Impact of SIMMER-II model uncertainties on predicted postdisassembly dynamics

The SIMMER-II calculation of the system kinetic energy developed during a voided core postdisassembly expansion in a hypothetical loss of flow (LOF) accident sequence gives results which are more than an order of magnitude below that for an ideal expansion. This work attempts to determine the extent to which uncertainties in the various phenomenological models in SIMMER-II influence the calculated results. A series of 15 separate SIMMER-II calculations were designed to make this assessment. The system kinetic energies which resulted ranged from 2.5 to 20 MJ compared to 100 MJ for the ideal expansion. It is concluded that experimental research in the area of voided core expansions should entail a balance between two areas. First, experiments should be performed that test the major uncertainties in the sequence of events as outlined in this report. Second, in order to increase confidence in the ability of SIMMER to predict other classes of expansion, testing of isolated phenomenological models should proceed