Evaluation of fracture resistance of ruptured, oxidized, and quenched Zircaloy cladding by four-point-bend tests

4点曲げ試験を用いた破裂,酸化,急冷されたジルカロイ被覆管の耐破断性能評価

大和 正明; 永瀬 文久 ; 天谷 政樹  

Yamato, Masaaki; Nagase, Fumihisa; Amaya, Masaki

軽水炉燃料のLOCA条件及びLOCA後の冷却条件での耐破断性能を評価するために、破裂,高温酸化,急冷させた未照射ジルカロイ被覆管に対する4点曲げ試験を行った。曲げ試験手法は、破裂領域に対して均一な曲げモーメントが働くよう、破裂側に引張応力が働くように設計した。破断時曲げモーメントは酸化量だけでなく、酸化温度や水素濃度の増大に伴って減少した。設計基準地震動から予想される曲げモーメントとの比較から、高温での酸化量が15%ECR、すなわち我が国のLOCA基準以下であれば、LOCA後の冷却時に地震があった場合にも被覆管は破断しないと考えられる。

To evaluate fracture resistance of LWR fuel rods under LOCA and post-LOCA cooling conditions, four-point-bend tests were performed on non-irradiated Zircaloy cladding samples that were ruptured, oxidized in high-temperature steam, and quenched in flooding water. The bend test methodology was designed to apply a uniform bending moment to the entire rupture region and to generate tensile stress on the ruptured side. The fracture bending moment of the cladding decreased with oxidation temperature and hydrogen concentration as well as oxidation amount. Comparison with bending moments estimated from design basis seismic ground motion indicated that the cladding is unlikely to be fractured by seismic loads during post-LOCA cooling if high-temperature oxidation is kept below 15% ECR, the oxidation limit of the Japanese LOCA criteria.