小破断LOCA時高圧注入系不作動事象への統計的手法の適用: 被覆管酸化，崩壊熱，被覆管変形および伝熱管凝縮に係るRELAP5モデルの不確かさの定量化

摘要

統計的安全評価手法の適用により，最適評価結果に対する不確かさが定量的に評価され，過度の保守性を合理的に排除することにより信頼性の高い評価結果が期待される.現在，小破断LOCA(冷却材喪失事故)時高圧注入系不作動事象におけるアクシデントマネジメント策「2次系強制冷却による低圧注入」解析への統計的安全評価手法の適用を進めている.PIRTの作成により抽出した24個の重要現象のうち，評価パラメータであるPCTへの影響が大きく，かつ試験解析を用いずに解析モデルの不確かさ.を定量化できる現象として，被覆管酸化，崩壊熱，被覆管変形および伝熱管凝縮がある.本研究では，これらの重要現象についてRELAP5/MOD3.2コード組込みモデルの相関式の不確かさを定量化した.相関式の計算結果と試験結果の比較，または崩壊熱標準データの誤差の整理により，RELAP5モデルの不確かさの分布を決定，すなわちRELAP5モデルの不確かさを定量化した.%By applying the Best Estimate Plus Uncertainty (BEPU) method, the uncertainties of best estimate results can be estimated quantitatively, and as a consequence, excessive conservatism can be reasonably removed to obtain evaluation results with enhanced reliability. Application of the BEPU method is being made to analyses of the "low pressure injection by intentional depressurization of the steam generator secondary siae" which is an accident management approach in a SBLOCA (small break loss-of-coolant accident) with HPI (high pressure injection)failure. Among the 24th important phenomena extracted by making the PIRT (phenomena identification and ranking table), the phenomena which have the great influence on the PCT (peak clad temperature) and whose model uncertainties are able to be quantified without test analyses are "fuel clad oxidization , decay heat", "fuel clad deformation", and "SG U-tube condensation". In this research, the uncertainties of the correlation of the RELAP5/MOD3.2 model about these important phenomena were quantified. By comparison of the calculation results of the correlation and test results or arrangement with the error of decay heat standard data, the distribution of the RELAP5 model uncertainties were determined, that is to say, the distribution of the RELAP5 model uncertainties were quantified.