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Co inventory in the core of the Fukushima Daiichi Nuclear Power Plant; Contribution of fuel deposits to the reactor core inventoryUchida, Shunsuke*; Kino, Chiaki*; Karasawa, Hidetoshi; Takahatake, Yoko; Koma, Yoshikazu
Journal of Nuclear Science and Technology, 17 Pages, 2025/07
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Evaluation of radioactive nuclide behavior on and after the accident is important for the estimating radioactive nuclide composition in the wastes. The reactor core inventories have been obtained from the ORIGEN2 analysis, but the inventory of activation products is determined by the amount of their parent nuclides which are impurities contained in the structural materials. The ORIGEN2 does not treat fuel deposits including the impurities. Estimation of the initial Co-60 inventory in accurate is needed on the evaluation of some kinds of radioactive nuclide amount, since it is possible Co-60 is standard in the scaling factor. In this study, contribution of fuel deposits to the reactor core inventory was estimated by comparing the amount of Co-60 and Ni-63 calculated by the amounts of deposition by the microlayer-evaporation and drying-out model (MEDO model) and the result of the ORIGEN2 analysis, and then the method of estimating the reactor core inventory was proposed.
/MOX fuel oxidation under severe light water reactor accident conditionsLiu, J.; Miwa, Shuhei; Karasawa, Hidetoshi; Osaka, Masahiko
Nuclear Materials and Energy (Internet), 37, p.101532_1 - 101532_5, 2023/12
Times Cited Count：0 Percentile：16.48(Nuclear Science & Technology)Katsumura, Kosuke*; Takagi, Junichi*; Hosomi, Kenji*; Miyahara, Naoya*; Koma, Yoshikazu; Imoto, Jumpei; Karasawa, Hidetoshi; Miwa, Shuhei; Shiotsu, Hiroyuki; Hidaka, Akihide*; et al.
Nihon Genshiryoku Gakkai-Shi ATOMO
, 65(11), p.674 - 679, 2023/11
no abstracts in English
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.
Uchida, Shunsuke; Karasawa, Hidetoshi; Kino, Chiaki*; Pellegrini, M.*; Naito, Masanori*; Osaka, Masahiko
Nuclear Engineering and Design, 380, p.111256_1 - 111256_19, 2021/08
Times Cited Count：7 Percentile：56.12(Nuclear Science & Technology)It is essential to grasp the long-term distributions of FP as well as fuel debris all over the Fukushima Daiichi Nuclear Power Plant (1F) for safe completion of its decommissioning projects. The fuel debris is going to be removed from the plant under the severe conditions of FP being scattered during major decommissioning work, and then, the decommissioning projects are going to be terminated by storing safely the removed debris as recovered fertile materials or as materials for final radioactive disposal. In order to determine the FP distribution in the plant for the long period from the accident occurrence to the termination of the plant decommissioning, procedures for analyzing multi-term FP behaviors were proposed. The proposed procedures should be improved by applying the FP data measured in the plant and validated based on the feedback data. Then, the accuracy-improved procedures should be applied to estimate FP distribution during each period of the decommissioning projects.
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; 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.
-ray irradiation on the high temperature oxidation of austenitic stainless steel in supercritical waterNakahara, Yukio; Yamamoto, Masahiro; Karasawa, Hidetoshi*; Kiuchi, Kiyoshi; Katsumura, Yosuke*
Proceedings of 16th Pacific Basin Nuclear Conference (PBNC-16) (CD-ROM), 6 Pages, 2008/10
Three types of commercial-grade austenitic stainless steel, Type 304L, Type 316L, and Type 310S, were immersed in deaerated supercritical water (SCW) of 25 MPa, 550 
C with -ray irradiation for 1000 hours in total. Absorbed dose rates in SCW are estimated at 5-15 kGy h
. High temperature oxidation experiments resulted in the formation of two-layer oxide film in which the outer layer is porous iron oxide and the inner layer is dense iron-chromium-nickel oxide. Rate constants of parabolic rate law in net weight gains of Type 304L SS and Type 310S SS are decreased as the -ray exposure rate is increased. The net weight gain of -ray irradiated Type 316L SS is sharply fluctuating and decreasing, because the flaking of the outer layer occurred. Hematite is formed in the outer layer on all irradiated samples of examined alloys. The concentration of chromium on the surface is increased by -ray irradiation. A chromium-rich part in the inner layer accompanying a nickel-rich part in the metal is formed along to the oxide/metal interface of -ray irradiated Type 304L SS, non-irradiated and -ray irradiated Type 316L SS.
Karasawa, Hidetoshi; Kino, Chiaki*; Suzuki, Eriko; Nakajima, Kunihisa; Miwa, Shuhei; Osaka, Masahiko
no journal, ,
The chemisorption velocities of CsOH vapor on stainless steels were examined experimentally by the Cs chemisorption test apparatus named CREST. Using obtained adsorption velocities, the amounts of CsOH vapors chemisorbed on SS walls of the steam separator and the steam dryer were evaluated using the SA code of SAMPSON under SA conditions in Fukushima Daiichi Nuclear Power Plants.
Imoto, Jumpei; Miwa, Shuhei; Miyahara, Naoya; Nakajima, Kunihisa; Nishioka, Shunichiro; Suzuki, Eriko; Horiguchi, Naoki; Liu, J.; Miradji, F.; Afiqa, B. M.; et al.
no journal, ,
Fission product (FP) chemistry database ECUME (Effective Chemistry database of fission products Under Multiphase rEaction) consists of three kinds of datasets: CRK (dataset for Chemical Reaction Kinetics), EM (Elemental Model set) and TD (ThermoDynamic dataset). The present ECUME is equipped with the CRK for the reaction of Cs-I-B-Mo-O-H system in gas phase, the EM for the Cs chemical reaction with stainless steel (SS) (Cs chemisorption onto SS) and the TD for CsBO vapor species and solid CsSiO and CsFeSiO. The Cs chemisorption behavior model has successfully reproduced the effects of CsOH vapor concentration in gas phase and Si content in SS on the Cs chemisorption behavior which were not able to be considered by the existing model. The ECUME are expected to contribute to more accurate evaluation of FP distribution in Fukushima Daiichi Nuclear Power Station.
Nakajima, Kunihisa; Suzuki, Eriko; Nishioka, Shunichiro*; Miwa, Shuhei; Horiguchi, Naoki; Imoto, Jumpei; Liu, J.; Karasawa, Hidetoshi; Osaka, Masahiko
no journal, ,
Thermodynamic data of cesium compounds with boron and silicon are included in the thermodynamic dataset (TM) of ECUME. Chemical forms and fractions of cesium compounds formed in high temperature regions of nuclear reactors and revaporization amount of Cs chemisorbed onto stainless steel can be more accurately estimated by using the TM of ECUME. Incorporation of ECUME into severe accident analysis codes can cope with chemical behaviors of FPs influencing their release and transport behaviors and can be expected to improve source term estimations.
Miwa, Shuhei; Horiguchi, Naoki; Miyahara, Naoya*; Nakajima, Kunihisa; Suzuki, Eriko; Imoto, Jumpei; Liu, J.; Karasawa, Hidetoshi; Osaka, Masahiko
no journal, ,
We developed the fission product chemistry database named ECUME (
ffective 
hemistry database of fission products 
nder 
ultiphase raction) for the LWR severe accident. The dataset for chemical reaction kinetics of ECUME consists of main chemical reactions and their effective chemical reaction kinetic constants. This dataset has the advantages in kinetics evaluation of the effects of molybdenum and BWR control material boron on cesium and iodine chemistry. This can improve prediction accuracy of chemical forms and their fraction in lower temperature region such as a primary containment vessel and a reactor building.
Uchida, Shunsuke*; Karasawa, Hidetoshi*; Kino, Chiaki*; Naito, Masanori*; Osaka, Masahiko
no journal, ,
Development of analysis code of FP behavior both for short and long terms after severe accident is conduced. A risk analysis method for workers' radiation and FP release is proposed based on the evaluation result for FP distribution during 10 years after the accident.
Karasawa, Hidetoshi*; Uchida, Shunsuke*; Kino, Chiaki*; Naito, Masanori*; Osaka, Masahiko
no journal, ,
FPs that can have impact on the fuel-debris retrieval are selected and amount and radioactivities are evaluated based on FP distribution inside containment predicted by SA analysis code.
Mizokami, Shinya; Osaka, Masahiko; Ito, Kenichi*; Karasawa, Hidetoshi*; Honda, Takeshi*
no journal, ,
Overview of the activity conducted in the project (Upgrading level of grasping state inside reactor) by cesium chemistry team will be introduced as a start point of the series presentation.
Kino, Chiaki*; Karasawa, Hidetoshi*; Uchida, Shunsuke*; Nishioka, Shunichiro; Osaka, Masahiko
no journal, ,
Analysis of the long-term transport behavior of fission products (FP) is important for decommissioning of Fukushima-Daiichi Nuclear Power Station, "Decommissioning analysis code" which can analyze thermal-hydraulic and FP behavior for 10 years after the severe accident has been developed based on SAMPSON code. As the results of test analysis for 2 months after SA, Cs concentration in the wet-well (W/W) decreased slower than that in the case of consideration only with treatment of contaminated water. This result indicates a possible long-term contribution of accumulated Cs in W/W as the Cs contamination source.
Miwa, Shuhei; Karasawa, Hidetoshi; Kino, Chiaki*; Nakajima, Kunihisa; Suzuki, Eriko; Imoto, Jumpei
no journal, ,
We investigated the Cs distribution and characteristics in the upper structure of the reactor pressure vessel in TEPCO Fukushima Daiichi Nuclear Power Station (1F) based on the data on the amount of Cs chemisorbed compound onto stainless steel in the upper structure calculated by severe accident analysis code SAMPSON with improved Cs chemisorption model, the chemical form and water solubility of Cs chemisorbed compounds obtained by experiments which are prerequisite for the evaluation of long-term behaviors. The results indicate that the amount of insoluble Cs chemisorbed compounds can be lower than that estimated by using existing Cs chemisorption model.
Suzuki, Eriko; Nakajima, Kunihisa; Nishioka, Shunichiro*; Miwa, Shuhei; Horiguchi, Naoki; Imoto, Jumpei; Liu, J.; Karasawa, Hidetoshi; Osaka, Masahiko
no journal, ,
The elemental model set (EM) of ECUME consists of improved models which can be directly incorporated into the present severe accident analysis codes. The models of EM has advantages in considering various chemical conditions. The improved model for cesium (Cs) chemisorption has successfully reproduced the effects of Cs vapor concentration in gas phase and silicon content in stainless steel on the Cs chemisorption behavior. This improved model can contribute to more accurate estimation of Cs distribution in a high temperature area.
Uchida, Shunsuke; Osaka, Masahiko; Karasawa, Hidetoshi; Kino, Chiaki*
no journal, ,
The Cs amounts in the major partial zone of the D/W and S/C of Units 1-3 have been evaluated by applying the BEP with the previously reported dose rate conversion factors. As a result of comparing the BEP results with those of the FEP based on the SA analysis code, the conclusions are summarized as follows. The measured dose rate for A and B detectors of D/W CAMS for Unit 1 showed the different patterns, which could be clearly explained by applying local wash-out effects. The Cs amounts in the D/W bottom regions for Units 1-3 could be evaluated by the BEP. The Cs amounts obtained with the BEP in the D/W bottom region and S/C for Unit 1 were consistent to those with the FEP. The Cs amounts obtained with the BEP in the D/W bottom regions for Units 2 and 3 were more than 10 times as large as those with the FEP.
Liu, J.; Nakajima, Kunihisa; Miwa, Shuhei; Karasawa, Hidetoshi; Osaka, Masahiko
no journal, ,
