Actinide purity

Because of the relatively short half-lives of many later actinides, purity of samples and correct identification of lines can be a matter of uncertainty, but Figure 12.7 shows how this... 

Mullins, L.J. Christensen, D.C. Babcock, B.R. "Fused Salt Processing of Impure Plutonium Dioxide to High Purity Metal", Los Alamos Nat. Lab. Report LA-9154-MS also Symposium on Actinide Recovery from Waste and Low Grade Sources, ACS, New York City August 23-28, 1981 (in press). 

These early studies were carried out on metals of typically 90-99% purity, which sufficed to determine at least their gross properties. During the 1960s, interest diminished somewhat in actinide metallurgy due in part to the increasing use of ceramic rather than metallic fuel elements in nuclear reactors. The bulk of actinide metal research was for secret military purposes and only a fraction of the fundamental research was published. 

The actual situation with regard to the purity of most of the actinide metals is far from ideal. Only thorixun (99), uranium 11,17), neptunium 20), and plutonium 60) have been produced at a purity > 99.9 at %. Due to the many grams required for preparation and for accurate analysis, it is probable that these abundant and relatively inexpensive elements (Table I) are the only ones whose metals can be prepared and refined to give such high purities, and whose purity can be verified by accurate analysis. The purity levels achieved for some of the actinide metals are listed in Table II. For actinium (Ac), berkelium (Bk), californium (Cf),... 

The yield and rate of the tantalothermic reduction of plutonium carbide at 1975 K are given in Fig. 3. Producing actinide metals by metallothermic reduction of their carbides has some interesting advantages. The process is applicable in principle to all of the actinide metals, without exception, and at an acceptable purity level, even if quite impure starting material (waste) is used. High decontamination factors result from the selectivities achieved at the different steps of the process. Volatile oxides and metals are eliminated hy vaporization during the carboreduction. Lanthanides, Y, Ti, Zr, Hf, V, Nb, Ta, Mo, and W form stable carbides, whereas Rh, Os, Ir, Pt, and Pd remain as nonvolatile metals in the actinide carbides. Thus, these latter elements... 

The Preparation of High Purity Actinide Metals and Compounds... 

High purity actinide metals are subject to sophisticated investigations of bonding related properties they are starting materials for the synthesis of compounds. 

Since uranium continues in being one of the most interesting elements of the actinide series, available in sufficient quantity and purity without necessitating special handling precautions, it is obvious that frequently crystal growth techniques have been developed with uranium compounds. 

The preparation of larger quantities of high purity actinide metals is being based increasingly on separation or purification via evaporation of the actinide metal In these methods, actinide compounds (oxides or carbides) are reduced by metals forming nonvolatile oxides or carbides under conditions where the actinide metals can be volatilized ... 

The vapour pressure ratio of actinides to noble metals is also the basis of the actinide metal preparation by thermal dissociation of intermetallic compounds. Such intermetallic compounds of An and noble metals can be prepared by hydrogen reduction of a mixture of an An oxide and a finely divided noble metal (Pt, Ir.. in the absence of noble metals, hydrogen reduction of An oxides is impossible. Am and Cm metals have been obtained by thermal dissociation of their intermetallic compounds with Pt and Ir High purity Th and Pa, the least volatile actinide metals, can be prepared by thermal dissociation of their iodides, which form readily by reaction of iodine vapour with car-... 

As many physical properties of the actinide metals depend significantly on the sample purity, refining of the metals is mandatory. The choice of the refining methods is determined by the chemical reactivity of the actinide metal in the presence of the constituents of air, by high temperature reactions with crucible materials, by the specific radioactivity and the availability of the actinide elements. 

In tlie PUREX process, the spent fuel and blanket materials are dissolved in nitric acid to form nitrates of plutonium and uranium. These are separated chemically from the other fission products, including the highly radioactive actinides, and then the two nitrates are separated into tv/o streams of partially purified plutonium and uranium. Additional processing will yield whatever purity of the two elements is desired. The process yields purified plutonium, purified uranium, and high-level wastes. See also Radioactive Wastes in the entry1 on Nuclear Power Technology. Because of the yield of purified plutonium, the PUREX process is most undesirable from a nuclear weapons proliferation standpoint,... 

Modolo, G., Odoj, R. 1998. Influence of the purity and irradiation stability of Cyanex 301 on the separation of trivalent actinides from lanthanides by solvent extraction. J. Radioanal. Nucl. Chem. 228 (1-2) 83-89. 

Among the lanthanides and actinides there are several metals with the unusual 4P (ABAC) structure, and Sm has the strange 9P (ABAB CBCAC) structure. There are uncertainties of the structures of some of the metals beyond U. For most of these metals only small samples are available, purity is a problem, and in some cases samples are deposited on a filament. Impurities and deposition on another metal can change the structure. 

Although ICP-MS has been used for analysis of nuclear materials, often the entire instrument must be in an enclosed hot enclosure [350]. Sample preparation equipment, inlets to sample introduction systems, vacuum pump exhaust, and instrument ventilation must be properly isolated. Many of the materials used in the nuclear industry must be of very high purity, so the low detection limits provided by ICP-MS are essential. The fission products and actinide elements have been measured by using isotope dilution ICP-MS [351]. Because isotope ratios are not predictable, isobaric and molecular oxide ion spectral overlaps cannot be corrected mathematically, so chemical separation is required. 

One possible application in which large amounts of rare earths and actinides would be processed occurs in some schemes for nuclear waste management. If it should prove to be advantageous to remove transplutonium elements from nuclear waste, for example, the recovery of Am and Cm from the much larger amounts of rare earths would be required. This problem has been investigated by the author in tracer tests with rare earth mixtures typical of fission products, using a heavy rare earth such as holmium as a stand-in for Am and Cm (Fig. 5). It is clear that the bulk of the holmium can be recovered in reasonable purity, and that the bulk of the lighter rare earths is effectively separated from the very small amount of heavy rare earths, Am, and Cm. 

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