Analysis of Field Measurements on UF6 Cylinders at a Commercial Enrichment Plant

Currently, the International Atomic Energy Agency (IAEA) performs nondestructive assay (NDA) measurements on uranium hexafluoride (UF6) cylinders at uranium enrichment plants to verify operator declarations for the uranium and 235U material balances. With the 235U enrichment and the measured cylinder gross weight combined with the operator declared cylinder tare weight, the mass of uranium and 235U in a cylinder can be calculated. The large measurement uncertainties the IAEA has experienced with these field NDA techniques have required them to collect more samples for destructive analysis (DA). While the DA is much more accurate than NDA, it is much more expensive for the IAEA, requires more operator support and expense, and requires additional time to ship and analyze the samples, which impedes the timeliness of the inspection process. An initial step for identifying portable NDA techniques that are more accurate and faster in determining 235U is to evaluate the current applications where portable instruments are utilized, identify the challenges with using these instruments and investigate options for improving the use of these instruments. A survey was conducted by the United States Enrichment Corporation (USEC) to evaluate relevant reports, data and operational experience important to characterizing and evaluating each NDA method currently used for cylinders received at their enrichment facilities. The hardware and software developed by USEC were used on a daily basis to verify the declared enrichment of cylinders received on site. This survey analyzed existing data to determine the total measurement uncertainty of the USEC field portable NDA UF6 cylinder measurement systems. The survey also addressed potential improvements to the hardware and software that could be made to reduce the measurement uncertainties for cylinders containing low-enriched, natural, and depleted uranium.