Preplanning for D and D: Monitoring the Vadose Zone at Radioactive Waste Trenches
- Washington Group, Safety Management Solutions, 2131 S. Centennial Dr., Aiken, SC 29803 (United States)
Planning for ultimate Decontamination and Decommissioning (D and D) of a nuclear facility is as much a part of a successful nuclear strategy as is the ultimate disposal of radioactive waste. As facilities, in this case radioactive waste disposal trenches, are closed and abandoned leading to ultimate decommissioning, long term monitoring may be required. However, preplanning by characterizing, modeling, and monitoring the environment around the facility prior to and during operations will allow a performance assessment to be made and future behavior predicted. In the radioactive waste burial grounds of the Savannah River Site new slit trenches were constructed to receive demolition debris associated with site foot print reduction. Some of the construction debris and associated process waste contained small amounts of tritium. Since the trenches were constructed over an existing tritium groundwater plume the monitoring and performance assessment of the trench, particularly with respect to tritium contributions to the vadose zone and groundwater, were important. These disposal trenches vary in length and width but are typically constructed within the upper 7 to 8 meters (21 to 24 feet) of the local sediments. The unconfined aquifer (water table) typically underlies the area at depths varying from 20 to 24 meters (60 to 72 feet), depending on elevation. Therefore, with downward flow and 13 to 16 meters (40 to 48 feet) of unsaturated sediments separating the base of the waste trenches from the unconfined aquifer, there was potential for an environmental impact to the sediments within the vadose zone and to the underlying groundwater. Monitoring and predicting this impact can support ultimate D and D activities and future performance assessment evaluation. From this work several key observations were made that will support long term monitoring and subsequent D and D: - The observed lateral variation of thinly bedded sands and clays may be less than 20 meters particularly if lenticular sands are present. Ultimate D and D should consider monitoring and remedial activities that consider sampling on scales to address this issue. - The detailed modeling, when compared with the modeled depositional patterns, indicates flow paths for vadose zone fluids, therefore a plan should allow for these flow paths. - Detailed lithostratigraphic modeling, when based on correlations between soil properties, CPT soundings and borehole geophysical logs, can aid in precision placement of subsurface sensors and sample points for performance monitoring and D and D assessment.
- Research Organization:
- American Nuclear Society, 555 North Kensington Avenue, La Grange Park, Illinois 60526 (United States)
- OSTI ID:
- 21144209
- Resource Relation:
- Conference: DD and R 2007: ANS Topical Meeting on Decommissioning, Decontamination, and Reutilization 2007, Chattanooga, TN (United States), 16-19 Sep 2007; Other Information: Country of input: France; 4 refs; Related Information: In: Proceedings of the 2007 ANS Topical Meeting on Decommissioning, Decontamination, and Reutilization - DD and R 2007, 336 pages.
- Country of Publication:
- United States
- Language:
- English
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