FISSION PRODUCTS CREDIT FOR PWR MOX BURNUP CREDIT IMPLEMENTATION

摘要

Burnup Credit allows considering the reactivity decrease due to fuel irradiation in nuclear criticality safety studies for the nuclear fuel cycle. Its implementation requires to carefully analyze the validity of the assumptions made to define the axial burnup profile, to determine the composition of the irradiated fuel and to perform the criticality simulation. This paper concerns Burnup Credit implementation for PWR MOX fuels and focuses on the determination of a conservative inventory of the fresh fuel for PWR MOX Burnup Credit applications to perform criticality safety studies. A solution, already examined, is to set up a method to determine, for a given ratio of Pu/(U+Pu), a bounding plutonium vector for the fresh fuel that gives, after irradiation, the most reactive composition whatever the irradiation history. The goal of this paper is to explore an alternative solution by taking a credit from fission products absorption for PWR MOX Burnup Credit implementation. For that purpose, the studies presented in this paper concern the evolution of the fission products contribution to the reactivity decrease as a function of the initial composition of MOX fuels selected from a database of more than 600 MOX fuels produced in France.