Effect of molybdenum release on UO/MOX fuel oxidation under severe light water reactor accident conditions

Liu, J.; Miwa, Shuhei; Karasawa, Hidetoshi; Osaka, Masahiko

Nuclear Materials and Energy (Internet), 37, p.101532_1 - 101532_5, 2023/12

https://doi.org/10.1016/j.nme.2023.101532

Improvement of model for cesium chemisorption onto stainless steel in severe accident analysis code SAMPSON (Joint research)

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:1.41MB
JAEA-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.

A New method of measuring ruthenium activity in ruthenium-containing alloys by using thermogravimetric analysis

Liu, J.; Nakajima, Kunihisa; Miwa, Shuhei; Shirasu, Noriko; Osaka, Masahiko

Journal of Nuclear Science and Technology, 59(4), p.484 - 490, 2022/04

https://doi.org/10.1080/00223131.2021.1979432

Synthesis of simulated fuels containing CsI under gas-tight condition

Liu, J.; Miwa, Shuhei; Nakajima, Kunihisa; Osaka, Masahiko

Nuclear Materials and Energy (Internet), 26, p.100916_1 - 100916_6, 2021/03

https://doi.org/10.1016/j.nme.2021.100916

Development of fission product chemistry database ECUME for the LWR severe accident

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

https://doi.org/10.1299/mej.19-00537

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.

Evaporation of ruthenium from simulated fission-produced alloy precipitates in a nuclear fuel

Liu, J.; Miyahara, Naoya; Miwa, Shuhei; Takano, Masahide; Hidaka, Akihide; Osaka, Masahiko

Journal of Nuclear Materials, 527, p.151819_1 - 151819_7, 2019/12

https://doi.org/10.1016/j.jnucmat.2019.151819

To evaluate the effect of each constituent element on the evaporation rate of ruthenium (Ru) from fission-produced alloy precipitates, the oxidation and evaporation behaviors of metallic Ru, molybdenum (Mo), palladium (Pd), rhodium (Rh) and Mo-Ru-Pd-Rh alloy powders were investigated by thermogravimetric analysis under oxidizing atmospheres from 1473 to 1723 K. The findings led to the following conclusions: (1) The quick oxidation of Mo into condensed Mo oxides can effectively suppress the oxidation and evaporation of Ru in alloy powders; (2) After the complete evaporation of Mo, the evaporation loss rate of Ru would be directly influenced by the Ru activity in the Ru-Pd-Rh alloys, which is determined by the composition of alloys.

Chemical trapping of Sr vapor species by Zircaloy cladding under a specific chemical condition

Mohamad, A.*; Nakajima, Kunihisa; Suzuki, Eriko; Miwa, Shuhei; Osaka, Masahiko; Oishi, Yuji*; Muta, Hiroaki*; Kurosaki, Ken*

Proceedings of International Topical Workshop on Fukushima Decommissioning Research (FDR 2019) (Internet), 4 Pages, 2019/05

In the accident of Fukushima Daiichi Nuclear Power Station, formation of a volatile SrCl could have occurred by the sea-water injection into the core. This can cause the release of non-volatile group Sr from the fuel to induce chemical reactions with reactor structural materials, such as stainless steel and Zircaloy (Zry) cladding. Such reactions could cause the changes in distribution of Sr in the reactor. Chemical reactions between Sr species and Zry were therefore investigated experimentally. As the result, it can be said that Sr vapor species were chemically trapped right after the release from fuel. This trapping effect of Sr by Zry-cladding implies a possibility of preferable Sr retention in the oxide phase of debris.

Chemical reaction kinetics dataset of Cs-I-B-Mo-O-H system for evaluation of fission product chemistry under LWR severe accident conditions

Miyahara, Naoya; Miwa, Shuhei; Horiguchi, Naoki; Sato, Isamu*; Osaka, Masahiko

Journal of Nuclear Science and Technology, 56(2), p.228 - 240, 2019/02

https://doi.org/10.1080/00223131.2018.1544939

In order to improve LWR source term under severe accident conditions, the first version of a fission product (FP) chemistry database named "ECUME" was developed. The ECUME is intended to include major chemical reactions and their effective kinetic constants for representative SA sequences. It is expected that the ECUME can serve as a fundamental basis from which FP chemical models in the SA analysis codes can be elaborated. The implemented chemical reactions in the first version were those for representative gas species in Cs-I-B-Mo-O-H system. The chemical reaction kinetic constants were evaluated from either literature data or calculated values using ab-initio calculations. The sample chemical reaction calculation using the presently constructed dataset showed meaningful kinetics effects at 1000 K. Comparison of the chemical equilibrium compositions by using the dataset with those by chemical equilibrium calculations has shown rather good consistency for the representative Cs-I-B-Mo-O-H species. From these results, it was concluded that the present dataset should be useful to evaluate FP chemistry in Cs-I-B-Mo-O-H system under LWA SA conditions.

Release and transport behaviors of non-gamma-emitting fission products and actinides in steam and hydrogen atmospheres

Miwa, Shuhei; Ducros, G.*; Hanus, E.*; Bottomley, P. D. W.*; Van Winckel, S.*; Osaka, Masahiko

Nuclear Engineering and Design, 326, p.143 - 149, 2018/01

https://doi.org/10.1016/j.nucengdes.2017.11.017

The release and transport behaviors of 13 non-gamma-emitting fission products (FPs) and actinides in steam and hydrogen atmospheres were investigated based on the chemical analysis of their deposits on the components of VERCORS test loops. The new findings were obtained; strontium release was significantly enhanced in hydrogen atmosphere and a part of released strontium was transported towards the lower temperature region, uranium release was enhanced in steam atmosphere but most of released uranium deposited at high temperature region.

Development of experimental and analytical technologies for fission product chemistry under LWR severe accident condition

Miyahara, Naoya; Miwa, Shuhei; Nakajima, Kunihisa; Osaka, Masahiko

Proceedings of 2017 Water Reactor Fuel Performance Meeting (WRFPM 2017) (USB Flash Drive), 9 Pages, 2017/09

This paper presents the development of a reproductive experimental setup for FP release and transport and an analysis tool considering chemical reaction kinetics for the construction of the FP chemistry database. The performance test of the reproductive experimental setup TeRRa using CsI compounds show that TeRRa can reproduce well a FP chemistry-related behavior such as aerosol formation, growth and deposition behavior. An analytical tool has been developed based on the commercial ANSYS-FLUENT code. Some additional models was added to evaluate detailed FP chemistry during release and transport in this study. A test analysis simulating the CsI heating test in steam atmosphere was carried out to demonstrate the performance of the improved code. The result shows the appropriateness of the additional models.