Progress and Limitations of an Equilibrium Thermodynamics Approach to Palladium Diffusion Through TRISO Fuel Particles

Abstract

We have developed a framework for modelling fission product diffusion through the various TRISO layers and accounting for fixed fission products. The framework applies mass transport simulation provided by the Thermochimica software package, coupled to the fuel performance code BISON, which simulates heat transfer and other fuel physics. We found that an equilibrium thermodynamics approach for palladium diffusion was not suitable for the carbon layers. Theexperimental evidence does not support the assumption that the thermodynamic equilibrium is faster than the timescale for palladium diffusion. A kinetics approach for the carbon layers is proposed as a resolution for future work.