Influence of the heat transfer coefficient on the level of residual stress after heat treatment of the VVER-1000 reactor baffle

Abstract

Background. Improvement of the methodology for the computational analysis of residual stresses in the structural elements of the reactor is an integral part of the work when extending the service life of NPP power units.
 Objective. Determine the value of residual technological stress arising in the baffle of a VVER-1000 reactor during welding and postweld heat treatment according to the austenitizing mode. To evaluate the effect of considering the dependence of the heat transfer coefficient on the temperature of the baffle surface at cooling in air during heat treatment.
 Methods. Numerical modeling of the stress-strain state of the baffle during welding and postweld heat treatment was carried out using the finite element method.
 Results. It was determined that in the process of heat treatment according to the austenitizing mode, the residual welding stress in the baffle are almost completely relaxed. Due to the high temperature gradient during rapid cooling in air after heating in the process of austenitization, new rather high residual stresses are formed in the zones of the baffle with the greatest metal thickness.
 Conclusions. Based on the results of the investigation, a high level of residual technological stress was determined, which should be considered when calculating the justification for extending the service life of the VVER-1000 reactor baffle.