Burnup credit for BWR UOX used fuels: criticality-safety sensitivity studies for reprocessing - 14609

Actinides Only Burnup Credit (BUC) has been successfully used for years for PWR UOX fuels at AREVA La Hague reprocessing plant. For BWR UOX fuel assemblies, the application of the methodology developed for PWR fuel is not straightforward. Indeed, BWR UOX fuel assemblies have specific and various design characteristics and progress can be made on our understanding of the impact of such characteristics on the rotary dissolver k_eff value, taking into account various irradiation conditions. Moreover, the void fraction introduces a new variable, compared to PWR fuels. The purpose of this paper is to present, for a reference BWR UOX fuel assembly, the impact of design characteristics and irradiation conditions on the rotary dissolver k-effective. The impacts of each parameter are studied in an uncorrelated way and are defined according to burnup and void fraction. The design characteristics and irradiation conditions of the Fukushima-Daini benchmark are taken into account as reference values for all these parameters. A range of values is defined for each of these parameters in order to consider a large variety of design characteristics and irradiation conditions Depletion, with APOLLO2-A code, and criticality, with CRISTAL V1.2 package, calculations are successively performed to define impact of each parameter on dissolver reactivity. Then a ranking of these parameters according to their impact on the dissolver's reactivity is done. This ranking could be useful in a general BWR UOX burnup credit approach to cover a collection of BWR UOX fuel assemblies by a penalizing fuel assembly defined with a particular set of parameters. (authors)