The Fission Properties of Curium Separated from Spent Nuclear Fuel

Abstract

Curium poses special problems in the chemical preparation of spent nuclear fuel for transmutation. Once separated from the other minor actinides, the seven curium isotopes in spent fuel can lead to nuclear fission with the subsequent release of a large amount of radiation. Several isotopes of curium also generate a significant amount of heat by radioactive decay. Sustained fission can be avoided by preventing the accumulation by more that a critical mass of curium. The heat generation of curium presents even more restriction on the mass of curium that can safely be contained in one location.\nTo analyze the nuclear and thermal properties of curium, the curium isotopes within spent fuel were quantified using RADDB, a light water reactor radiological database. The critical mass of curium was analyzed for shielded and unshielded cylindrical and spherical geometries. The criticality studies were completed using SCALE 4.4a, a Monte Carlo code approved by the Nuclear Regulatory Commission for the analysis of critical nuclear reactors. The results include recommendations on the maximum mass of curium that may be safely handled.\nFinally, a conservative case for the buildup of decay heat was analyzed to determine the equilibrium temperature of a curium-filled container. Both natural convection and radiation heat transfer were considered. The equilibrium temperature was used to recommend the maximum mass of curium that can be safely handled or stored before melting occurs.