모사시편을 이용한 설계기준초과지진 하중 조건에서 변형 및 손상 거동 평가

Abstract

Interest in the structural integrity of systems, structures, and components (SSCs) of nuclear power plants (NPPs) during a seismic event increased greatly after the nuclear accident in the Fukushima Daiichi NPPs. Since several NPPs experienced a beyond design basis earthquake (BDBE), in particular, structural integrity under beyond design basis earthquake conditions has come under greater scrutiny; recently, integrity assessments for SSCs under beyond design basis earthquake conditions are required for newly designed NPPs. Thus, the reliability of integrity assessments under beyond design basis earthquake conditions has become an important issue, and several studies have conducted to improve and develop integrity assessment procedure for SSCs under beyond design basis earthquake condition. For such studies, the verification of analytical model and acceptance failure criteria using experimental data are essential to ensure the reliability of assessment procedure. In general, the experiment data for verification are obtained from the large-scale system tests that can take into account realistic seismic loading characteristics and geometry effects. However, these are too expensive and difficult to handle. Therefore, this study designed specimen and loading, which can simulate strain accumulation and crack initiation in SSCs of NPPs under beyond design basis earthquake loading condition, and conducted failure test at RT and 316oC using these specimen and loading. From the results, the deformation and damage behaviors under beyond design basis earthquake loading condition are investigated. The results showed, regardless of test material and temperature, the cracks initiated at the center of round notch, at which the maximum strain appeared from the finite element analysis. For SA312 TP316 SS, the cracks were detected at cyclic load of 7×SSE for RT and at cyclic load of 6×SSE for 316oC. The cracks for SA508 Gr.3 Cl.1 LAS were detected at 4×SSE for both RT and 316oC. From these results, it is concluded that for both materials the failure of specimen occurs under seismic load levels several times higher than the design basis earthquake. Also, SA316 TP316 SS has higher safety margin under excessive seismic loading condition than SA508 Gr.3 Cl.1 LAS regardless of test temperature. Finally, it is confirmed that the specimen used in this study can adequately simulate the deformation and failure behaviors of SSCs under excessive seismic loading condition.