原子炉配管溶接部における残留応力の不確かさ評価に基づく確率論的構造健全性評価

Probabilistic structural integrity assessment based on uncertainty of weld residual stress at the piping butt-welds of nuclear reactor components

勝山 仁哉  ; 伊藤 裕人; 飛田 徹; 鬼沢 邦雄 

Katsuyama, Jinya; Ito, Hiroto; Tobita, Toru; Onizawa, Kunio

配管溶接部に生じる引張残留応力は、応力腐食割れの駆動力となるため、構造健全性の観点で最も重要な因子の1つである。本研究では、配管突合せ溶接部試験体を対象として入熱量や溶接速度等の溶接条件を変化させた熱弾塑性解析を実施し、実測値との比較により妥当性を確認するとともに、溶接条件の不確かさが溶接残留応力に及ぼす影響を明らかにした。また、確率論的破壊力学解析コード(PASCAL-SP)を用いて、溶接残留応力にかかわる不確かさが破損確率に及ぼす影響を評価した結果、残留応力のばらつきが大きくなるほど、配管が破断に至る確率は増加することを示した。

Weld residual stress near the welded joint of pipe is one of the most important factors to assess the structural integrity of piping because the tensile residual stress becomes a driving force of a stress corrosion cracking (SCC). In this study, a weld simulation method has been developed and verified. An effect of uncertainty of welding conditions, such as scatters of heat input and welding speed during welding, on weld residual stress at the piping butt-welds was evaluated using the simulation method by varying the welding conditions. Probabilistic fracture mechanics analysis using PASCAL-SP was also performed to evaluate the effect of uncertainty of weld residual stress on the break probability of piping. It was clarified that the break probability increased with increasing the uncertainties of residual stress.