実力基準保全による検査頻度の合理化(確率論的破壊力学による機器破損確率への影響評価）

摘要

This study is aimed at applying the performance-based maintenance (PBM) concept to determine inspection schedule. Previously, the time-based maintenance concept has been applied to determine the inspection schedule for nuclear plant components. In the PBM concept, frequency of inspection is determined by operation time before the inspection. Duration before the next inspection is extended if the component indicates no cracking for a long time. In this study, the change in structural reliability due to applying the PBM concept was investigated by probabilistic fracture mechanics analyses. In order to calculate the probability of leakage or fracture (failure probability), growth of fatigue cracks initiated at the primary coolant pipe of pressurized water reactor nuclear power plants was simulated considering variations in yield and tensile strengths, fatigue crack growth rate, initial crack shape and so on. It was demonstrated that the failure probability was reduced by performing inspections according to the time-based maintenance concept. Frequency rather than detectability of inspection had a larger impact on reducing the failure probability. It was shown that, by applying the PBM concept, the number of inspections could be reduced significantly without increasing the failure probability. It was concluded that the PBM concept could optimize the inspection schedule.%本報は，実力基準保全の考え方を検査間隔の決定に適用することを口的とした.原子力発電プラント構造物には.従来，時間基準保全の考え方が適用されてきた.実力基準保全では，検査の間隔を運転期間に応じて決定する.もし，長期間亀裂が発見されなければ，次回の検査までの間隔を長く設定できる.本報では.実力基準保全を適用することによる構造信頼性の変化を確率論的破壊力学解析で調べた.漏洩または破壊の確率（破損確率）を計算するため，加圧水型原子炉一次冷却材管に発生した疲労き裂を対象に.降伏強度，引張強さ，疲労亀裂進展速度，初期亀裂形状などのばらつきを考慮した疲労亀裂進展シミュレーションを行った.時間基準による定期的な点検により破損確率を減少させることができた.この際，検査の性能よりも検査の頻度が，破損確率の減少に対する寄与が大きかった.実力基準保全を適用することで，破損確率を増加させることなく，検査の数量を減らせることが示された.実力基準保全は検査スケジュールを最適化できる有効な手段であることが示された.