Actinide irradiation

Planet pluto) Plutonium was the second transuranium element of the actinide series to be discovered. The isotope 238pu was produced in 1940 by Seaborg, McMillan, Kennedy, and Wahl by deuteron bombardment of uranium in the 60-inch cyclotron at Berkeley, California. Plutonium also exists in trace quantities in naturally occurring uranium ores. It is formed in much the same manner as neptunium, by irradiation of natural uranium with the neutrons which are present. 

The throwaway fuel cycle does not recover the energy values present ia the irradiated fuel. Instead, all of the long-Hved actinides are routed to the final waste repository along with the fission products. Whether or not this is a desirable alternative is determined largely by the scope of the evaluation study. For instance, when only the value of the recovered yellow cake and SWU equivalents are considered, the world market values for these commodities do not fully cover the cost of reprocessing (2). However, when costs attributable to the disposal of large quantities of actinides are considered, the classical fuel cycle has been the choice of virtually all countries except the United States. 

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). 

The uptake of plutonium by bone has received considerable attention as irradiation of bone marrow has been associated with leukaemia-type diseases. As Durbin (192) has observed the uptake of plutonium into mineralised material is not restricted to mammals but can occur in any creature, invertebrate or vertebrate, which contains calcium phosphate or calcium carbonate structures. It can be expected that the trivalent actinides will also deposit in similar material. 

Fig. 12.12 Extraction of actinide ions by irradiated 1 mol dm [DMDB-(2-3,6-OD,l,3-DA)P] (C4H9CH3NC0)2CHC2H40C2H40C6Hi3 into i-butylbenzene solutions solid line, irradiated in presence of Smoldm HNO3 broken line, irradiated in presence of 0.5moldm HNO3. 

Because of the multivalent nature of the actinide ions, understanding the radiation-induced change of the valence-state of the actinide in solutions under self-irradiation or external irradiation is a challenge in radiation chemistry. Some of the ions are strong a-emitters. It is also important from a practical viewpoint that the solution chemistry of actinide ions is closely related to the storage and the repository of the wastes. Much work combined with experiment and simulation has been conducted and reviews were summarized [136,140-144]. 

The research programme of the European Institute for Transuranium Elements was, from its very beginning, devoted to both basic research on advanced plutonium containing fuel and to fundamental research on actinide elements. Non-fuel actinide research in Europe started more than 20 years ago with the reprocessing of irradiated actinide samples. Since the first isolation and purification of transplutonium elements, actinide research developed steadily in close contact and cooperation with specialised laboratories in Western Europe and in the United States. 

Utsonomiya, S., Wang, L. M., Yudintsev, S. V. Ewing, R. C. 2002. Ion irradiation effects in synthetic garnets incorporating actinides. Materials Research Society Symposium Proceedings, 713, 495-500. 

This paper describes a new reaction which may yield useful amounts of the product isotope following neutron capture by lanthanide or actinide elements. The trivalent target ion is exchanged into Linde X or Y zeolite, fixed in the structure by appropriate heat treatment, and irradiated in a nuclear realtor. The (n, y) product isotope, one mass unit heavier than the target, is ejected from its exchange site location by y recoil. It may then be selectively eluted from the zeolite. The reaction has been demonstrated with several rare earths, and with americium and curium. Products typically contain about 50% of the neutron capture isotope, accompanied by about 1% of the target isotope. The effect of experimental variables on enrichment is discussed. 

The amount of unreacted target element that eluted was determined by measuring its radioactivity directly in the case of actinides, and by activation analysis in the case of lanthanides. The distribution of the radioactive neutron capture product was determined by counting both the eluate and the eluted zeolite. All irradiations were done in the Oak Ridge Research reactor in a pneumatic tube facility with a thermal neutron flux of about 4 X 1013 neutrons cm-2 sec-1 or, for a few long irradiations, in a tube adjacent to the reactor core at the fluxes stated in Table VI. 

In the chemistry of the fuel cycle and reactor operations, one must deal with the chemical properties of the actinide elements, particularly uranium and plutonium and those of the fission products. In this section, we focus on the fission products and then chemistry. In Figures 16.2 and 16.3, we show the chemical composition and associated fission product activities in irradiated fuel. The fission products include the elements from zinc to dysprosium, with all periodic table groups being represented. 

The Purex process is used for almost all fuel reprocessing today. Irradiated UO2 fuel is dissolved in HNO3 with the uranium being oxidized to U02(N03)2 and the plutonium oxidized to Pu(NC>3)4. A solution of TBP in a high-boiling hydrocarbon, such as n-dodecane, is used to selectively extract the hexavalent U02(N03)2 and the tetravalent Pu(NC>3)4 from the other actinides and fission products in the aqueous phase. The overall reactions are... 

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. 

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