Predicting long-term moisture contents of earthen covers at uranium mill tailings sites
The three methods for long-term moisture prediction covered in this report are: estimates from water retention (permanent wilting point) data, correlation with climate and soil type, and detailed model simulation. The test results have shown: soils vary greatly in residual moisture. Expected long-term moisture saturation ratios (based on generalized soil characteristics) range from 0.2 to 0.8 for soils ranging in texture from sand to clay, respectively. These values hold for noncompacted field soils. Measured radon diffusion coefficients for soils at 15-bar water contents ranged from 5.0E-2 cm/sup 2//s to 5.0E-3 cm/sup 2//s for sands and clays, respectively, at typical field densities. In contrast, fine-textured pit-run earthen materials, subjected to optimum compaction (>85% Proctor density) and dried to the 15-bar water content, ranged from 0.7 to 0.9 moisture saturation. Compacted pit-run soils at these moisture contents exhibited radon diffusion coefficients as low as 3.0E-4 cm/sup 2//s. The residual moisture saturation for cover soils is not known since no engineered barrier has been in place for more than a few years. A comparison of methods for predicting moisture saturation indicates that model simulations are useful for predicting effects of climatic changes on residual soil moisture, but that long-term moisture also can be predicted with some degree of confidence using generalized soil properties or empirical correlations based both on soils and climatic information. The optimal soil cover design will likely include more than one layer of soil. A two-layer system using a thick (1-m minimum) plant root zone of uncompacted soil placed over a moistened, tightly compacted fine-textured soil is recommended. This design concept has been tested successfully at the Grand Junction, Colorado, tailings piles.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 6432626
- Report Number(s):
- DOE/UMT-0220; PNL-5047; ON: DE85000777
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
COVERINGS
MOISTURE
MILL TAILINGS
COMPACTING
DIFFUSION
RADON 222
SOILS
THICKNESS
ALPHA DECAY RADIOISOTOPES
DAYS LIVING RADIOISOTOPES
DIMENSIONS
EVEN-EVEN NUCLEI
HEAVY NUCLEI
ISOTOPES
NUCLEI
RADIOISOTOPES
RADON ISOTOPES
SOLID WASTES
TAILINGS
WASTES
054000* - Nuclear Fuels- Health & Safety
053000 - Nuclear Fuels- Environmental Aspects
052002 - Nuclear Fuels- Waste Disposal & Storage