Comparative analyses concerning integrity of a VVER-440 reactor pressure vessel

Comparative analyses have been performed with 3-D finite element (FE) models for a six loop cladded reactor pressure vessel with an assumed circumferential surface crack. In the analyses, a thermomechanical transient due to a loss of coolant with high pressure injection has been considered.
The transient is characterized by an axisymmetric cooling phase which is followed by an asymmetric, strip-like cooling period. For the fracture assessment, stress intensity factors calculated from local J-integral values have been compared. It has been shown that with different FE programs and meshes, the crack loading can be calculated within a 10% scatter.
Furthermore, simplified fracture methods show a much larger scatter, mainly due to approximation of the non-linear stress distribution by membrane and bending stress.