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

Hodgkin's disease and birth outcome: a Danish nationwide cohort study

In a Danish nationwide cohort study of 292 births from 1973 to 2002 in women with Hodgkin's disease (HD), we compared birth outcome with 14 042 births from a cohort of mothers without cancer. We found no substantially increased risk of preterm birth, low birth weight at term, or stillbirth and no difference in proportion of male newborns for 192 children of women with HD before pregnancy. The prevalence odds ratio (POR) for congenital abnormalities was 1.7 (95% confidence interval (CI): 0.9–3.1). Among 15 newborns of mothers diagnosed during pregnancy, the POR of preterm birth was 26.6 (95% CI: 8.5–83.0), but five out of the eight preterm deliveries among these women were elective. We found no substantially increased risk of adverse birth outcome among 85 newborns of women diagnosed within 2 years postpartum, though effect estimates were imprecise. The overall findings are reassuring, they cannot exclude the possibility of an increased risk of congenital abnormalities for newborns of women diagnosed with HD before pregnancy

Bench-scale study of the reduction and hydrofluorination reactions in the catalysed fluorox process.

Catalysed reduction of U02F2 by hydrogen and the hydrofluorina-tion of the UO2 produced were investigated in separate and simultaneous reactions. The production of UO2F2 by hydrofluorination of UO3 was also studied. Some catalysed reduction of UO2F2 occurred at temperatures as low as 375ºC. However, with particles of 100 to 300 ym diameter, only 50 per cent conversion was achieved at the catalysed rate for temperatures up to 460ºC. Recombination of the active hydrogen atoms before they penetrated to the core of individual UO2F2 particles prevented the reduction from proceeding further at the catalysed rate. Hydrofluorination of UO2 produced from U02F2 yielded 75 per cent conversion to OFt* at 375 ºC and 50 per cent at 460ºC, the low yields being due to sintering of the UF^ which prevented further reaction. With UO2F2 particles of 100 to 300 Vim diameter, the maximum conversion to UFu in simultaneous reduction and hydrofluorination experiments was 32 per cent at 365ºC over 3 hours. The low yield was due to the size of the U02F2 particles which limited the amount of catalysed reduction, and also to the sintering of UF^. Production of UO2F2 with a low surface area (1.6 m g~ ) was achieved by hydrofluorination between 300 and 400ºC of denitrator U03 which was activated by vapour phase hydration over 10 per cent nitric acid

Investigation of batch-tray calcination-reduction of ammonium diuranate to uranium dioxide.

Process cycles have been developed on the half-kilogram scale for the conversion of ADU to UO2 powder of specified surface area in the range 3-10 m2/g. The recommended cycle involves calcination of ADU in nitrogen during heating to the reduction temperature, followed by reaction with 30 volume per cent hydrogen in nitrogen and stabilisation at ambient temperature with 2 volume per cent oxygen in nitrogen. UO2 surface area increased from 3 to 10 m2/g as the reduction temperature changed from 700 to 500°C, but was not sensitive to the surface area of the precursor ADU or the hydrogen flow rate

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

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