Simulation of the fission-induced swelling and creep in the CERCER fuel pellets

A ceramic-ceramic (CERCER) fuel is selected as a dedicated composite fuel for an Accelerator Driven System (ADS), with minor-actinide-enriched ceramic fuel particles dispersed in a ceramic MgO matrix. The multi-scale simulation method of the irradiation-induced thermo-mechanical behavior evolution in the CERCER fuel pellets is developed. The semi-analytical fission-induced gaseous swelling model is established with considering recrystallization process and gas atom resolution in fuel grain scale. It is involved in the macro-scale three-dimensional large-deformation incremental constitutive relation for fuel particles. The stress update algorithms are developed respectively for the fuel, and the MgO matrix in which different fission-induced creep effects are taken into account. The user subroutines to define their mechanical constitutive relations are correspondingly written and validated. The simulation results indicate that (1) recrystallization leads to accelerated intergranular bubble swelling, and the maximum bubble swelling locates in the central particle where the temperature is the highest; (2) the creep coefficient in the MgO fission-induced creep model has a remarkable effect on its mechanical behavior evolution; and it can be determined by the fracture pattern in the matrix; (3) the matrix can effectively shorten the radial deformation of the composite pellet. (C) 2015 Elsevier Ltd. All rights reserved.