An analytical study of gas-bubble nucleation mechanisms in uranium-alloy nuclear fuel at high temperature

A multi-atom gas-bubble nucleation mechanism in uranium-alloy nuclear fuel operating in the high-temperature equilibrium gamma phase is proposed based on interpretation of measured intragranular bubble-size distribution data. This model is contrasted with the conventional two-atom nucleation mechanism within the context of a mechanistic calculation of the fission-gas bubble-size distribution. The results of the analysis enable the calculation of safety margins for unrestrained fuel swelling. These safety margins contain an uncertainty primarily tied to uncertainties in the values of the volume and Xe diffusion coefficients.