Plutonium purification

Chemical Separation. A reprocessing facility typically utilizes multiple extraction/reextraction (stripping) cycles for the recovery and purification of uranium and plutonium. For example, a co-decontamination and partitioning cycle is followed by one or more cycles of uranium and plutonium purification. The basic process is illustrated in Figure 3. 

Historically, ferrous sulfamate, Fe(NH2S02)2, was added to the HNO scmbbing solution in sufficient excess to ensure the destmction of nitrite ions and the resulting reduction of the Pu to the less extractable Pu . However, the sulfate ion is undesirable because sulfate complexes with the plutonium to compHcate the subsequent plutonium purification step, adds to corrosion problems, and as SO2 is an off-gas pollutant during any subsequent high temperature waste solidification operations. The associated ferric ion contributes significantly to the solidified waste volume. 

Plutonium Purification. The aqueous feed for the second plutonium cycle is typically prepared by adding HNO and an excess of sodium nitrite, NaN02, to destroy the excess reductant and oxidize the Pu to the more extractable Pu . An alternative approach which reduces the amount of salt in the Hquid waste involves absorbing nitrogen tetroxide, N2O4, as a substitute for the NaN02 ... 

Plutonium Purification Using Solvent Extraction. The Hanford Plutonium Reclamation Facility (PRF) uses a 20 percent TBP-CClt, solution to extract Pu(IV) from HNO3-HF-AI(NO3)3 solutions of dissolved scrap. The final product solution from the... 

Pyroredox. This is a three-step plutonium purification process ( 3). Impure plutonium metal is reacted with ZnCl2 in a solvent salt of KC1-CaCl 2 > as follows ... 

Pyroredox is currently under development. Several problems have been identified and work is underway to overcome these obstacles. As mentioned previously, this process has immediate application as a primary plutonium purification process and as a means to process spent electrorefining anodes for direct recycle back to electrorefining. 

A decrease in the number of uranium and plutonium purification cycles from three to two, or even one, would be highly advantageous. First-cycle decontamination factors of uranium from neptunium and from the fission products ruthenium and zirconium must be significantly improved to realize such a decrease. 

An alternative method of plutonium purification by solvent extraction is given in Experiment 16. In that experiment, the counting source is prepared by co-precipitation with sub-milligram amounts of lanthanum fluoride. 

The following is a the description of plutonium purification by anion-exchange separation. 

Plutonium Purification. The same purification approach is used for plutonium separated from sediments or seawater. In case reduction may have occurred, the plutonium is oxidized to the quadrivalent state with either hydrogen peroxide or sodium nitrite and adsorbed on an anion exchange resin from 8M nitric acid as the nitrate complex. Americium, curium, transcurium elements, and lanthanides pass through this column unadsorbed and are collected for subsequent radiochemical purification. Thorium is also adsorbed on this column and is eluted with 12M hydrochloric acid. Plutonium is then eluted from the column with 12M hydrochloric acid containing ammonium iodide to reduce plutonium to the non-adsorbed tervalent state. For seawater samples, adequate cleanup from natural-series isotopes is obtained with this single column step so the plutonium fraction is electroplated on a stainless steel plate and stored for a-spectrometry measurement. Further purification, especially from thorium, is usually needed for sediment samples. Two additional column cycles of this type using fresh resin are usually required to reduce the thorium content of the separated plutonium fraction to insignificant levels. 

In two extractive plutonium purification cycles plutonium is separated from small quantities of coextracted fission products. The plutonium(III) is oxidized with nitrogen(IV) oxide to plutonium(IV), which is extracted with tributylphosphate. This oxidation can also take place anodically. 

Knighton, J. B. Johnson, I. Steunenberg, R. K., "Uranium and Plutonium Purification hy the Salt Transport Method," in "Symposium on Reprocessing of Nuclear Fuels, The Metallurgical Society of AIME, Ames, IA, August 1979," Nucl. Metallurgy,... 

While a low HNO3 concentration is possible in plutonium purification cycles, a higher HN03 concentration is necessary to retain the uranium in the organic phase during the primary U-Pu partitioning. Plant-scale experience was obtained at Hanford with HAN in the second Pu and U cycles (3), and at Savannah River in the primary partitioning cycle, where HAN was particularly effective when used with Fe(N03)2, as well as in the second plutonium cycle ( 6, 9) ... 

In order to evaluate the plutonium purification process with TBP, a calculation code has been developed for the system composed of TBP, nitric acid and plutonium on the basis of a batchwise counter-current extraction cascade (28). The code computes not only number of theoretical stages required, but also concentration profile for steady or transient state. The profiles of calculated... 

Plutonium purification proceeds by reducing the aqueous phase pH that oxidizes the plutonium to Pu" +, which then extracts into the TBP phase. Impurities stay in the aqueous phase. The TBP phase strip-ping/extraction cycle is repeated to complete the plutonium purification. The uranium is purified using the same TBP/nitric acid extraction/stripping cycle. Careful control of the each element s oxidation state in the extraction cascade produces the plant-scale separations of uranium from plutonium of 10 . Fission product decontamination factor was 10. The plutonium and uranium recovery is about 99.9% with 95% of the nitric acid values and 99.7 /o of the organic solvent recycled. ... 

The nitric acid evaporated from the high-level waste concentrator is too dilute and contains too much entrained radioactivity to be recycled without additional treatment. This acid, together with dilute acid waste streams from the uranium and plutonium purification solvent extraction systems, is decontaminated in the nitric acid evaporator. Entrainment can be suppressed by providing partial reflux through a few bubble-plate or perforated-plate trays, backed up by wire-mesh mist eliminators. 

Solvent recovery. To prevent cross-contamination of products and to allow for the greater degradation of solvent by high concentrations of fission products and plutonium, two independent solvent recovery systems are provided. Solvent recovery system 1 processes solvent ICW, stream 13, which has been used in the high-activity codecontamination, partitioning, and plutonium purification cycles. System 2 processes the low-activity solvent 2EW, stream 23, which has been used only for final uranium decontamination. Solvent in both systems is processed before recycle by a sodium carbonate wash, filtration and a nitric acid wash. System 1 also uses a second sodium carbonate wash. 

The principal causes of radiolysis in a Purex plant are beta and gamma radiation in the first extracting unit (HA) and alpha radiation from plutonium in the plutonium purification units. Accurate calculation of radiation absorption by solvent is difficult, because it depends on details of the dispersion of aqueous and organic phases and contactor geometry. Blake [Bll] has given equations for estimating solvent radiation absorption when these details are known. 

The PRF also recovers Am from the raffinate of the TBP-solvent extraction plutonium-purification process. The process employs 30 v/o dibutyl butylphosphonate in CCI4 as the solvent to extract both americium and residual plutonium from the high-nitrate feed solution, adjusted to about pH 1 by the addition of NaOH. Americium is selectively stripped from the solvent and purified by a cation-exchange procedure. 

The plutonium purification may be achieved by additional TBP extraction cycles. U(IV) cannot be used as reductant in this part of the process. The final uranium and plutonium products are nitrate solutions whose conversion to oxides, fluorides, etc., have been described earlier ( 5.5.3). 

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