NONDESTRUCTIVE MEASUREMENT OF UF6 CYLINDERS AT THE PORTSMOUTH GASEOUS DIFFUSION PLANT

The International Atomic Energy Agency is conducting an experiment at the Portsmouth Gaseous Diffusion Plant to verify that excess highly enriched uranium is being converted into low-enriched uranium. An important component of this experiment is the verification of the 235U enrichment of the uranium hexafluoride (UF6) contained in cylinders being fed into the process. During the project, the contents of over 700 5-, 8-, and 12-in.-diameter cylinders with 235U enrichments greater than 20% were scheduled to be fed. The IAEA measured a representative sampling of these cylinders to independently verify the enrichment declared by the plant. To support this effort, a portable gamma-ray spectroscopy system was developed to nondestructively determine the enrichment. This system includes a collimated high-purity germanium detector and a portable multichannel analyzer system. Measurement complications include: (1) UF6 fill levels frequently drop below the detector field-of-view, (2) 228Th daughters (from the decay of 232U) are present, and (3) the thorium daughters are not in secular equilibrium. Enrichment-meter principles were applied, and a software program was written for online analysis of UF6 in containers of different materials and thicknesses.