reactors from the analysis results using the severe accident analysis codes and the reverse analysis from contaminated water. Since cesium is known to form stable compounds with uranium and zirconium, chemisorption experiments with uranium dioxide pellets and iron-zirconium melts for cesium hydroxide vapor were carried out. As the results, formations of cesium uranate, CsUO, and cesium zirconate, CsZrO, were confirmed, indicating that cesium was chemisorbed on both of the uranium dioxide pellets and the iron-zirconium melts in an Ar-H-HO flow and an Ar-H flow, respectively. Therefore, it was considered that cesium released from fuel might be trapped by chemisorption with fuels and/or iron-zirconium melts during light water reactor severe accidents.

Advances in understanding cesium retention on calcium silicate material

Rizaal, M.; Nakajima, Kunihisa

Chemosphere, 363, p.142870_1 - 142870_9, 2024/09

https://doi.org/10.1016/j.chemosphere.2024.142870

Gaseous and aerosol formations in the pseudo-binary CsI-MoO reaction system

Rizaal, M.; Nakajima, Kunihisa; Suzuki, Eriko; Miwa, Shuhei

Proceedings of 11th European Review Meeting on Severe Accident Research Conference (ERMSAR 2024) (Internet), 11 Pages, 2024/05

https://doi.org/10.5445/IR/1000174165

Characterization of Cs deposits formed by the interaction of simulated fission product CsOH in the gas phase and concrete at 200C

Luu, V. N.; Nakajima, Kunihisa

Mechanical Engineering Journal (Internet), 11(2), p.23-00446_1 - 23-00446_11, 2024/01

https://doi.org/10.1299/mej.23-00446

Chemical interaction between Sr vapor species and nuclear reactor core structure

Mohamad, A. B.; Nakajima, Kunihisa; Miwa, Shuhei; Osaka, Masahiko

Journal of Nuclear Science and Technology, 60(3), p.215 - 222, 2023/03

https://doi.org/10.1080/00223131.2022.2092227

Improvement of model for cesium chemisorption onto stainless steel in severe accident analysis code SAMPSON (Joint research)

Miwa, Shuhei; Karasawa, Hidetoshi; Nakajima, Kunihisa; Kino, Chiaki*; Suzuki, Eriko; Imoto, Jumpei

JAEA-Data/Code 2021-022, 32 Pages, 2023/01

JAEA-Data-Code-2021-022.pdf:1.41MB
JAEA-Data-Code-2021-022(errata).pdf:0.17MB

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.

A New method of measuring ruthenium activity in ruthenium-containing alloys by using thermogravimetric analysis

Liu, J.; Nakajima, Kunihisa; Miwa, Shuhei; Shirasu, Noriko; Osaka, Masahiko

Journal of Nuclear Science and Technology, 59(4), p.484 - 490, 2022/04

https://doi.org/10.1080/00223131.2021.1979432

Phase stability of Cs-Si-O and Cs-Si-Fe-O compounds on stainless steel

Suzuki, Chikashi; Nakajima, Kunihisa; Osaka, Masahiko

Journal of Nuclear Science and Technology, 59(3), p.345 - 356, 2022/03

https://doi.org/10.1080/00223131.2021.1971576

During a severe accident (SA) such as the Fukushima Daiichi Nuclear Power Plant accident, fission products (FP) can be retained on the surface of structural materials in reactors. Cesium (Cs) is an important FP, and various Cs compounds such as Cs silicates are formed on the surface of stainless steel (SS) in a reactor during a SA. We calculated total energies of Cs-Si-O compounds for evaluation on phase stability within an adiabatic approximation. The calculations indicate that CsSiO is the most stable of the Cs-Si-O compounds. We calculated, furthermore, total energies of Cs-Si-Fe-O compounds. These calculations indicate that Cs-Si-Fe-O compounds are more stable than C-Si-O compounds and that CsSiFeO is the most stable of these C-Si-O and Cs-Si-Fe-O compounds within an adiabatic approximation. The results of our present calculations and our previous experiments lead to the conclusion that Cs-Si-Fe-O compounds can be stably formed on SS surface by Cs chemisorption.

Toward evaluation of cesium chemistry during transportation in a boiling water reactor; Effects of boron on cesium chemistry

Miwa, Shuhei; Miyahara, Naoya*; Nakajima, Kunihisa; Imoto, Jumpei; Suzuki, Eriko

Nihon Genshiryoku Gakkai-Shi ATOMO, 63(12), p.825 - 829, 2021/12

https://doi.org/10.3327/jaesjb.63.12_825

In the BWR severe accident, it was indicated that the control material boron significantly influences chemical behavior and transition behavior of cesium, which is important from the viewpoint of exposure, and it causes great uncertainty in the prediction of environmental release and distribution in the reactor. Therefore, in order to elucidate the important chemistry to be considered in severe accident analysis, we have developed the experimental setup that enables the evaluation of chemistry during transportation in the reactor, and evaluated cesium chemistry. Based on the results, we developed the chemistry database named ECUME composed of datasets and models that are the basis of chemical reaction analysis so that chemical behavior could be evaluated by severe accident analysis code.

Computational approach to the evaluation of fission product behaviors

Miwa, Shuhei; Nakajima, Kunihisa; Suzuki, Chikashi; Rizaal, M.; Suzuki, Eriko; Horiguchi, Naoki; Osaka, Masahiko

Proceedings of Joint International Conference on Supercomputing in Nuclear Applications + Monte Carlo 2020 (SNA + MC 2020), p.253 - 260, 2020/12

We have proceeded the fundamental study for the improvement of the evaluation of fission product (FP) chemistry and the treatment of fine space resolution which are main issues for the evaluation of FP behaviors in a severe accident (SA). We have been developing FP chemistry database named ECUME for the improvement of SA analysis codes. We prepared thermodynamic data for Cs compounds which is no experimental data available by computational approach. Regarding the space resolution issue, we have been developing analysis tool named CHASER based on 3D-CFD code with the model for FP chemistry. More accurate evaluation of FP behavior can be achieved by incorporating ECUME to the CHASER.