Fission Product Decay Heat Modeling for Disrupted Fuel Regions (FDECAY)

This report describes a model to account for the reduction in fission product decay power resulting from volatile element loss following fuel liquefaction or quench-induced fragmentation. The model was developed for the Severe Core Damage Analysis Package (SCDAP) computer code and the report will be incorporated into the SCDAP user's manual. The model assumes that the ANS-5.1 standard or a similar model will be used to find decay heat for intact fuel that has not lost any fission products. After a major disruptive event, such as liquefaction or quench-induced fuel fragmentation, the model return a fraction which is to be multiplied times the decay heat value for intact fuel. Smaller volatile element losses, such as those accompanying loss of cladding integrity, are not treated explicitly. This first version of FDECAY also assumes that the case being modeled is similar to one of the decay heat source removal scenarios described in this report. The model is designed to accommodate additional scenarios if any significantly different fission product release scenarios are identified