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Real-time Radiological Analyses of Transuranic Soil Cores

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

Instruments & Techniques Used:

  1. Broad Energy Germanium (BEGe) detectors
  2. ISOCS™ Mathematical Efficiency Calibration
  3. Genie™ 2000 Gamma Analysis

CANBERRA™ Solution:

  • 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.

Achievements

  • 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.

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