Pyrochemical processes reduction

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. 

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... 

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

Pu metal has recently been produced in kilogram batches in a coordinated reduction-purification sequence (pyrochemical processing) with Ca reductant, CaCL flux, and subsequent molten salt Am extraction (9.2.2.6.1), yielding single ingots of Pu metal. ... 

Based on available information, we believe that transfer of the uranate to a molten chloride system with electrolytic reduction is the most feasible method. Electrolytic deposition from molten alkali metal chlorides was an integral step in the pyro-chemical process known as the Hanford Salt Cycle. Documentation of this phase of the process was extensive and also represents one of the very few pyrochemical processes that has been carried through pilot-plant scale on irradiated fuel. Unknowns exist, such as the rate and conditions of uranate dissolution, but considerable use could be made of previously documented results. 

Electrorefining (ER) Salt Recovery. Approximately 8% (500 g) of the plutonium in an electrorefining run is lost to the salt phase. Historically, this waste stream was recovered by aqueous processing. The salts are now recovered pyrochemically by salt stripping. This operation consists of contacting the molten salt residue with calcium metal, resulting in the reduction of PuCls to metal and the coalescence of metallic plutonium shot. The process results in the formation of a metallic plutonium button (96% yield), a large white salt phase, and a small black salt phase. 

As indicated in the reference flow sheet for oxide fuels (Fig. 1) the processing of the fuel constituents requires a reduction step. Pyrochemical reduction of UO2 >(14) Pu02, (15) and... 

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