Nonequilibrium Evaporation and Condensation in Liquid-Metal Fast Breeder Reactor Fuel Expansion

The effect of nonequilibrium mass transfer on two-phase oxide fuel expansion was studied. An analytical model was applied to fuel expansion tests being planned at Oak Ridge National Laboratory (ORNL) and to whole-core expansion of a uniform bubble in Clinch River Breeder Reactor geometry. Among the parameters varied in the study are the liquid droplet radius (R_p) and the condensation and evaporation coefficients (σ). It was found that allowance for nonequilibrium mass transfer increased the expansion times for the ORNL tests when the ratio of σ/R_p was <1000 m^−1. Nonequilibrium mass transfer had little effect on the whole-core expansions until σ/R_p reached unrealistically low values of <10 m⁻¹.