Performance of Asphalt and Clay Liners as a Uranium Mill Tailings Leachate Barrier
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THE SCIENTIFIC BASIS FOR NUCLEAR WASTE MANAGEMENT Stephen V. Topp,editor
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PERFORMANCE OF ASPHALT AND CLAY LINERS AS A URANIUM MILL TAILINGS LEACHATE BARRIER
JAMES BUELT AND STEVE BARNES Pacific Northwest Laboratory, P.O. Box 999, Richland, WA,USA Work supported by the U.S. Department of Energy under Contract DE-ACO6-76RLO 1830
ABSTRACT Pacific Northwest Laboratory is evaluating the long-term effectiveness of various asphalt and clay liner materials as a radionuclide and process chemical barrier from uranium mill tailings. A field test is being conducted by monitoring asphalt and clay liners installed at the Grand Junction, Colorado tailings site. In addition eight prospective liners have undergone three months exposure to accelerated conditions to predict their behavior over a 1000 year period. High calcium leachates have been forced through thin layers of clay to determine the ability of the clay to resist ion exchange, which reduces its swelling capabilities. Asphalt liners have been exposed to elevated temperatures and increased strengths of oxidizing agents to accelerate their aging process. The permeability coefficients measured during this exposure were then used to predict each liners stability with time. The analyses thus far show that clay soils with bentonite amendments and most asphalt compositions have good long-term performance characteristics.
INTRODUCTION In 1978, Public Law 95-604 was passed requiring the remedial action of 25 inactive uranium mill tailings piles located throughout the United States. For some of the 25 sites, it may be necessary under this law to relocate the tailings piles with appropriate leachate, radon, animal, and vegetative barriers that will be effective for 1000 years. Pacific Northwest Laboratory (PNL) is performing for the U.S. Department of Energy a comparative evaluation of the performance of various liner materials as long-term leachate barriers. This report presents the results of that study. MATERIALS AND METHODOLOGY The approach of this study has been to expose various liner materials to accelerated aging conditions in the laboratory and actual conditions in the field. A screening study was employed to identify the eight most promising materials based on the results of industrial experience and past studies published in the literature [1]. The eight materials selected were:
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natural soil as it exists at the disposal site natural soil amended with sodium bentonite
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natural soil amended with Saline Seal - 100*
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natural soil amended with GSR-60* hydraulic asphalt concrete catalytic airblown asphalt rubberized asphalt
chlorosulfanated polyethylene (hypalon)
Accelerated aging conditions The behavior of soil amendments and asphalt and synthetic liners is such that different accelerated testing methodologies had to be employed. The soils and amendments degrade by ion exchange of Na with Ca which reduces their swelling capabilities. The ion exchange rate is being accelerated with time by forcing a large number of pore volumes of leachate
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