Modeling Transient Fission Gas Behavior for Solid, Melting, and Molten Fuel in the Computer Program LAKU

The model for transient fission gas behavior in melting and molten fuel contained in the Karlsruhe code LAKU is revised to include the effect of capillary forces, which cause rapid gas bubble coalescence and the formation of big bubbles in the fuel at and beyond the liquidus. Some emphasis is also put on treating the transition from solid to liquid fuel; this is of importance for interpreting the less energetic experiments of the CABRI series and may also have a significant effect for slow transients. The LAKU model is reviewed and recent calculational results are presented.