Plutonium uranium extraction

The solvent extraction process that uses TBP solutions to recover plutonium and uranium from irradiated nuclear fuels is called Purex (plutonium uranium extraction). The Purex process provides recovery of more than 99% of both uranium and plutonium with excellent decontamination of both elements from fission products. The Purex process is used worldwide to reprocess spent reactor fuel. During the last several decades, many variations of the Purex process have been developed and demonstrated on a plant scale. 

The centrifugal contactor was first used to reprocess spent nuclear fuel at the SRS in 1966 (Webster et al., 1969). For almost 40 years, this 18-stage 25-cm SRL contactor was used for the extraction and scrub sections (the A-bank) of the PUREX (plutonium-uranium extraction) process at the SRS. Contactor operation stopped when the facility in which they were housed was shut down in 2003. This 18-stage contactor replaced a 24-stage mixer-settler. Mixer-settlers continued to be used for the rest of the processing, as most of the radiation was removed in the A-bank. The ability to... 

The reprocessing involves separating the fission products from the actinides, and then separating the plntoninm from the uranium. The best known procedure of this type is the PUREX (Plutonium, URanium Extraction) process that is used for recovery of uranium and plutonium from irradiated fuel (see details in Chapter 2). The separated plutonium can be used for the production of nuclear weapons or converted into the oxide form, mixed with nraninm oxide and can be used as MOX nuclear fuel. 

As mentioned in Chapter 1, the PUREX (Plutonium, URanium Extraction) process is most widely used for recovery of uranium and plutonium from irradiated fuel. A schematic of a generic PUREX process is shown in Figure 2.11. 

Temporary storage was originally planned for no more than 3 years, until the fuel could be processed at the Plutonium-Uranium Extraction (PUREX) Plant. 

The centerpiece of spent fuel reprocessing is the Purex process (Plutonium-Uranium-Extraction). The solvent is tributyl phosphate in a hydrocarbon diluent, and the process was first used at the Ames Laboratory for uranium purification, then at Oak Ridge National Laboratory for spent fuel. Although other processes were used in earlier days, the Purex... 

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... 

Martella, L. L. Navratil, J. D. "Recovery of Uranium from Mixed Plutonium-Uranium Residues by an Extraction Chromatography Process," U.S. DOE Rept. RFP-3289, Rockwell International, Golden, Colorado, May 15,1982. 

The effect of irradiation on the extractability of sulfoxides towards plutonium, uranium and some fission products were studied by Subramanian and coworkers . They studied mainly the effect of irradiation on dihexyl sulfoxide (DHSO) and found that irradiation did not change the distribution coefficient for Ru, Eu and Ce but increases the distribution coefficient for Zr and Pu. When comparing DHSO and tributyl phosphate (TBP), the usual solvent for the recovery and purification of plutonium and uranium from spent nuclear fuels, the effect of irradiation to deteriorate the extraction capability is much larger in TBP. Lan and coworkers studied diphenyl sulfoxides as protectors for the gamma radiolysis of TBP. It was found that diphenyl sulfoxide can accept energy from two different kinds of excited TBP and thus inhibits the decomposition of the latter. 

The Purex process, ie, plutonium uranium reduction extraction, employs an organic phase consisting of 30 wt % TBP dissolved in a kerosene-type diluent. Purification and separation of U and Pu is achieved because of the extractability of U02+2 and Pu(IV) nitrates by TBP and the relative inextractability of Pu(III) and most fission product nitrates. Plutonium nitrate and U02(N03)2 are extracted into the organic phase by the formation of compounds, eg, Pu(N03)4 -2TBP. The plutonium is reduced to Pu(III) by treatment with ferrous sulfamate, hydrazine, or hydroxylamine and is transferred to the aqueous phase U remains in the organic phase. Further purification is achieved by oxidation of Pu(III) to Pu(IV) and re-extraction with TBP. The plutonium is transferred to an aqueous product. Plutonium recovery from the Purex process is ca 99.9 wt % (128). Decontamination factors are 106 — 10s (97,126,129). A flow sheet of the Purex process is shown in Figure 7. 

Many variants of the Purex (Plutonium Uranium Reduction Extraction) process23S based on TBP extraction have been developed but a basic outline flowsheet is illustrated in Figure 38. This shows the so-called early split flowsheet most commonly used in existing plants. It involves the separation of the uranium and plutonium using two different back-extractant streams during the first solvent extraction cycle. Additional solvent extraction cycles are then carried out independently on the uranium and plutonium streams to effect further purification. An alternative arrangement is the iate split flowsheet used at the Cap La Hague plant in France, and the... 

In the second-generation reprocessing, the applied separation technology has been the PUREX process, an acronym of Plutonium Uranium Reduction Extraction (4) based on a liquid-liquid extraction with tri-n-butyl phosphate (TBP) in //-paraffin diluent, which selectively recovers Pu and U on an industrial scale. 

Co-extraction of Np and Pu The waste from the uranium extraction battery is adjusted to 5 M LiNO and then passed through an IRA-400 column at a high flow rate (30 L/h). The americium is not sorbed. Neptunium and plutonium are stripped by a dilute nitric acid solution and precipitated as a hydroxide, and calcined to yield mixture of oxides. 

Bruns, L. E. "Plutonium - Uranium Partitioning by a Reflux Extraction Flowsheet," in "Proceedings, ISEC 71," Society of Chemical Industry, London, 1971, Vol. 1, p. 186. 

Solvent extraction to separate the plutonium, uranium, and fission products... 

The control of the actinide metal ion valence state plays a pivotal role in the separation and purification of uranium and plutonium during the processing of spent nuclear fuel. Most commercial plants use the plutonium-uranium reduction extraction process (PUREX) [58], wherein spent fuel rods are initially dissolved in nitric acid. The dissolved U and Pu are subsequently extracted from the nitric solution into a non-aqueous phase of tributyl phosphate (TBP) dissolved in an inert hydrocarbon diluent such as dodecane or odourless kerosene (OK). The organic phase is then subjected to solvent extraction techniques to partition the U from the Pu, the extractability of the ions into the TBP/OK phase being strongly dependent upon the valence state of the actinide in question. 

The mixture is extracted with a counter-current of a solution of TBP in kerosene. Uranium and plutonium are extracted into kerosene as the complexes [U02(N03)2(tbp)2] and [Pu(N03)4(tbp)2], but the other nitrates, of metals such as the lanthanides and actinides beyond Pu, as well as fission products, do not form strong complexes with TBP and stay in the aqueous layer. 

---