Qualification of the APOLLO2.8 code package for the calculation of the fuel inventory and reactivity loss of UOx spent fuels in BWRs

This document describes the neutronics qualification of the APOLLO2.8 code package for the calculation of UOx fuel inventory and reactivity loss with burn-up in Boiling Water Reactors (BWR). In a first part, the study deals with the analyses of spent fuels through the isotopic content of actinides (U, Pu, Np, Am, Cm), fission products used to evaluate the burn-up (Nd, Cs) and the most absorbing fission products (Sm, Eu, Gd). The interpretation performed with the APOLLO2.8 code package shows that the concentrations of the main fissile isotopes - 235U, 239Pu and 241Pu - are predicted at better than 8% on the overall height of the fissile column, with an experimental uncertainty under 5% (1σ). In a second part, reactivity worth measurements of irradiated UOx fuel rod cuts were performed in the MINERVE facility using an oscillation technique. The analysis shows a very good agreement between the calculated and the experimental value of reactivity loss for the three samples, with different void fractions and burn-up. The Calculation - Experiment biases (C/E - 1) are lower than +1.8%, with an uncertainty of 2.8% (1σ). (authors)