The debris module: An effective tool for the analysis of melt progression in LWRs

The DEBRIS module was developed to deal with the analysis of core melt processes in light water reactors (LWR's). It was designed to address the important processes associated with the late phase of a core meltdown. This phase encompasses the period following the loss of intact rod geometry and ending with vessel head failure. It is characterized by the melting and relocation of ceramic rich materials through a rubblized medium composed primarily of fuel pellet and oxidized cladding fragments. Of particular interest are the dynamics of the melting process, the relocation of the components, the formation of crusts, retention of molten materials by the crust, and remelting of crusts.'ne DEBRIS module treats these processes in a two-dimensional (r,z) geometry solving the continuity, momentum, and energy equations to describe the dynamics of meltdown. The DEBRIS models are described together with some of the analyses to which the module has been applied. In particular, a description is given of the DEBRIS module analysis of the MP-1 experiment. The DEBRIS module appears to have significant potential for the analysis of late phase meltdown processes and can be effectively used both in a stand-alone mode or in conjunction with the severe accident analysis codes (MELCOR, SCDAP). In addition, the module may prove effective for treatment of the early phase processes as well