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Study on the structural integrity of RPV using PFM analysis concerning inhomogeneity of the heat-affected zone

溶接熱影響部の非均質性を考慮した確率論的破壊力学解析による原子炉圧力容器構造健全性に関する研究

眞崎 浩一; 勝山 仁哉 ; 鬼沢 邦雄 

Masaki, Koichi; Katsuyama, Jinya; Onizawa, Kunio

原子炉圧力容器鋼の熱影響部に対する監視試験片の必要性判断に資するため、HAZの非均質な特性に関する研究を行った。溶接材に近い位置のHAZは、マルテンサイトと下部ベイナイトの混合組織により、母材に比べて高い破壊靭性を示した。一方で母材に近い位置のHAZは、上部ベイナイトの母材と同じ相に起因して、母材に比べ同等もしくはわずかに低い破壊靭性を示した。原子力機構ではHAZの非均質性を考慮した加圧熱衝撃時の非延性き裂進展解析手法を整備し、確率論的破壊力学コードPASCAL3に導入した。想定欠陥の分布と化学組成を変えた事例解析をPASCAL3を用いて実施した。高照射量を仮定し、欠陥が溶接材近くの熱影響部に存在すると想定した場合、加圧熱衝撃時のRPVの破壊確率が母材よりも小さくなり、母材に近い位置に存在する場合には、母材とほぼ同等となることが示された。

In order to obtain the technical basis to judge the needs of surveillance test specimens from HAZ materials, the features of inhomogeneity of HAZ in RPV steels were investigated. Concerning on the fracture toughness in HAZ, HAZ materials close to weld metal indicated higher toughness than that of base metal due to high-toughness phase, while HAZ materials close to base metal were equivalent or slightly lower toughness than that of base metal due to the same phase as base metal. A structural integrity assessment method concerning such inhomogeneous distribution of fracture toughness for HAZ materials was developed and incorporated into PFM analysis code PASCAL3. Case studies on postulated flaws distribution and chemical composition were performed by using PASCAL3. It was shown that in highly irradiated conditions, CPI and CPF in HAZ close to weld metal are lower than base metal, while those in HAZ close to base metal were almost equivalent to base metal.

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