Thermal ratchetting in pressure vessels

During its lifetime a nuclear power plant undergoes cyclic thermal loadings, i.e. time variations of temperature spatial distribution; these thermal cycles combined with methanical loads (pressure), can produce dimensional changes for creep, plastic cycling and/or ratchetting. This problem is in special way important for a Liquid Metal Fast Breeder Reactor (LMFBR) because temperatures in it are high (about 5000C) and change either in radial direction or in axial direction. While the plastic behaviour of a structure subjected to mechanical loads and/or mechanical cycle loads can be well studied by Finite Element analyses and several different computer programs, the thermal plastic behaviour was studied for simplified conditions only. Actually, the Bree, Miller, Burgreen model considers a thin cylindrical shell with a radial thermal gradient and in uniaxial stress state while Kalnins, Updike extend this model to a biaxial stress state. To obtain numerical results of the thermo-plastic behaviour of cylindrical shells, a mathematical model was developed and the special purpose computer program PLAST was implemented. (Auth.)