Nuclear and Chemical Waste Management最新文献

An extensive well installation program of approximately 600 wells in the ORNL area was initiated in December, 1985. At that time it was recognized that subcontractor personnel involved in the Laboratory's characterization effort might encounter radioactive or other hazardous materials that could result in significant levels of exposure. A program was established to provide for categorization of health hazard protection for those individuals involved in the characterization effort. This paper will address the steps that were taken to evaluate proposed sites for subcontractor activity, assumptions used to categorize the level of health risk, and the procedures established for assignment of appropriate protective equipment.

Significant amounts of cobalt are present in readily accessible spent copper leach solutions. The Bureau of Mines investigated the feasibility of extracting cobalt from one of these solutions in a multiple-compartment ionexchange (MCIX) column. The effects of aqueous flow rate, resin flow rate, column height, and compartment height on cobalt extraction were determined. Cobalt extractions of 92% or higher were achieved at solution flow rates of up to 5.5 gpm/ft² (13.4 m³/h m²) of column cross-sectional area and an aqueous-to-resin flow ratio of 40:1. Overall cobalt extraction increased as the column height increased, but cobalt extraction per unit of height was more efficient in 2.4 and 3.7 m columns that in a 5.5 m column. Solvent extraction procedures were utilized to purify and concentrate the MCIX column eluates and produce a cobalt sulfate solution containing 70 to 80 g/L Co. Metallic cathodes, containing over 99% Co, were electrowon from this solution. Nickel, zinc, and copper byproducts were also recovered during processing of the ion-exchange eluates.

Estimated total capital cost for a commercial-scale plant processing 10,000 gpm (2,270 m3/h) of a spent leach solution containing 26 mg/L Co was $23.1 million (U.S.). With credits for zinc, nickel, and copper byproducts, the estimated net operating cost was $5.10/lb ($11.24/kg) of cobalt.

Understanding of container corrosion is fundamental to long term isolation of nuclear waste. One aspect of corrosion which is difficult to examine experimentally is the formation of large scale corrosion cells. Initiation of the phenomenon in environments where diffusional transport dominates requires very long time periods, generally longer than experimental time frames. A mathematical model is developed to evaluate formation of large scale corrosion cells surrounding steel containers. The model includes transport of nine species by diffusion and electromigration with simultaneous chemical reaction. The model can be applied in partially or fully water saturated environments. The governing equations are first examined in dimensionless format to illustrate some of the important factors controlling cell strength. Numerical solutions to two general classes of problem are examined (a) differential aeration, and (b) spatial variation in passivation current. The focus is on whether predicted changes in solution composition attributable to the cells are large enough to significantly impact further corrosion and/or radionuclide release rate subsequent to localized container breach. The analysis suggests that large scale cells are likely to be an important factor in waste isolation.

Fatigue-crack propagation tests were conducted on a candidate container material (ASTM A27 steel) tested in Hanford groundwater at 150°C for application in a potential basalt repository. Tests were run at a single value of stress intensity factor on groups of identical specimens undergoing gamma irradiation and control specimens not exposed to irradiation. The gamma flux levels (approx. 123 rad/hour) were prototypic of the maximum levels expected at the outer surface of the waste container. A statistical evaluation suggested that there were no significant differences between crack growth rates in the unirradiated and irradiated specimens.