Post irradiation examination of uranium inclusions in inert matrices.

The inert matrix materials CeO2, MgO, Y2O3, MgAl2O4 and Y3Al5O12 were selec ted as candidates for inert matrices for the EFTTRA(a)-T3 neutron irradiati on experiment. Most targets contain 20% enriched U-235 fissile inclusions w ith an average size of roughly 150 mum. The volume fraction of the fissile phase is either 2.5 vol% UO2 or 19.6 vol% of Y5.78UOx in the inert matrices . The samples were irradiated for 198.9 full power days in the High Flux Re actor 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 Y3Al5O12 and Mg Al2O4 with macro dispersions of UO2; the other targets with a macro dispers ion of UO2 show a volume change of less than + 1 vol%. The fractional relea se of the fission gas Xe is more than 40% for the MgAl2O4 and Y3Al5O12 matr ices with a macro dispersion of UO2, the other targets show a fractional re lease of Xe of less than 15%. Cracks are observed in MgO and MgAl2O4 target s which is possibly related to the stress caused by swelling of the UO2 inc lusions. (C) 2001 Published by Elsevier Science Ltd. All rights reserved.