Pressure Measurement Instrument for Liquid Metal Reactors

The theory of operation and initial experimental results given in this paper pertain to a microwave frequency pressure sensor applicable to measurements within liquid metal cooled, fast breeder reactors. The basis of operation of the pressure sensor depends on the deflection of one end wall of a cylindrical microwave cavity and on the measurement of the resultant change of cavity resonant frequency. Temperature dependence of the sensor output signal is significantly reduced by measuring the difference frequency between two identical resonant cavities. The dual cavity (1.9-cm long by 3.3-cm diameter) sensor yielded nearly linear response over the temperature range 75 to 1200??F and for pressures up to one atmosphere, with sensitivities of 0.5 and 0.8 MHz/psi at 75 and 1200??F, respectively. The 0.015-cm thick stainless steel diaphragm also responded without permanent deformation for applied pressure of 45 psi. Pressure sensor time response to abrupt changes of pressure equals about 7.5 ms. The sensor and associated transmission waveguide fabricated of metal only should be immersible in the liquid metal coolant.