Part II: Fuel Oxidation Kinetics Model for Operating Defective Fuel Elements

Abstract

A theoretical treatment has been developed to predict the fuel oxidation behaviour in operating defective nuclear fuel elements. The equilibrium stoichiometry deviation in the hyperstoichiometric fuel has been derived from thermodynamic considerations. The kinetics model accounts for multi-phase transport including interstitial oxygen diffusion in the solid and gas-phase transport of hydrogen and steam in the fuel cracks. The fuel oxidation model is further coupled to a heat conduction model to account for the feedback effect of a reduced thermal conductivity in the hyperstoichiome tric fuel. A numerical solution has been developed using a finite element technique with the FEMLAB software package. The model has been compared to available data from several in-reactor X-2 loop experiments with defective fuel conducted at the Chalk River Laboratories. The model has also been benchmarked against an 0/U profile measurement for a spent defective fuel element discharged from a commercial reactor.