Analysis of fission gas behavior and foaming of molten uranium- aluminum alloy fuel for nuclear reactors. New Production Reactors Program.

摘要

This report begins with a review of the models selected to analyze fission-gas foaming in molten U-Al alloy fuel for nuclear reactors. The models were incorporated into the FRAS/FOAM code for initial testing and scoping calculations. The FRAS/FOAM calculations were verified by comparing the results for a simplified problem to analytical results. The molten-fuel models were then incorporated into the FRAS3 code for further model developments that extend the analysis into the foaming regime for molten U-Al fuel. The most significant of the new models is the one for bubble sweeping, which extends the earlier pair-wise coalescence model to conditions appropriate for foaming to occur. Results are presented that indicate foaming can occur on time scales as short as 10 to l00ms after melting begins. The dependence of the timing and potential amount of foaming on the pressure and fuel burnup are also presented. A number of assumptions applied in these calculations, however, tend to overestimate the rate of bubble coalescence and growth. Directions for further work in this modeling effort are described. They include incorporation of a fuel-melting model into the FRAS3 code, so that a two-field calculation of melting fuel can be carried out. (ERA citation 18:023547)