An ideal strategy for the sustainability of nuclear energy is to implement closed fuel cycles in fast reactors, i.e. to recover all the actinides in the spent fuel and recycle them in the reactor itself. In this way input uranium feed and output long-term wastes are minimized: the fuel cycle can have as input only depleted (or natural) uranium and as final waste only the fission products and the losses due to fuel reprocessing. From the neutronic point of view, the feasibility of this approach depends on the equilibrium fuel vector, whose solution therefore becomes crucial. The equilibrium vector is usually calculated by an approximate steady-state approach or by a direct irradiation simulation. Here a different approach has been devised, imposing a priori the equilibrium requirement and taking into account the evolution of the fuel during irradiation, as well as its cooling time before being reprocessed and reloaded. The equilibrium for the transuranic elements becomes thus 'cyclic'. The method is based on a recursive integration of the Bateman equation, and is validated by the codes FISPACT and MCNPX. The differences with respect to the steady-state approach are shown. The method is then applied to the European lead fast reactor ELSY. The fraction (on the total actinides) at equilibrium turns out to be in this case 0.9% for the MA and 17.2% for the Pu. The reduction of transuranic mass waste is calculated with respect to once-through fuel cycles (resulting lower by two orders of magnitude).
Solution of the equilibrium fuel vector in closed fuel cycles and application to a lead fast reactor
Petrovich, C.
2010-05-31
Abstract
An ideal strategy for the sustainability of nuclear energy is to implement closed fuel cycles in fast reactors, i.e. to recover all the actinides in the spent fuel and recycle them in the reactor itself. In this way input uranium feed and output long-term wastes are minimized: the fuel cycle can have as input only depleted (or natural) uranium and as final waste only the fission products and the losses due to fuel reprocessing. From the neutronic point of view, the feasibility of this approach depends on the equilibrium fuel vector, whose solution therefore becomes crucial. The equilibrium vector is usually calculated by an approximate steady-state approach or by a direct irradiation simulation. Here a different approach has been devised, imposing a priori the equilibrium requirement and taking into account the evolution of the fuel during irradiation, as well as its cooling time before being reprocessed and reloaded. The equilibrium for the transuranic elements becomes thus 'cyclic'. The method is based on a recursive integration of the Bateman equation, and is validated by the codes FISPACT and MCNPX. The differences with respect to the steady-state approach are shown. The method is then applied to the European lead fast reactor ELSY. The fraction (on the total actinides) at equilibrium turns out to be in this case 0.9% for the MA and 17.2% for the Pu. The reduction of transuranic mass waste is calculated with respect to once-through fuel cycles (resulting lower by two orders of magnitude).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
