Deposits in commercial uranium processing facilities of interest to nuclear safeguards are predominantly low enriched uranium (LEU). The shapes and sizes of holdup deposits can vary significantly, thus making it difficult to model the deposits accurately for calibration purposes. This presents a challenge to currently employed methods such as the Generalized Geometry Holdup (GGH) that rely on quantifying 235 U mass by simplifying deposit shapes as a point, a line, or an area. In this work, gamma ray imaging using high energy resolution Germanium Gamma Imagers (GeGI™) is employed to determine the distribution of uranium inside the source containment. Two types of imaging methods are employed; coded aperture imaging and Compton imaging. Gamma ray emissions seen in different regions of the image are quantified using an inverse gamma ray transport solver being developed at ORNL. Using measured data, the inverse method will be used to solve for unknown source parameters such as source matrix thickness, density, and attenuation due to container wall and shielding. The intrinsic efficiency of the detector is determined based on a library of built-in response functions and key dimensions of the detector (e.g., thickness and radius of the detector crystal). Measurements are performed in both imaging modalities using uranium sources of well-known masses and enrichments configured inside mocked up holdup fixtures. Results from the 2 imaging modalities are intercompared. The mock-up holdup configurations are also measured using a traditional collimated and shielded NaI(Tl) detector as typically used at uranium facilities and analysis is carried out using the GGH method. The GGH results are compared with the results from imaging-based methods. The paper presents preliminary results of the imaging measurements and the progress made in the computational methods to quantify uranium mass.
Year
2020
Abstract