Chemical species of plutonium in Hanford radioactive tank waste

Conference · Wed Oct 22 00:00:00 EDT 1997

OSTI ID:10154060

Barney, G S

Large quantities of radioactive wastes have been generated at the Hanford Site over its operating life. The wastes with the highest activities are stored underground in 177 large (mostly one million gallon volume) concrete tanks with steel liners. The wastes contain processing chemicals, cladding chemicals, fission products, and actinides that were neutralized to a basic pH before addition to the tanks to prevent corrosion of the steel liners. Because the mission of the Hanford Site was to provide plutonium for defense purposes, the amount of plutonium lost to the wastes was relatively small. The best estimate of the amount of plutonium lost to all the waste tanks is about 500 kg. Given uncertainties in the measurements, some estimates are as high as 1,000 kg (Roetman et al. 1994). The wastes generally consist of (1) a sludge layer generated by precipitation of dissolved metals from aqueous wastes solutions during neutralization with sodium hydroxide, (2) a salt cake layer formed by crystallization of salts after evaporation of the supernate solution, and (3) an aqueous supernate solution that exists as a separate layer or as liquid contained in cavities between sludge or salt cake particles. The identity of chemical species of plutonium in these wastes will allow a better understanding of the behavior of the plutonium during storage in tanks, retrieval of the wastes, and processing of the wastes. Plutonium chemistry in the wastes is important to criticality and environmental concerns, and in processing the wastes for final disposal. Plutonium has been found to exist mainly in the sludge layers of the tanks along with other precipitated metal hydrous oxides. This is expected due to its low solubility in basic aqueous solutions. Tank supernate solutions do not contain high concentrations of plutonium even though some tanks contain high concentrations of complexing agents. The solutions also contain significant concentrations of hydroxide which competes with other potential complexants. The sodium nitrate and sodium phosphate salts that form most of the salt cake layers have little interaction with plutonium in the wastes and contain relatively small plutonium concentrations. For these reasons the authors consider plutonium species in the sludges and supernate solutions only. The low concentrations of plutonium in waste tank supernate solutions and in the solid sludges prevent identification of chemical species of plutonium by ordinary analytical techniques. Spectrophotometric measurements are not sensitive enough to identify plutons oxidation states or complexes in these waste solutions. Identification of solid phases containing plutonium in sludge solids by x-ray diffraction or by microscopic techniques would be extremely difficult. Because of these technical problems, plutonium speciation was extrapolated from known behavior observed in laboratory studies of synthetic waste or of more chemically simple systems.

• Research Organization: Fluor Daniel Hanford Inc., Richland, WA (United States)
• Sponsoring Organization: USDOE Office of Environmental Restoration and Waste Management, Washington, DC (United States)
• DOE Contract Number: AC06-96RL13200
• OSTI ID: 10154060
• Report Number(s): HNF-SA-3181-FP; CONF-9708192-; ON: DE99050331; BR: EW3120071; TRN: AHC29928%%3
• Resource Relation: Conference: American Chemical Society symposium,Orlando, FL (United States),25 Aug 1997; Other Information: PBD: 22 Oct 1997
• Country of Publication: United States
• Language: English

Related Subjects

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
HANFORD RESERVATION
RADIOACTIVE WASTE STORAGE
PLUTONIUM COMPOUNDS
SPECIFICITY
RADIOACTIVE WASTES
TRACE AMOUNTS
400702
052002
PROPERTIES OF RADIOACTIVE MATERIALS
WASTE DISPOSAL AND STORAGE