As part of the liquid-metal fast breeder reactor (LMFBR) safety program, the consequences of a hypothetical molten-fuel release into sodium coolant following fuel pin failure(s) must be evaluated, in order that design constraints can be established to maximize the safety and minimize the economical penalties of such an event. This work represents the first attempt to interpret the voiding rates obtained from an in-pile, fuel-failure experiment in the TREAT reactor in terms of a molten fuel-coolant interaction. Results indicate that it is not only possible to reduce in-pile data to a workable form, but also to obtain representation of loop conditions for simple geometries. The analysis has been successful in reproducing the experimental voiding history in a selected TREAT experiment. It is further shown that the formation of condensate at cold boundaries significantly reduces the amount of energy imparted to the expanding vapor bubble, which in turn limits the extent of the thermal-to-mechanical energy conversion process. It is important to account for this effect when extrapolating in-pile results to reactor conditions.