JEFF3.1.1 validation of the fuel inventory calculation for high burn-up PWR fuel (up to 85 GWd/t) with the ALIX experiment

The ALIX programme relies on experimental analyses of 4 fuel samples irradiated between 5 and 7 cycles in the French Gravelines-5 reactor. These analyses are dedicated to the inventory of actinides (U, Pu, Np, Am, Cm) and fission products indicative of burn-up (Nd, Cs). This programme provides unique experimental data for a fuel sample with a burn-up reaching 85 GWd/t: the burn-up of French spent fuel samples never exceeds 70 GWd/t up to now. The fuel inventory of each fuel sample in the ALIX programme is interpreted by assembly calculations with the APOLLO2/REL2005/CEA2005v4 package. The depletion calculation route consists in a two-level approach, based on the 281 energy group SHEM mesh for the first level calculation with the Pij multicell model, and on cross sections collapsed into 26 energy groups in the second level calculation with the Method Of Characteristics for a 2D-exact heterogeneous geometry of the assembly. An accurate modeling of the irradiation history is used in the APOLLO2 calculations, in terms of power level, inter-cycle shut-downs, and modification of operation parameters during irradiation cycles. This refined core follow-up is required for a satisfactory prediction of the 239Pu / 241Pu consumption, and Am - Cm inventories. The comparison between Experiment and Calculation shows satisfactory results with a distinct improvement of the results thanks to the JEFF3.1.1 library (with regard to JEF2.2) for 236U, 238Pu, 242Pu and the americium concentrations. The 239Pu concentration is always predicted within 4% target) accuracy. (authors)