Development of a homogenous disposal MOX powder for plutonium immobilisation

Abstract Disposal MOX (dMOX), a sintered mixed U, Pu, oxide containing a neutron poison, such as Gd, is currently under consideration for immobilisation of the UK’s civil plutonium inventory. Prior to deployment, it is important to understand how material homogeneity impacts overall behavior of the wasteform. Therefore, while using Ce as a non-active Pu surrogate, this study outlines a methodology for the production of a homogenous dMOX precursor powder to be subsequently sintered to a homogenous dMOX pellet. The powder was produced via reverse-strike oxalate co-precipitation of a Ce(III), Gd(III), and photochemically conditioned U(IV) precursor solution, which was then calcined to a mixed oxide in a 5%H 2 /95% N 2 reaction atmosphere. SEM–EDX and PXRD analysis revealed the oxalate and mixed oxide to be fully homogeneous, with no evidence of segregated phases. TGA decomposition found the oxalate to decompose in several distinct stages, agreeing with established literature, resulting in a fully homogenous mixed oxide powder. Graphical abstract