Analysis of KROTOS Steam Explosion Experiments Using the Improved Fuel-Coolant-Interaction Code TEXAS-VI

In the present study, we propose a new fragmentation criterion for the explosion phase to take account of the effect of partial fuel melt solidification on the rapid fragmentation process. This new criterion judges whether or not the explosive fragmentation can occur by comparing the impact stress induced by vapor film collapse and water jet impingement with the fracture toughness of the corium crust layer. The fragmentation criterion was incorporated into the revised Thermal EXplosion Analysis Simulation (TEXAS) fuel-coolant-interaction (FCI) model TEXAS-VI and combined with the previously proposed fuel particle solidification model and the fragmentation criterion for the mixing phase. TEXAS-VI was compared to KROTOS alumina test K-44 and corium tests K-52 and K-53, and good agreement was obtained. The simulation results indicate that TEXAS-VI has the capability to consider the effect of partial solidification for both the mixing and the explosion phases of the FCI process and can capture the effect of fuel solidification, which reduces corium-water explosion energetics. Experiments K-52 and K-53 also demonstrate the ability of TEXAS-VI to model the effects of ambient pressure on energetics.