Safety analysis for a reactor pressure vessel considering the effects of finite crack lengths, cladding and warm pre-stress -WPS-

A safety analysis for a nuclear reactor pressure vessel based on linear elastic fracture mechanics concepts is presented. A variety of hypothetical cracks are analysed with respect to possible initiation and arrest, utilising analytical methods as well as two- and three-dimensional finite element analyses. Radial and azimutal variation of the neutron flux is considered with respect to its effect on the fracture toughness. The influence of finite crack geometry, the presence of the austenitic cladding and the warm pre-stress effect are taken into account. It can be demonstrated that the WPS-effect prohibits initiation of any flaw subjected to any transient investigated for material situations up to end-of-life. Without WPS, rather small flaws would initiate but be arrested within 55% of the wall thickness due to increase in fracture toughness with temperature and due to the decreasing neutron embrittlement inside the wall. To demonstrate the presence of the WPS-effect for the critical w eld material and for the specific transients under investigation, an experimental and numerical program was run. Here, a series of compact specimens were loaded by loading paths (force, temperature) representing actual and idealized loading paths in the pressure vessel. The existence of the WPS-effect could be demonstrated in every experiment. (IWM)