Analysis of the late core melt progression phase of severe reactor accidents using the MELPROG code

The two-dimensional (r-z) melt progression (MELPROG) computer code is being developed to analyze severe light water reactor accidents from accident initiation through vessel failure. The MELPROG code is comprised of several explicitly linked modules that analyze different aspects of an accident. If the fuel rods fragment, as happened at Three Mile Island (TMI), core melt progression is analyzed in the DEBRIS module (this module is also used to model rubble beds that can form in the lower plenum). Heat transfer, oxidation, melting, dissolution, melt relocation, and refreezing are all considered in the DEBRIS module. Vapor and coolant flow in the core and through the vessel are treated in the FLUIDS module. This module also models the relocation of solid and molten materials from the reactor core into the lower plenum. Detailed heat transfer and structural mechanics calculations are performed in the STRUCTURES module for the vessel walls, various support plates, the core baffle, the core barrel, core support columns, and other structures in the vessel. Three-dimensional, dynamic view factors are calculated in the RADIATION module that provides boundary conditions for the CORE, DEBRIS, and STRUCTURES modules. Results from a sample calculation are presented to demonstrate the capabilities of the code.