原子炉圧力容器を対象とした確率論的破壊力学に基づく健全性評価に関する標準的解析要領(受託研究)

Guideline on a structural integrity assessment for reactor pressure vessel based on probabilistic fracture mechanics (Contract research)

勝山 仁哉  ; 小坂部 和也*; 宇野 隼平; Li, Y. 

Katsuyama, Jinya; Osakabe, Kazuya*; Uno, Shumpei; Li, Y.

国内では、原子炉圧力容器(RPV)の中性子照射脆化に伴う非延性破壊を防止するため、健全性評価上最も厳しい加圧熱衝撃事象(PTS)を考慮して、決定論的手法による健全性評価が行われている。一方、長期供用に伴う機器の経年劣化に関連する様々な因子の統計的な不確実さ等を考慮して、合理的に機器の破損頻度等を算出する確率論的破壊力学(PFM)に基づく健全性評価手法が、近年欧米において規制への導入が進められている。本報告書は、国内のRPVに対するPFMに基づく健全性評価の実施を念頭に、国内外の最新知見や専門家の意見等を反映し、整備された標準的解析要領を取りまとめたものである。

For reactor pressure vessels (RPVs) in the light water reactors, the fracture toughness decreases due to the neutron irradiation embrittlement with operating years. In Japan, to prevent RPVs from a nil-ductile fracture, deterministic fracture mechanics methods in accordance with the codes provided by the Japan Electric Association are performed for assessing the structural integrity of RPVs under the pressurized thermal shock (PTS) events by taking the neutron irradiation embrittlement into account. On the other hand, in recent years, probabilistic methodologies for PTS evaluation are introduced into regulations in Europe and the United States. For example, in the United States, a PTS screening criterion related to the reference temperature derived by the probabilistic method is stipulated. If the screening criterion is not satisfied, it is approved to perform the evaluation based on the probabilistic method by calculating numerical index such as through-wall crack frequency (TWCF). To reach the objectives that persons who have knowledge on the fracture mechanics can carry out the PFM analyses and obtain TWCF for a domestic RPVs by referring to this report, we develop the guideline on a structural integrity assessment method based on PFM by reflecting the latest knowledge and expertise.