Production of uranium hexafluoride by the catalysed fluorox process: pilot plant and supporting bench-scale studies.

The feasibility of producing UF 6 by the catalysed reaction of UF 4 with oxygen (the Fluorox process) was investigated in a 150 mm diameter fluidised bed reactor and in supporting bench-scale experiments. The rate of the Fluorox reaction in batch experiments was increased by an order of magnitude with 1 to 5 per cent catalyst (containing 3 to 4 per cent platinum on alumina). The maximum UF 6 production rate at 650 deg. C was 0.9 kg h -1. However the platinum catalyst was completely poisoned after production of only 1 and 20 kg UF 6 per kg of catalyst when using respectively French and British UF 4. Regeneration of the catalyst was demonstrated to be technically feasible by washing with water or ammonium oxalate solution or treating with hydrogen and hydrogen fluoride at 350-650 deg. C. However since the very fast rate of poisoning would necessitate higher catalyst concentrations and/or frequent regeneration the catalysed Fluorox process in unlikely to be economically competitive with the direct fluorination of UF sub 4

Influence of precipitation conditions on the properties of ammonium diuranate and uranium dioxide powders.

A comprehensive investigation of the factors affecting the properties of ADU precipitates in relation to the properties of the subsequent UO2 powders in pellet fabrication is reported and the importance of precipitation parameters is demonstrated. Variables investigated include continuous single-versus two-stage precipitation, pH, residence time, washing of ADU to remove nitrate, and calcination-reduction conditions. The most important variable was the pH at which precipitation occurred. In particular, this governed the size of agglomerate which determined the settling and filtering characteristics of the ADU slurry. In two-stage precipitation, the ADU properties were determined by the proportion of uranium precipitated at different pH values

Pilot plant development of processes for the production of ammonium diuranate.

Nuclear grade ammonium diuranate (ADU) and UO powders were produced on a pilot plant scale by the continuous single-stage precipitation of ADU with ammonium hydroxide, dewatering with a rotary drum vacuum filter or a solid bowl centrifuge, and batch-tray drying and calcination-reduction to UO powder. Precipitation at 50ºC and pH values in the range 7.2 to 8.0 produced ADU materials which could be converted to UO powder by calcination and reduction at temperatures of 600 to 730ºC, and fabricated into sintered pellets with densities of 10.37 to 10.77 g cm-3. The lower the pH of precipitation the lower was the reduction temperature required to achieve a specified pellet density. Precipitation with ammonium hydroxide at 80ºC and with ammonia gas at 50ºC offered no advantages over precipitation with ammonium hydroxide at 50ºC. The UO2 powders and sintered pellets produced from ADU powders precipitated by the three methods were similar. Precipitation at pH 7.5 and 50ºC is recommended since a reasonably filterable precipitate can be produced reproducibly without a need for stringent control, and considerable flexibility is available in the subsequent production of a sinterable UO2 powder. Dewatering of ADU slurries was carried out more efficiently using a solid bowl centrifuge rather than a rotary drum vacuum filter. Clearer discharge liquids were produced at a higher rate of throughput in the solid bowl centrifuge