A Model of the Fission Products Release from the Melt Pool during Severe Accident in a Liquid Metal Cooled Fast Reactor

Abstract

Accident scenarios implying the failure of the active and passive reactor protection system are the most severe in their consequences since they are accompanied by the melting of fuel elements, fuel assemblies, and the entire core and, as a consequence, the release of fission products (FP) from the fuel melt and structural materials. The location of reactor facilities near populated areas requires an understanding of the consequences of hypothetical accidents with the destruction of the core. The most important is information on the amount of FP released into the environment. To assess the possible dose load on personnel and the environment in a hypothetical accident, data on the release of radioactive nuclides from the damaged, including molten, core are required. This work presents approaches that can be used to calculate the amount of fission products released from the fuel melt. The proposed approaches are based on general patterns of behavior and release of impurities from liquid solutions. To simulate this process, a system of differential equations is solved. The proposed approaches were implemented in the form of a software module for calculating the release of FP from the melt. Using the developed module, a test problem for the release of FP from a molten oxide fuel was solved, and an analysis of the results of real experiments carried out at the National Laboratory in Oak Ridge was carried out. Satisfactory convergence of the calculated data on the yield of both nonvolatile (Ce, Sr) and volatile (Xe, Kr) fission products is shown.