Sensitive, Fast Response Reactor Coolant Impurity Measurement Instrument

Microwave techniques, as used for the detection and measurement of moisture in reactor coolant gases, operate because of the resonant frequency change of a microwave cavity (sensor) through which the sample gas flows, due to the corresponding change in its dielectric constant. For the experimental system, a moisture detection sensitivity of 15 ppmv/µV for sample gas at STP results for 10 mW of microwave oscillator power. The minimum moisture detection level of about 2 ppmv depends upon total system noise. Gas transport time limits the speed of response, as does the time constant of the synchronous demodulator of the sample phase-lock amplifier. For thermal equilibrium conditions, the maximum instrument drift for a one-hour interval equates to an equivalent moisture concentration range of 10 ppmv.