Investigation of Technology for Monitoring UF6 Mass Flow

The applicability of gas flow meters, in-line enrichment monitors, and instruments for measuring uranium or UFe concentrations in process streams as a means for verifying declared plant throughput have been investigated. The study was performed to assist the International Atomic Energy Agency in the development of an effective international safeguards approach for aerodynamic uranium enrichment plants. Because the process gas in an aerodynamic enrichment facility is a mixture of UFe and HZ, a mass flow measurement in conjunction with a measurement of the uranium (or UFe) concentration in the process gas is required to quantify the amount of uranium being fed into, and withdrawn from, the cascades for nuclear materials accountability verification. In-line enrichment monitors developed for the U.S. gas centrifuge enrichment plant are found to be applicable only to pure UFe streams. Of the five gas flow meters evaluated, the orifice meter and the pitot tube meter are judged the best choices for the proposed applications: the first is recommended for lowvelocity gas, small diameter piping; the latter, for high-velocity gas, large diameter piping. Of the six procedures evaluated for measurement of uranium or UFe concentration in a mixed process stream, infrared-ultraviolet-visible spectrophotometry is judged to be the best procedure currently available to perform the required measurement.