Composite Temperature-Pressure Measurement Instrument for Advanced Reactors

Operating theory and characteristics given in this paper concern a dual property measurement sensor and associated instrumentation for use with liquid metal cooled, fast breeder nuclear reactors. The sensor may also be applied in other similar severe environments. Pressure variations are sensed by deflection of a thin diaphragm which forms one end wall of a resonant cylindrical microwave cavity. Temperature changes cause the cavity size, and thus its resonant frequency to vary. Both physical properties may be continuously monitored as each relates to a distinct mode of cavity resonance. Precise digital readout of the resonant frequencies indicated a sensor sensitivity to pressure of about 9 MHz/psi (for null pressure scheme of operation), and to temperature of 350 kHz/°F. As both the sensor and connecting waveguide are entirely of metal, direct immersion in a liquid metal coolant should be possible.