Failure assessment of RPV nozzle under loss of coolant accident

In case of a postulated loss of coolant accident (LOCA) of a reactor pressu re vessel (RPV), the nozzle region experiences higher stresses and lower te mperatures than the remaining part of the RPV. Thus, the nozzle is to be co nsidered in the RPV safety assessment. For a LOCA event, three-dimensional elastic-plastic finite element calculations of stresses and strains in the intact RPV were performed. Using the substructure technique, fracture mecha nics analyses were then carried out for several postulated cracks in the no zzle corner and in the circumferential weld below the nozzle. For different crack geometries and locations, the J-integral and the stress intensity fa ctor were calculated as functions of the crack tip temperature. Based on th e K-IC-reference curve and the J(R) curve, both brittle and ductile instabi lity of the postulated cracks were excluded. In order to reduce the expense s of three-dimensional finite element analyses for various crack geometries , an analytical procedure for calculating stress intensity factors of subcl ad cracks in cylindrical components was extended for cracks in the nozzle c orner. (C) 1999 Elsevier Science S.A. All rights reserved.