Assay of uranium in U-bearing waste produced at Natural Uranium Metal Fuel Fabrication Plants by gamma-ray spectrometry

A passive gamma measurement technique is investigated for the assay of U-bearing wastes generated at the Natural Uranium Metal Fuel Fabrication Plants. A 3 in.x3 in. NaI(Tl) detector was used in conjunction with a multichannel analyzer (MCA). The observed count rate of the 1 MeV γ-ray from the 238U in the sample was corrected for sample self-absorption and for absorption in the walls of the sample container. These correction factors were determined using one reference standard and from a knowledge of the sample weight, composition and the geometry of the sample container made of pure aluminium. The amount of 238U in the samples were measured by comparing the corrected area under the 1 MeV gamma ray peak of the known reference standard with the corresponding corrected peak areas of the samples to be measured. To compare the nondestructive assay (NDA) results with another independent method, chemical analysis of all the U-bearing waste samples was also carried out. The NDA results were found to agree within ±15% with the chemical analysis results. To make the method cost-effective, rapid and useful for plant operation on a routine basis, all the measurements were repeated using a single channel analyzer (SCA) also. The NDA results obtained with SCA agree within ±30% with the chemical analysis results. (orig.)