Plutonium metal

Its importance depends on the nuclear property of being readily fissionable with neutrons and its availability in quantity. The world s nuclear-power reactors are now producing about 20,000 kg of plutonium/yr. By 1982 it was estimated that about 300,000 kg had accumulated. The various nuclear applications of plutonium are well known. 238Pu has been used in the Apollo lunar missions to power seismic and other equipment on the lunar surface. As with neptunium and uranium, plutonium metal can be prepared by reduction of the trifluoride with alkaline-earth metals. 

Fig. 1. Piessuie—volume—tempeiatuie phase diagram of plutonium metal (35). To convert MPa to atm, multiply by 9.9.

Table 6. Phase Relationships and Crystallographic Properties of Plutonium Metal ...

Fig. 2. Electrical resistivity, R, of plutonium metal, plotted as 100 R/R y versus absolute temperature (47).

Fig. 3. Magnetic susceptibility of plutonium metal as a function of temperature where represent initially high density plutonium and , cast plutonium...

The corrosion behavior of plutonium metal has been summarized (60,61). a-Plutonium oxidizes very slowly in dry air, typically <10 mm/yr. The rate is accelerated by water vapor. Thus, a bright metal surface tarnishes rapidly in normal environments and a powdery surface soon forms. Eventually green PUO2 [12059-95-9] covers the surface. Plutonium is similar to uranium with respect to corrosion characteristics. The stabilization of 5-Pu confers substantial corrosion resistance to Pu in the same way that stabilization of y-U yields a more corrosion-resistant metal. The reaction of Pu metal with Hquid water produces both oxides and oxide-hydrides (62). The reaction with water vapor above 100°C also produces oxides and hydride (63). 

Preparation of Plutonium Metal from Fluorides. Plutonium fluoride, PuF or PuF, is reduced to the metal with calcium (31). Although the reactions of Ca with both fluorides are exothermic, iodine is added to provide additional heat. The thermodynamics of the process have been described (133). The purity of production-grade Pu metal by this method is ca 99.87 wt % (134). Metal of greater than 99.99 wt % purity can be produced by electrorefining, which is appHcable for Pu alloys as well as to purify Pu metal. The electrorefining has been conducted at 740°C in a NaCl—KCl electrolyte containing PuCl [13569-62-5], PuF, or PuF. Processing was done routinely on a 4-kg Pu batch basis (135). 

W. C. Hazen, Remote Control Equipment for Plutonium Metal Production, LA-1387, Los Alamos Scientific Laboratory, N.M., 1951. 

M. W. Gibson and D. H. Nyman, Recent Plutonium Metal Production Experience at Hanford, WHC-SA-0616, Westinghouse Hanford Co., Wash., 1989. 

The first definite production of plutonium metal was made in November, 1943 by Baumbach and coworkers (1958). Approximately 35 micrograms of PuFi in a small thoria crucible in a high vacuum was reacted with barium metal at 1400 C to yield plutonium metal. The metal was found to have a silvery lustre, a density of about 16 grams j>er cubic centimeter and it rapidly absorbed hydrogen at about 210 C to form a black powder subsequently identified as PUH3 (a proof that metal had been produced). 

A good deal was learned about plutonium metal, including the determination of its density by both capillary displacement and x-ray diffraction methods, its melting point and vapor pressure. 

P. L. 1958. The microscale preparation and micrometallurgy of plutonium metal. J. Inorg. Nucl. Chem. 5, 182-189. 

Materials. THF and ethyl ether were purified by distillation from LiAlH in an argon atmosphere. Toluene and petroleum ether (b.p., 20-40 C) were stirred overnight with CaH2 and filtered before use. Alpha-phase plutonium metal pieces, prepared at Rocky Flats (Rockwell International, Golden, Colorado), were cleaned with a THF solution of C2H I2 before use. 

Preparations. All preparations, purifications, etc. were performed in a purified argon atmosphere. The plutonium metal and a THF solution of CjH Ig were stirred together at room temperature in the dark, to minimize C l decomposition. In a typical preparation, a 3.0 g piece of alpha-plutonium metal was stirred for three days with a solution of 2.1g in 50 mL THF. An... 

They are centered on the elements manganese, cerium, and plutonium. There is much theoretical work underway on all of these elements. The only inadequacy in the experimental side is that there remains a tremendous shortage of even fundamental data on plutonium metallic compounds. The reasons for the shortage are known to all plutonium scientists, but there is also no doubt that there is still a lot of science to be done. 

Plutonium metal is prepared by two methods--direct reduction of the oxide by calcium (DOR)U,2J, and reduction of PuF by calcium in our metal preparation line (MPL)(3) (see Figure 1). In the DOR process, the plutonium contenF of the reduction slag is so low that the slag can be sent to retrievable storage without further processing. Metal buttons that are produced are no purer than the oxide feed and/or the calcium chloride salt. Los Alamos purifies the buttons by electrorefin-ing(4i,5 ), yielding metal rings that are > 99.96 percent plutonium. 

Chemical processing activities involve the recovery of plutonium from Rocky Flats Plant scrap, waste materials and residues, and effluent streams. The final product of this recovery and purification effort is high-purity plutonium metal for use in foundry operations. 

Figure 3 shows a flowsheet for plutonium processing at Rocky Flats. Impure plutonium metal is sent through a molten salt extraction (MSE) process to remove americium. The purified plutonium metal is sent to the foundry. Plutonium metal that does not meet foundry requirements is processed further, either through an aqueous or electrorefining process. The waste chloride salt from MSE is dissolved then the actinides are precipitated with carbonate and redissolved in 7f1 HN03 and finally, the plutonium is recovered by an anion exchange process. 

MSE Processing of High-Grade Plutonium Scrap. Americium is remove3 from plutonium in a liquid-liquid extraction process using molten salt (KC1, NaCl, MgCl2) and molten plutonium metal... 

Other Pyrochemical Processes. The chemistry of pyrochemi-cal separation processes is another fertile area of research e.g., new molten salt systems, scrub alloys, etc. and the behavior of plutonium in these systems. Studies of liquid plutonium metal processes should also be explored, such as filtration methods to remove impurities. Since Rocky Flats uses plutonium in the metal form, methods to convert plutonium compounds to metal and purify the metal directly are high-priority research projects. 

An overview is presented of plutonium process chemistry at Rocky Flats and of research in progress to improve plutonium processing operations or to develop new processes. Both pyrochemical and aqueous methods are used to process plutonium metal scrap, oxide, and other residues. The pyrochemical processes currently in production include electrorefining, fluorination, hydriding, molten salt extraction, calcination, and reduction operations. Aqueous processing and waste treatment methods involve nitric acid dissolution, ion exchange, solvent extraction, and precipitation techniques. 

Electrorefining. Impure plutonium metal from MSE and Direct Oxide Reduction (DOR) is sent to an electrorefining operation (J3). In plutonium electrorefining, impure plutonium... 

Pyroredox. This is a three-step plutonium purification process ( 3). Impure plutonium metal is reacted with ZnCl2 in a solvent salt of KC1-CaCl 2 > as follows ... 

The PuFit is then loaded in ceramic (MgO) crucibles, where it is reacted with calcium to form CaF2 and plutonium metal as follows 7J ... 

The products of the reaction, once cooled to room temperature, are easily separated. The plutonium metal is sent to the foundry, while the CaF2 salt is stored until it can be dissolved in 9M HNO3 for recovery of residual amounts of plutonium. 

R. C. "Molten Salt Extraction of Americium from Molten Plutonium Metal," U.S. ERDA Rept. RFP-2365, Dow Chemical Co., Golden, Colorado, March 12, 1976. 

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