NOTICE This document contains information of a preliminary nature. It is subject to revision or correction and therefore does not represent a final report. ABSTRACT Geochemical information relevant to the potential mobility of radionuclides at the Hanford Site and the Yucca Mountain site, candidate sites for highlevel nuclear waste geologic repositories being developed by Department of Energy projects, is being evaluated by Oak Ridge National Laboratory (ORNL) for the U.S. Nuclear Regulatory

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... mission. Neptunium(V) sorption isotherms in three different basalt/synthetic groundwater systems were initiated this quarter. Uranium(V1) sorption isotherms were completed with McCoy Canyon basalt and synthetic groundwater GR-2. The control of U(V1) solutions at a level of -loe4 mol/L is apparently dominated by the precipitation of sodium boltwoodite. Different apparent concentration limits for uranium were obtained with GR-2 and GR-4 solutions. The results suggest that uranium sorption/solubility behavior could be substantially different in the various basalt units likely t o be encountered by groundwater during migration from the waste package to the accessible environment. The EQ3/6 software package was implemented and tested on the ORNL computer system.