Scope

Tank W-1A at Oak Ridge National Laboratory (ORNL) collected wastes from three high-radiation-level analytical facilities between 1951 and 1986. A groundwater contamination plume containing Cs-137, transuranics, uranium, and other isotopes emanated from contaminated soil surrounding the tank. URSıCH2M Hill Oak Ridge (UCOR) was the DOE environmental management contractor.
Sampling and radiological analysis of subsurface soils to determine the extent and depth of the contamination and to estimate the volume of transuranic soil to be excavated.

Key Drivers:

Quantify transuranic components in the presence of high Cs-137.
Maintain Am-241 Minimum Detectable Activity (MDA) <10 nCi/g for all soil samples.
Report all nuclides that contribute to 99% of the total activity.
Real-time analysis required to guide the evolving sampling plan.
Keep radiation doses to all personnel ALARA.
Maintain sample integrity with no spread of radiological contamination.

Map of Subsurface Cs-137 Contamination

Divide the 36-inch soil core samples into 12-inch segments.
Lead shielding to isolate the gamma flux from each segment.
Scan each segment with NaI detector to check for hotspots.
Perform ISOCS high-resolution gamma spectroscopy measurement on each segment.
Variable detector-segment standoff distance to allow for high dose rate samples.
Create custom ISOCS efficiency model for each measurement geometry.
Analyze gamma spectrum, generate Radioassay Data Sheet for, and deliver to onsite Project Manager within 30 minutes.

More than 300 soil segments collected from 45 bore holes analyzed.
Transuranic constituents quantified in every sample.
Am-241 MDA’s maintained <10nCi/g for all ISOCS measurements.
Analytical results delivered within 30 minutes.
Customer’s sampling plan evolved based on ISOCS results.
Customer generated 3D subsurface maps of transuranic and other radiological contaminants.
3D maps were used to guide next-phase soil excavation.