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Journal Articles

Study on loss-of-cooling and loss-of-coolant accidents in spent fuel pool, 1; Overview

Kaji, Yoshiyuki; Nemoto, Yoshiyuki; Nagatake, Taku; Yoshida, Hiroyuki; Tojo, Masayuki*; Goto, Daisuke*; Nishimura, Satoshi*; Suzuki, Hiroaki*; Yamato, Masaaki*; Watanabe, Satoshi*

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

In this research program, cladding oxidation model in SFP accident condition, and numerical simulation method to evaluate capability of spray cooling system which was deployed for spent fuel cooling during SFP accident, have been developed. These were introduced into the severe accident codes such as MAAP and SAMPSON, and SFP accident analyses were conducted. Analyses using Computational Fluid Dynamics (CFD) code were conducted as well for the comparison with SA code analyses and investigation of detail in the SFP accident. In addition, three-dimensional criticality analysis method was developed as well, and safer loading pattern of spent fuels in pool was investigated.

Journal Articles

Evaluation of fracture resistance of ruptured, oxidized, and quenched Zircaloy cladding by four-point-bend tests

Yamato, Masaaki; Nagase, Fumihisa; Amaya, Masaki

Journal of Nuclear Science and Technology, 51(9), p.1125 - 1132, 2014/09

 Times Cited Count:7 Percentile:57.39(Nuclear Science & Technology)

To evaluate fracture resistance of LWR fuel rods under LOCA and post-LOCA cooling conditions, four-point-bend tests were performed on non-irradiated Zircaloy cladding samples that were ruptured, oxidized in high-temperature steam, and quenched in flooding water. The bend test methodology was designed to apply a uniform bending moment to the entire rupture region and to generate tensile stress on the ruptured side. The fracture bending moment of the cladding decreased with oxidation temperature and hydrogen concentration as well as oxidation amount. Comparison with bending moments estimated from design basis seismic ground motion indicated that the cladding is unlikely to be fractured by seismic loads during post-LOCA cooling if high-temperature oxidation is kept below 15% ECR, the oxidation limit of the Japanese LOCA criteria.

Journal Articles

Reduction in the onset time of breakaway oxidation on zircaloy cladding ruptured under simulated LOCA conditions

Yamato, Masaaki; Nagase, Fumihisa; Amaya, Masaki

Journal of Nuclear Materials, 445(1-3), p.78 - 83, 2014/02

 Times Cited Count:6 Percentile:43.23(Materials Science, Multidisciplinary)

Breakaway oxidation, which is characterized by sudden increases in oxidation rate and significant hydrogen absorption after longer exposure in high-temperature steam, was examined for the ballooned and ruptured cladding. As a result, the onset time of breakaway oxidation for ruptured claddings was significantly reduced compared with that for non-ruptured claddings. The onset time of breakaway oxidation was reduced only in the case where thick and porous oxide was formed on the inner surface of the cladding after rupture. Results of the parametric experiments suggest that the tensile stress in the circumferential direction generated by the thick oxide film formed on the inner surface is a main cause of the reduction of the onset time of breakaway oxidation.

Journal Articles

Studies on possibility for alleviation of lifestyle diseases by low-dose irradiation or radon inhalation

Kataoka, Takahiro*; Sakoda, Akihiro*; Yoshimoto, Masaaki*; Nakagawa, Shinya*; Toyota, Teruaki*; Nishiyama, Yuichi*; Yamato, Keiko*; Ishimori, Yuu; Kawabe, Atsushi*; Hanamoto, Katsumi*; et al.

Radiation Protection Dosimetry, 146(1-3), p.360 - 363, 2011/07

 Times Cited Count:6 Percentile:44.45(Environmental Sciences)

Our previous studies showed the possibility that activation of the antioxidative function alleviates various oxidative damages, which are related to lifestyle diseases. Results showed that, low-dose X-ray irradiation activated superoxide dismutase and inhibits oedema following ischaemia-reperfusion. To alleviate ischaemia-reperfusion injury with transplantation, the changes of the antioxidative function in liver graft using low-dose X-ray irradiation immediately after exenteration were examined. Results showed that liver grafts activate the antioxidative function as a result of irradiation. In addition, radon inhalation enhances the antioxidative function in some organs, and alleviates alcohol-induced oxidative damage of mouse liver. Moreover, in order to determine the most effective condition of radon inhalation, mice inhaled radon before or after carbon tetrachloride (CCl$$_{4}$$) administration. Results showed that radon inhalation alleviates CCl$$_{4}$$-induced hepatopathy, especially prior inhalation. It is highly possible that adequate activation of antioxidative functions induced by low-dose irradiation can contribute to preventing or reducing oxidative damages, which are related to lifestyle diseases.

Oral presentation

The Effect of sea water component on the cladding oxidation at high temperature

Yamato, Masaaki; Fukuda, Takuji; Amaya, Masaki; Nagase, Fumihisa

no journal, , 

After the Great East Japan Earthquake, the reactor and spent fuel pool in Fukushima Daiichi Nuclear Plant was cooled by sea water. In order to evaluate the effect of sea component on the cladding oxidation at high temperature, isothermal oxidation tests in steam or Ar+O$$_{2}$$ were performed with zircaloy-2 cladding specimens whose surface was attached sea component. As a result, influence of sea component is not significant for the oxidation thickness, but oxidation atmosphere was influenced the adherence of the oxidation and metallic layer.

Oral presentation

Research on LWR fuel behavior under accident conditions

Yamato, Masaaki; Sugiyama, Tomoyuki; Nagase, Fumihisa

no journal, , 

To confirm the reactor safety design, safety reviews are performed under accident conditions as well as under normal operation conditions. One of such Design Basis Accidents is the Loss-of-Coolant Accident (LOCA) in which the reactor coolant water is lost typically due to a pipe break. This presentation shows the concept of the current LOCA safety regulation, and presents the results from the recently started experiments on mechanical properties of post-LOCA cladding, breakaway phenomenon in cladding high temperature oxidation, and influence of sea water on the cladding high temperature oxidation.

Oral presentation

Bending strength at the fuel claddings quenched during LOCA

Yamato, Masaaki; Nagase, Fumihisa

no journal, , 

The loss of coolant accident (LOCA) is included in the design standard phenomenon of the light water reactor. The safety criteria for LOCA are established for the purpose of core cooling at the time of an accident and after the accident. In JAEA, the four points bending tests has been developed to evaluate the embrittlement of cladding which is important to core cooling. In this study, it was measured the bending strength by the four points bending tests for the non-irradiation cladding experienced fuel behavior assumed LOCA. As a result, it was confirmed that oxidation temperature isn't influenced on bending strength and bending strength was reduced with increasing oxidation rate. In addition, it found that the bending strength of cladding oxidized to 15% ECR, which is the upper limit of oxidation rate in the safety criteria, was higher than the bending load at design basic earthquake ground motion S $$_{2}$$.

Oral presentation

The Feasibility study on SiC composite fuel cladding for the accident tolerant fuel to the existing PWR plants, 7; LOCA simulated test

Sato, Daiki*; Watanabe, Seiichi*; Komiyama, Daisuke*; Furumoto, Kenichiro*; Okamoto, Michiaki*; Yamato, Masaaki*; Yamashita, Shinichiro; Fukahori, Tokio

no journal, , 

It is expected that SiC cladding tube has high corrosion resistance and high strength under LOCA condition in existing PWR. There is little data for SiC cladding tube in the high temperature environment. So the apparatus which was capable of testing at LOCA simulated condition was manufactured for SiC cladding tube. The modified LOCA test was carried out for investigating the behavior of SiC cladding tube.

Oral presentation

Study on improvement of safety for accident conditions in spent fuel pool, 20; Overview

Kaji, Yoshiyuki; Nemoto, Yoshiyuki; Nagatake, Taku; Yoshida, Hiroyuki; Tojo, Masayuki*; Goto, Daisuke*; Nishimura, Satoshi*; Suzuki, Hiroaki*; Yamato, Masaaki*

no journal, , 

The objectives of this study is to enhance the analytical method and safety of spent fuel pool under severe accident conditions. In this presentation, we explain about general view of results of this project.

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