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Zheng, X.; 玉置 等史; 塩津 弘之; 杉山 智之; 丸山 結
Proceedings of Asian Symposium on Risk Assessment and Management 2017 (ASRAM 2017) (USB Flash Drive), 11 Pages, 2017/11
Nuclear reactor severe accident simulation involves uncertainties, which may result from incompleteness of modeling of accident scenarios, selection of alternative models and unrealistic setting of parameters during the numerical simulation, etc. Both deterministic and probabilistic methods are required to reach reasonable estimation of risk for severe accidents. Computational codes are widely used for the deterministic accident simulations. Bayesian approaches, including both parametric and nonparametric, are applied to the simulation-based severe accident researches at Japan Atomic Energy Agency (JAEA). In the paper, an overview of these research activities is introduced: (1) Dirichlet process models, a nonparametric Bayesian approach, are applied to source term uncertainty and sensitivity analyses; (2) Gaussian process models are applied to the optimization for operations of severe accident countermeasures; (3) Nonparametric models, include models based on Dirichlet process and K-nearest neighbors algorithm, are built to predict the chemical forms of fission products. Simplified models are integrated into the integral severe accident code, THALES2/KICHE; (4) We have also launched the research of dynamic probabilistic risk assessment (DPRA), and because a great number of accident scenarios will be generated during DPRA, Bayesian approaches would be useful for the boosting of computational efficiency.
大塚 英男; 北條 喜一; 前田 裕司*; 大津 仁; 須貝 宏行; 山本 博之
European Physical Journal D, 16(1-3), p.309 - 311, 2001/09
超微粒子の持つ表面効果に着目し、耐照射性を発現する新素材の開発を行っている。ここでは、微粒子単体内部における欠陥の挙動を調べた。低・高2種類のエネルギーのイオン照射を行い、欠陥の観察は等価型電顕を用いた。低エネルギーイオン照射の場合、微粒子中にバブルが形成され、そのバブルの大きさや分布は、温度に大きく依存していることを見いだした。高エネルギーイオン照射においても、積層欠陥が形成され、前記同様の挙動を示した。さらに、これらの現象の解析のために、シミュレーションプログラムを開発した。シミュレーションにおいては、欠陥(空孔)の拡散係数を変化させることで実験結果とよい一致を得た。これらの結果から、ナノクリスタルにおける照射欠陥の制御の方法の見通しを得た。
丸山 結; 石川 淳; Zheng, X.; 城戸 健太朗; 松本 俊慶; 塩津 弘之; 伊藤 裕人; 玉置 等史
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An integral code system for severe accident analysis in light water reactors, THALES2/KICHE, has been developed at Japan Atomic Energy Agency (JAEA). The core melt progression and the transportation of radioactive materials within reactor coolant system (RCS) and containment vessel (CV) are analyzed with THALES2 code in conjunction with KICHE code for the iodine reaction kinetics in aqueous phase. The applications of THALES2/KICHE code have been made in various analytical studies for severe accident progression, including analyses for the accident at the Fukushima Daiichi Nuclear Power Plant (1F) in order to obtain technical knowledge on the source term into the environment and the core damage state.