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Rizaal, M.; Nakajima, Kunihisa; Suzuki, Eriko; Miwa, Shuhei
Annals of Nuclear Energy, 218, p.111433_1 - 111433_10, 2025/08
Rizaal, M.; Luu, V. N.; Nakajima, Kunihisa; Miwa, Shuhei
Proceedings of International Topical Workshop on Fukushima-Daiichi Decommissioning Research 2024 (FDR2024) (Internet), 4 Pages, 2024/10
Rizaal, M.; Nakajima, Kunihisa
Chemosphere, 363, p.142870_1 - 142870_9, 2024/09
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
Rizaal, M.; Nakajima, Kunihisa; Saito, Takumi*; Osaka, Masahiko; Okamoto, Koji*
ACS Omega (Internet), 7(33), p.29326 - 29336, 2022/08
Times Cited Count:4 Percentile:31.35(Chemistry, Multidisciplinary)Rizaal, M.; Miwa, Shuhei; Suzuki, Eriko; Imoto, Jumpei; Osaka, Masahiko; Goullo, M.*
ACS Omega (Internet), 6(48), p.32695 - 32708, 2021/12
Times Cited Count:4 Percentile:21.06(Chemistry, Multidisciplinary)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.
Rizaal, M.; Nakajima, Kunihisa; Saito, Takumi*; Osaka, Masahiko; Okamoto, Koji*
Journal of Nuclear Science and Technology, 57(9), p.1062 - 1073, 2020/09
Times Cited Count:9 Percentile:66.49(Nuclear Science & Technology)The interaction of cesium hydroxide and a calcium silicate insulation material was experimentally investigated at high temperature conditions. A thermogravimetry equipped with differential thermal analysis was used to analyze thermal events in the samples of mixed calcium silicate and cesium hydroxide under Ar-5%H and Ar-4%H
-20%H
0 with maximum temperature of 1100
C. Prior being mixed with cesium hydroxide, a part of calcium silicate was pretreated at high temperature to evaluate the effect of possible structural changes of this material due to a preceding thermal history and also the sake of thermodynamic evaluation to those available ones. Based upon the initial condition (preliminary heat treatment) of calcium silicate, it was found that if the original material consisted of xonotlite (Ca
Si
0
(0H)
), the endothermic reaction with cesium hydroxide occurred over the temperature range 575-730
C meanwhile if the crystal phase of original material was changed to wollastonite (CaSi0
), the interaction occurred over temperature range 700-1100
C. Furthermore, the X-ray diffraction analyses have indicated on both type of pretreated calsils that regardless of Ar-5%H
and Ar-4%H
-20%H
0 atmosphere, cesium aluminum silicate, CsAlSi0
was formed with aluminum in the samples as an impurity or adduct.
Rizaal, M.; Saito, Takumi*; Okamoto, Koji*; Erkan, N.*; Nakajima, Kunihisa; Osaka, Masahiko
Mechanical Engineering Journal (Internet), 7(3), p.19-00563_1 - 19-00563_10, 2020/06
The adsorption of cesium (Cs) on calcium silicate insulation of primary piping system is postulated to contribute in high dose rate of surrounding pedestal area in Fukushima Daiichi NPP unit 2. In this study, room-temperature experiment of Cs adsorption on calcium silicate has been studied as an initial approach of Cs adsorption behavior toward higher temperature condition. As the result of analyzing of Cs adsorption kinetics, it was expected that the underlying adsorption mechanism is chemisorption. Furthermore, analysis of adsorption isotherm suggested unrestricted monolayer formation followed by multilayer formation.
Rizaal, M.; Nakajima, Kunihisa; Osaka, Masahiko; Saito, Takumi*; Erkan, N.*; Okamoto, Koji*
no journal, ,
Experimental study using thermogravimetry and X-ray diffractometry was conducted to investigate chemical interaction between calcium silicate insulation and cesium hydroxide under steam and hydrogen atmospheres. This interaction might be one of the causes for the high dose rate reading outside the pedestal in 1F, Unit2. Our results suggested that some chemical interaction occurred in temperature range of 575-730C regardless of atmospheres.
Rizaal, M.; Miwa, Shuhei; Suzuki, Eriko; Imoto, Jumpei; Osaka, Masahiko; Goullo, M.*
no journal, ,
Karasawa, Hidetoshi; Rizaal, M.; Miwa, Shuhei; Kino, Chiaki*
no journal, ,
In SA analysis, the importance of chemical reactions related to FP behavior has been pointed out. For this reason, the amount of gaseous iodine produced was evaluated by a gaseous chemical reaction model using the ECUME database in the previous CsI-TeRRa experiment. In this study, we investigated the gas phase chemical reaction model for the CsI-BO
-TeRRa experiment, which evaluated the influence of B on CsI behavior. In the experiment, the addition of B
O
increased the production of gaseous iodine by about 10 times. To explain this behavior, we set up a Cs-I-B-H-O reaction mechanism in which HBO
generated from B
O
is reacted with CsI and CsOH to produce gaseous iodine. Calculations of the chemical reaction model using chemical reaction rates in the ECUME database confirmed an increase in gaseous iodine (about 26 times at 1,273 K) due to the addition of B
O
. The results showed that gaseous iodine was sufficiently produced at high temperatures, indicating the possibility of reproducing the TeRRa experiment by calculating chemical reactions during the transition of decreasing temperature.
Miwa, Shuhei; Nakajima, Kunihisa; Karasawa, Hidetoshi; Rizaal, M.; Luu, V. N.; Mohamad, A. B.
no journal, ,
no abstracts in English
Rizaal, M.; Nakajima, Kunihisa; Karasawa, Hidetoshi; Miwa, Shuhei
no journal, ,
Rizaal, M.; Nakajima, Kunihisa; Osaka, Masahiko; Saito, Takumi*; Okamoto, Koji*
no journal, ,
Mohamad, A. B.; Yamashita, Shinichiro; Soma, Yasutaka; Nemoto, Yoshiyuki; Pham, V. H.; Abe, Yosuke; Ioka, Ikuo; Sato, Tomonori; Ishijima, Yasuhiro; Miwa, Shuhei; et al.
no journal, ,
Rizaal, M.; Nakajima, Kunihisa; Karasawa, Hidetoshi; Luu, V. N.; Miwa, Shuhei
no journal, ,
Rizaal, M.; Miwa, Shuhei; Suzuki, Eriko; Imoto, Jumpei; Osaka, Masahiko; Goullo, M.*
no journal, ,