Hydrogen Generation Behavior in the LOFT FP-2 and Other Experiments: Comparative Assessment for Mitigated Severe Accident Conditions

Zircaloy oxidation and hydrogen generation data for the loss-of-fluid test (LOFT) FP-2 test are presented and compared with findings from other severe fuel damage experiments. In the LOFT FP-2 test, the majority of hydrogen generation occurred as a consequence of bundle reflooding, where significant hydrogen production was also noted in other reflood experiments and in the Three Mile Island Unit 2 accident. Common findings also indicate that during fuel uncovery, bundle oxidation is largely controlled by steam supply conditions, that high rates of hydrogen production continue after melt formation and relocation, and that partial flow-area blockages do not drastically reduce the rates of hydrogen production. Tests results thus indicate no apparent limitations to Zircaloy oxidation other than that due to steam supply conditions and known reaction kinetics, and that the potential for significant hydrogen generation exists during reflooding of cores containing molten metallic debris.