Creep and Irradiation Effects in Reactor Vessel Internals

Abstract

The paper is devoted to the presentation of the calculation method for determining the stress–strain state and long-term strength of reactor vessel internals (RVI) and the description of the results obtained with its help. The method is based on a complete mathematical formulation of the boundary- initial value problems of creep accompanied by irradiation effects. Deformation and damage accumulation caused by irradiation effects in the material when interacting with the effects caused by thermal creep, can significantly limit the safe operation of RVI. Elastic, thermoelastic, thermal and irradiation creep, irradiation swelling strains, creep damage and fracture are considered. The numerical solution of the boundary value problems is performed by the FEM, and the initial value problems are solved by time integration. To estimate cyclic deformation and fracture, the procedures of asymptotic methods and averaging over cycle periods are used. As an examples of the use of this calculation method, the results of creep modelling of fuel element, T-joint of tubes and notched plates are given. The issues of interaction of stresses, strains and damages of different nature under complex stress state are discussed.