PNNL

Abstract

n monolithic UMo fuels, the interaction between Al cladding constraint and large gas bubble volumetric swelling causes elastic-plastic and creep deformation. In this work, a phase field model of gas bubble evolution in polycrystalline UMo under elastic-plastic deformation was developed for studying the dynamic interaction between evolving gas bubble/voids and deformation. A crystal plasticity model, which assumes that the plastic strain rate is proportional to resolved shear stresses of dislocation slip systems on their slip planes, was used to describe plastic deformation in polycrystalline UMo. Xe diffusion and gas bubble evolution are driven by the minimization of chemical and deformation energies in the phase-field model while evolving gas bubble structure was used to update the mechanical properties in the crystal plasticity model. With the developed model we simulated the effect of gas bubble structures (different volume fractions and internal gas pressures) on stress-strain curves and the effect of local stresses on gas bubble evolution. The results shows that 1) the effective Young’s modulus and yield stress decrease with the increase of gas bubble volume fraction; 2) the hardening coefficient increases with the increase of gas bubble volume fraction, especially for gas bubbles with higher internal pressure; and 3) pressure dependence of thermodynamic and kinetics of Xe and local stress state determine gas bubble growth or shrink. The simulated results can guide to improve material property models for macroscale fuel performance modeling.