Effect of cladding thickness on brittle fracture prevention of the base wall of reactor pressure vessel

Abstract

In case of a loss of coolant accident, the cooling water is injected into the downcomer of reactor pressure vessel (RPV) and produces a pressurized thermal shock (PTS). Considering that the current cladding thickness is small, thermal shock and neutron irradiation are easy to cause brittle fracture of base material. The transient stress intensity factors of the crack tips at the base-cladding interface are obtained by the interaction integral method. Since the test of the crack propagation on the cladding-base interface is quite difficult and dangerous, the allowable internal pressure values obtained from the K-T curves are verified by XFEM in the thermo-mechanical coupling fields. By increasing the cladding thickness, the resulting temperature fields are compared with each other to demonstrate the different embrittlement effects caused by thermal shock. Then the elastic-plastic fracture mechanics (EPFM) method and the linear elastic interaction integral method are used to study the structural integrity at relatively low and high nil-ductility reference temperatures respectively. Furthermore, the influence of the crack size on the ultimate bearing capacity of the structure is quantitatively analyzed for various thicknesses of cladding and base wall. The size effect of crack decreases obviously with the increase of cladding thickness.