Engineering-level system code for severe accident analysis: MELCOR

MELCOR is a fully modular, engineering-level reactor simulation program that calculates the progression of serious accidents in light-water reactors. It was initiated by the US Nuclear Regulatory Commission developed by Sandia National Laboratories for the purpose of risk assessment for second-generation nuclear power plants. A broad spectrum of severe accident phenomena in both boiling- and pressurized-water reactors, respectively, can be handled in MELCOR within a unified framework. This includes the thermal-hydraulic response of the reactor’s primary coolant system, the reactor cavity, the containment, and the confinement buildings. In addition, accident scenarios are fully simulated, including loss of coolant (core uncovering), core heat up, fuel degradation, and core material melting and relocation. Later portions of accident simulation are possible as well, including core-concrete attack and hydrogen production, transport, and combustion, as well as fission product release and transport behavior. MELCOR can handle severe accident management actions, such as flooding a damaged core, hydrogen ignition-recombination, and IVMR. MELCOR can also be applied to analyze beyond-design-basis accident, which contains the estimation of severe accident source terms and their sensitivities, and uncertainty analysis.