MELMACCS is a Windows based program developed by SNL in 2002 that is used to create a MACCS source term input file from the MELCOR plot file. MELCOR plot files contain large amounts of data, only a small fraction of which is needed for MACCS calculations. The MELMACCS software was created to provide an interface utility between MELCOR and MACCS to extract and evaluate the required source term data for a consequence analysis.

MELMACCS obtains two classes of data from the MELCOR plot files. The first is time independent data, which are data that remain constant throughout the MELCOR calculation. The second class is time-dependent data, which is written to the MELCOR plot file for each plot file time step.

MELMACCS uses a graphical user interface (GUI) to allow the user to convert one MELCOR plot file into a source term input file (.INP) for MACCS. The inputs contained in this file are used in the ATMOS portion of MACCS.