Uranium purification

Uranium Purification. Subsequent uranium cycles provide additional separation from residual plutonium and fission products, particularly zirconium— niobium and mthenium (30). This is accompHshed by repeating the extraction/stripping cycle. Decontamination factors greater than 10 at losses of less than 0.1 wt % are routinely attainable. However, mthenium can exist in several valence states simultaneously and can form several nitrosyl—nitrate complexes, some for which are extracted readily by TBP. Under certain conditions, the nitrates of zirconium and niobium form soluble compounds or hydrous coUoids that compHcate the Hquid—Hquid extraction. SiUca-gel adsorption or one of the similar Hquid—soHd techniques may also be used to further purify the product streams. 

Vanadate, dioxybis(oxamato)-bond-length ratios, 1,57 Vanadate, heptacyano-potassium salt structure, I, 72 Vanadate, hexafluoro-dipotassium salt history, I, 21 potassium salt history, 1,21 tripotassium salt history, 1,21 Vanadate, pentachloro-stereochemistry, 1,40 Vanadate, pentafluorooxy-stereochemistry, I, 50 Vanadates biochemistry, 3,456 calcium/magnesium ATPase inhibition, 6, 567 competition with phosphates physiology, 6,665 protonation, 3,1026 sodium pump, 6, 557 in uranium purification from ore, 6, 899 Vanadates, hexafluoro-, 3. 482,531 Vanadates, oxoperoxo-, 3,501 Vanadates, pentacarbonyl-, 3, 457 Vanadium biology, 6,665 determination, 1. 548 extraction... 

Figure 5.33 Uranium purification process by tributyl phosphate (TBP).

Allow most of the neptunium to coextract with U(VI) as Np(IV) or Np(VI) and separate it in downstream uranium purification cycles... 

Table 12.10 Performance of Two-Stage Thorex Process and a Uranium Purification Cycle...

Figure 13 Outline flowsheets for uranium purification using the DPPA, DAPEX or AMEX processes51...

Nitric acid is used to digest crude uranium concentrates (UjOg, yellowcake) in some uranium purification processes. About 1,000 tonnes of nitric acid may be used to process yellowcake in the United States. 

In two further extractive uranium purification cycles, each consisting of extraction and stripping, the uranium solution is further purified to remove residual plutonium, neptunium and technetium. 

No definite reason for these fluctuations could be identified, but it is known that neptunium, due to its complicated redox chemistry, reacts in a very sensitive way to even minor process variations (7,8). Based on these results the proposal was made (J5) to recover the "co-extracted" portion of the neptunium by running the second plutonium and uranium purification cycles under conditions where the Np is directed into the aqueous raffinates (2AW and 2DW streams). In the Pu purification cycle, this can be done by adding sufficient nitrous acid to keep the Np pentavalent, while in the U purification cycle (which is run under slightly reducing conditions) a low acidity and a high loading help to reject Np into the aqueous 2DW stream. The two raffinate streams are combined in WAK in the 3W evaporator, and the Np is thus collected in the concentrate from this unit (3WW stream). Consequently the proposal was made to recover the Np from this 3WW stream by use of the well-known anion exchange process (9,J ). 

Concentrates are shipped from the uranium mill to a uranium refinery or conversion plant. Here chemical impurities are removed and the purified uranium is converted into the chemical form needed for the next step in the fuel cycle. Figure 1.14 shows concentrates being converted into uranium hexafluoride (UF ), the form used as process gas in the gaseous diffusion process for enriching U. Other possible products of a uranium refinery used in other fuel cycles are uranium metal, uranium dioxide, or uranium carbide. Uranium purification and conversion processes are also described in Chap. 5. 

The great improvement in performance of pulse columns over other column-type contactors, and the simple and reliable equipment involved, have led to the widespread use of pulse columns in many solvent extraction operations separating and purifying nuclear materials. In addition to their use in some fuel reprocessing operations, as mentioned above, pulse columns have been used in uranium purification plants at Femald, Ohio [Cl], and Gore, Oklahoma (cf. Chap. 5). 

Tributyl phosphate (C4H,)3P04 Uranium purification and irradiated fuel Purex... 

A well-designed Purex plant aims for as complete recycle of solvent as possible, to minimize costs of solvent makeup and disposal. Solvent from the uranium purification section usually contains so few contaminants or degradation products that it can be reused a number of times without cleanup. On the other hand, solvent that has processed solutions containing hi activity of fission products and plutonium carries traces of these contaminants, uranium, nitric acid, dibutyl phosphate, and other radiolytic degradation products of TBP and dodecane. Uranium and plutonium should be recovered because of their value. Fission products should be removed to prevent product contamination in later cycles. Dibutyl phosphate should be removed because it forms strong complexes with tetravalent zirconium and plutonium that would impair ability of the solvent to reject zirconium and separate plutonium from uranium. 

Uranium purification. Uranium is purified by a second solvent extraction cycle and by silica gel adsorption. To this end, the uranium-bearing aqueous stream 14, ICU, leaving the 1C column is concentrated by evaporation, reacidified, and passed through the 2D column. There uranium is extracted by 30 v/o TBP in solvent 2DX, stream 18. Extract 2DU, stream 21, leaving this column is scrubbed with dilute nitric acid 2DS, stream 19, containing hydroxylamine and hydrazine. The scrub stream is intended to free the uranium of traces of plutonium and fission products, which leave column 2D in the aqueous raffinate 2DW, stream 20. 

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