Study on buckling and post buckling behavior of cylinders under severe vibration

Abstract

Buckling is one of the expected failure modes for fast reactor vessels under excessive seismic load. However, buckling occurrence condition under vibration load is not necessarily clear. Under BDBE(Beyond Design Basis Events), even if buckling occurs, as long as the coolant inside the main vessel is retained, the safety function is maintained. Therefore, in addition to buckling occurrence condition, it is important to investigate the post-buckling behavior. In order to investigate the buckling occurrence condition and post-buckling behavior of reactor vessels under excessive seismic load, vibration tests and FEM analyses applying vibration loads to two types of specimens were conducted. The specimens were columns which were basic structural member and thin cylindrical shells which were simplified and scaled down of fast reactor vessels. The results showed that buckling caused by vibration load is essentially different from buckling caused by static load. After buckling, the natural frequency was lower than the input frequency, which caused a phase delay, and the phase was opposite to the input, which prevented energy from being input, and the shape of the specimen was stable without excessive deformation. However, cracks could initiate on thin-walled cylinders. Identifying the likelihood and location of crack initiation and extension is a future issue.