Evaluation of Long-Life Transuranics Breakeven and Burner Cores for Waste Minimization in a PB-GCFR Fuel Cycle

Transuranics (TRU) breakeven and burner core designs have been studied for the Pebble-Bed Gas-Cooled Fast Reactor (PB-GCFR), which was developed under a 2-yr U.S. Department of Energy Nuclear Energy Research Initiative project. The issues of minimizing waste production, fuel cost, and burnup reactivity swing, and maximizing TRU burning have been investigated primarily from a neutronics viewpoint. For TRU breakeven cores, it was found that for the given core power [300 MW(thermal)] and power density (50 MW/m³), the lowest amount of radiotoxic TRU to be processed is obtained for a long-life (single-batch) core of 30-yr duration. Minimizing the TRU processed results in a minimization of the TRU losses that ultimately will have to be entombed in a geologic repository.

The results show that the single-batch, long-life PB-GCFR could be designed to operate over a wide range of cycle lengths and fuel loadings. By modifying the TRU feed to have a higher minor actinide (MA) fraction than contained in light water reactor spent fuel, the burnup reactivity swing for the long-life core can be reduced significantly. With this approach, it is also possible to configure the long-life PB-GCFR core as a TRU burner using nonuranium fuel. A nonuranium fuel PB-GCFR with 24% plutonium and 76% MAs can operate for 17 full-power years and achieve 25% burnup with a reactivity swing of 3%k.