Post-irradiation characterization of zirconia- and spinel-based inert matrix fuels - the OTTO experiment (abstract and presentation slides)

The OTTO experiment is a joint project between JAERI, PSI and NRG, initiated to study the incineration of plutonium by means of non-reprocess able inert matrix fuels (once-through mode). The sample set comprises i) spinel-based targets with micro-dispersed (d<25 micrometer) and macro-dispersed (d-250 micrometer) Pu-bearing zirconia microspheres and ii) zirconia-based solid solutions. Irradiation was performed in the High Flux Reactor (HFR) in Petten for 548 full power days, and was completed in December 2002. Gamma spectrometry and tomography reveal the effect of the temperature during irradiation on the spatial distribution of the fission products. Fission gas releases appear to be very low for the micro-dispersed targets; the other targets show significantly higher values, 5-10%. On the other hand the micro-dispersed target shows unacceptable swelling. The macro-dispersed targets do not exhibit swelling; the fission product damage is confined within the fissile phase. Shrinkage of the zirconia-based fissile inclusions has been observed in both types of the spinel-based targets, concurrent with increased porosity and increased Xe-concentration around fissile inclusions. Shrinkage of the zirconia-based solid solution targets has resulted in severe cracking, but their overall behaviour compares to that of UO2. (Author)