Demonstration of industrially-fabricated plutonium disposition MOX

The safe and secure management of civil separated plutonium is a UK government and NDA priority. One potential solution to address this considers the manufacture of a modified version of mixed oxide (MOX) fuel, comprising PuO₂ dispersed within a UO₂ matrix and doped with a suitable neutron absorbing element to maintain criticality control. As an initial step to understand whether an industrially-relevant, proven MOX fuel fabrication process could offer a potential route to the production of a Pu-disposition matrix based on MOX, a series of Gd-doped UO₂ pellets were prepared by Orano at the CDA workshop of the MELOX facility in France. Characterisation was performed to quantify the density, morphology (grain size and porosity), Gd distribution and Gd incorporation mechanism. It was found that the materials produced were highly reproducible and similar in density and morphology, irrespective of the variables investigated, and similar to unirradiated UOX and MOX fuel. Gd was distributed in a similar manner to the distribution of PuO₂ in unirradiated MIMAS (MIcronisation of a MASter Blend) MOX fuel and evidence for the existence of a solid solution between Gd₂O₃ and UO₂ was ascertained, which could be viewed as favourable from a GDF post-closure criticality control perspective. The source of the powder had the greatest effect on the final characteristics of the Pu-disposition MOX pellets, due to sintering reactivity; however, these differences were minor. These results are a promising step towards the full-scale manufacture of ceramics suitable for the immobilisation and disposition of separated PuO₂ in a GDF, should policy dictate.