Thermal denitration

The complete chemistry of plutonium 1 iquid-to-solid conversion processes, especially peroxide and oxalate precipitation, should be further studied. Research and development of direct thermal denitration methods should also be pursued. 

Precipitation Processes. Plutonium peroxide precipitation is used at Rocky Flats to convert the purified plutonium nitrate solution to a solid (14) the plutonium peroxide is then calcined to Pu02 and sent to the reduction step. The chemistry of the plutonium peroxide precipitation process is being studied, as well as alternative precipitation processes such as oxalate, carbonate, fluoride, and thermal denitration. The latter method shows the most promise for cost and waste reduction. 

In the production of uranium(lV) oxide in the wet process, the uranium concentrate is first converted into a uranyl nitrate solution with nitric acid. After the purification of the uranyl nitrate by solvent extraction, it can be converted into uranium(IV) oxide by two different routes either by thermal denitration to uranium(VI) oxide which is then reduced to uranium(IV) oxide or by conversion of uranyl nitrate into ammonium diuranate which is reduced to uranium(IV) oxide. Purification proceeds by extraction of the uranyl nitrate hydrate from the acidic solution with tri-n-butylphosphate in kerosene and stripping this organic phase with water, whereupon uranium goes into the aqueous phase. 

A batch of UO -Tc O calcine was prepared in the laboratory by adding ammonium pertechnetate (NH TcO ) to UNH which was then thermally denitrated at 350°C. Alumina was subsequently added to form a granular product. 

A. G. Fane, B. G. Charlton and P. G. Alfredson, The Thermal Denitration of Uranyl Nitrate in a Fluidized-bed Reactor, Australian Atomic Energy Commission Establishment Lucas Heights. 

Uranium Finishing. In both the THORP and Magnox plants, the uranyl nitrate stream is converted to uranium trioxide powder through concentration by evaporation and thermal denitration. The material is then stored prior to further processing into new uranium oxide or mixed oxide fuel ... 

The uranium product solution, after evaporation, is suitable for precipitation of ammonium di-uranate and conversion to uranium oxide. The major proportion at the present time is evaporated to uranyl nitrate and converted to oxide by thermal denitration, and then to fiuoride, using a fluidization process. 

Fluidized bed processes have been devised which convert uranyl nitrate solution to uranium trioxide, by thermal denitration, reduce to the dioxide with hydrogen and finally hydrofluorinate to uranium tetrafluoride. Three separate fluidization systems are needed, with solids transfer throughout. In addition, nitric acid can be recovered from the denitration process and the excess of hydrogen fluoride can be recovered from the hydrofluorina-tion process. 

The UO3 product from a fluid bed thermal denitration process tends to be less reactive than that produced by ammonium di-uranate precipitation and calcination. It can be considerably improved by the addition of a little sulphuric acid to the feed solution, corresponding to about 0-1 per cent of the uranium content.23 The product is then very suitable for the subsequent hydrogen reduction and hydrofluorination stages. 

The cheapest type of nitrate-to-oxide conversion process, based upon thermal denitration, has been shown in Fig. 9.3. This can be carried out in a simple batch type of pot denitrator or in more elegant continuous plant for larger scale production. If a little iron impurity is introduced, the molten salt electrolysis stage which follows allows an opportunity for purification again before the metal powder is produced. 

M. G. MENDEL and D. C. BONFER, Determination of the ReacUon Path During Thermal Denitration of Uranyl Nitrate and Plant Equipment, Summary Technical Report for foe period October 1, 1968 to December 31, 1968, NLCO-1035, n>. 1.1-1.2, National Lead Company of Ohio (January 1969). 

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