報告書番号

222

タイトル（和文）

原子炉ステンレス鋼配管の破断前漏洩成立性に関する解析的研究

タイトル（英文）

ANALYSIS OF LEAK-BEFORE-BREAK FOR STAINLESS STEEL PIPING SYSTEM IN LIGHT WATER REACTOR

概要 （図表や脚注は「報告書全文」に掲載しております）

本研究は，近年沸騰水型原子炉の一次冷却系配管で発生した応力腐食割れのような周方向き裂に関してその伝播挙動を力学的に検討し，ステンレス鋼配管における破断前漏洩（ＬＢＢ）の成立性評価に関する解析的手法の開発を行ったものである。周方向き裂の伝播挙動を検討するため，弾塑性有限要素解析コードを開発してき裂伝播時の荷重，変形特性を推定し，実測結果との比較により解の妥当性を調べた。続いてき裂先端部の開口角に基づく進展条件を用いた簡単な微分方程式モデルを導き，き裂の不安定伝播条件が荷重系のコンプライアンスで定まる実断面応力値によって支配されることを明らかにした。上記の簡易解析手法を用いて，原子炉の実機設計条件下における配管破断条件及び漏洩検出条件をき裂長さの限界値として推定した。これより破断前漏洩の成立性が，実機条件下のス

概要 （英文）

LBB CONCEPT IN NUCLEAR PIPING SYSTEM HAS GAINED MUCH IMPORTANCE FROM THE STANDPOINTS OF NOT ONLY STRUCTURAL INTEGRITY BUT ALSO RATIONAL DESIGN OF PIPING SYSTEM. OCCURRENCE OF STRESS CORROSION CRACKINGS IN BWR PLANTS IN 1970S STIMULATED THE LBB STUDY FOR STAINLESS STEEL PIPING. THIS REPORT DESCRIBES SOME THEORETICAL ANALYSES OFFRACTURE BEHAVIOR OF CIRCUMFERENTIALLY CRACKED PIPE TO ESTABLISH THE LBB CONCEPT FOR BWR PLANTS UNDER DESIGN CONDITIONS. ELASTIC-PLASTIC FINITE ELEMENT COMPUTER CODE HAS BEEN DEVELOPED TO STUDY THE MECHANICAL CHARACTERISTICS OF CIRCUMFERENTIAL CRACK PROPAGATION IN TYPE 304 STAINLESSSTEEL PIPE. VARIATION OF LOAD AND DEFORMATION WITH STABLE CRACK GROWTHWAS PREDICTED AND GOOD AGREEMENT WAS OBTAINED BETWEEN THE EXPERIMENTALRESULTS AND THE FINITE ELEMENT SOLUTIONS. BASED ON SOME FRACTURE CHARACTERISTICS OBTAINED FROM THE ANALYSES AND THE EXPERIMENTS, A SIMPLIFIEDDIFFERENTIAL-EQUATION MODEL WAS NEWLY DEVELOPED. IN THIS MODEL, CTOA (CRACK TIP OPENING ANGLE) CRITERION WAS EMPLOYED TO DESCRIBE THE STABLE CRACK EXTENSION IN STAINLESS STEEL. CRACK INSTABILITY WAS DERIVED FROM THE DISPLACEMENT-CONTROLLED CONDITION, INCLUDING THE EFFECT OF COMPLIANCE IN LOADING SYSTEM. IT WAS FOUND THAT CRACK INSTABILITY MIGHT OCCUR AT THE CRITICAL NET STRESS WHICH WAS SPECIFIED BY THE COMPLIANCE VALUE IN A LOADING SYSTEM. BY USING SUCH A CRITERIA OF INSTABILITY, FRACTURE CONDITION OF THE CRACKED PIPE UNDER THE DESIGN CONDITIONS WERE ESTIMATEDAS A CRITICAL CRACK LENGTH, WHILE LEAK DETECTION WAS EVALUATED FROM THE CRITICAL LEAK RATE (5GPM). COMPARISON OF THE UNSTABLE CONDITION WITH THE LEAK CONDITION SHOWED THAT LEAK-BEFORE-BREAK CAN BE SATISFIED IN THE STAINLESS STEEL PIPING UNDER THE DESIGN CONDITIONS OF BWR PLANTS.

報告者

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