MOX fuel in-pile behavior up to 60000 MWd/t

The MOX fuel rods irradiated in the frame of Belgonucleaire's R and D program behaved satisfactorily and at least as well as UO2 rods, up to burn-ups beyond 60000 MWd/t. From the results so far, one may conclude that additional data should be obtained to better predict and understand the fission gas release behavior of the present industrial MOX fuel pellets obtained by the MIMAS (Micronization of a Master blend) process. In particular, more data are needed on: high burn-up behavior of MIMAS fuel (above 40000 MWd/t); understanding of the influence of the fuel microstructure (including the type and characteristics of UO2 powder) on the in-pile (mainly thermal) behavior; MOX fuel chemistry behavior at high burn-up, in relation to cycling, fission gas release and internal cladding corrosion; helium production and release in MOX rods and contribution to the internal pressure. The good understanding of the MOX behavior will not only allow improvements in the models used for its prediction and licensing but also in the fabrication process and the design characteristics. Core data will also be complemented by new basic experiments on representative MOX fuel from a neutronic point of view, needed to improve models and computational aids. 3 figs., 1 tab