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Nondestructive Waste Assay Using Gamma-Ray Active and Passive Computed Tomography

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Tech ID: 2123
Project Overview
Current NDA techniques, used to characterize mixed waste, have a high total uncertainty associated with the measurement for a large number of waste streams. The measurement uncertainty is high for waste containers with: high density waste forms; lumps of fissile material; heterogenious wastes; non-uniform radionuclide distributions; and variable isotopics. This instrument will reduce the measurement uncertainty associated with characterizing these waste containers.

Technology Description
Gamma-ray-based computed tomography (CT) requires that two different measurements be made on a closed waste container. The two measurement modes are called active (A) and Passive (P) computed tomography. In the ACT mode, a collimated gamma-ray source external to the waste container emits multiple, mono-energetic gamma rays that pass through the container and are detected on the opposite side. The attenuated gamma-rays transmitted are measured as a function of both energy and position of the container. Through this method the container is mapped. Information about the density and effective atomic number is also obtained. In the PCT measurement mode, the external radioactive source is shuttered, and the waste container is moved through similar positions used for the ACT measurements. In these measurements the radiation detectors record any gamma-rays emitted by radioactive sources within the container. With these data the internal contents of the container can be mapped providing accurate and quantitive values for every isotope detected within the waste. These results will then provide the necessary data to ´certify´ and categorize the wastes so they can be transported and disposed.

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