Application of Thermo-Hydraulic Power Monitors at Large Research Reactors.

The unrecorded production of direct-use material constitutes a potential misuse of large thermal research reactors (with thermal power greater than 25 MWth). The introduction of fertile material into the reactor core or around the core region is a possible diversion strategy that is of considerable safeguards concern. To address this concern, the potential use of the thermo-hydraulic power monitors for monitoring reactor operating conditions and confirmation of the absence of unrecorded plutonium production is described. The system measures the reactor coolant inlet and outlet temperature (using resistance temperature detectors) and the coolant flow rate (using ultrasonic flowmeter). Temperature and flow rate data are transferred to a computer that calculates the rated reactor thermal power and the time integrated reactor power from basic the rmodynamics. The system is serviced at regular inspections and the data is pre-evaluated on site and saved on disk for further evaluation. An accuracy of less than 2% for the reactor power measurements has been achieved with the power monitors.