RESUMO
A "proof of concept" was conducted to determine the effectiveness of a survey method for cost-effective recovery of depleted uranium (DU) fragments from contaminated soil piles at Sandia National Laboratories. First, DU fragments ranging from less than a gram up to 48 g were covered by various thicknesses of soil and used for detector efficiency measurements. The efficiencies were measured for three different sodium iodide detectors: a 5.1-cm by 5.1-cm (2-inch by 2-inch) detector, a 7.6-cm by 7.6-cm (3-inch by 3-inch) detector, and a Field Instrument for the Detection of Low Energy Radiation (FIDLER) detector. The FIDLER detector was found to be superior to the other detectors in each measurement. Next, multiple 7.6-cm (3-inch) layers of soil, taken from the contaminated piles, were applied to a clean pad of soil. Each layer was scanned by an array of eight FIDLER detectors pulled by a tractor. The array, moving 10.2 to 12.7 cm s(-1) (4 to 5 inches per second), automatically recorded radiation count data along with associated detector coordinates at 3-s intervals. The DU fragments were located and identified with a handheld system consisting of a FIDLER detector and a positioning system and then removed. After DU removal, the affected areas were re-scanned and a new lift of contaminated soil was applied. The detection capability of the system as a function of DU fragment mass and burial depth was modeled and determined to be sufficient to ensure that the dose-based site concentration goals would be met. Finally, confirmation soil samples were taken from random locations and from decontaminated soil areas. All samples had concentrations of U that met the goal of 400-500 pCi g(-1).
