Plutonium isotopes, nuclear fuel reprocessing

Other reasons for investigating plutonium photochemistry in the mid-seventies included the widely known uranyl photochemistry and the similarities of the actinyl species, the exciting possibilities of isotope separation or enrichment, the potential for chemical separation or interference in separation processes for nuclear fuel reprocessing, the possible photoredox effects on plutonium in the environment, and the desire to expand the fundamental knowledge of plutonium chemistry. 

Nuclear Fuel Reprocessing. Spent fuel front a nuclear reactor contains - tsy easy cwpu Mc-py, ant many other radioaclive isnlopes (fission products). Reprocessing involves the treatment of the spent fuel to separate plutonium and unconsumed uranium from other isotopes so that these can be recycled or safely stored. 

The seas are a source of aerosol (i.e. small particles), which transfer to the atmosphere. These will subsequently deposit, possibly after chemical modification, either back in the sea (the major part) or on land (the minor part). Marine aerosol comprises largely unfractionated seawater, but may also contain some abnormally enriched components. One example of abnormal enrichment occurs on the eastern coast of the Irish Sea. Liquid effluents from the Sellafield nuclear fuel reprocessing plant in west Cumbria are discharged into the Irish Sea by pipeline. At one time, permitted discharges were appreciable and as a result radioisotopes such as Cs and several isotopes of plutonium have accumulated in the waters and sediments of the Irish Sea. A small fraction of these radioisotopes were carried back inland in marine aerosol and deposited predominantly in the coastal zone. While the abundance of Cs in marine aerosol was refiective only of its abundance in seawater (an enrichment factor - see Chapter 4 - of close to unity), plutonium was abnormally enriched due to selective incorporation of small suspended sediment particles in the aerosol. This has manifested itself in enrichment of plutonium in soils on the west Cumbrian coast,shown as contours of 239+240p deposition (pCi cm ) to soil in Figure 3. 

Neutron-rich lanthanide isotopes occur in the fission of uranium or plutonium and ate separated during the reprocessing of nuclear fuel wastes (see Nuclearreactors). Lanthanide isotopes can be produced by neutron bombardment, by radioactive decay of neighboring atoms, and by nuclear reactions in accelerators where the rate earths ate bombarded with charged particles. The rare-earth content of solid samples can be determined by neutron... 

High-level wastes consist of spent nuclear fuel and reprocessed wastes. Isotopes of uranium make up by far the majority of high-level wastes, accounting for about 94 percent of the mass of all such wastes. An additional 1 percent consists of plutonium isotopes, and the remaining 5 percent, of isotopes of other elements. 

Liquid wastes. Historically, the most important radioactive wastes have been liquid wastes that arise from chemical reprocessing of spent nuclear fuel for defense production purposes, i.e., for the purpose of extracting plutonium for use in nuclear weapons. These wastes contain varying concentrations of many radionuclides, primarily fission products and long-lived, alpha-emitting transuranium isotopes. 

The application of nuclear forensic techniques to samples of purified heavy elements is well developed however, when applied to unseparated spent reactor fuel, the methods become more complicated. The radionuclide content of a spent fuel sample is not controlled solely by radioactive decay, but is strongly influenced by neutron-induced transmutation. Chronometry based on the decay of the light plutonium isotopes cannot be performed due to the initial presence of an overwhelming quantity of uranium. The isotopic distribution of the plutonium isotopes and the concentration of fission products can provide a means by which the degree of transmutation can be estimated, unless the material started out as MOX fuel (where reprocessed plutonium is incorporated into fuel fabricated from uranium with insufficient fissile content to support the reactor application). More study is needed to extend the methodology to unprocessed fuel. 

The operations and facilities include ore exploration (not included in NFCIS list), mining, ore processing, uranium recovery, chemical conversion to UO2, UO3, UF4, UFg, and uranium metal, isotope enrichment, reconversion of UF to UO2 (after enrichment), and fuel fabrication and assembly that are all part of the front end of the NFC. The central part of the NFC is the production of electric power in the nuclear reactor (fuel irradiation). The back end of the NFC includes facilities to deal with the spent nuclear fuel (SNF) after irradiation in a reactor and the disposal of the spent fuel (SF). The spent fuel first has to be stored for some period to allow decay of the short-lived fission products and activation products and then disposed at waste management facilities without, or after, reprocessing to separate the fission products from the useful actinides (uranium and plutonium). Note the relatively large number of facilities in Table 2.1 dedicated to dealing with the spent fuel. Also listed in Table 2.1 are related industrial activities that do not involve uranium, like heavy water (D2O) production, zirconium alloy manufacturing, and fabrication of fuel assembly components. 

Uranium is a naturally occurring radioactive element and, therefore, fresh nuclear fuel also contains radionuclides. Plutonium and reprocessed uranium, on the other hand, are accompanied by isotopes which were generated during the preceding exposure of nuclear fuel in a reactor. All the radionuclides present in fresh nuclear fuel are of minor importance in reactor operation nonetheless, they have to be taken into consideration in fuel fabrication in order to protect the employees from undue radiation exposure. 

Argon-40 [7440-37-1] is created by the decay of potassium-40. The various isotopes of radon, all having short half-Hves, are formed by the radioactive decay of radium, actinium, and thorium. Krypton and xenon are products of uranium and plutonium fission, and appreciable quantities of both are evolved during the reprocessing of spent fuel elements from nuclear reactors (qv) (see Radioactive tracers). 

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