Unattended Mass Flow Meter for Gas Centrifuge Enrichment Plants

Modern commercial-scale gas centrifuge enrichment plants (GCEPs) havesufficient separative work capacity to produce many significant quantities (SQs)of highly enriched uranium (HEU) over a much shorter period of time than thetypical interval between IAEA safeguards inspections. However, such misuserequires changes in the UF6 flows within the plant. We are developing a conceptfor a simple unattended mass flow meter based on a modification of theconventional thermal mass flow meter technology. We eliminate the intrusive “hotwire” feature of such systems, and heat is instead injected onto the surface of asection of pipe, and removed from a nearby section, using thermoelectric heatingand cooling. For typical GCEP unit header pipe parameters the heating andcooling power required to achieve a ±7.5o C temperature excursion in the heatedand cooled regions is 5 W each, and is strongly dependent on the mass flow. Asa result, measurement of the power needed to achieve the target ΔT underfeedback control constitutes a direct indication of the mass flow. Differences inthe required heating and cooling powers reveal any attempt to “spoof” the systemby heating or cooling the gas relative to the pipe surface. The goal of this work isto develop a non-intrusive, simple, spoof-resistant, low-power mass flow meterwith percent-scale accuracy and hour-scale time resolution, fully independent ofthe operator’s systems. Such a system would provide an independent tool fordetecting misuse of a commercial GCEP on a time scale short compared to thatrequired to produce one SQ of HEU. Our concept is non-intrusive, since it onlycontacts the outer surface of the operator’s piping, simple because it solelymeasures temperature along the surface, resists spoofing by its bipolar heatingand cooling scheme, and requires little power for operation. Commercial thermalflow meters achieve 1% accuracy, after calibration, which should also beachievable in our configuration. The characteristic time constant of our system isabout one hour. Simple, highly reliable, redundant, spoof-resistant unattendedmonitoring systems, such as this, will be required to provide confidence in thetimely detection of misuse.