Nuclear fuel element solutions

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... 

Later studies by investigators (Alberts ei al 1979) have shown lhai 1 >7Cs introduced into a watershed is attached to soil panicles, which arc removed by erosion and runoff. Some of the eroded soil panicles comprise he sediments of the catchment basins in the watersheds and act as "sinks for, 7Cs. Other investigators have reponed an almost irreversible fixation of this clement in clay imerlattice sites in freshwater environments, and. that it is unlikely that this nuclide will he removed from these sediments under normal environmental conditions other than by exposure to solutions ol high ionic strength, such as may occur in estuarine environments. Studies of 15 Cs have been important because ihe element can be introduced into a water system from a leak in a nuclear fuel element. These findings are reported in some detail by Alberts ct al. in Science, 203. 649-651 (1979). 

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- -butyl phosphate (TBP) in kerosene. First operated by the U.S. Atomic Energy Commission at its Savannah River plant, SC, in 1954 and at Hanford, WA, in 1956. Now in operation, with modifications, in several countries. Sites include Savannah River (SC), Cap de la Hague (France), Marcoule (France), Sellafield (England), Karlsruhe (Germany), and Trombay (India). See also Recuplex. 

The fission products are not extracted by the TBP and the aqueous solution is directed to the tail-end processes of nuclear waste mauagement. The organic phase is washed by nitric acid, the plutonium is reduced to Pu(in) that is stripped from the organic phase by moderately concentrated nitric acid leaving the uranium behind in the organic phase. The latter is finally stripped by dilute nitric acid and sent to refabrication of nuclear fuel elements. 

One of the many problems of nuclear power is the availability of fuel uranium-235 reserves are only about 0.7% those of the nonfissile uranium-238, and the separation of the isotopes is costly (Section 17.12). One solution is to synthesize fissile nuclides from other elements. In a breeder reactor, a reactor that is used to create nuclear fuel, the neutrons are not moderated. Their high speeds result in... 

A recent and extremely important development lies in the application of the technique of liquid extraction to metallurgical processes. The successful development of methods for the purification of uranium fuel and for the recovery of spent fuel elements in the nuclear power industry by extraction methods, mainly based on packed, including pulsed, columns as discussed in Section 13.5 has led to their application to other metallurgical processes. Of these, the recovery of copper from acid leach liquors and subsequent electro-winning from these liquors is the most extensive, although further applications to nickel and other metals are being developed. In many of these processes, some form of chemical complex is formed between the solute and the solvent so that the kinetics of the process become important. The extraction operation may be either a physical operation, as discussed previously, or a chemical operation. Chemical operations have been classified by Hanson(1) as follows ... 

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. 

Interest in the reprocessing of spent nuclear fuels has prompted studies of the solution photochemistries of Np and Pu. A recent review summarizes the photoredox behavior of the various oxidation states of these elements.169... 

The redox chemistry of the actinide elements, especially plutonium, is complex (Katz et al., 1980). Disproportionation reactions are especially important for the +4 and +5 oxidation states. Some of the equilibria are kinetically slow and irreversible. All transuranium elements undergo extensive hydrolysis with the +4 cations reacting most readily due to their large charge/radius ratio. Pu (IV) hydrolyzes extensively in acid solution and forms polymers. The polymers are of colloidal dimensions and are a serious problem in nuclear fuel reprocessing. 

SFAs with destroyed fuel elements, including nuclear fuel spillage, for which special handling technologies would be necessary (dissolving in chemical solutions or monolithization for everlasting storage) ... 

The process route of uranium as nuclear fuel is shown in Fig. 11.7. It begins with processing of uranium ores, from which pure uranium compounds are produced. These may be used in the natural isotopic composition or transformed into other compounds suitable for isotope separation. The next step is the production of fuel elements for the special requirements of reactor operation. Solutions of uranium compounds are applied only in homogeneous reactors. 

Macaskie L. E., Lloyd J. R., Thomas R. A. P., and Tolley M. R. (1996) The use of micro-organisms for the remediation of solutions contaminated with actinide elements, other radionuclides, and organic contaminants generated by nuclear fuel cycle activities. Nuclear Technol. 35, 257-271. 

The mutual separation of actinide elements and the selective isolation of useful actinides from fission products are indispensable for the nuclear fuel cycle and have become important subjects of investigation for the development of advanced nuclear fuel reprocessing and TRU (TRans Uranium elements) waste management [1], A variety of research concerning the separation chemistry of actinides has so far been accumulated [2]. There are, however, only a few theoretical studies on actinides in solution[3-5]. Schreckenbach et a), discussed the stability of uranyl (VI) tetrahydroxide [UO,(OH) ] [3] and Spencer and co-workers calculated the optimized structures of some uranyl and plutonyl hydrates [AcO, nH,0 (Ac = U, Pu and n = 4,5,6)] [4],... 

Most of the present nuclear reactors have been burning solid fuel elements of either normal or enriched uranium. Thus far, it has been necessary to reprocess fuel in order to recover valuable fissionable or fissile material. It is possible that fuel elements will be developed for future reactors which can be burned to the point where it is not economically justifiable to recover fissionable materials. Obviously, this depends upon the value of these materials. Such a procedure would provide an optimum solution to the major part of the waste disposal problem. The fission products would still be locked in the fuel element, simple disposal techniques could be employed, and in fact, spent fuel elements would probably have secondary uses as radiation sources. 

Several X-ray fluorescence speclromelric delerminations of lechnelium were reported. Hie lines X.,2=0.67927 A, X,i=0.67493 A, X, i=0.6()141 A, and X,(2= 0.59018 A can be used for detection and determination of the element 30,31]. From neutron irradiated molybdenum milligram quantities of Tc could be isolated and detected by the Ka and Kjn lines [46]. Because of its simplicity and selectivity, an X-ray fluorescence method was developed for the determination of technetium in solution. At concentrations of less than 1.0 mg Tc per ml no interelcment effects were observed. Therefore, it is possible to ascertain technetium in its compounds without their prior decomposition, provided the compounds are soluble in water or dioxane. The detection limit is about 4- lO g Tc [47. For the determination of Tc in nuclear fuel processing wastes by X-ray fluorescence, a rapid, simple, and accurate method was reported [48]. 

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