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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:1.41MBJAEA-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.
Rizaal, M.; Miwa, Shuhei; Suzuki, Eriko; Imoto, Jumpei; Osaka, Masahiko; Gou
llo, M.*
ACS Omega (Internet), 6(48), p.32695 - 32708, 2021/12
Times Cited Count：1 Percentile：6.77(Chemistry, Multidisciplinary)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 CsMoO in water at 20
C and 25C. The solubilities of CsI at 25C 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 20C obtained by the OECD test guideline 105 flask method (test guideline) was also in good agreement with the literature value. The measured solubility of CsMoO was 256.8 
6.2 (g/100 g HO) at 20C using the test guideline. This measured solubility of CsMoO was found to be comparable to those of other alkaline molybdates and considered to be more reliable than the literature value.
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
Times Cited Count：5 Percentile：53.85(Nuclear Science & Technology)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.
Miwa, Shuhei; Nakajima, Kunihisa; Miyahara, Naoya; Nishioka, Shunichiro; Suzuki, Eriko; Horiguchi, Naoki; Liu, J.; Miradji, F.; Imoto, Jumpei; Afiqa, B. M.; et al.
Mechanical Engineering Journal (Internet), 7(3), p.19-00537_1 - 19-00537_11, 2020/06
We constructed the fission product (FP) chemistry database named ECUME for LWR severe accident. This version of ECUME is equipped with dataset of the chemical reactions and their kinetics constants for the reactions of cesium(Cs)-iodine(I)-boron(B)-molybdenum(Mo)-oxygen(O)-hydrogen(H) system in gas phase, the elemental model for the high temperature chemical reaction of Cs with stainless steel applied as the structural material in a reactor, and thermodynamic data for CsBO vapor species and solids of CsSiO and CsFeSiO for these chemical reactions. The ECUME will provide estimation of Cs distribution due to the evaluation of effects of interaction with BWR control material B and stainless steel on Cs behavior in the Fukushima Daiichi Nuclear Power Station.
Miwa, Shuhei; Takase, Gaku; Imoto, Jumpei; Nishioka, Shunichiro; Miyahara, Naoya; Osaka, Masahiko
Journal of Nuclear Science and Technology, 57(3), p.291 - 300, 2020/03
Times Cited Count：7 Percentile：55.67(Nuclear Science & Technology)For the evaluation of transport behavior of control material boron in a severe accident of BWR from the viewpoint of chemical effects on cesium and iodine behavior, boron chemistry during transportation in the high temperature region above 400 K was experimentally investigated. The heating tests of boron oxide specimen were conducted using the dedicated experimental apparatus reproducing fission product release and transport in steam atmosphere. Released boron oxide vapor was deposited above 1,000 K by the condensation onto stainless steel. The boron deposits and/or vapors significantly reacted with stainless steel above 1,000 K and formed the stable iron-boron mixed oxide (FeO)BO
. These results indicate that released boron from degraded BWR control blade in a severe accident could remain in the high temperature region such as a Reactor Pressure Vessel. Based on these results, it can be said that the existence of boron deposits in the high temperature region would decrease the amount of transported cesium vapors from a Reactor Pressure Vessel due to possible formation of low volatile cesium borate compounds by the reaction of boron deposits with cesium vapors.
Miwa, Shuhei; Miyahara, Naoya; Nakajima, Kunihisa; Nishioka, Shunichiro; Suzuki, Eriko; Horiguchi, Naoki; Liu, J.; Miradji, F.; Imoto, Jumpei; Afiqa, B. M.; et al.
Proceedings of 27th International Conference on Nuclear Engineering (ICONE-27) (Internet), 8 Pages, 2019/05
We constructed the first version of fission product (FP) chemistry database named ECUME for LWR severe accident. The first version of ECUME is equipped with dataset of the chemical reactions and their kinetics constants for the reactions of cesium(Cs)-iodine(I)-boron(B)-molybdenum(Mo)-oxygen(O)-hydrogen(H) system in gas phase, the elemental model for the high temperature chemical reaction of Cs with stainless steel, and thermodynamic data for CsBO vapor species and solids of CsSiO and CsFeSiO. The ECUME will provide more accurate estimation of Cs distribution due to the evaluation of effects of interaction with BWR control material B and stainless steel on Cs behavior in the Fukushima Daiichi Nuclear Power Station.
Imoto, Jumpei; Miwa, Shuhei; Osaka, Masahiko
Proceedings of International Topical Workshop on Fukushima Decommissioning Research (FDR 2019) (Internet), 4 Pages, 2019/05
Boron (B) oxidative vaporization processes from the representative alloys of Fe-B and Zr-B formed in the mixed melt of BWR control material boron carbide, stainless steel and Zircaloy were experimentally investigated toward the construction of B release model under severe accident. The results show that B oxidative vaporization from ZrB would proceed in the formation of ZrO and BO due to the oxidation of ZrB, followed by the formation of volatile H-B-O vapor species by the reaction of BO with steam. On the other hand, for FeB and FeB, the B oxidative vaporization processes would proceed in the same manner. Complex Fe-B-O compounds formation in addition to amorphous BO were observed by the oxidation of FeB and FeB. Then the B vaporization would occur by the formation of volatile H-B-O compound by the reaction of BO, which were derived from both oxidation of FeB and decomposition of Fe-B-O compounds.
Yamasaki, Shinya*; Imoto, Jumpei*; Furuki, Genki*; Ochiai, Asumi*; Onuki, Toshihiko; Sueki, Keisuke*; Namba, Kenji*; Ewing, R. C.*; Utsunomiya, Satoshi*
Science of the Total Environment, 551-552, p.155 - 162, 2016/05
Times Cited Count：32 Percentile：70.18(Environmental Sciences)Cesium-137 (
Cs) of estuary sediment impacted by the FDNPP was measured. Increasing radioactivity was observed from surface to bottom. 90% of the Cs was strongly bound to clay minerals in the estuary sediments. These results suggest that Cs is being transported from contaminated paddy fields to the estuary.
Kaneko, Makoto*; Iwata, Hajime; Shiotsu, Hiroyuki; Masaki, Shota*; Kawamoto, Yuji*; Yamasaki, Shinya*; Nakamatsu, Yuki*; Imoto, Jumpei*; Furuki, Genki*; Ochiai, Asumi*; et al.
Frontiers in Energy Research (Internet), 3, p.37_1 - 37_10, 2015/09
The mobility of the aggregates of submicron-sized sheet aluminosilicate in the surface environment is a key factor controlling the current Cs migration in Fukushima.
Osaka, Masahiko; Nakajima, Kunihisa; Miwa, Shuhei; Miyahara, Naoya; Suzuki, Eriko; Suzuki, Chikashi; Horiguchi, Naoki; Imoto, Jumpei; Liu, J.; Nishioka, Shunichiro; et al.
no journal, ,
Fundamental research on fission product (FP) chemistry is underway at Japan Atomic Energy Agency. The purpose is to establish a FP chemistry database in each region of a LWR under severe accident conditions. Improvement of FP chemical models based on this database is also an important task of the research. Research outputs are reflected to the research and development of decommissioning of Fukushima Daiichi Nuclear Power Station (1F) and the enhancement of LWR safety. Four research items have thus been established considering the specific issues of 1F and the priority in the source term research area, as follows: - Effects of boron (B) release kinetics and thermal-hydraulic conditions on FP behavior, - Cesium (Cs) chemisorption and reactions with structural materials, - Establishment of a thermodynamic and thermophysical properties database for FP compounds, - Development of experimental and analytical techniques for the reproduction of FP behavior. In this paper, results and progress of the research are presented.
Imoto, Jumpei; Miwa, Shuhei; Osaka, Masahiko
no journal, ,
The release behavior of Boron from Fe-B compounds formed by BC control rod melting in severe accident were experimentally investigated. The B release from Fe-B compounds was different according to the chemical composition of Fe and B, which was attributed to the formation of different oxide on surface of Fe-B compounds. B release was suppressed by the formation of stable Fe-B-O compounds in the FeB compound.
Miwa, Shuhei; Miyahara, Naoya; Horiguchi, Naoki; Imoto, Jumpei; Nakajima, Kunihisa; Osaka, Masahiko
no journal, ,
The chemical behavior of boron compounds such as chemical reaction and condensation during their transport in a reactor coolant system under severe accident conditions was estimated considering effects of Boron release kinetics from control blade melts and atmosphere for evaluation of boron effects on the cesium and iodine chemistry. The most of boron is transported as boric acid to the lower temperature region of a reactor coolant system in steam atmosphere. On the other hand, the release of boron from control blade is suppressed in steam-starvation atmosphere due to the formation of stable iron borate, and the chemical forms of boron during transport becomes boron oxide and cesium borate, which lead to a suppression of transport to the lower temperature region due to their condensation at higher temperature.
Imoto, Jumpei; Di Lemma, F. G.*; Miwa, Shuhei; Takano, Masahide; Osaka, Masahiko
no journal, ,
In order to investigate the Boron (B) release behavior from a Fe-B compounds formed in the melt of BWR control blade under a severe accident, a thermal analysis on a synthesized Fe-B sample was performed to evaluate the oxidation and vaporization behavior. It was found that the oxidation rate of the Fe-B compound was several magnitude of order lower than that of BC. This result support the previous report that the vaporization of B through the main release path of the oxidation product BO is suppressed by the formation of Fe-B-O compounds in the case of Fe-B compounds.
Imoto, Jumpei; Miwa, Shuhei; Takano, Masahide; Osaka, Masahiko
no journal, ,
In order to improve the boron release model from the molten BWR control blade under LWR severe accident, chemical reaction during the boron release was investigated experimentally. Thermal analysis of the Fe-B compound formed in molten control blade was carried out and the reaction products were analyzed. Fe-B-O compound was detected as reaction product at oxidation of the FeB compound in 1200-1400K using X-ray diffraction. It was found that B release from FeB occurred via oxidation formation of BO and stable Fe-B-O compound.
Miwa, Shuhei; Imoto, Jumpei; Miyahara, Naoya; Osaka, Masahiko
no journal, ,
BWR control material, boron, would influence the transport behavior of fission product (FP) such as cesium in a reactor coolant system under LWR severe accident. Thus the boron transport behavior was experimentally investigated by using Test bench for FP release and transport (TeRRa). The analysis results of deposits show that changes in weight of tube increase above 900 K and around 700 K, which would be attributed to chemical reaction with stainless steel and condensation of boron vapor onto stainless tubes, respectively. From these results, it is concluded that the released boron vapor would react with stainless steel and condense in the temperature range of reactor coolant system.
Takase, Gaku; Suzuki, Eriko; Imoto, Jumpei; Nakajima, Kunihisa; Miwa, Shuhei; Ogawa, Hiroaki; Osaka, Masahiko
no journal, ,
A chemical reaction experiment between boron vapor, which is from BWR control material, and stainless steel at high temperature was conducted under the condition in nuclear reactor cooling system during LWR severe accident. It was found from the analysis of reaction products that boron may chemically react with iron at the surface of stainless steel and adhere as Fe-B-O compounds over 940 K.
Imoto, Jumpei; Miwa, Shuhei; Osaka, Masahiko
no journal, ,
The chemical reactions for release of B from Fe-B and Zr-B compounds formed in the BWR control blade melts at severe accident in light water reactor were experimentally estimated by thermal analysis and X-ray diffraction analysis. For the Zr-B compounds, it was found that B was released via only BO formed by oxidation. On the other hand, for the Fe-B compounds, it was found that B were released via two kinds of B oxides, BO and stable Fe-B-O compounds.
Miwa, Shuhei; Nakajima, Kunihisa; Miyahara, Naoya; Nishioka, Shunichiro; Suzuki, Chikashi; Suzuki, Eriko; Horiguchi, Naoki; Imoto, Jumpei; Liu, J.; Miradji, F.; et al.
no journal, ,
We have been conducting the fundamental study on fission product (FP) chemistry under severe accident (SA) conditions. The objective is to construct the FP chemistry database and to improve FP chemistry model for the improvement of source term evaluation technology. We have established the technical basis, such as experimental set-up and analysis tool, for the evaluation of FP chemistry in SA conditions. Fundamental knowledges on the effects of boron on the cesium and iodine chemistry were also obtained.
Nishioka, Shunichiro; Nakajima, Kunihisa; Suzuki, Eriko; Imoto, Jumpei; Osaka, Masahiko
no journal, ,
Fundamental data of degradation by moisture absorbent of Cs compounds was obtained experimentally so as to contribute to evaluation of the aging degradation behavior of deposited Cs on the structure materials under LWR severe accident condition. It was found the moisture absorbent behavior was varied depending on the chemical form of Cs.
