Closed Fuel Cycle and Minor Actinide Multirecycling in a Gas-Cooled Fast Reactor

The Generation IV International Forum has identified the Gas-CooledFast Reactor (GCFR) as one of the reactor concepts for future deployment. The GCFR targets sustainability, which is achieved by the use of a closed nuclear fuel cycle where only fission products are discharged to a repository; all Heavy Metal isotopes are to be recycled in the reactor. In this paper, an overview is presented of recent results obtainedin the study of the closed fuel cycle and the influence of the addition ofextra Minor Actinide (MA) isotopes from existing LWR stockpiles. Inthe presented work, up to 10% of the fuel was homogeneously replacedby an MA-mixture. The results are that addition of MA increases thepotential of obtaining a closed fuel cycle. Reactivity coefficients generallydecrease with increasing MA content. Addition of MA reducesthe reactivity swing and allows very long irradiation intervals up to 10% FIMA with a small reactivity swing. Multirecycling studies show that a 600 MWth GCFR can transmute the MA from several PWRs. By acareful choice of the MA-fraction in the fuel, the reactivity of the fuelcan be tuned to obtain a preset multiplication factor at end of cycle.Preliminary decay heat calculations show that the presence of MA in thefuel significantly increases the decay heat for time periods relevant toaccidents (104–105 s after shutdown). The paper ends with some recommendationsfor future research in this promising area of the nuclear fuel cycle