原子炉圧力容器鋼溶接熱影響部の監視試験片省略に関する検討,5; 中性子照射脆化感受性の評価

Investigation on surveillance specimen exclusion for heat affected zone materials of reactor pressure vessel steels, 5; Evaluation of the susceptibility to neutron irradiation embrittlement

飛田 徹; 勝山 仁哉  ; 富施 正治; 大津 拓与*; 鬼沢 邦雄 

Tobita, Toru; Katsuyama, Jinya; Fuse, Masaharu; Otsu, Takuyo*; Onizawa, Kunio

原子炉圧力容器鋼の溶接熱影響部(HAZ)に対する監視試験片の必要性判断に資するため、不純物元素等の含有率を調整した圧力容器鋼の母材とHAZ再現熱処理材について、JRR-3で中性子照射試験を行った。ミニシャルピー遷移温度、破壊靱性等の機械的性質について、不純物元素含有率や金属組織等の影響に関するデータを取得し、HAZと母材との中性子照射脆化感受性に関する比較評価を行った。その結果、HAZの照射脆化にかかわる機械的性質について、未照射状態では母材とほぼ同等以上の靭性を示し、照射による硬化及び脆化もおおむね同等であった。しかしながら、局所的に母材より大きな脆化を示す組織・部位が存在する可能性のあることが示された。

In order to obtain the technical basis to judge the necessity of surveillance specimens from heat-affected zone (HAZ) materials of reactor pressure vessel (RPV) steels, the neutron irradiation program for base metals and simulated HAZ materials was performed at JRR-3. The materials used were fabricated as typical RPV steels varying impurity levels. It was indicated that the fracture toughness of simulated HAZ materials was equivalent to or better than that of base metal before neutron irradiation. Concerning the effects of impurities and metallographic structures on the mechanical properties the neutron irradiation embrittlement susceptibility of simulated HAZ materials was compared with that of base metal. The irradiation embrittlement as well as irradiation hardening of simulated HAZ materials was evaluated to be roughly equivalent to those of base metal. However, it was suggested that there may be a local region in HAZ susceptible more to irradiation embrittlement than base metal.