Some Implications of Recycling Used CANDU Fuel in Fast Reactors

Abstract

This paper presents the potential implications of adopting an advanced nuclear fuel cycle where used CANDU fuel is reprocessed and supplied to fast reactors designed to burn actinides. The analysis assumes that used CANDU fuel is reprocessed to recover uranium, plutonium and other actinides, which are then used to fabricate fresh fuel for the fast reactors. Once in operation, the used fast reactor fuel is reprocessed and recycled together with makeup from used CANDU fuel to produce energy. Pyroprocessing is assumed for reprocessing of CANDU and fast reactor used fuels.Deployment of fast reactors in the nuclear energy system is assumed as a method for waste management and for electricity production. With respect to waste management, mass flow calculations estimate that the reduction in mass of transuranics for disposal would be accompanied by a larger increase in the mass of fission products. The time required to consume most of the transuranics in the used CANDU fuel is also estimated.Understanding the long-term hazard of the wastes from an advanced fuel cycle is important to assess options for their long-term management. Estimates of the radioactivity, radiotoxicity, thermal power and unshielded dose from a reprocessing/fast reactor wasteform and from used CANDU fuel are presented.The long-term safety of the fast reactor waste is also addressed. Two options are considered, placement in a deep geological repository, and placement after 300 years decay in a near surface landfill. The analysis estimates that the dose consequences as a result of surface disposal of reprocessing wastes could exceed regulatory limits over long periods of time. That is, even after a few hundred years of decay, the fast reactor wasteform is sufficiently radioactive that it would require appropriate long-term management, such as in a deep geological repository.