Plutonium chemical properties

Most chemical iavestigations with plutonium to date have been performed with Pu, but the isotopes Pu and Pu (produced by iatensive neutron irradiation of plutonium) are more suitable for such work because of their longer half-Hves and consequendy lower specific activities. Much work on the chemical properties of americium has been carried out with Am, which is also difficult to handle because of its relatively high specific alpha radioactivity, about 7 x 10 alpha particles/(mg-min). The isotope Am has a specific alpha activity about twenty times less than Am and is thus a more attractive isotope for chemical iavestigations. Much of the earher work with curium used the isotopes and Cm, but the heavier isotopes... 

The last forty years have seen an extensive, world-wide investigation of the chemical properties of the synthetic element, plutonium. As a result, as much is known about the chemical properties of this element as is known about the chemical properties of most of the naturally occurring elements. The papers in this volume, presented at the Symposium on the Chemistry of Plutonium held during the Kansas City meeting of the American Chemical Society, in September, 1982, represent an up-dating of this large amount of information. 

Investigations of the chemical properties of plutonium have continued in many laboratories throughout the world as it has become available. This has led to the situation where the chemistry of this relative newcomer is as well understood as is that of most of the well-studied elements. The four oxidation states of plutonium—III, IV, V, and VI—lead to a chemistry which is as complex as that of any other element. It is unique among the elements in that these four oxidation states can all exist simultaneously in aqueous solution at appreciable concentration. As a metal, also, its properties are unique. Metallic plutonium has six allotropic forms, in the temperature range from room temperature to its melting point (640 C), and some of these have properties not found in any other known metal. 

This account of the beginnings and early days of the forty years of plutonium chemistry should serve as a background for the following papers which illuminate many of the accomplishments of the intervening years and emphasize the high level of the present status of information on the chemical properties of this remarkable synthetic element. 

Rand, M.H. in "Plutonium Physico-Chemical Properties of Its Compounds and Alloys" Atomic Energy Review 1966, , Special Issue n° 1, I.A.E.A. Vienna, p. 7. 

Rand, M. "Plutonium Physico-Chemical Properties of Its Compounds and Alloys, Kubaschewski, 0., Ed., Atomic Energy Review, Vol. k. Special Issue No. 1, International Atomic Energy Agency, Vienna, 1966 p. 7. 

A primary goal of chemical separation processes in the nuclear industry is to recover actinide isotopes contained in mixtures of fission products. To separate the actinide cations, advantage can be taken of their general chemical properties [18]. The different oxidation states of the actinide ions lead to ions of charges from +1 (e.g., NpOj) to +4 (e.g., Pu" " ) (see Fig. 12.1), which allows the design of processes based on oxidation reduction reactions. In the Purex process, for example, uranium is separated from plutonium by reducing extractable Pu(IV) to nonextractable Pu(III). Under these conditions, U(VI) (as U02 ) and also U(IV) (as if present, remain in the... 

The most studied non-stoichiometric system in actinide CaF2-structured compounds is the An-0 system all actinide dioxides (with the exception of Th02) present large departures from stoichiometry. Since uranium and plutonium dioxides (and their solid solutions) are employed as fuels in nuclear reactors, a very large effort has been dedicated to the study of their physical and physico-chemical properties. All these properties are affected by the oxygen composition of the compound. 

All the early work on plutonium was done with unweighable amounts on a tracer scale. When it became apparent that large amounts would be needed for the atomic bomb, it was necessary to have a more detailed knowledge of the chemical properties of this element. Intensive bombardment of hundreds of pounds of uranium was therefore begun in the cyclotrons at Berkeley and at Washington University in St. Louis. Sepa-ration of plutonium from neptunium was based on the fact that neptunium is oxidized by bromate while plutonium is not, and that reduced fluorides of the two metals are carried down by precipitation of rare earth fluorides, while the fluorides of the oxidized states of the two elements are not. Therefore a separation results by repeated bromate oxidations and precipitations with rare earth fluorides. 

Since this is so, it was inevitable that as soon as Seaborg and his collaborators had clearly established the identity and properties of neptunium and plutonium, they would look for the next higher elements, numbers 95 and 96. The general similarity in chemical properties of uranium, neptunium, and plutonium led Seaborg to believe that these new elements could be isolated by methods similar to those already used. 

Hexavalent plutonium, Pu(VI), is relatively stable in aqueous solution and exists as the oxyion plutonyl, Pu022+ (40). The chemical properties of Pu(VI) compounds are somewhat similar to those of U(VI). 

Processes for the isolation and purification of plutonium, including the enrichment of spent nuclear reactor fuels, arc described in the entry on Nuclear Power Technology. These processes take advantage of Pu s several oxidation states, each of which has different chemical properties. The processes may involve carrier precipitation, solvent extraction, and ion exchange. 

Handling Precautions. Care must be taken in the handling of plutonium to avoid unintentional formation of a critical mass. Plutonium in liquid solutions is more apt to become critical than solid plutonium. The shape of the mass also determines criticality. Plutonium s chemical properties also increase handling difficulty, Metallic plutonium is pyrophoric, particularly... 

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. 

Especially interesting in a discussion of radionuclide speciation is the behaviour of the transuranium elements neptunium, plutonium, americium and curium. These form part of the actinide series of elements which resemble the lanthanides in that electrons are progressively added to the 5f instead of the 4f orbital electron shell. The effective shielding of these 5f electrons is less than for the 4f electrons of the lanthanides and the differences in energy between adjacent shells is also smaller, with the result that the actinide elements tend to display more complex chemical properties than the lanthanides, especially in relation to their oxidation-reduction behaviour (Bagnall, 1972). The effect is especially noticeable in the case of uranium, neptunium and plutonium, the last of which has the unique feature that four oxidation states Pum, Pu, Puv and Pu are... 

DU has 40% less radioactivity than natural uranium, but may contain trace levels of plutonium, neptunium, americium, technetiiun, and U, which increase the radioactivity by 1% but are insignificant with respect to chemical and radiological toxicity (Force Health Protection Readiness Policy Programs, 2008 Sztajnkrycer and Often, 2004 WHO, 2001). Because of the decreased radioactivity of DU, it is believed that DU is a safer form than natural uranium, while maintaining the same chemical properties. As the heaviest occurring element, uranium is extremely dense and both uranium and DU are often used in applications which require such dense metals. 

Gindler JE. 1973. Physical and chemical properties of uranium. In Hodge HC et al., eds. Uranium, plutonium transplutonic elements. New York, NY Springer-Verlag, 69-164. 

It is well known that anthropogenic radionuclides such as radiocaesium and plutonium together with natural Pb are accumulated in sediments and can be used for the dating/growth rate determination of the sediments. The flux of these radionuclides depends on factors, such as physical and chemical properties, biological factors etc,. Water dams along rivers will stop the water flow and might act as effective traps by sedimentation processes and accumulate material that otherwise would be transported to the sea. 

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