Long-Term Performance of Uranium Tailings Disposal Cells - 13340

Conference · Mon Jul 01 00:00:00 EDT 2013

OSTI ID:22221333

Bostick, Kent; Daniel, Anamary; Pill, Ken ^[1]; Tachiev, Georgio; Noosai, Nantaporn; Villamizar, Viviana ^[2]

---

1. Professional Project Services, Inc., 1100 Bethel Valley Road, Oak Ridge, TN, 37922 (United States)
2. Florida International University, 10555 W. Flagler St., EC 2100, Miami FL, 33174 (United States)

Recently, there has been interest in the performance and evolution of Uranium Mill Tailings Remedial Action (UMTRA) Project disposal cell covers because some sites are not compliant with groundwater standards. Field observations of UMTRA disposal cells indicate that rock covers tend to become vegetated and that saturated conductivities in the upper portion of radon barriers may increase due to freeze/thaw cycles and biointrusion. This paper describes the results of modeling that addresses whether these potential changes and transient drainage of moisture in the tailings affect overall performance of the disposal cells. A numerical unsaturated/saturated 3-dimensional flow model was used to simulate whether increases in saturated conductivities in radon barriers with rock covers affect the overall performance of the disposal cells using field data from the Shiprock, NM, UMTRA site. A unique modeling approach allowed simulation with daily climatic conditions to determine changes in moisture and moisture flux from the disposal cell. Modeling results indicated that increases in the saturated conductivity at the top of radon barrier do not influence flux from the tailings with time because the tailings behave similar hydraulically to the radon barrier. The presence of a thin layer of low conductivity material anywhere in the cover or tailings restricts flux in the worst case to the saturated conductivity of that material. Where materials are unsaturated at depth within the radon barrier of tailings slimes, conductivities are typically less than 10{sup -8} centimeters per second. If the low conductivity layer is deep within the disposal cell, its saturated properties are less likely to change with time. The significance of this modeling is that operation and maintenance of the disposal cells can be minimized if they are allowed to progress to a natural condition with some vegetation and soil genesis. Because the covers and underlying tailings have a very low saturated hydraulic conductivity after transient drainage, eventually the amount of moisture leaving the tailings has a negligible effect on groundwater quality. Although some of the UMTRA sites are not in compliance with the groundwater standards, the explanation may be legacy contamination from mining, or earlier higher fluxes from the tailings or unlined processing ponds. Investigation of other legacy sources at the UMTRA sites may help explain persistent groundwater contamination. (authors)

• Research Organization: WM Symposia, 1628 E. Southern Avenue, Suite 9-332, Tempe, AZ 85282 (United States)
• OSTI ID: 22221333
• Report Number(s): INIS-US-13-WM-13340; TRN: US14V0524042288
• Resource Relation: Conference: Waste Management 2013 - WM2013 Conference: International collaboration and continuous improvement, Phoenix, AZ (United States), 24-28 Feb 2013; Other Information: Country of input: France; 10 refs.
• Country of Publication: United States
• Language: English

Related Subjects

12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
54 ENVIRONMENTAL SCIENCES
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
BIOINTRUSION
COMPLIANCE
DIFFUSION BARRIERS
FEED MATERIALS PLANTS
FLOW MODELS
GROUND WATER
HYDRAULIC CONDUCTIVITY
MAINTENANCE
MOISTURE
PERFORMANCE
RADIOACTIVE WASTE DISPOSAL
RADON
REMEDIAL ACTION
SIMULATION
SOILS
TAILINGS
THIN FILMS
URANIUM