Modem commercial-scale gas centrifuge enrichment plants (GCEPs) have sufficient separative work capacity to produce many significant quantities (SQs) of highly enriched uranium (HEU) over a much shorter period of time than the typical interval between IAEA safeguards inspections. However, such misuse requires changes in the UF_6 flows within the plant. We are developing a concept for a simple unattended mass flow meter based on a modification of the conventional thermal mass flow meter technology. We eliminate the intrusive "hot wire" feature of such systems, and heat is instead injected onto the surface of a section of pipe, and removed from a nearby section, using thermoelectric heating and cooling. For typical GCEP unit header pipe parameters the heating and cooling power required to achieve a ±7.5° C temperature excursion in the heated and cooled regions is 5 W each, and is strongly dependent on the mass flow. As a result, measurement of the power needed to achieve the target AT under feedback control constitutes a direct indication of the mass flow. Differences in the required heating and cooling powers reveal any attempt to "spoof the system by heating or cooling the gas relative to the pipe surface. The goal of this work is to develop a non-intrusive, simple, spoof-resistant, low-power mass flow meter with percent-scale accuracy and hour-scale time resolution, fully independent of the operator's systems. Such a system would provide an independent tool for detecting misuse of a commercial GCEP on a time scale short compared to that required to produce one SQ of HEU. Our concept is non-intrusive, since it only contacts the outer surface of the operator's piping, simple because it solely measures temperature along the surface, resists spoofing by its bipolar heating and cooling scheme, and requires little power for operation. Commercial thermal flow meters achieve 1% accuracy, after calibration, which should also be achievable in our configuration. The characteristic time constant of our system is about one hour. Simple, highly reliable, redundant, spoof-resistant unattended monitoring systems, such as this, will be required to provide confidence in the timely detection of misuse.
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