No abstract

The high sensitivity technique of laser photoacoustic spectroscopy and optical absorption spectroscopy were utilized to investigate the hydrolysis of Pu(VI) in perchlorate media. Absorption bands attributed to the hydrolysis of Pu(VI) were characterized in the pH = 6–8 regime which is of most interest to the proposed repository site at Yucca Mountain. Evidence was presented that supported the assignment of the polynuclear species (640 nm species) reported previously \1] as (PuO2)3(OH)5+1. Some temperature-dependent LPAS spectra are reported. The results obtained were compared to the predicted speciation of the geochemical code EQ3NR using the associated data base.

Uranium concentrate (yellowcake) composites from four mills (Anaconda, Kerr-McGee, Highland, and Uravan) were analyzed for U-238, U-235, U-234, Th-230, Ra-226 and Pb-210. The ratio of specific activities of U-238 to U-234 in the composites suggested that secular radioactive equilibrium exists in the ore. The average activity ratios in the yellowcake were determined to be 2.7 x |0-3 (Th-230/U-238), 5 * \0~h (Ra-226/U-238) and 2 x lO" 1 * (Pb-2IO/U-238). Based on earlier EPA measurements of the release rates from the stacks, the amount of yellowcake released was determined to be 0.\% of the amount processed. The purpose of this study was to characterize yellowcake by its radioisotopic composition and estimate the release rate from stacks and packaging operations. Accordingly, samples were obtained from the following uranium mills: Anaconda Company (Grants, NM), Kerr-McGee Nuclear Corporation (Grants, NM), Union Carbide (Uravan, CO) and Exxon (Douglas, WY). These mills process the major portion of uranium mined in the United States and also represent the different geographical uranium-producing regions. Their processing characteristics are summarized below and have been previously reported in detail by Merritt (1971), Guccione (1974) and Coleman (1978). Anaconda Company, Bluewater, NM Leaching: Sulfuric acid and Mn02 Uranium Separation: Resin-in-pulp ion exchange (IRA-430 anion exchange resin with FeSO^ and MgO) to January 1, 1978. The process for extraction was changed to solvent extraction after an expansion in 1978.

Studies of inactive uranium tailings piles have shown that tailings sands containing Ra-226 and other radionuclides may be dispersed by wind and water erosion, causing contamination of adjacent areas. To conduct an effective cleanup operation, it is necessary that boundaries of contamination be well defined. To accomplish this, data from surface gamma-ray surveys made under the Measurement Monitoring Program of the U.S. DOE's Uranium Mill Tailings Remedial Action Project (UMTRAP) are first used to delineate a general outline of the contaminated area. Then, data fram portable scintillometer surveys and fran sealed-can gammaray analyses of soil samples are used to more precisely define the perimeter of Ra-226 contamination. These field measurements are supported by radiochemical analyses of randomly selected samples. Because of its adaptability to the widely varying chemical composition of the material in these samples, the camplexing agent EDTA is used in a complexometric leaching procedure to analyze Ra-226. By this procedure, natural concentrations of Ra-226 in soil (∼1 pCi/g) can be measured routinely. The potential limit of detection is in the 0.1–0.5 pCi/g range. Details of the method, which includes leaching of radium followed by radon de-eranation, are described. Comparative data for various soil and tailings samples are presented.

Effective diffusion coefficients for selected radionuclides have been measured in ocean floor sediments to provide data for the assessment of barrier effectiveness in subseabed repositories for nuclear waste. The sediments tested include illite-rich and smectite-rich red clays from the mid plate gyre region of the Pacific Ocean, reducing sediment from the continental shelf of the northwest coast of North America, and Atlantic Ocean sediments from the Southern Nares Abyssal Plain and the Great Meteor East region. Results show extremely small effective diffusion coefficients with values less than 10−14 m2s−1 for plutonium, americium, curium, thorium, and tin. Radionuclides with high diffusion coefficients of approximately 10−10 m2s− include the anionic species pertechnetate, TcO4−, iodide, I−, and selenite, SO3−2. Uranyl(VI) and neptunyl(V) ions which are stable in solution, have diffusion coefficients around 10−12m2s−1. The diffusion behavior of most radionuclides is similar in the oxygenated Pacific sediments and in the anoxic sediments from the Atlantic. An exception is neptunium, which is immobilized by Great Meteor East sedi-ment, but has high mobility in Southern Nares Abyssal Plain sediment. Under stagnant conditions a 30 m thick sediment layer forms an effective geologic barrier isolating radionuclides in a subseabed repository from the biosphere.