Modeling Fission‐Gas Behavior in Metallic Fuels

The FRAS3 code, developed to model transient fission-gas behavior in oxide fuel, has been modified for application to metallic fuel. The code has been applied to analyze a series of experiments on irradiated uranium fuel, in which fission-gas bubble distributions were measured following isothermal anneals under various pressures. Comparison of the calculated bubble-size distributions to those measured indicates that grain-boundary bubbles are an important components of the observed size distributions. The calculated results agree will with the observed results in both the general nature of the distributions and their variation with pressure. Results are not as consistent for an anneal under vacuum, during which a large amount of gas was released.