Numerical analysis of the BWR-5 beltline region containing a crack postulated for an extended period of operation

Abstract

In the case of a BWR-5, the wall of the reactor vessel located adjacent to the core is named beltline and it is subjected to neutron embrittlement, lowering the fracture toughness and increasing the yield strength of the material. Cracks can be developed in the internal surface of this area. In this paper, a semi elliptical part through thickness crack has been postulated along the axial direction. Its depth is 1.25 inch which is 0.25 of the thickness of the wall vessel and its length is 6 times the crack depth (7.5 inches). The material of the vessel is a low alloy carbon steel.In order to consider an extended period of operation, the analysis must cover sixty years of operation. The normal conditions of operation and start-up and shutdown transients have to be taken into account. For this purpose, a numerical evaluation was done with the Finite Element Method in conjunction with linear elastic fracture mechanics. This analysis was compared with the results of the procedure under the scope of the Appendix G of the ASME Code Section XI and the NUREG-0800. The results were used to establish the pressure and temperature limits.