Extensive characterisation of a material for understanding its behaviour as a nuclear fuel: the case of a zirconia-plutonia inert-matrix fuel

Recent developments of an inert-matrix fuel (IMF) have led to the selection of yttria-stabilised zirconia (YSZ) doped with erbia and plutonia at PSI, Switzerland. This IMF is foreseen to utilize plutonium in LWRs and to destroy it in a more effective manner than MOX. After utilisation in LWR, the plutonium isotopic vector in the spent IMF foreseen for direct disposal will be devaluated far beyond the standard spent fuel. The physical properties of the material depend on the choice of stabilizer as well as on other dopants, e.g. burnable poison or fissile material. As a result of an iterative study, a (Er,Y,Pu,Zr)O2 solid solution with a defined fraction of fissile and burnable poison was selected. Among others this material has been fabricated for irradiation experiments in the Petten High Flux Reactor, and in the Halden Reactor. For the material qualification, relevant fuel properties were considered. Among them, the material lattice parameter, fuel and component densities, micro/nano structural studies, thermal conductivity, stability under irradiation, efficient retention of fission products and solubility are key properties for the fuel in reactor as well as for the geologic disposal of the spent fuel. (author)