Limits to Fuel/Coolant Mixing

The vapor explosion process involves the mixing of fuel with coolant prior to the explosion. A number of analysts have identified limits to the amount of fuel/coolant mixing that could occur within the reactor vessel following a core melt accident. Past models are reviewed and a simplified approach is suggested to estimate the upper limit on the amount of fuel/coolant mixing possible. The approach uses concepts first advanced by Fauske in a different way. The results indicate that water depth is an important parameter as well as the mixing length scale D_mix, and for large values of D_mix the fuel mass mixed is limited to <7% of the core mass.