Stress analysis with simplified model for a LMFBR fuel rod system

Abstract

This paper is concerned with an approximate closed solution for stresses in an idealized nuclear reactor fuel system under a steady state condition. This analysis is based on the thermo-mechanical response of the fuel rod system. The pellet is modeled as elastic-plastic continuum governed by the Mohr-Coulomb yield criterion and by the flow rule. The cladding is modeled as elastic-plastic continuum governed by the Treasca criterion and by the flow rule under plane strain. Although the present model is very simplified, this can be used as a yardstick to check the accuracy of the approximate solutions obtained by the numerical technique. Numerical results, illustrating the variation of displacement and stresses under the typical Liquid Metal Fast Breeder Reactor condition, are given. A comparision between results by the present work and by the previous work shows: Interaction between the pellet and the clad occurs at high burn up, and if interaction occurs, the cladding hoop stresses due to the contact is greater than that in the creep model. This agrees with the previous discovery that, when the interaction occurs, the plasticity has a greater effect on the stresses than the creep. The lower the central void size is, the earlier the interaction takes place. This means that the existence of central void makes diminished the contact pressure.