A conservative approach to account for used fast-neutron reactor blankets in criticality-safety studies
Résumé
The current prospect of reprocessing the assemblies of the PHENIX Fast-neutron Reactor in France and the development of the 4th-Generation Fast-neutron Reactors (FR) enable research projects in relevant fuel cycle operations. Under these circumstances, the CEA and Orano Cycle have decided to investigate an approach to account for the depletion of the PHENIX reactor fuels in criticality-safety studies. Nowadays FR fertile assemblies are considered as fresh fissile assemblies in criticality studies. Obviously, accounting for the fertile assemblies’ depletion will offer substantial economic incentives, but it requires the use of a conservative approach. By definition, the fertile assemblies are more reactive after irradiation. That means the evaluation of the maximum of reactivity they can reach should be provided. The definition of such an approach is structured around two major points: 1- The first one concerns the determination of a set of penalizing conditions for the irradiation and depletion calculations. These conditions should conduct to a conservative fuel inventory, maximizing the reactivity of the irradiated fuel for the considered configuration; 2- The second one focuses on the definition of penalties to apply on the irradiated isotopic concentrations and on the reactivity worth of the isotopes. These penalties derive from the biases and uncertainties issued from the experimental validation of the involved calculation codes. This paper focuses on the first point and so describes the different steps to define a conservative set of irradiation/depletion calculation options to account for the irradiation of fertile assemblies in criticality-safety analyses.
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