Modelling of fuel oxidation behaviour in operating defective fuel rods

A fuel oxidation model is proposed for operating defective nuclear fuel rods. The present model is based on adsorption theory and accounts for high pressure effects. This model is in agreement with the fuel oxidation kinetics observed in high temperature annealing experiments conducted at 1 473 to 1 623 K in steam over a range of pressure from 0.001 to 0.1 MPa. Using a Freundlich adsorption isotherm, the current model is also consistent with recent experiments conducted at a higher pressure of 7 MPa. The model also considers radiolytic effects as a consequence of fission fragment bombardment in the fuel-to-clad gap. This treatment suggests that radiolysis-assisted oxidation is insignificant in operating defective rods (as compared to thermal effects), as supported by limited in-reactor data. The effects of diffusion of the interstitial oxygen ions in the solid in the operating rod is further discussed. (authors)