Thermo NUTtech (Segmented Gate System)

THERMO NUTECH

(formerly TMA THERMO ANALYTICAL, INC.)
(Segmented Gate System)

TECHNOLOGY DESCRIPTION:

TMA Thermo Analytical, Inc. (TMA), has conducted many radiological surveys of soil contaminated with low and intermediate levels of radioactivity. Cleanup of these sites is a highly labor-intensive process requiring numerous personnel to conduct radiological surveys with portable hand-held instruments. When contamination is encountered, an attempt is made to manually excise it. When surveys disclose larger areas of contamination, heavy equipment is used to remove the contaminated material. Since pinpoint excision with earthmoving equipment is difficult, large amounts of uncontaminated soil are removed along with the contaminant. Few sites have been characterized to be uniformly and/or homogeneously contaminated above release criteria over the entire site area.

As a result, TMA developed the Segmented Gate System (SGS) to physically separate and segregate radioactive material from otherwise "clean" soil (see figure below). The SGS removes only a minimal amount of clean soil with the radioactive particles, significantly reducing the overall amount of material requiring disposal. The SGS works by conveying radiologically contaminated feed material on moving conveyor belts under an array of sensitive, rapidly reacting radiation detectors. The moving material is assayed, and radioactivity content is logged. Copyrighted computer software tracks the radioactive material as it is transported by the conveyor and triggers a diversion by one or more of the SGS chutes when the material reaches the end of the conveyor. Clean soil goes in one direction, and contaminated material in another.

The key advantage to this system is automation, which affords a much higher degree of accuracy compared to manual methods. Contaminants can be isolated and removed by locating small particles of radioactive material dispersed throughout the soil. All of the soil is analyzed continuously during processing to document the level of radioactivity in the waste and to demonstrate that cleaned soil meets release criteria. This automation and analysis results in a significant cost reduction for special handling, packaging, and disposal of the site's radioactive waste.

WASTE APPLICABILITY:

The SGS locates, analyzes, and removes gamma ray-emitting radionuclides from soil, sand, dry sludge, or any host matrix that can be transported by conveyor belts. The SGS can identify hot particles, which are assayed in units of picoCuries, and can quantify distributed radioactivity, which is assayed in units of picoCuries per gram (pCi/g) of host material. The lower limit of detection (LLD) for the system depends on the ambient radiation background, conveyor belt speed, thickness of host material on conveyor, and contaminant gamma ray energy and abundance. However, LLDs for americium-241 of 2 pCi/g and for radium-226 of 5 pCi/g have been successfully demonstrated.

STATUS:

This technology was accepted into the SITE Emerging Technology Program in July 1994. Pilot- and field-scale tests using TMA-owned mobile equipment were initiated at a U.S. Department of Energy facility in March 1995. Further evaluations have been temporarily postponed. Future tests will demonstrate the technology's applicability to other radionuclides and other host matrices.

A similar system has been used on Johnston Atoll in the mid-Pacific since January 1992; TMA is currently under contract to the U.S Defense Nuclear Agency to process coral soil contaminated with plutonium and americium using the SGS.

FOR FURTHER INFORMATION:

EPA PROJECT MANAGER:
Joan Mattox
U.S. EPA
National Risk Management Research Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
513-569-7624
Fax: 513-569-7676