Pu extraction

Musikas and co-workers studied extensively the extraction behavior of inorganic acids and U/Pu extraction chemistry with A/,A-dialkyl amides (202-205). Based on the extraction data, they proposed certain dialkyl amides suitable for the reprocessing of irradiated nuclear fuels in nitric acid media. Most of the work reported earlier on amides referred to either aromatic or substituted aliphatic hydrocarbons employed as diluents. However, these diluents are not suitable for commercial-scale reprocessing due to their poor radiation and chemical stability in the presence of nitric acid, as well as their tendency to form a three-phase system. 

The extraction of Pu " from nitric acid by TBP involves the solvate Pu(N03)4-2TBP formed in a reaction stoichiometry analogous to that proposed for Th and shown in equation (167). The variation in with HNO3 concentration is shown in Figure 43 for extraction by 19% TBP/OK. This shows that Pu is more extractable than U or Np but that Pu is substantially less extractable than The thermodynamics of Pu extraction have been investigated ... 

The exhaustive U, Pu extraction step is best achieved in pulsed columns rather than in mixer settlers in order to keep the contact time lower at the very high radiation level. This operation is expected to produce as its main product a HAW raffinate that is virtually free of Pu (and Np, U) a scrub appears therefore superfluous and would dilute only the HAW. In order to attain still a good extraction efficiency within a few stages, A/O phase ratios < 3 should be avoided. This ratio corresponds to a TBP saturation by heavy metals of about 18%. Considerable amounts of Zr are therefore co-extracted, being however present essentially as inactive isotope. Either a complexing or a reductive stripping is advisable in order to keep the aqueous flow small and the acidity sufficiently high to avoid hydrolysis of Zr. 

PUREX U, Pu extraction and partitioning Extension to Np partitioning TBP/kerosene Dileep et al. (2008)... 

Pu extraction by hexone has received the most attention, undoubtedly because of its use in processing. The extraction of Pu(IV) and Pu(VI) as a ftmction of nitric acid concentration and the concentration of various salts has been measured by several groups. 

Stewart compiled a table of extraction data for a large number of ethers, alcohols, ketones, etc, for Pu in the tri-, quadri-and hexavalant oxidation states from ammonium nitrate-nitric acid mixtures. These data are reproduced in their entirety as Tables IV-21, and IV-22, to show the variety of compounds tried and to indicate the types of compounds which are efficient as Pu extractants. In general, the ability of these compounds to extract correlates with the basicity of the oxygen, nitrogen or other functional group. Thus, electronegative substituents invariably decrease the extractibility of Pu (see e. g. diethyl ether vs dichlorodiethyl-ether). 

Composition of aqueous phase before % by Pu extracted equal volume of solvent ... 

TABLE IV-26. Synergistic and Antagonistic Effects in Two Extractant Systems in U and Pu Extractions.38 ... 

Japan has a national plan to introduce fast breeder reactors (FBRs) to utilize Pu extracted from spent fuel of existing light water reactors (LWRs). CRIEPI is supporting this national plan as a utility laboratory, and has proposed several innovative FBR concepts for future deployment. The 4S-LMR is one of the innovative reactor concepts proposed by CRIEPI. 

No Pu extraction from spent nuclear fuel (SNF) while closing the fuel cycle and... 

Pu (86 years) is formed from Np. Pu is separated by selective oxidation and solvent extraction. The metal is formed by reduction of PuF with calcium there are six crystal forms. Pu is used in nuclear weapons and reactors Pu is used as a nuclear power source (e.g. in space exploration). The ionizing radiation of plutonium can be a health hazard if the material is inhaled. 

Kilogram quantities of americium as Am can be obtained by the processing of reactor-produced plutonium. Much of this material contains an appreciable proportion of Pu, which is the parent of Am. Separation of the americium is effected by precipitation, ion exchange, or solvent extraction. 

The distribution of highly extractable solutes such as and Pu between the aqueous and organic phases is strongly dependent upon the nitrate anion concentration in the aqueous phase. This salting effect permits extraction or reextraction (stripping) of the solute by controlling the nitric acid concentration in the aqueous phase. The distribution coefficient, D, of the solute is expressed as... 

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 ... 

Only slightly less accurate ( 0.3—0.5%) and more versatile in scale are other titration techniques. Plutonium maybe oxidized in aqueous solution to PuO " 2 using AgO, and then reduced to Pu" " by a known excess of Fe", which is back-titrated with Ce" ". Pu" " may be titrated complexometricaHy with EDTA and a colorimetric indicator such as Arsenazo(I), even in the presence of a large excess of UO " 2- Solution spectrophotometry (Figs. 4 and 5) can be utilized if the plutonium oxidation state is known or controlled. The spectrophotometric method is very sensitive if a colored complex such as Arsenazo(III) is used. Analytically usehil absorption maxima and molar absorption coefficients ( s) are given in Table 10. Laser photoacoustic spectroscopy has been developed for both elemental analysis and speciation (oxidation state) at concentrations of lO " — 10 M (118). Chemical extraction can also be used to enhance this technique. 

A large number of radiometric techniques have been developed for Pu analysis on tracer, biochemical, and environmental samples (119,120). In general the a-particles of most Pu isotopes are detected by gas-proportional, surface-barrier, or scintillation detectors. When the level of Pu is lower than 10 g/g sample, radiometric techniques must be enhanced by preliminary extraction of the Pu to concentrate the Pu and separate it from other radioisotopes (121,122). Alternatively, fission—fragment track detection can detect Pu at a level of 10 g/g sample or better (123). Chemical concentration of Pu from urine, neutron irradiation in a research reactor, followed by fission track detection, can achieve a sensitivity for Pu of better than 1 mBq/L (4 X 10 g/g sample) (124). 

The first successflil production method for the separation of Pu from U and its fission products was the bismuth phosphate process, based on the carrying of Pu by a precipitate of BiPO (126). That process has been superseded by Hquid-Hquid extraction (qv) and ion exchange (qv). In the Hquid-Hquid... 

The plutonium extracted by the Purex process usually has been in the form of a concentrated nitrate solution or symp, which must be converted to anhydrous PuF [13842-83-6] or PuF, which are charge materials for metal production. The nitrate solution is sufficientiy pure for the processing to be conducted in gloveboxes without P- or y-shielding (130). The Pu is first precipitated as plutonium(IV) peroxide [12412-68-9], plutonium(Ill) oxalate [56609-10-0], plutonium(IV) oxalate [13278-81-4], or plutonium(Ill) fluoride. These precipitates are converted to anhydrous PuF or PuF. The precipitation process used depends on numerous factors, eg, derived purity of product, safety considerations, ease of recovering wastes, and required process equipment. The peroxide precipitation yields the purest product and generally is the preferred route (131). The peroxide precipitate is converted to PuF by HF—O2 gas or to PuF by HF—H2 gas (31,132). 

Then the fuel elements are dissolved in 7m HNO3 to give a solution containing U and Pu which, in the widely used plutonium-uranium-reduction, or Purex process, are extracted into 20% tributyl phosphate (TBP) in kerosene leaving most of the fission products... 

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