Pilot and Field-Scale Uranium Lysimeter Studies at the Oak Ridge Y-12 Plant
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PILOT AND FIELD-SCALE URANIUM LYSIMETER STUDIES AT THE OAK RIDGE Y-12 PLANT DIANNE D. GATES', CHET W. FRANCIS', LISA M. LASTER** and ROD KIMMITI** *Oak Ridge National Laboratory, Environmental Sciences Division, Oak Ridge, TN 37831 "*Oak Ridge Y-12 Plant, Waste Management Division, Oak Ridge, TN 37831
ABSTRACT
Field- and pilot-scale uranium leaching facilities (lysimeters) have been constructed at the Oak Ridge Y-12 Plant to investigate the rate of uranium (U) leaching and the residual U concentration that can be expected when low level radioactive waste (LLW) is buried in landfills. Current plans are to load three large standard column lysimeters with compacted production trash (blotter, waste wipes, paper etc.) and apply groundwater to the surface of the lysimeters. Several issues had to be addressed before the field lysimeters could be loaded with the LLW. Predominate among these concerns was how to adequately characterize the waste placed in the lysimeters (- 10 yd3 waste per lysimeter) and how to effectively collect in situ leachate samples from compacted wasteforms in the absence of soil. Pilot scale studies revealed that monitoring individual bags (30 gal) of LLW with a waste curie monitor would be sufficient to determine the initial U loading and that conventional suction candles would perform adequately within the compacted waste for extended time periods if they are installed properly. In the pilot leaching studies, the highest U concentration (- 0.2 mg/1) in the leachate was observed during the first month of leaching, before active biological decomposition processes became dominant making the lysimeter anoxic. After the initial oxic flushing, U concentrations in the leachate became very low (mean = 0.021 mg/I).
INTRODUCTION
The Oak Ridge Y-12 Plant initiated the Uranium Lysimeter Demonstration Project in 1988 to investigate potential impacts of new disposal facilities for solid low-level waste (LLW) generated at the Plant. The research activities were designed to provide comprehensive data on the long term fate of depleted uranium disposed of in the Oak Ridge Y-12 landfills. Previous lysimeter studies involving radionuclides typically included radioactive wasteforms buried in soil filled lysimeters outfitted with a variety of standard soil monitoring equipment.'," Determining the radionuclide source term for pathway models using such data is difficult because the effect of soil attenuation on nuclide transport cannot be assessed independently. The Y-12 Uranium Lysimeter Demonstration activities were designed to evaluate the fate of radionuclides independent of soil attenuation, although wastes will have a soil cover to simulate the inflow typically formed beneath an earthen cap. This paper describes the field lysimeter facilities that were constructed and gives the results of pilot-scale studies designed to assist in the loading and operation of the field lysimeters.
Mat. Res. Soc. Symp. Proc. Vol. 294. 01993 Materials Research Society
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FIELD LYSIMETER FACILITIES
The Y-12 field lysimeter fac
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