Plutonium processing solid

The complete chemistry of plutonium 1 iquid-to-solid conversion processes, especially peroxide and oxalate precipitation, should be further studied. Research and development of direct thermal denitration methods should also be pursued. 

Precipitation Processes. Plutonium peroxide precipitation is used at Rocky Flats to convert the purified plutonium nitrate solution to a solid (14) the plutonium peroxide is then calcined to Pu02 and sent to the reduction step. The chemistry of the plutonium peroxide precipitation process is being studied, as well as alternative precipitation processes such as oxalate, carbonate, fluoride, and thermal denitration. The latter method shows the most promise for cost and waste reduction. 

Waste Treatment. Figure 2 outlines the current waste recovery and treatment processes, and proposed changes. Acid waste streams are sent through nitric acid and secondary plutonium recovery processes before being neutralized with potassium hydroxide and filtered. This stream and basic and laundry waste streams are sent to waste treatment. During waste treatment, the actinides in the aqueous waste are removed by three stages of hydroxide-iron carrier-flocculant precipitation. The filtrate solution is then evaporated to a solid with a spray dryer and the solids are cemented and sent to retrievable storage. 

Both preformed and in situ ferrite lowered plutonium concentrations in simulated process waste from 10-4 g/1 to 10-8 g/1 in one treatment step. Two or three flocculant precipitations, as currently used for waste processing, were required to achieve the same result. Ferrite waste treatment produced 4.1 g/1 solids, while production waste processing during the past year, using the flocculant process, produced 7.9 g/1 solids. 

Allhough Ihe ceramification and SYNROC lechnologies are being researched to develop a final waste form for plutonium-contaminated materials, no experiments with plutonium have been performed. The SMITE process is designed for the treatment of solid, inorganic materials. The final waste form will leach in acidic solutions so storage in a basic environment is recommended. 

Reprocessing is based on liquid-liquid extraction for the recovery of uranium and plutonium from used nuclear fuel (PUREX process). The spent fuel is first dissolved in nitric acid. After the dissolution step and the removal of fine insoluble solids, an organic solvent composed of 30% TriButyl Phosphate (TBP) in TetraPropylene Hydrogenated (TPH) or Isopar L is used to recover both uranium and plutonium the great majority of fission products remain in the aqueous nitric acid phase. Once separated from the fission products, back-extraction combined with a reduction of Pu(I V) to Pu(III) allows plutonium to be separated from uranium these two compounds can be recycled.2... 

A variety of methods have been used to characterize the solubility-limiting radionuclide solids and the nature of sorbed species at the solid/water interface in experimental studies. Electron microscopy and standard X-ray diffraction techniques can be used to identify some of the solids from precipitation experiments. X-ray absorption spectroscopy (XAS) can be used to obtain structural information on solids and is particularly useful for investigating noncrystalline and polymeric actinide compounds that cannot be characterized by X-ray diffraction analysis (Silva and Nitsche, 1995). X-ray absorption near edge spectroscopy (XANES) can provide information about the oxidation state and local structure of actinides in solution, solids, or at the solution/ solid interface. For example, Bertsch et al. (1994) used this technique to investigate uranium speciation in soils and sediments at uranium processing facilities. Many of the surface spectroscopic techniques have been reviewed recently by Bertsch and Hunter (2001) and Brown et al. (1999). Specihc recent applications of the spectroscopic techniques to radionuclides are described by Runde et al. (2002b). Rai and co-workers have carried out a number of experimental studies of the solubility and speciation of plutonium, neptunium, americium, and uranium that illustrate combinations of various solution and spectroscopic techniques (Rai et al, 1980, 1997, 1998 Felmy et al, 1989, 1990 Xia et al., 2001). 

A prime responsibility of the Rocky Flats Plant since it was built by the Atomic Energy Commission some 25 years ago has been the recovery and purification of plutonium. This recovery and purification has been done using an aqueous process. One of the major steps in that process is the precipitation of plutonium peroxide. This step converts the plutonium from an aqueous to a solid form for further processing and conversion to metal. 

The solid (U,Pu)2Zni7 intermetallic compound, containing FP-3 and selective FP-4 fission products for proliferation resistance is vacuum distilled to remove the zinc, which is recycled. The uranium/plutonium concentrate is injection cast into rods suitable as feed to the refabrication process. 

At the tail end of a solvent extraction process, the solvents are separated from the solutes for recycle. In this application of solvent extraction, vacuum distillation is used to separate volatile zinc and magnesium from coprocessed uranium and plutonium and from the uranium product. Feed to vacuum distillation is solid alloy. Overhead and bottom products are likwise cast into a solid alloy. These vacuum distillation operations are conducted in separate cells. The actinide products are converted to oxide for fuel fabrication. 

Ferrous sulfamate has been the reductant for plutonium during partitioning of uranium and plutonium in the Purex process at SRP since startup. In recent years, a desire to reduce waste volumes has led to studies of alternative reductants or combinations of FeSA with other reductants. The FeSA in the Pu strip solution produces Fe(OH) 3 and Na2S0i in neutralized waste these compounds account for a large percentage of the solid material in Purex low activity waste. In an effort to reduce these wastes, we investigated HAN as a substitute for part or all of the FeSA in the Purex first cycle. 

---