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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.
Suzuki, Hiroaki*; Morita, Yoshihiro*; Naito, Masanori*; Nemoto, Yoshiyuki; Kaji, Yoshiyuki
Mechanical Engineering Journal (Internet), 7(3), p.19-00450_1 - 19-00450_17, 2020/06
In this study, the SAMPSON code was modified to evaluate severe accidents in a spent fuel pool (SFP). Air oxidation models based on oxidation data obtained on the Zircaroy-4 cladding (ANL model) and the Zircaroy-2 cladding (JAEA model) were included in the modified SAMPSON code. Experiments done by Sandia National Laboratory using simulated fuel assemblies equivalent to those of an actual BWR plant were analyzed by the modified SAMPSON code to confirm the functions for analysis of the severe SFP accidents. The rapid fuel rod temperature rise due to the Zr air oxidation reaction could be reasonably evaluated by the SAMPSON analysis. The SFP accident analyses were conducted with different initial water levels which were no water, water level at bottom of active fuel, and water level at half of active fuel. The present analysis showed that the earliest temperature rise of the fuel rod surface occurred when there was no water in the SFP and natural circulation of air became possible.
Morita, Yoshihiro*; Suzuki, Hiroaki*; Naito, Masanori*; Kaji, Yoshiyuki; Nemoto, Yoshiyuki
no journal, ,
We conducted the preliminary analysis for the phenomenon of loss of coolant in Spent Fuel Pool by MAAP code and reported the analytical results for temperature and relocation behavior of spent fuel channels.
Morita, Yoshihiro*; Suzuki, Hiroaki*; Naito, Masanori*; Nemoto, Yoshiyuki; Kaji, Yoshiyuki
no journal, ,
A new model including the spent fuel pool (SFP) or Zr oxidation behavior which is necessary to evaluate the SFP accident caused by cooling function loss was developed and implanted in the severe accident code SAMPSON in this work. Results of the evaluation using the improved code will be presented.
Kino, Chiaki*; Karasawa, Hidetoshi*; Uchida, Shunsuke*; Naito, Masanori*; Osaka, Masahiko
no journal, ,
FP distribution in 1F was phenomenologically evaluated in views of accident scenario. Possible retention of chemisorbed Cs in the separator etc. was implied.
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.
Karasawa, Hidetoshi; Miwa, Shuhei; Kino, Chiaki*
no journal, ,
Amount of CsOH chemisorbed on surfaces of structural materials such as separators and dryers in unit1, unit2, unit3 were evaluated by the SAMPSON code under the Fukushima Daiichi Nuclear Power Plant severe accident conditions. Concentrations of CsOH vapors are decreased due to reaction with Mo vapors and to produce aerosols under decreasing gas temperature. As an existing chemisorption model is independent on CsOH concentrations, an ECUME has developed a new chemisorption model with a function of CsOH concentrations and gas temperature. Cs absorbed amounts were changed unit by unit due to different CsOH concentrations and gas temperature. Evaluation of CsOH chemisorption in a SA analysis needs the new chemisorption model with dependency of CsOH concentrations.
Karasawa, Hidetoshi; Miwa, Shuhei; Suzuki, Eriko; Nakajima, Kunihisa; Kino, Chiaki*
no journal, ,
Temperature effects of chemisorption of CsOH vapor generated at about 1000K on SUS were examined using TeRRa test apparatus with temperature gradient tube from 1273K to 473K. The chemisorption amounts were measured using IPS after dissolving test coupons. These results were calculated using the SA code, SAMPSON. For the test analysis, the thermal hydraulic analysis (THA) module and the FP transport analysis (FPTA) module were used. The FPTA could calculated the chemisorption amount within the experimental error range using the gas temperature calculated by the THA module. So the temperature dependency of the chemisorption model used in the calculation was validated.
Tezuka, Kennichi*; Kino, Chiaki*; Yamashita, Susumu; Mohamad, A. B.; Nemoto, Yoshiyuki
no journal, ,
no abstracts in English
Karasawa, Hidetoshi; Miwa, Shuhei; Kino, Chiaki*
no journal, ,
Re-vaporization of CsOH in primary system was observed after a core shutdown in the Phebus FPT1 experiment. This behavior was examined using the SAMPSON code with the model of aerosol formation. The re-vaporization behavior was confirmed in the analysis, that is, deposited CsOH was evaporated when the vapor concentration became less than the saturated concentration and re-deposited in simulated steam generator walls with the lower temperature. As to FPs other than CsOH, the amount of each FP deposited in the simulated steam generator was found to be proportion to the FP component of aerosols as expected in the aerosol formation model.
Karasawa, Hidetoshi; Miwa, Shuhei; Kino, Chiaki*
no journal, ,
As CsI is the main fission product, the transport behavior was examined using the TeRRa apparatus and found to produce gaseous iodine. To analyze CsI behavior, a chemical reaction model was made and evaluated. The chemical model was introduced to the SAMPSON code and analyzed the TeRRa experiment. We could explain the experimental results such as the formation of gaseous iodine, formation of aerosol and deposition of aerosol due to thermophoresis.
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 BO 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 BO 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 BO. 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.
