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Effect of large-scale seismic loading on crack growth rate and structural reliability of nuclear reactor piping

過大な地震動が原子力配管のき裂進展速度及び構造信頼性に及ぼす影響

山口 義仁; Li, Y.*; 勝山 仁哉; 鬼沢 邦雄

Yamaguchi, Yoshihito; Li, Y.*; Katsuyama, Jinya; Onizawa, Kunio

新潟県中越沖地震や東日本大震災では、原子力発電所の耐震設計時に想定した値を超える地震動が観測され、原子炉機器の耐震安全性に関して、塑性変形を伴うような過大な繰返し荷重に対するき裂進展評価法の確立が重要な課題である。このような過大な地震荷重を受ける際のき裂進展挙動について、弾塑性破壊力学パラメータJ積分を用いた評価法を実験的に検討した。この結果、過大な繰返し荷重によるき裂進展時には疲労き裂進展と延性き裂進展が重畳すること、及び過大引張荷重負荷後にき裂進展が遅延することが示された。J積分に基づいてこれらの挙動を考慮したき裂進展評価法を提案した。また、本評価法を確率論的破壊力学解析コードPASCAL-SPに導入し、地震による配管の破損確率に及ぼす延性き裂進展及び遅延効果の影響を評価した。

In recent years, Japanese nuclear power plants experienced multiple large earthquakes, such as Niigata-ken Chuetsu-Oki Earthquake in 2007 and the Great East Japan Earthquake in 2011. The magnitude of these earthquakes exceeded the design-base condition for some nuclear power plants. Therefore it is an important issue to establish the evaluation method of excessive loading on the structural integrity of reactor components. In this study, the crack growth behaviors were investigated based on an elastic-plastic fracture mechanics parameter, J-integral. It was indicated that the crack growth due to the cyclic excesive loading could be the sum of fatigue and ductile crack growth. The retardation effect on the crack growth due to excessive loading was observed from experiments. An evaluation method for the amount of crack growth under cyclic excessive loading is suggested based on J-integral. The effect of excessive loading on the failure probability of piping is also evaluated by probabilistic fracture mechanics analysis.

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