[en] This report summarizes the results of developmental work of methods of core modeling for use in the analyses of the progression of accidents that involve core damage in BWRs. Accomplishments include the development of an analytical model for channel box and control rod heatup, oxidation, and melting and a mechanistic core-wide meltdown and relocation model. These are provided in the form of a FORTRAN subroutine denoted MELRPI that can be exercised with an existing version of the MARCH code. The modeling concept and the modular structure employed in MELRPI have been designed so that new models subsequently developed for specific phenomena can be rapidly incorporated when they become available