THE SEVERE ACCIDENT ANALYSIS PROGRAM FOR THE SAVANNAH RIVER NUCLEAR PRODUCTION REACTORS

Severe accident phenomena pertinent to the heavy-water-moderated production reactors of the U.S. Department of Energy are being studied in the Severe Accident Analysis Program (SAAP) at the Savannah River Site. The SAAP has sought to define the behavior of the Savannah River reactors in accident scenarios involving significant fuel melting. The goal of the program is to make possible accident analyses of the production reactors that are of comparable quality to those done for power reactors. These large Savannah River reactors differ from power reactors in several important respects: they operate at low temperature and pressure, their fuel is uranium metal alloyed and clad with aluminum, and radioactive releases are contained by a filtered confinement system rather than by static containment. These differences have guided the experimental and calculational development of the SAAP, which also draws where possible on analyses made for other types of reactors. Major experimental research areas in the SAAP have included fuel-melting phenomena, melt relocation and its interactions with water and concrete, fission-product release and mobility, and the response of the confinement system under accident conditions. The MELCOR and SCDAP/RELAP5 code packages, developed for severe accident analyses of commercial power reactors, have also been adapted to the Savannah River reactors under the SAAP. These are already being used in accident analyses. Calculational tools have also been developed for estimating the potential effects of steam explosions. Experimental work is continuing, as is the validation and application of the code packages.