Integrity analysis of a reactor pressure vessel with quasi laminar flaws subjected to pressurized thermal shocks

Abstract

Thousands of quasi laminar defects, which are parallel to the surface, were recently observed in the Belgian reactors pressure vessels of Doel 3 and Tihange 2 nuclear power plants. This is the first time that such kind of cracks has been detected in a reactor pressure vessel (RPV) by using new non-destructive testing (NDT) equipment (in service inspection). These flaws are likely to be originated during the vessels production and it seems improbable that the flaws further evolved since their formation. However, a structural integrity analysis for the case of pressurized thermal shock loads is necessary to assess the safe operation. The existence of such cracks was never before assumed in pressurized thermal shocks (PTSs) analyses as these defects are supposed as nonexistent in the RPV or their effect regarded as non-dangerous. However, up to the author's knowledge, there are no evidences or studies that support these assumptions as no former comparison has been found. Hence, we present a PTS analysis for such type of crack where the eXtended Finite Element Method (XFEM) is employed to simplify the finite element meshing. The analysis includes the comparison of different crack locations, size and configurations and allows concluding that such kind of defects are not dangerous from a structural mechanics point of view, as long as they remain parallel to the surface.