Creep-fatigue test of a thick-walled vessel under thermal transient loadings

To improve the damage evaluation methods in the design code for Fast Breeder Reactors (FBRs), a series of creep-fatigue tests of structural models under thermal transient loadings are going on at Oarai Engineering Center of the Power Reactor and Nuclear Fuel Development Corporation (PNC). Test models are designed to incorporate representative structures of components and pipings used in FBRs and are subjected to severer cyclic thermal transients than those experienced in FBRs. The test is planned to be continued until failure occurs. This paper describes the creep-fatigue test results and their damage evaluation for the first test model. A 40 mm thick vessel model made of SUS304 austenitic stainless stell was subjected to cyclic thermal transients, in which sodium at 600deg C and 250deg C flow repeatedly. The period of each transient was 2 h. Cracks were observed at seven test portions in the model after 1002 cycles of the thermal transients. Elastic and inelastic analyses were performed to evaluate creep-fatigue damage and crack propagation. The safety margins included in the creep-fatigue design methods based on elastic analysis as well as those based on inelastic analysis are discussed. Finally fracture mechanics analyses were performed to explain the observed crack growth. (orig.)