Actinides irradiated nuclear fuel

Actinides have significant abundance in irradiated nuclear fuel, long radioactive half-lives, and high radiological and chemical toxicities, and they raise concerns with criticality and nuclear proliferation. Accordingly, actinide analyses are important in process solutions, nuclear wastes, and environmental samples. 

Separation of Actinides from the Samples of Irradiated Nuclear Fuels. For the purpose of chemical measurements of burnup and other parameters such as accumulation of transuranium nuclides in irradiated nuclear fuels, an ion-exchange method has been developed to separate systematically the transuranium elements and some fission products selected for burnup monitors (16) Anion exchange was used in hydrochloric acid media to separate the groups of uranium, of neptunium and plutonium, and of the transplutonium elements. Then, cation and anion exchange are combined and applied to each of those groups for further separation and purification. Uranium, neptunium, plutonium, americium and curium can be separated quantitatively and systematically from a spent fuel specimen, as well as cesium and neodymium fission products. 

Uranyl nitrate has an unusual property, shared only by nitrates of a few other actinides, of being very soluble in a number of organic solvents. When such an organic solvent is immiscible with water, it can be used in a solvent extraction process to extract uranium from aqueous solutions and separate it from associated impurities. Such applications of solvent extraction are very important in extracting and purifying uranium from leach solution of uranium ores or from nitric acid solution of irradiated nuclear fuel. Examples of extractants that have been used for such separation processes are listed in Table 5.14. 

Actinide Separations from Irradiated Nuclear Fuels and/or Waste Solutions... 

Calculational methods used to determine the neutron multiplication should be validated, preferably against applicable measured data (see Appendix VII). For irradiated nuclear fuel this vahdation should include comparison with measured radionuclide data. The results of this validation should be included in determining the uncertainties and biases normally associated with the calculated neutron multiplication. Fission product cross-sections can be important in criticality safety analyses for irradiated nuclear fuel. Fission product cross-section measurements and evaluations over broad energy ranges have not been emphasized to the extent that actinide cross-sections have. Therefore, the adequacy of fission product cross-sections used in the assessment should be considered and justified by the safety analyst. 

RepU that is defined as uranium recovered from reprocessed irradiated nuclear fuel (also known as spent fuel) and thus will contain artificial uranium isotopes like U and (and also traces of other actinides and fission products) or SEU for slightly enriched uranium that contains 0.9%-2.0% of... 

The major interest of the actinide-based alloys is due to applications in the nuclear industry for example, the interest in metallic fuels for liquid-metal fast breeder reactors and the interest in high-temperature techniques for the reprocessing of irradiated nuclear fuel have always persisted. 

Actinides occurrence and preparation. With the exception of U and Th, the availability of the actinides of the first half of the series ranges from the g to kg scale that of the elements of the second half of the series from the mg scale for Cf to the sub-mg scale for Es. Isotopes of Np, Pu, Am, Cm can be available as byproducts of nuclear fuel processing other elements such as Ac, Cf, Bk, Es can be obtained by irradiation of selected isotopes in high flux reactors, or by reprocessing large quantities of ore (Pa). 

Viewed in the context of the actinide lifespan, the nuclear fuel cycle involves the diversion of actinides from their natural decay sequence into an accelerated fission decay sequence. The radioactive by-products of this energy producing process will themselves ultimately decay but along quite different pathways. Coordination chemistry plays a role at various stages in this diversionary process, the most prominent being in the extraction of actinides from ore concentrate and the reprocessing of irradiated fuel. However, before considering these topics in detail it is appropriate to consider briefly the vital role played by coordination chemistry in the formation of uranium ore deposits. 

A research and development program on the recovery and purification of potentially useful by-product actinides from the nuclear fuel cycle was carried out some years ago in the Federal Republic of Germany as part of the "Actinides Project" (PACT). In the course of this program, procedures for the recovery of neptunium, americium and curium isotopes from power reactor fuels, as well as procedures for the processing of irradiated targets of neptunium and americium to produce heat-source isotopes, have been developed. The history of the PACT Program has been reviewed previously (1). Most of the PACT activities were terminated towards the end of 1973, when it became evident that no major commercial market for the products in question was likely to develop. 

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. 

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. 

In addition to the fission products, actinide nuclides are generated in the nuclear fuel during irradiation. The main starting reaction for the buildup of the transuranium nuclides is neutron capture in the nucleus leading to short-lived... 

In terms of amount, by far the most significant of the synthetic actinide elements is plutonium. Nuclear power production by fission in uranium produces as a byproduct approximately 50 tons per year world-wide of a mixture of plutonium isotopes. About 250 tons of plutonium is estimated to be in the world plutonium inventory, some still in unprocessed spent fuel assemblies from nuclear reactors. World inventory of plutonium by the year 2000 has been estimated at 2400 tons [57], Plutonium produced for nuclear weapons is mainly Pu, but plutonium produced as a by-product of energy production contains substantial amounts of °Pu, Pu, and Pu and small amounts of Pu [64]. The plutonium in the environment is due, in decreasing order of importance, to the testing of nuclear weapons in the atmosphere, the re-entry into the atmosphere and disintegration of satellites equipped with Pu power sources, and the processing of irradiated uranium fuel from nuclear reactors. 

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