LMFBR Loss of Flow Simulations in the Sodium Loop Safety Facility

A series of three LMFBR unprotected loss of flow (LOF) accidents has been simulated in the Sodium Loop Safety Facility (SLSF). The results of these in-reactor experiments verify that the dynamics of sodium voiding are, in general, well represented by current single channel slug expulsion models. Some refinement in the models in the very early stages of voiding would be desirable to account for minor two dimensional effects. However, cladding motion is not as well understood and current modeling does not accurately predict all of the aspects of blockage formation. Two of the three experiments produced partial rather than complete upper blockages as had been predicted. Predictions of time of fuel melting appear relatively accurate. In general, the sequence of events is correctly predicted and the timing of these events is relatively accurate. Reactivity measurements and post-test examinations indicate that no significant fuel compaction occurred. This behavior would prevent an energetic recriticality in an LOF accident.