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Maruyama, Yu; Ishikawa, Jun; Zheng, X.; Kido, Kentaro; Matsumoto, Toshinori; Shiotsu, Hiroyuki; Ito, Hiroto; Tamaki, Hitoshi
no journal, ,
Takano, Masahide; Nishi, Tsuyoshi; Onozawa, Atsushi
no journal, ,
Since the severe accident at the Fukushima Daiichi Nuclear Power Plant, we have been studying the characteristics of fuel debris in order to contribute to its removal operation and management. First, a series of reaction experiment on (U,Zr)O
with natural sea salt were performed to clarify the chemical influence of sea salt deposit on high-temperature corium. It was found that CaO decomposed from sulphate is most reactive to form (U,Zr,Ca)O solid solution or Ca-U-O uranate on the surface, depending on the oxygen partial pressure. Then, some compacted mixtures of B
C, stainless steel, Zr, and (U,Zr)O were arc-melted to investigate the boron-containing compounds in the fuel debris. ZrB and (Fe,Cr,Ni)B were found to precipitate in the alloy part of solidified sample. The phase relationships within these borides and alloy phases can be characterized by the initial B/Zr ratio in the mixture.
Nagase, Fumihisa; Yoshida, Hiroyuki; Nemoto, Yoshiyuki; Amaya, Masaki; Yamashita, Shinichiro
no journal, ,
In order to conduct decommissioning of the Fukushima-Daiichi NPP properly and reliably, increase of accuracy is required in estimation of the accident progress and status inside the reactors. It is also required to improve analytical methods to estimate severe accident progression in the existing light water reactors. Therefore, JAEA conducts fundamental studies in terms of thermal hydraulic behaviour in reactor, fuel damage and degradation process, behaviour of structural materials and pressure vessel, release and migration of fission products, and so on under severe accident conditions. The present paper reports overview of the fundamental studies and recent results.
Takeda, Seiji; Takai, Shizuka; Kimura, Hideo
no journal, ,
Reuse of slightly contaminated disaster wastes is effective for volume reduction of disaster wastes. Reuse of the contaminated wastes should be carried out based on ensuring the safety of radiation for the workers and the public by dose estimation approach. As a first step, we derived the cesium concentration for the limited purposes of reuse based on two types of scenarios; reuse for subbase course materials of pavements and that for embankment materials of seaside protection forest. The calculated results concluded that concrete wastes less than about 3,000 Bq/kg can be used for two types of scenarios under the design conditions such as thickness of shielding materials. As a next step, it is important to confirm the validity of the criteria of 100 Bq/kg by the effective dose estimation for comprehensive scenarios relate to reusing wooden wastes. In this study, we estimated the dose for reuse of wooden wastes to confirm the validity of 100 Bq/kg in the present reuse.
Yonomoto, Taisuke; Shibamoto, Yasuteru; Ishigaki, Masahiro; Abe, Satoshi
no journal, ,
The thermal-hydraulic safety research group in JAEA is conducting the ROSA-SA (severe accident) project on containment thermal hydraulics based on the consideration of research issues after the Fukushima Dai-Ichi Nuclear Power Station accident. The project investigates phenomena related to over-temperature containment damage, hydrogen risk and fission product transport. Until now, we have designed a large-scale containment vessel test facility called CIGMA (Containment InteGral Measurement Apparatus), and analyzed phenomena including the erosion of density stratified layer by impinging jet and condensation with noncondensables using the computational fluid dynamics (CFD) code OpenFOAM. In this presentation, plans for researches and results obtained thus far are described.
Kitagaki, Toru; Yano, Kimihiko; Washiya, Tadahiro
no journal, ,