The J integral evaluation of a nozzle corner crack under thermal transient loading condition

Abstract

This paper presents the results of the evaluation of the three dimensional J integral of a nozzle corner crack which is initiated by fatigue under thermal transient loading conditions of a BWR type reactor vessel. Analyses are carried out by using the finite element method in the following two cases. One case consideres the effect of the stainless steel cladding deposited over the inside surface of the reactor vessel, and the other neglects it. In both cases, the extended J integral concept, called J ̂ integral, is used to obtain the path independent J value in the thermal stress fields. By changing the shapes and the dimensions of the crack, some elastic analyses are carried out in the two dimensional space. The effects of the cladding are studied qualitatively, and the J ̂ integrals are compared with the critical J value, and discussed. Three dimensional J ̂ values along the three dimensional crack front are evaluated for the embedded crack. The results are compared with those for two dimensional analysis. The nozzle corner crack is treated under thermal transient condition and distributions of J ̂ values, and their change with time is obtained. The shapes and dimensions are changed by the assumption that the crack growth occurs at the point where the J ̂ vector has its maximum, and the three dimensional shape of the propagating crack is estimated.