Plutonium processing solvent

The wastes from uranium and plutonium processing of the reactor fuel usually contain the neptunium. Precipitation, solvent extraction, ion exchange, and volatihty procedures (see Diffusion separation methods) can be used to isolate and purify the neptunium. 

Waste Handling for Unirradiated Plutonium Processing. Higher capacity, better-performing, and more radiation-resistant separation materials such as new ion exchange resins(21) and solvent extractants, similar to dihexyl-N,N-di ethyl carbamoyl methylphosphonate,(22) are needed to selectively recover actinides from acidic wastes. The application of membranes and other new techniques should be explored. 

An overview is presented of plutonium process chemistry at Rocky Flats and of research in progress to improve plutonium processing operations or to develop new processes. Both pyrochemical and aqueous methods are used to process plutonium metal scrap, oxide, and other residues. The pyrochemical processes currently in production include electrorefining, fluorination, hydriding, molten salt extraction, calcination, and reduction operations. Aqueous processing and waste treatment methods involve nitric acid dissolution, ion exchange, solvent extraction, and precipitation techniques. 

Degraded TBP process solvent is typically cleaned by washing with sodium carbonate or sodium hydroxide solutions, or both. Such washes eliminate retained uranium and plutonium as well as HDBP and H2MBP. Part of the low-molecular-weight neutral molecules such as butanol and nitrobutane, entrained in the aqueous phase, and 90-95% of the fission products ruthenium and zirconium are also removed by the alkaline washes. Alkaline washing is not sufficient, however, to completely restore the interfacial properties of the TBP solvent, because some surfactants still remain in the organic phase. 

In April of 1955, a facility utilizing the Recuplex solvent extraction process(2j was installed in the 234-5Z Building at Hanford. This facility provided the capability of recovering plutonium from unirradiated plutonium scrap from Hanford plutonium processing operations. By 1960, the Recuplex facility was inadequate with respect to contemplated production loads, shielding requirements, and criticality prevention safety. A project was authorized in March 1961 to provide a new facility for the adequate reclamation of plutonium from both wet and dry plutonium scrap generated from both on and offsite operations. This facility, the 236-Z Building, was completed in June 1964 and is referred to as the PRF. Details on the new plant were first published in 1967.(2)... 

Fluoride is known to separate zirconium fission product and plutonium from solvent degradation products. (5) Since fluoride is used to speed dissolution of thoria in nitric acid, and is already present in thorium solvent extraction process feed solutions, it was the first choice as an agent to use to improve thorium-DPB separation. 

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 plutonium usually contains isotopes of higher mass number (Fig. 1). A variety of industrial-scale processes have been devised for the recovery and purification of plutonium. These can be divided, in general, into the categories of precipitation, solvent extraction, and ion exchange. 

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. 

These variations permit the separation of other components, if desired. Additional data on uranium, plutonium, and nitric acid distribution coefficients as a function of TBP concentration, solvent saturation, and salting strength are available (24,25). Algorithms have also been developed for the prediction of fission product distributions in the PUREX process (23). 

In addition to fuel and targets(15J6) from SRP reactors, SRP also reprocesses a wide variety of fuels from offsite research reactors and a wide range of unirradiated plutonium scrap materials.(17) Following customary Savannah River practice, initial processing of each offsite material is designed to transform the actinides to a solution that is compatible with one of the solvent extraction cycles in either of the separations areas. A major advantage of this practice is that the... 

We are not aware of any previous studies of the removal of plutonium or americium from (NH )2ZrF6-NHltF-NH N03 solutions. For ready plant-scale application, precipitation, sorption on inorganic materials, or batch solvent extraction processes may all be satisfactory. An inexpensive inorganic material with great selectivity and capacity for sorbing actinides, and with suitable hydraulic properties, would be especially attractive. 

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 ... 

Solvent Extraction. A modified, one-cycle PUREX process is used at Rocky Flats to recover plutonium from miscellaneous Pu-U residues (11). The process utilizes the extraction of uranium (VI) into tributyl phosphate (TBP), leaving plutonium (III) in the raffinate. The plutonium is then sent to ion exchange for... 

Commercial-scale application of solvents coming under the category of neutral reagents is largely found as applied to the nuclear industry materials, as in example, for the separation and refining of uranium, plutonium, thorium, zirconium, and niobium. A process flowsheet for extracting niobium and tantalum from various resources is shown in Figure 5.23. It will... 

Purex [Plutonium and uranium recovery by extraction] A process for the solvent extraction of plutonium from solutions of uranium and fission products, obtained by dissolving spent nuclear fuel elements in nitric acid. The solvent is tri-n-butyl phosphate (TBP) in... 

Redox [Reduction oxidation] A process for separating the components of used nuclear fuel by solvent extraction. It was the first process to be used and was brought into operation at Hanford, United States, in 1951, but was superseded in 1954 by the Purex process. The key to the process was the alternate reduction and oxidation of the plutonium, hence the name. The solvent was Hexone (4-methyl-2-pentanone, methyl isobutyl ketone), so the process was also known as the Hexone process. The aqueous phase contained a high... 

Tramex [Transuranic metal (or amine) extraction] A process for separating transuranic elements from fission products by solvent extraction from chloride solutions into a tertiary amine solution. Developed at Oak Ridge National Laboratory, TN, for processing irradiated plutonium. 

In some countries, the main purpose of reprocessing is to recover plutonium for weapons use. The main separation process in all known reprocessing plants is solvent extraction. 

In 1942, the Mallinckrodt Chemical Company adapted a diethylether extraction process to purify tons of uranium for the U.S. Manhattan Project [2] later, after an explosion, the process was switched to less volatile extractants. For simultaneous large-scale recovery of the plutonium in the spent fuel elements from the production reactors at Hanford, United States, methyl isobutyl ketone (MIBK) was originally chosen as extractant/solvent in the so-called Redox solvent extraction process. In the British Windscale plant, now Sellafield, another extractant/solvent, dibutylcarbitol (DBC or Butex), was preferred for reprocessing spent nuclear reactor fuels. These early extractants have now been replaced by tributylphosphate [TBP], diluted in an aliphatic hydrocarbon or mixture of such hydrocarbons, following the discovery of Warf [9] in 1945 that TBP separates tetravalent cerium from... 

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. 

Neptunium-237 is obtained as a by-product of making plutonium from uranium isotopes in nuclear reactors. Significant amounts of this element may be recovered from plutonium plant nuclear wastes. Both the recovery and purification of neptunium can be carried out by various chemical processes, including precipitation, solvent extraction and ion exchange. 

Plutonium is recovered from uranium and fission products by solvent extraction, precipitation, and other chemical methods. In most chemical processes, plutonium first is converted to one of its salts, usually plutonium fluoride, before it is recovered in purified metallic form. The fluoride is reduced with calcium metal to yield plutonium. Electrorefining may produce material of higher purity. 

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