Sizing Requirements for Flow-Through Geochemical Tests: Theoretical Considerations and Model Results
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SIZING REQUIREMENTS FOR FLOW-THROUGH GEOCHEMICAL TESTS: THEORETICAL CONSIDERATIONS AND MODEL RESULTS
JAMES D.HOOVER and EDWARD C. THORNTON Westinghouse Hanford Company, P.O. Box 1970, Richland, WA 99352 ABSTRACT A methodology for evaluating test apparatus size requirements has been applied to the sizing of flow-through tests used in the evaluation of coupled reaction and transport processes. The results of the sizing evaluation constrain the apparatus dimensions and test conditions capable of yielding results representative of the processes of interest. The size requirements of flow-through tests involving a system of simplified granite and groundwater were determined in order to demonstrate the feasibility and implications of sizing evaluations. Reaction path simulations were performed using the E03/6 codes at temperatures of 25 0 C, 100 0 C, and 200 0C. The determination of reaction path as a function of time was then used to obtain minimum column residence time requirements. Simulation results indicate that column lengths required for development of quasistatic equilibrium reaction zones at 2000 C are three times smaller than at 100oC, and over 36 times smaller than at 25 0 C. A range of possible combinations of column dimensions and flow rates for a set of model test conditions exist for a given residence time. The most appropriate combinations depend on the purpose of the test, the process of interest, and factors such as test duration, sampling requirements, and engineering limitations. Size and scale evaluations thus provide a technical basis for the design and construction of flow-through tests, and have profound implications for the interpretation of test results. INTRODUCTION
Flow-through reaction column tests can be utilized in evaluating coupled reaction and transport processes in open systems. The processes most commonly investigated with the flow-through apparatus include dissolution, precipitation, and sorption associated with the interactions between a geologic medium and groundwater. Tests related to environmental activities may also involve waste constituents and associated components. Flow-through tests designed to simulate the processes expected in the vicinity of underground geologic repositories include evaluation of hydrothermal and metasomatic reactions, oxidation-reduction reactions, and colloidal processes. The most important, and often overlooked, aspect of such tests is whether they are designed to yield results that accurately represent the processes and conditions of interest. Determination of the operable processes and appropriate conditions of testing are integral to the test design. Failure to consider size/scale requirements can yield unrepresentative or misleading information that can adversely impact Mat. Res. Soc. Symp. Proc. Vol. 176. 91990 Materials Research Society
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assessments of performance. This study represents an attempt to quantitatively determine the size and scale requirements for advection dominated flow-through tests. Theoretical considerations of the size a
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