Physical modelling of the in-vessel phases of severe reactor accidents: The MELPROG/TRAC computer code

The MELPROG/TRAC computer code is the U.S.N.R.C. best-estimate model for analysis of phenomena in the reactor vessel and reactor coolant system associated with the progression of severe accidents in light water reactors. Although versions exist for both boiling water reactors and pressurized water reactors, the discussion is confined to the pressurized water reactor. The structure of MELPROG/TRAC is briefly summarized, its capabilities outlined, and results from typical analyses noted. As a specific example, differences in the initiation phase of a station blackout accident caused by pump seal failures are described. Finally, experimental and analytical efforts to assess the modelling basis for MELPROG/TRAC are outlined. (author). 14 refs, 4 figs