Irradiation-enhanced interdiffusion in the diffusion zone of U-Mo dispersion fuel in Al

Abstract

Uranium-molybdenum (U-Mo) alloy fuel particles dispersed in an aluminum (Al) matrix, designated as U-Mo/Al dispersion fuel, is in the development stage in the worldwide RERTR (Reduced Enrichment for Research and Test Reactors) program. The main issue in developing U-Mo/Al dispersion fuel is the diffusion reaction occurring at the interface between the fuel particles and matrix. To accurately analyze fuel performance, a model to predict the diffusion kinetics is necessary. For this purpose, the authors developed a diffusion layer growth rate correlation for out-of-pile annealing tests and a similar correlation for in-reactor tests. The correlation for in-reactor tests is considerably different from that of out-of-pile tests because it contains factors that amplify diffusion kinetics by fission damage in the diffusion reaction zone. This irradiation enhancement was formulated by a combination of the fission rate in the fuel and fission fragment damage distribution in the diffusion reaction zone. Using a computer code, fission damage factors were obtained as a function of diffusion reaction layer thickness and composition. The model correlation was established and fitted to the in-reactor data. As a result of this data fitting, the interaction layer growth rate is found to be proportional to the square root of the fission fragment damage rate and to have a temperature dependence characterized by the effective activation energy of 46 to 76 kJ/mole, which is smaller by a factor of 4 to 7 than that of out-of-pile tests.