MELCOR 1.8.0: A computer code for nuclear reactor severe accident source term and risk assessment analyses

MELCOR is a fully integrated, engineering-level computer code that models the progression of severe accidents in light water reactor nuclear power plants. MELCOR is being developed at Sandia National Laboratories for the US Nuclear Regulatory Commission as a second-generation plant risk assessment tool and the successor to the Source Term Code Package. The entire spectrum of severe accident phenomena, including reactor coolant system and containment thermal-hydraulic response, core heatup, degradation and relocation, and fission product release and transport, is treated in MELCOR in a unified framework for both boiling water reactors and pressurized water reactors. MELCOR has been especially designed to facilitate sensitivity and uncertainty analyses. Its current uses include estimation of severe accident source terms and their sensitivities and uncertainties in a variety of applications. This report is a summary of MELCOR 1.8.0, the code version released in March 1989. Condensed information is presented on its developmental history, structure, modeling features and capabilities, verification and validation, and quality assurance. Detailed documentation on these aspects of MELCOR, including users' guides, reference manuals, programmers' guides, and assessment and application reports, is available in draft form and is distributed to MELCOR users