Microwave based oxidation process for recycling the off-specification (U,Pu)O₂ fuel pellets

This paper reports development of a process named MicroWave Direct Oxidation (MWDO) for recycling the off-specification (U,Pu)O₂ mixed oxide (MOX) fuel pellets generated during fabrication of typical fast reactor fuels. MWDO is a two-stage, single-cycle process based on oxidative pulverisation of pellets using 2450 MHz microwave. The powder sinterability was evaluated by bulk density and BET specific surface area. The oxidised powders were analyzed for phases using XRD and stoichiometry by thermogravimetry. The sinterability was significantly enhanced by carrying out oxidation in higher oxygen partial pressure and by subjecting MOX to multiple micronisation-oxidation cycles. After three cycles, the recycled powder from (U,28%Pu)O₂ resulted surface area >3 m²/g and 100% re-used for MOX fabrication. The flow sheet was developed for maximum utilization of recycled powder describable by a parameter called Scrap Recycling Ratio (SRR). The process demonstrates smaller processing cycle, better powder properties and higher oxidative pulverisation over conventional method. - Highlights: • A process for recycling the off-specification (U,Pu)O₂ sintered fuel pellets of fast reactors was demonstrated. • The method is a two-stage, single cycle process based on oxidative pulverization of MOX pellets using 2450 MHz microwave. • The process demonstrated utilization of recycled powder with SRR of 1.