Multidimensional simulation of radon diffusion through earthen covers
The purpose of this report is to document applications of the RADMD model used at PNL to perform analyses of radon diffusion through uranium mill tailings cover systems. The accuracy of the numerical formulation of the RADMD model was demonstrated through a comparison with a two-dimensional analytic solution to the radon diffusion equation. Excellent agreement was obtained between two-dimensional radon concentration profiles predicted by RADMD and those obtained with the analytic solution. A simulation was made of radon diffusion into a test canister using the two dimensional capabilities of RADMD. The radon flux profile was computed and illustrates the effects of the canister on the surface radon flux. The influence of the canister on the radon flux was shown to be significant under certain circumstances. Defects in earthen cover systems were evaluated using the three dimensional capabilities of RADMD. The results support the expectation that defective covers can increase the surface flux from a covered talings pile. Compared to a cover with no defects, radon flux could be elevated by as much as a factor of three when 20% of the radon control layer area contained pockets of reduced moisture. The effects of temporal and spatial variations in moisture content have been modeled by coupling RADMD with a variable saturated flow model. Two dimensional simulations were made of the time dependence of radon flux from a tailings site before and after cover placement. The results demonstrated the expected flux reduction produced by a thick earthen cover. Time dependence of the radon flux after cover placement was attributed to slight changes in moisture content of the cover material with time. The particular cover studied had a compacted clay layer that effectively attenuated the radon.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 6612136
- Report Number(s):
- DOE/UMT-0212; PNL-4458; ON: DE83005253
- Country of Publication:
- United States
- Language:
- English
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RADIOACTIVE WASTE DISPOSAL
MILL TAILINGS
RADON
DIFFUSION
SOILS
RADIONUCLIDE MIGRATION
COMPUTERIZED SIMULATION
COVERINGS
ENGINEERED SAFETY SYSTEMS
RADIATION MONITORING
ELEMENTS
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FLUIDS
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RARE GASES
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WASTE DISPOSAL
WASTE MANAGEMENT
WASTES
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052002 - Nuclear Fuels- Waste Disposal & Storage
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Terrestrial- Radioactive Materials Monitoring & Transport- Soil- (-1987)