Evaluation of Radionuclide Transport: Effect of Radionuclide Sorption and Solubility
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EVALUATION OF RADIONUCLIDE TRANSPORT:
EFFECT OF RADIONUCLIDE
SORPTION AND SOLUBILITY P. F. SALTER AND G. K. JACOBS Basalt Waste Isolation Project, Rockwell Hanford Operations, Richland, Washington 99352
P. 0. Box 800,
INTRODUCTION The current strategy for the permanent isolation of nuclear wastes in the United States involves the storage of these wastes within repositories mined in deep geologic formations.
In this disposal strategy, the isola-
tion of nuclear wastes relies on a series of natural and engineered barriers to prevent the unacceptable release of radionuclides to the accessible environment.
An integral part of the development of a qualified
subsurface nuclear waste repository, therefore, is the assessment of the ability of these barriers to adequately prevent or retard the migration of radionuclides to the accessible environment. Project (BWIP)
The Basalt Waste Isolation
under guidance from the Department of Energy (DOE)
is investigating the feasibility of storing nuclear w-stes in the basalts beneath the Hanford Site. The most probable mechanism for radionuclide release from a repository in the basalt geohydrologic system at the Hanford Site is dissolution and subsequent transport in groundwater. Therefore, the most important elements to be considered in evaluating radionuclide release and transport are: (1) the hydrologic properties of the system, (2) the physicochemical environment of the system, and (3) radionuclide sorption and solubility. The physicochemical
parameters are particularly important because they
control radionuclide sorption and solubility, the two dominant mechanisms for retardation of radionuclide transport in the basalt-groundwater system. An understanding of the sorption and solubility behavior of key radionuclides under relevant physicochemical conditions is necessary, therefore, to complete a safety assessment of the permanent storage of nuclear waste in basalt. In this paper, the sorption and solubility behavior of several potentially hazardous (key)
radionuclides in the Columbia River Basalt geohy-
drologic system is discussed.
Utilizing the transport characteristics of
the site and the available sorption and solubility data, a preliminary
802
site performance analysis then is performed through comparison of the resultant predicted radionuclide transport behavior with proposed U.S. environmental regulations. COLUMBIA RIVER BASALT ENVIRONMENT Geohydrology. The Columbia Plateau basalts in Southeastern Washington are tholeitic, continental, flood basalts. The basalt beneath the Hanford Site consists of a thick sequence of basalt flows of the Columbia River Basalt Group. Three formations within this group are of interest in the assessment of site performance. Sequentially up the stratigraphic column, they are the Grande Ronde (%50 flows), the Wanapum (%14 flows), and the Saddle Mountain (-,10 flows, shallowest) basalts. The Umtanum basalt flow within the Grande Ronde formation has been designated the reference repository horizon. A typical basalt flow is severa
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