Progress in evaluation of radionuclide geochemical information developed by DOE high-level nuclear waste repository site projects; Report for October 1987--June 1989

Abstract

Information that is being developed by projects within the Department of Energy (DOE) pertinent to the potential geochemical behavior of radionuclides at candidate sites for a high-level radioactive waste repository is being evaluated by Oak Ridge National Laboratory (ORNL) for the Nuclear Regulatory Commission (NRC). During this report period, all experiments were conducted with tuff from the proposed high-level nuclear waste site at Yucca Mountain, Nevada. The principal emphasis in this report period was on column studies of migration of uranium and technetium in water from well J-13 at the Yucca Mountain site. Columns 1 cm in diameter and about 5 cm long were constructed and carefully packed with ground tuff. The characteristics of the columns were tested by determination of elution curves of tritium and TcO{sub 4}{sup {minus}}. Elution peaks obtained in past studies with uranium were asymmetrical and the shapes were often complex, observations that suggested irreversibilities in the sorption reaction. To try to understand these observations, the effects of flow rate and temperature on uranium migration were studied in detail. Sorption ratios calculated from the elution peaks became larger as the flow rate decreased and as the temperature increased. These observations support the conclusion that the sorptionmore » of uranium is kinetically hindered. To confirm this, batch sorption ratio experiments were completed for uranium as a function of time for a variety of conditions. « less

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