PERFORMANCE OF TRANSMISSION-CORRECTED HIGH-RESOLUTION GAMMA ASSAYS IN A NUCLEAR FUEL FABRICATION FACILITY

The usefulness of a portable high resolution gamma assay unit in a nuclear fuel fabrication facility quickly becomes apparent when improved characterization of intermediate products, wastes, and other materials within the operating facility is desired. The performance of this high-resolution gamma assay method was examined and the method was qualified for a wide variety of intermediate products and wastes. The method proved to be versatile and accurate and was quickly integrated into an operating facility for fuel processes, criticality safety, nuclear material accountability, material storage, and waste disposal. High-purity germanium (HPGe) detector-based spectrum data were transmission-corrected for container and matrix attenuation, geometry, collimator effects, and shifting facility background radiation levels. The assay results were compared against standards for validation and functional testing. The assay method was then qualified for each different type of uranium-bearing material by comparison with traditional methods of characterization involving grab and composite sampling, chemical extraction, and inductively coupled plasma/mass spectroscopy (ICP/MS) analysis methods. Results for the HPGe compared favorably with ICP/MS under a wide range of physical characteristics such as specific gravity (0.3 -1.9), container thickness (0.05 – 0.1 inch), %U-235 enrichment (0.7 – 5%), uranium concentration (0.01 – 70 gU/l), and configurations such as metal and plastic drums, B-25 boxes, in-situ soil and sands, buckets and pails, and a variety of sample bottles. An overall correlation coefficient R 2 > 0.998 is reported for a variety of containers and materials containing between 2 to 15,000 grams of enriched U under in-plant operating conditions.