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Journal Articles

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

Miwa, Shuhei; Miyahara, Naoya; Nakajima, Kunihisa; Nishioka, Shunichiro; Suzuki, Eriko; Horiguchi, Naoki; Liu, J.; Miradji, F.; Imoto, Jumpei; Mohamad, B. A.; 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$$_{2}$$ vapor species and solids of Cs$$_{2}$$Si$$_{4}$$O$$_{9}$$ and CsFeSiO$$_{4}$$. 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.

Journal Articles

Study on chemisorption model of cesium hydroxide onto stainless steel type 304

Nakajima, Kunihisa; Nishioka, Shunichiro; Suzuki, Eriko; Osaka, Masahiko

Proceedings of 27th International Conference on Nuclear Engineering (ICONE-27) (Internet), 8 Pages, 2019/05

Cesium chemisorption models were developed for estimation of amount of cesium chemisorbed onto stainless steel type 304 (SS304) during light water reactor severe accident. However, existing chemisorption models cannot accurately reproduce experimental results. In this study, a modified cesium chemisorption model was constructed based on a penetration theory for gas-liquid mass transfer with chemical reaction and was able to adequately describe effects on concentration of cesium hydroxide in gaseous phase and silicon content in SS304. It was found that the modified model can more accurately reproduce the experimental data than the existing model.

Journal Articles

Experimental study on Cs chemisorption behaviour onto stainless steel at around 873 K

Suzuki, Eriko; Takase, Gaku; Nakajima, Kunihisa; Nishioka, Shunichiro; Hashimoto, Naoyuki*; Isobe, Shigehito*; Osaka, Masahiko

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

In order to acquire the knowledge of the Cs chemisorption behaviour in the lower temperature region, the Cs chemisorbed compounds and the surface reaction rates were investigated by conducting the Cs chemisorption tests onto stainless steel at 873 and 973 K. As a result, The cesium ferrate compounds were revealed to be formed at this temperatures. It was seen that the dependences of surface reaction rate constant on this temperature were different from that at the higher temperature region. This behaviour leads to the conclusion that the Cs chemisorption model in the low temperature region should be newly constructed.

Oral presentation

Results and progress of fundamental research on FP chemistry

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.

Oral presentation

A Study of cesium chemisorption onto surface of stainless steel

Nishioka, Shunichiro; Nakajima, Kunihisa; Suzuki, Eriko; Osaka, Masahiko

no journal, , 

An experimental study has been conducted in order to construct a Cs chemisorption model. The model is reflected to an improvement of Cs distribution evaluation by severe accident analysis codes. Influencing factors on the chemisorption behaviors were investigated experimentally. It was found that temperature, atmosphere and Si contents in the stainless steel (SS) were the main influencing factors. Of note is the implication of revaporization of Cs chemisorbed compounds from the SS surface. It can be said from this result that the Cs chemisorption behaviors should be considered in relation to chemical properties of compounds formed.

Oral presentation

Cs chemical reaction with stainless steel under a LWR severe accident, 1; Effect of temperature and atmosphere on Cs chemisorbed amounts

Suzuki, Eriko; Nishioka, Shunichiro; Nakajima, Kunihisa; Osaka, Masahiko

no journal, , 

In order to clarify the behaviour of Cs chemisorption onto stainless steel under various LWR severe accident conditions, simulated Cs chemisorption tests, the parameters were temperature and atmosphere, were performed. As a results, it was observed that Cs chemisorbed amounts and Cs revaporization behaviour from Cs chemisorbed compounds were different between the atmosphere containing H$$_{2}$$O or not. It means that Cs chemisorption behaviour is greatly affected by not only temperature but also atmosphere.

Oral presentation

Cs chemical reaction with stainless steel under a LWR severe accident, 4; Evaluation of surface reaction rate between Cs and stainless steel for modeling study

Nishioka, Shunichiro; Nakajima, Kunihisa; Suzuki, Eriko; Osaka, Masahiko

no journal, , 

Validation of existing models of Cs chemisorption onto stainless steel (SS), incorporated in the severe accident (SA) analysis code, was carried out. The surface reaction rates between Cs and SS were calculated using newly obtained experimental data, and then compared with the old ones. The applicable range of the model was considered based on the comparison under various atmospheric condition.

Oral presentation

Investigation of in-reactor cesium chemical behavior in TEPCO's Fukushima Daiichi Nuclear Power Station accident, 3; Analysis of Cs chemisorption behavior onto stainless steel by mass transfer model

Nishioka, Shunichiro; Nakajima, Kunihisa; Miradji, F.; Suzuki, Eriko; Osaka, Masahiko

no journal, , 

The temperature dependency of surface reaction rate of Cs onto stainless steel, which is obtained by experimental test was analyzed by using mass transfer model. It was found that Cs concentration in gas phase influenced on the surface reaction rate.

Oral presentation

Investigation of in-reactor cesium chemical behavior in TEPCO's Fukushima Daiichi Nuclear Power Station accident, 5; Simulation study on Cs-bearing formation with vaporized Si and Cs

Suzuki, Akihiro*; Ito, Kenichi*; Nishioka, Shunichiro; Osaka, Masahiko

no journal, , 

To simulate the formation of micron-size spherical Cs-bearing particles, vaporized Cs and Si were reacted under high temperature water-vapor atmosphere and solidified in the gas phase experimentally. With this simulation study, the possibility that the Cs-bearing particles (type A spherical particles) in the environment were formed by reaction-and-solidification process under the high temperature gas phase in RPV was confirmed.

Oral presentation

Investigation of in-reactor cesium chemical behavior in TEPCO's Fukushima Daiichi Nuclear Power Station accident, 2; Experimental investigation of Cs chemisorption behavior onto stainless steel

Nakajima, Kunihisa; Suzuki, Eriko; Nishioka, Shunichiro; Osaka, Masahiko

no journal, , 

Information on the Cs distribution inside the reactors at Fukushima Daiichi Nuclear Power Station (1F) is important to proceed the decommissioning. For contribution to analysis of the Cs distribution, Cs chemisorption behaviors and chemical characteristics of the chemisorbed products have been investigated to establish a chemisorption model considering influences of the chemical reaction and the chemical characteristics of reaction products. As a first step, reproducibility tests were carried out to validate the existing model incorporated into sever accident analysis codes such as SAMPSON. As a result, reaction rate constants under an argon and hydrogen gas atmosphere do not increase with temperature as expected by the existing model and the chemisorbed amounts at 1000$$^{circ}$$C become lower than those at 800$$^{circ}$$C. On the other hand, in the case of steam-containing argon hydrogen gas atmosphere, the reaction rate constants in such a high concentration Cs gas as expected in 1F tend to become lower than those derived from the existing model. Therefore, it was found that a chemisorption model considering difference of reducing and oxidizing atmospheres and dependence of Cs concentration in gas phase was necessary.

Oral presentation

Modelling of Cs chemisorption behaviour under LWR severe accident

Nishioka, Shunichiro; Nakajima, Kunihisa; Suzuki, Eriko; Miradji, F.; Osaka, Masahiko

no journal, , 

In order to contribute to Cs distribution analysis in Fukushima Daiichi Nuclear Power Station reactors by using severe accident analysis code, the influence of chemical factors (temperature, atmosphere etc.) on the Cs chemisorption behaviour onto stainless steel was investigated experimentally. An improved Cs chemisorption model was then established considering the effect of chemical factors obtained by the experiment. The accuracy of the present model is greatly improved by 1 order of magnitude compared with that incorporated in the existing SA codes.

Oral presentation

Fundamental research on FP chemistry; Boron effects on cesium and iodine chemistry

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.

Oral presentation

Cesium chemisorption behavior onto stainless steel at temperatures higher than 1073 K

Nakajima, Kunihisa; Nishioka, Shunichiro; Suzuki, Eriko; Miradji, F.; Osaka, Masahiko

no journal, , 

Radioactive cesium (Cs) localized in the upper region of reactor pressure vessel (RPV) is one of the major concerns, especially in the case of the fuel debris retrieval accessing from top of the RPV. For estimation of amount of Cs chemisorbed onto structure materials, Cs chemisorption model is developed and incorporated into present severe accident codes. However, this chemisorption model cannot accurately reproduce experimental results. Therefore, this study elucidates essential factors influencing the Cs chemisorption behavior and construct the Cs chemisorption model considering these factors. It was found that this model can more accurately reproduce not only our experimental results but also the results used to construct the existing chemisorption model.

Oral presentation

Distribution measurement at microlevel of Cs chemisorbed compounds onto stainless steel under LWR severe accident

Suzuki, Eriko; Ogawa, Hiroaki; Nakajima, Kunihisa; Nishioka, Shunichiro; Osaka, Masahiko; Yamashita, Shinichiro; Kurishiba, Ryoko*; Endo, Takashi*; Isobe, Shigehito*; Hashimoto, Naoyuki*

no journal, , 

To elucidate Cs chemisorption behaviour onto stainless steel under LWR severe accident condition, elemental distribution measurement at microlevel was performed by using XPS and TEM. As a result, it was found that Cs-(Fe)-Si-O compounds, which have different composition, could be distributed.

Oral presentation

Comparative study of Cs silicates properties between DFT calculation and experimental data

Miradji, F.; Suzuki, Eriko; Nishioka, Shunichiro; Suzuki, Chikashi; Nakajima, Kunihisa; Oishi, Yuji*; Muta, Hiroaki*; Kurosaki, Ken*; Do, Thi Mai Dung*; Osaka, Masahiko

no journal, , 

Oral presentation

Degradation by moisture absorbent of Cs compounds formed in LWR severe accident

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.

Oral presentation

Chemical interaction between Sr compounds and Zircaloy

Afiqa, B. M.; Nakajima, Kunihisa; Nishioka, Shunichiro; Miwa, Shuhei; Osaka, Masahiko

no journal, , 

In the accident of Fukushima Daiichi Nuclear Power Station, release of Sr from fuel would be enhanced by formation of volatile SrCl$$_{2}$$ and chemical reaction of Sr onto reactor structural material such as Zircaloy (Zry) would occur. Then, chemical interaction between Sr related compounds and Zry were investigated to elucidate such a chemical behavior. As a result, SrCl$$_{2}$$ vapor does not directly react with Zry at 1273 K.

Oral presentation

Cs chemisorption behavior onto stainless steel during LWR severe accident, 2; Property change of Cs-chemisorbed deposit by temperature increase

Nishioka, Shunichiro; Takase, Gaku; Nakajima, Kunihisa; Suzuki, Eriko; Osaka, Masahiko

no journal, , 

The chemical/physical properties of Cs-chemisorbed deposit could change along with the progression of LWR severe accident (SA). In this study, the influence of temperature change on the properties of Cs-chemisorbed deposit was investigated experimentally. It was found that Cs-Fe-O compounds, which had been formed by chemisorption at 873 K, could transform into Cs-Si-(Fe)-O compounds at 1273 K.

Oral presentation

Cs chemisorption behaviour onto stainless steel during LWR severe accident, 1; Experimental study on Cs chemisorption behaviour at temperature around 600$$^{circ}$$C

Suzuki, Eriko; Takase, Gaku; Nakajima, Kunihisa; Nishioka, Shunichiro; Osaka, Masahiko

no journal, , 

In order to estimate the cesium (Cs) distribution in the reactor pressure vessel under severe accident (SA), Cs chemisorption behaviour onto stainless steel have been investigated. In our previous study on Cs chemisorption behaviour at above 800$$^{circ}$$C, it was found that the Cs silicate compounds were formed as Cs chemisorbed compounds. In this study, Cs chemisorption tests at lower temperatures around 600$$^{circ}$$C were carried out to investigate the Cs chemisorbed compounds at lower temperatures. As a result, cesium ferrate compounds were formed and it was suggested that the chemical reaction at lower temperatures would be different from that at above 800$$^{circ}$$C.

Oral presentation

Development of long term FP behavior analysis method for TEPCO's Fukushima Daiichi Nuclear Power Plants

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.

27 (Records 1-20 displayed on this page)