Evaluation of the Effect of Thermal Stratification on the Residual Life of the Surge Line of the Pressure Compensator in the No. 5 Unit of the Novovoronezh NPP

Abstract

This article is concerned with investigations of temperature stratification of the first-loop coolant in the surge line of the pressure compensator in the No. 5 unit of the Novovoronezh NPP. The actual stress-strain state and accumulated structural damage in the surge line in different operating regimes was analyzed by means of multiparametric computational and experimental monitoring. The experimental data demonstrate thermal stratification, giving rise to a temperature differential over the cross section ranging from 30°C under normal operating conditions to 150°C, as a result of disruption of the normal operating conditions, and high thermal stresses. The analysis shows that the cyclic strength of the weld connection of the surge line can be exhausted by the end of the 60-yr life of the No. 5 unit. It is concluded that the actual residual stresses must be measured and calculations of the cyclic strength and the residual life of the surge line must be performed. It is suggested that a technology be developed to strengthen the weld-joint metal in order to reduce the formation of operational surface defects.