Abstract
Nuclear power plants in Europe are entering in a phase of long-term operation (LTO) and one of the key safety assessments for continuing in operation is the evaluation of pressurized thermo-shock (PTS). Since conducting PTS experiments on real-scale reactor pressure vessels (RPVs) are unaffordable and challenging, the present contribution concerns the test facility for performing thermal shock-like cooling on small thick-walled cylindrical mock-ups. The mock-up contains four equally separated notches. Thermal shock (TS) loading condition without pressure is applied. It is expected Mode I of fracture (opening mode) due to pure tensile hoop stresses generated by the cooling. The loading condition represents a fast cooling (from 300°C to room temperature) similar to the transient due to a Loss of Coolant accident (LOCA) in the real RPV. RPV steel 17MoV 8-4 with an artificially (thermally treated material) increased ductile to brittle transition temperature (DBTT) to values similar to a highly-irradiated RPV at its end-of-life is used. The preliminary experimental results show good performance of the thermo-shock facility confirming that the loading conditions are adequate and demonstrating that the thermal stresses developed in the mock-up are high enough to trigger crack growth and arrest of the precracks in the embrittled steel. The results of the current experiment will be used to validate the ongoing numerical PTS assessment with XFEM.
