Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Rizaal, M.; Nakajima, Kunihisa; Suzuki, Eriko; Miwa, Shuhei
Annals of Nuclear Energy, 218, p.111433_1 - 111433_10, 2025/08
Times Cited Count:0 Percentile:0.00(Nuclear Science & Technology)Nakajima, Kunihisa; Takano, Masahide
Journal of Nuclear Science and Technology, 62(1), p.78 - 85, 2025/01
Times Cited Count:1 Percentile:57.00(Nuclear Science & Technology)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, Cs
ZrO
, were confirmed, indicating that cesium was chemisorbed on both of the uranium dioxide pellets and the iron-zirconium melts in an Ar-H
-H
O 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.
Rizaal, M.; Luu, V. N.; Nakajima, Kunihisa; Miwa, Shuhei
Proceedings of International Topical Workshop on Fukushima Decommissioning Research 2024 (FDR2024) (Internet), 4 Pages, 2024/10
Rizaal, M.; Nakajima, Kunihisa
Chemosphere, 363, p.142870_1 - 142870_9, 2024/09
Luu, V. N.; Nakajima, Kunihisa
Nuclear Engineering and Design, 426, p.113402_1 - 113402_7, 2024/09
Times Cited Count:0 Percentile:0.00(Nuclear Science & Technology)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
Li, N.*; Sun, Y.*; Nakajima, Kunihisa; Kurosaki, Ken*
Journal of Nuclear Science and Technology, 61(3), p.343 - 353, 2024/03
Times Cited Count:1 Percentile:25.62(Nuclear Science & Technology)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.
Luu, V. N.; Nakajima, Kunihisa
Mechanical Engineering Journal (Internet), 11(2), p.23-00446_1 - 23-00446_11, 2024/01
Luu, V. N.; Nakajima, Kunihisa
Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 9 Pages, 2023/05
Mohamad, A. B.; Nakajima, Kunihisa; Miwa, Shuhei; Osaka, Masahiko
Journal of Nuclear Science and Technology, 60(3), p.215 - 222, 2023/03
Times Cited Count:0 Percentile:0.00(Nuclear Science & Technology)Luu, V. N.; Nakajima, Kunihisa
Journal of Nuclear Science and Technology, 60(2), p.153 - 164, 2023/02
Times Cited Count:6 Percentile:68.73(Nuclear Science & Technology)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 Cs
Si
O
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.
Rizaal, M.; Nakajima, Kunihisa; Saito, Takumi*; Osaka, Masahiko; Okamoto, Koji*
ACS Omega (Internet), 7(33), p.29326 - 29336, 2022/08
Times Cited Count:5 Percentile:29.12(Chemistry, Multidisciplinary)Liu, J.; Nakajima, Kunihisa; Miwa, Shuhei; Shirasu, Noriko; Osaka, Masahiko
Journal of Nuclear Science and Technology, 59(4), p.484 - 490, 2022/04
Times Cited Count:0 Percentile:0.00(Nuclear Science & Technology)Osaka, Masahiko; Goullo, M.*; Nakajima, Kunihisa
Journal of Nuclear Science and Technology, 59(3), p.292 - 305, 2022/03
Times Cited Count:7 Percentile:62.34(Nuclear Science & Technology)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.
Suzuki, Chikashi; Nakajima, Kunihisa; Osaka, Masahiko
Journal of Nuclear Science and Technology, 59(3), p.345 - 356, 2022/03
Times Cited Count:3 Percentile:31.52(Nuclear Science & Technology)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 CsSi
O
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 CsSi
FeO
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.
Imoto, Jumpei; Nakajima, Kunihisa; Osaka, Masahiko
Nihon Genshiryoku Gakkai Wabun Rombunshi, 20(4), p.179 - 187, 2021/12
Some of the Cs inside the Fukushima Daiichi Nuclear Power Station would be deposited in chemical forms such as CsI and CsMoO
. Since Cs compounds are generally water-soluble, it is predicted that the migration of Cs through the aqueous phase occurs in the long term. Knowledge of the solubility in water is required as basic data for such migration behavior evaluation. Therefore, this study was conducted to investigate the dissolution properties of CsI and Cs
MoO
in water at 20
C and 25
C. The solubilities of CsI at 25
C calculated using thermodynamic data and the Pitzer ion interaction model were in good agreement with the literature value. It was found that the literature value of CsI at around room temperature is highly reliable. The experimental value of CsI at 20
C obtained by the OECD test guideline 105 flask method (test guideline) was also in good agreement with the literature value. The measured solubility of Cs
MoO
was 256.8
6.2 (g/100 g H
O) at 20
C using the test guideline. This measured solubility of Cs
MoO
was found to be comparable to those of other alkaline molybdates and considered to be more reliable than the literature value.
Miwa, Shuhei; Miyahara, Naoya*; Nakajima, Kunihisa; Imoto, Jumpei; Suzuki, Eriko
Nihon Genshiryoku Gakkai-Shi ATOMO, 63(12), p.825 - 829, 2021/12
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.
Liu, J.; Miwa, Shuhei; Nakajima, Kunihisa; Osaka, Masahiko
Nuclear Materials and Energy (Internet), 26, p.100916_1 - 100916_6, 2021/03
Times Cited Count:3 Percentile:31.52(Nuclear Science & Technology)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.