Pyrochemical processing

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. 

Figure 1 shows a simplified flow sheet for plutonium-239 recovery operations at Rocky Flats. Impure plutonium metal is sent through a pyrochemical process, called molten salt extraction (MSE), to remove the elemental impurity americium. The product plutonium metal, if it meets plant purity requirements, is sent to the foundry. Metal that does not meet foundry requirements is processed further, either through an aqueous process using ion exchange, or through a pyrochemical electrorefining process. The waste chloride salt from MSE is... 

The term "Pyrochemical Processing" is commonly applied to a family of chemical processes that utilize oxidation-reduction reactions to effect chemical separations at elevated temperatures. 

The following pages will describe several examples of pyrochemical processing as applied to the recycle of plutonium, and will briefly review the fundamental chemistry of these processes. We shall review the conversion of plutonium oxide to plutonium metal by the direct oxide reduction process (DOR),the removal of americium from metallic plutonium by molten salt extraction (MSE), and the purification of metallic... 

The anode residues must be chemically processed to recover the plutonium remaining in the residues. This may amount to about 10% of the feed mass if delta alloy is the feed metal. Either aqueous or pyrochemical processes may be used for anode recovery. One pyrochemical process used for recovery utilizes oxidation of the plutonium with zinc chloride to form plutonium chloride salt, followed by calcium reduction of the PUCI3 contained in the salt phase to produce pure plutonium metal (the impurities follow the zinc metal obtained from the oxidation reaction and are discarded to waste). Impurities more stable than calcium chloride remain in the salt phase and are also... 

The work presented in this article represents the combined effort of a large number of dedicated scientific workers at many Department of Energy facilities located throughout the United States. Particular credit must be given to the staff at Los Alamos, Argonne, Rocky Flats, Livermore, and Hanford. Without their diligent effort the pyrochemical process technologies described above would not have been developed. 

Felt, R.E. "A Pyrochemical Process for the Reduction of Plutonium Dioxide to Metal", Atlantic Richfield Hanford Co. Report ARH-1198, July 1969. 

Anode Residue Recovery. Approximately 10% of the plutonium present in a Pu- lwt% Ga electrorefining feed, ends up in the anode residue. This residue also contains most of the impurities which were present in the metal feed. The following pyrochemical processes have been considered for recovering plutonium from this residue. 

Plutonium pyrochemical processes are now the principal tools at Los Alamos for producing large amounts of high purity plutonium metal from impure metal and oxide scrap. Pyrochemical processing was selected because of its cost effectiveness. The processes are highly compact and require little floor space and manpower to operate. The processes are also operationally efficient in that one or two steps can be used to supplant multi-step operations found in the classical aqueous chemistry flow streams. The... 

In order to achieve this goal of a fully integrated process sequence, a concerted research and process development effort must take place. Present R D efforts are devoted to the development of cost-effective pyrochemical processes for the recycle of plutonium in residues. Future efforts will be aimed at the recycle of reagents in each individual process. The objectives of the recycle are to produce plutonium metal which can be further purified, and to generate small volumes of residues which can be discarded or recycled. 

Phil Horwitz asked me to comment on what I saw as potential disadvantages of the various plutonium pyrochemical processes extolled by speakers in the Tuesday sessions. I, too, am a fan of pyrochemical techniques. I recognize that pyrochemical processes for Pu processing are just in their infancy - on batch plant-scale. To be truly useful, such processes need to be operated on a continuous basis. Scientists and engineers concerned with such technology need to develop equipment and procedures required to operate pyrochemical processes in a cost-effective, continuous manner."... 

The pyrochemical process of zirconium-hafnium separation is particularly attractive not only because it makes the entire process of nuclear-grade zirconium metal production from zircon more economical than that involving a hydrometallurgical separation stage, but also... 

Figure 4.20 Flowsheet of the pyrochemical process for zirconium-hafnium separation.

Pyrocerams, 21 381 Pyro-Chek 68PB, 11 470-174 Pyrochemical processes, in plutonium metal preparation, 19 676 Pyrochlore, 17 133-134, 140, 141 colorants for ceramics, 7 347t Pyroelectricity, 11 95, 100, 106, 107 Pyroelectric materials, smart, 22 708t, 709 Pyroform process, 25 171 Pyrogallol... 

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