An Unsteady Dual Porosity Representation Of Concrete Rubble Disposal
Journal Article
·
OSTI ID:890054
Decontamination and decommissioning at the Savannah River Site have produced on-site disposals of low-level solid radioactive waste in the form of concrete rubble. In the case of a former tritium extraction facility, building demolition produced a significant volume of rubble embedded with tritium. The contaminated debris comprises a heterogeneous mixture of sizes, shapes, and internal tritium distributions. The rubble was disposed in long, shallow, unlined, earthen trenches, that were subsequently backfilled with excavated soil and exposed to normal infiltration. To forecast tritium flux to the water table, an unsteady dual porosity model was developed to describe vadose zone leaching and transport. Tritium was assumed to be released through unsteady, one-dimensional, molecular diffusion within concrete, while advective and diffusive transport occur in the surrounding backfill. Rubble size and shape variations were characterized through a combination of physical measurement and photographic image analysis. For simplicity, the characterization data were reduced to an approximately equivalent distribution of one-dimensional slab thicknesses for representation in the dual porosity formulation. Each size classification was simulated separately, and individual flux results were then blended in proportion to the thickness distribution to produce a composite flux. The fractional flux from concrete rubble was predicted to be roughly 40% of that from tritium-contaminated soil. The lower flux is a result of slower release to soil pore water, and a reduced effective trench conductivity from the presence of impervious concrete.
- Research Organization:
- SRS
- Sponsoring Organization:
- DOE
- OSTI ID:
- 890054
- Report Number(s):
- WSRC-MS-2006-00167
- Country of Publication:
- United States
- Language:
- English
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