Development of MARCH 2

The MARCH code has been widely used for describing the wide variety of physical processes associated with core meltdown accidents. The efforts associated with the development of MARCH 2, a revised version of the reference code, are described. These include changes in the code structure as well as improvements in the phenomenological models. The changes in code structure are designed to improve the flexibility for the treatment of a variety of accident sequences and facilitate the transportability of the code. The principal changes in phenomenological modeling are related to updated decay heating correlations, improved primary system blowdown for transients and small breaks, more detailed treatment of in-core heat transfer processes, extended modeling of metal-water reactions, more mechanistic treatment of core debris interaction with water, and improvements in the treatment of the burning of hydrogen and other combustibles. Results of comparisons between MARCH 2 predictions and those of MARCH 1.1 are presented