Strength Assessment of Critical Elements of Nuclear Power Plant Equipment: State-of-the-Art Calculation Approaches

Abstract

The results of application of modern approaches to the analysis of the stress-strain state and fracture resistance of the elements of the NPP WWER first-circuit equipment (in particular, the RPV cylindrical part, the welded joint of the coolant collector and the steam generator vessel, the lining, and the reactor internals) under operating and emergency load conditions are presented. The refined calculation methodology is based on the application of state-of-the-art models and methods for solving nonlinear boundary problems of non-isothermal thermo-viscoplasticity and radiation creep using improved mixed schemes of the finite element method of increased accuracy, providing stable and reliable solutions, that take into account the deformation history of loading, modern approaches to modeling brittle-ductile fracture defects, processes of radiation swelling and radiation creep under conditions of elevated temperatures, intense neutron irradiation, and non-stationary modes of thermal-force loading. Based on the developed models and methods, the calculation results on the WWER-1000 RPV, the welded joint of the coolant collector and the PGV-1000M steam generator vessel, the lining, and the internal shaft of the WWER-1000 reactor were obtained and analyzed. The results demonstrate the capabilities and advantages of the developed calculation methods for assessing the strength and service life of critical elements of the WWER-1000 primary circuit equipment.