Development and status of MELCOR

MELCOR is a fully integrated, relatively fast-running code which models the progression of severe accidents in light water reactor nuclear power plants. An entire spectrum of severe accident phenomena is modeled in MELCOR. Characteristics of severe accident progression that can be treated with MELCOR include the thermal hydraulic response in the reactor coolant system, reactor cavity, containment, and confinement buildings; core heatup and degradation; hydrogen production, transport and combustion; core-concrete attack; heat structure response; radionuclide release and transport; and the impact of engineered safety features on thermal hydraulic and radionuclide behavior. MELCOR is being developed at Sandia National Laboratories for the US Nuclear Regulatory Commission (NRC) to succeed the Source Term Code Package. MELCOR has been designed to facilitate sensitivity and uncertainty analyses, and is currently being used to estimate severe-accident progression, source terms and associated sensitivities and uncertainties for two NRC-sponsored PRAs