Kinetic limitations to adiabatic equilibrium models for direct containment heating (DCH)

Probabilistic risk assessment studies are being extended to include a wider spectrum of reactor plants than was considered in NUREG-1150. There is a need for computationally simple models of direct containment heating (DCH) that could be used for screening studies aimed at identifying potentially significant contributors to overall risk. The two-cell kinetic model developed here is an extension of the two-cell equilibrium model developed previously, which captured a major mitigating feature due to containment compartmentalization. This extension of the equilibrium model represents additional mitigating features resulting from two kinetic competitions: time-of-flight limitations to debris/gas heat transfer and debris oxidation, and the noncoherence or reactor coolant system blowdown with debris residence in the atmosphere. Predictions of containment pressurization and hydrogen production are compared to experiment data taken in the Surtsey facility located at Sandia National Laboratories.