Plutonium processing properties

Groves moved on to Berkeley more impressed with their work than his Met Lab auditors realized. I left Chicago feeling that the plutonium process seemed to ofier us the greatest chances for success in producing bomb material, he recalls. Every other process. .. depended upon the physical separation of materials having almost infinitesimal differences in their physical properties. Transmutation by chain reaction was entirely new, but the rest of the plutonium process, chemical separation, while extremely difficult and completely unprecedented, did not seem to be impossible. ... 

We are not aware of any previous studies of the removal of plutonium or americium from (NH )2ZrF6-NHltF-NH N03 solutions. For ready plant-scale application, precipitation, sorption on inorganic materials, or batch solvent extraction processes may all be satisfactory. An inexpensive inorganic material with great selectivity and capacity for sorbing actinides, and with suitable hydraulic properties, would be especially attractive. 

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... 

Degraded TBP process solvent is typically cleaned by washing with sodium carbonate or sodium hydroxide solutions, or both. Such washes eliminate retained uranium and plutonium as well as HDBP and H2MBP. Part of the low-molecular-weight neutral molecules such as butanol and nitrobutane, entrained in the aqueous phase, and 90-95% of the fission products ruthenium and zirconium are also removed by the alkaline washes. Alkaline washing is not sufficient, however, to completely restore the interfacial properties of the TBP solvent, because some surfactants still remain in the organic phase. 

Plutonium is the only transuranium element which has been found in nature. Until its properties were known it would have been impossible to detect it in the minute amounts in which it occurs, but when its behavior was understood, Seaborg and his co-workers were able to find it in pitchblende, monazite ores, and carnotite in concentrations of about one part in 1014 (63, 73, 76). Peppard and his group found it in somewhat greater amounts in pitchblende from the Belgian Congo (77). Seaborg believes that most of this plutonium arises by fission of the uranium in the ore, though other processes may also be involved (77, 78). 

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. 

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. 

From the above discussion it follows that tetravalent and hexavalent thorium, uranium, and plutonium can be separated from the trivalent rare-earth fission products by taking advantage of differences in complexing properties. More highly charged cation fission products, such as tetravalent cerium and the fifth-period transition elements zirconium, niobium, molybdenum, technetium, and ruthenium, complex more easily than the trivalent rare-earths and are more difficult to separate from uranium and plutonium by processes involving complex formation. 

This principle of oxidizing and reducing plutonium at various stages of the purification scheme has been retained in all subsequent processes. No other element has the same set of redox and chemical properties as plutonium, though some elemoits behave as Pu (o. g-the lanthanides), some like Pu (e,g. zirconium) and some like PuO (e.g. uranium). Numerous redox agents have been used, e.g. K2Cr20y (to PuC " ), NaN02 (to Pu " "), hydrazine, ferrous sulfamate, and U (to Pu "), cf. 16.3. 

Another development which should be mentioned was that in purifying the thorium salts, a process was developed at Ames using a liquid—liquid extraction with hexanone, where the thorium went into the hexanone and the impurities stayed in the water phase. While this process was successful and produced pure thorium, it had the disagreeable property that occasionally the apparatus would catch fire, so tributyl phosphate was substituted for the hexanone and this made the process completely satisfactory. It later also formed the basis, being used with uranium, for the Redox Process, which was used widely at Hanford and elsewhere for separating the radioactive fission product impurities from the uranium and plutonium. 

Pu(IV) and PuCVI) extract well from HCl solutions by amines, while Pu(ni) is poorly extracted, in analogy with the strong base anion exchange system. Plutonium chloride systems have found application mainly in analytical and radiochemical work rather than in processes because of the corrosive properties of HCl solutions. 

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