Continuous Conversion of Uranium/Plutonium Nitrates to Oxides

A continuous fluidized-bed process for the conversion of uranium/plutonium nitrates to oxides is under development to facilitate the recycle of plutonium in the nuclear fuel cycle. The basic process consists of two steps, each performed in a separate fluid-bed reactor: (a) codenitration at 375°C of uranyl nitrate-plutonium nitrate solutions to a UO₃-PuO₂ powder form, and (b) reduction of the UO₃-PuO₂ with hydrogen at 600°C to form UO₂-PuO₂. Pilot-plant denitration studies with uranyl nitrate-plutonium nitrate solutions containing uranium/plutonium ratios of 50 and 4, and plutonium nitrate solution alone are described, as well as reduction of UO₃-PuO₂ powder. Examination of the UO₃-PuO₂ denitration product by autoradiographic and electron microprobe techniques showed that the PuO₂ was distributed in the UO₃ matrix with a high degree of homogeneity. The conversion process appears to be applicable over the entire range of uranium-plutonium concentrations and for plutonium nitrate alone. The suitability of this product for the fabrication of fuel pellets is being studied in cooperation with nuclear fuel manufacturers.