Summary report on the French burnup credit working group. Knowledge regarding PWR UOX fuel. French Burnup Credit WG

The 'Burnup Credit' Working Group was established in 1997 to examine the various parameters, such as the irradiation conditions, the burnup profile and the nuclides (actinides and fission products), to be taken into consideration in the criticality studies that take credit from burnup. This report offers an overview of the work that has been completed or agreed under this framework. It presents the group findings on the following topics: - the axial distribution of nuclides or the axial burnup profile; - methods for validating the actual burnup and its axial distribution; - the calculation of nuclide concentrations after irradiation; - the calculation methods that will be used to determine the effective multiplication factor for systems containing used fuel assemblies. This document gathers together the work carried out by the French Burnup Credit Working Group; it is not a guide validating a particular method for taking burnup credit into account. All of the findings presented here may serve as a basis in industry for defining a method to take account of burnup credit in criticality studies; any industrial body effectively adopting such a method will also be responsible for defining it, based on its knowledge of the used fuel assemblies and the configuration to be addressed. This document forms a collection of the work completed by the Working Group up to 1 January 2007 but does not necessarily reflect ongoing work in the various institutes. (authors)