Technology:
Segmented Gate System (SGS)
- SGS is a combination of conveyor systems, radiation detectors (primarily gamma radiation), and computer control used to segregate waste by contamination levels
- Detectors monitored radioactivity content of soil traveling on belt and computer opened specified gates to separate portions of soil based on radioactivity criteria
- Contaminated soil on conveyor belt was diverted by segmented gates into stockpiles, based on the criteria
- Operating parameters included a belt speed of 30 ft/min, belt length of 16 18 ft, soil layer thickness of 1 - 2 in by width of 30.75 in, and soil density of 1.0 g/cm3
- Oversize debris and rock were pre-screened
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Cleanup Authority:
RCRA Corrective Action
Management Support:
Tom Burford
Sandia National Laboratories
(505) 845-9893 | Technical Contact:
Mike Hightower
Sandia National Laboratories
(505) 844-5499 |
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Contaminants:
Plutonium
- Concentrations reported as high as 1,100 pCi/g |
Waste Source:
Weapons test range |
Type/Quantity of Media Treated:
Soil and Debris
- 333 yds3 of soil were processed
- Soil was primarily sand and silt with some gravel and cobbles; soil type and moisture content optimal for SGS operation |
Purpose/Significance of Application:
Use of a gate system to reduce soil volume requiring off-site disposal |
Regulatory Requirements/Cleanup Goals:
- Reduce the volume of contaminated soil by separating soil that was above the specified criteria and that would require off-site storage and disposal, from soil that was below the criteria
- The sorting criterion was 50 1,500 pCi/g; demonstration results were to be used to define optimum operating parameters |
Results:
- 79 runs were conducted, each characterized by different soil activity levels, operating parameters, and end points (sorting criterion)
- Results showed that optimum separation criteria for soils with <400 pCi/g was about 300 pCi/g, resulting in a volume reduction of 60% and an average clean soil activity of 160 pCi/g
- Soils between 400 800 pCi/g did not appear to have an optimum separation criterion, and had a volume reduction of 30 40% and an average clean soil activity of 250 pCi/g
- Soils >800 pCi/g did not appear to have an optimum separation criterion, and had a volume reduction of 30% and an average clean soil activity of 500 pCi/g; this clean soil activity was too high and suggested that processing soil with >800 pCi/g would probably not be appropriate |
Cost Factors:
- Actual cost for SGS was $138,126, including $8,203 for regulatory and compliance issues, $29,614 for mobilization, $78,545 for physical treatment, and $21,764 for demobilization |
Description:
Tonapah Test Range is a DOE and DoD weapons testing range. The Clean Slate-2 soil remediation site of the range is in the northwest portion of Nellis Air Force Base. In 1963, a series of four nuclear weapons, component, and explosive vulnerability destruction experiments, known as Operation Roller Coaster, were conducted at the range. These experiments left varying levels of finely dispersed plutonium at the site. Approximately 32,000 yds3 of soil in Clean Site-2 are contaminated, with the site still being characterized.
A Segmented Gate System (SGS) was used to reduce the volume of contaminated soil that required off-site disposal. SGS is a combination of conveyor systems, radiation detectors, and computer control, where contaminated soil on a conveyor belt is diverted by segmented gates into stockpiles based on contamination levels. Detectors monitor the radioactivity content of the soil traveling on the belt and a computer opens specified gates to separate portions of the soil based on radioactivity criteria. At this site, 79 periods of operation (runs) were conducted, each characterized by different soil activity levels, operating parameters, and end points (sorting criterion) ranging from 50 to 1,500 pCi/g. Results showed that optimum separation criteria for soils with <400 pCi/g was about 300 pCi/g, resulting in a volume reduction of 60% and an average clean soil activity of 160 pCi/g. Soils >400 pCi/g did not appear to have an optimum separation criterion. Results suggested that processing soil with >800 pCi/g would probably not be appropriate for the SGS. Actual cost for SGS was $138,126, including $78,545 for soil processing. Results from these tests were used to develop potential treatment scenarios for the SGS at Clean Slate-2. Lessons learned covered topics such as the need for accurate site characterization data and the benefits of selective excavation of hot spots. |
