Post irradiation examination of uranium inclusions in inert matrices

Abstract The inert matrix materials CeO 2 , MgO, Y 2 O 3 , MgAl 2 O 4 and Y 3 Al 5 O 12 were selected as candidates for inert matrices for the EFTTRA 2 -T3 neutron irradiation experiment. Most targets contain 20% enriched 235 U fissile inclusions with an average size of roughly 150 μm. The volume fraction of the fissile phase is either 2.5 vol% UO 2 or 19.6 vol% of Y 5.78 UO x in the inert matrices. The samples were irradiated for 198.9 full power days in the High Flux Reactor in Petten. The calculated burn-up is between 17.3 and 19.5% FIMA. The temperature of the cladding was kept at 600 ± 25 K. A dimensional change of at least +5 % is measured after neutron irradiation for Y 3 Al 5 O 12 and MgAl 2 O 4 with macro dispersions of UO 2 ; the other targets with a macro dispersion of UO 2 show a volume change of less than + 1 vol%. The fractional release of the fission gas Xe is more than 40% for the MgAl 2 O 4 and Y 3 Al 5 O 12 matrices with a macro dispersion of UO 2 , the other targets show a fractional release of Xe of less than 15%. Cracks are observed in MgO and MgAl 2 O 4 targets which is possibly related to the stress caused by swelling of the UO 2 inclusions.