Fuel-coolant interaction analysis for corium molten materials

The Fukushima accident suggested that molten fuel may have quenched in residual water in-vessel and/or likely ex-vessel from molten fuel-coolant interactions (FCI) mixing and quenching. To better understand such behavior, we have developed a molten fuel breakup model that considers solidification effects and we apply it to corium molten fuel mixing with water using the TEXAS FCI model. FCI phenomena with molten corium materials have been observed to be less energetic than predicted and we hypothesize this is due to local solidification effects. We consider the effect of a solid crust layer during fuel-coolant mixing in this model. This solidification model predicts the transient temperature profile and crust layer thickness of the fuel particle by solving the heat conduction equation for each Lagrangian fuel particle. This fuel particle breakup model and transient temperature profile model were incorporated into the TEXAS FCI model; so called TEXAS-VI model. This revised TEXAS FCI model was compared to the FARO L14 experiment (ISP-39) where fuel-coolant mixing and quench data have been published. The LI4 pressure history, liquid water pool temperature, and vapor temperature were found to be in good agreement with the revised model predictions. This mixing behavior will also have an impact on FCI explosion energetics.