Numerical simulation of liquid entrainment by the Rayleigh-Taylor mechanism

A major consideration in the safety analysis of the consequences of hypothesised disruptive accidents involving the whole core of a liquid metal cooled fast breeder reactor is the extent to which the sodium coolant becomes entrained in the expanding core bubble and the timing of the entrainment. The specific safety goal is to show that the coolant impact upon the reactor vessel caused by the expanding bubble of hot gases above the core is below structural failure limits for prescribed initial core conditions. Parametric simulations of the expansion process show that sodium entrainment can either greatly reduce the effective work done by the bubble by cooling it, or in some circumstances can increase it by providing sufficient sodium vapour to act as the working fluid. On the assumption that one of the main mechanisms for sodium entrainment is the Rayleigh-Taylor instability at the bubble interface a study has been performed of the growth of spikes of coolant at the expanding interface