Systematic generation of effective thermophysical and thermo-mechanical properties for reduced-order modeling of TRISO fuel pellets

Abstract

This work presents a detailed methodology for generating effective material properties of tri-structural isotropic (TRISO) fuel pellets for use in reduced-order homogenized thermal and/or mechanical calculations. This is achieved by use of the finite-element (FE) method to perform simulations of explicitly modeled TRISO fuel pellets, in conjunction with derivation of analytical equations for analogous homogenous pellets which preserve a particular parameter of interest. This method is applied to several properties including thermal conductivity, specific heat capacity, thermal expansion coefficient, Young’s Modulus and Poisson’s Ratio. The properties generated are a function of temperature and packing fraction. It is demonstrated that the state-of-the-art for homogenizing thermal conductivity may be inadequate for realistic TRISO pellets, while for other properties existing homogenization standards are scarce in the literature. Finally, a multi-physics application of the reduced-order properties is demonstrated, which involves coupling neutronics with thermo-mechanical calculations. The fission power distribution is obtained from neutronic analysis, and then temperature, displacement and stress–strain distributions from the explicit finite-element model are compared with those from the homogenous calculations. For the finite-element simulations, the commercial software Abaqus (ABAQUS, 2014) is used, and the Monte Carlo code MCNP is used for neutronics to obtain the power distributions.