Gamma-Heated In-Core Thermoacoustic Sensor

We will develop an acoustically-telemetered, frequency-multiplexed, gamma-heated thermoacoustic sensors that can simultaneously monitor local gamma flux and coolant temperature at multiple locations in the core of an operating commercial nuclear reactor. These sensors will require no external power source and will telemeter temperature encoded as the frequency of the sound radiated by the sensor and gamma flux as amplitude of the sound radiated by the sensor. Since the frequency of the sound produced by the sensor depends on the sound speed of the gas that fills the sensor and the sensor’s length, several such sensors can operate simultaneously in a single core, at different frequencies, so that the information they transmit will be unique for each sensor location. The core of a nuclear reactor is one of the most challenging environments on the planet and there is a need to monitor temperature and energy flux without running electrical wires through the reactor. We proposed to handle this problem using acoustics.. In addition, it is somewhat ironic that such reactors might produce 1 GW of electrical power for sale to public utilities, but have serious difficulty providing 10 W of electrical power within the reactor vessel to operate sensors and telemeter the sensor’s information to operators outside the pressure vessel. We propose thermo- acoustic sensors can solve these problems. The thermoacoustics sensor provides both coolant temperature, (coded in the frequency) and gamma flux (coded as an amplitude ratio). The amplitude of the radiated sound energy produced by such a thermoacoustic sensor is proportional to the heating provided by gamma- absorption , but the received amplitude outside the reactor vessel will depend upon the conditions of the coolant that surround the resonator and provides the medium for transmission of the sound. By measuring the ratio of the fundamental resonance amplitude, A1, to the amplitude of second harmonic of that resonance, A2, the determination of the energetic particle flux becomes independent of the propagation characteristics of the surrounding coolant fluid or gas (e.g., temperature, pressure, gaseous inclusions). The fundamental frequency of the radiated sound, f1, is related to the absolute (Kelvin) temperature of the coolant, T, in a way that keeps the ratio, of frequency to root Temperature , equal to a constant. Multiple sensors will be frequency-division-multiplexed. The frequency- temperature invariant can be made different for each sensor in a core by adjustment of each sensor’s overall effective length by adjustment of the ratio of the gas mixture in the sensor, so that signals for flux and temperature from different sensor locations within the reactor’s core can be detected simultaneously. The sensor does not require an external electrical power supply nor does the telemetry require either cables or electrical power for a dedicated “data transmitter.” Thermoacoustic sensors would not have been incapacitated by the type of overall electrical power failure that occurred during the Fukushima disaster of 2011. Since external electrical power is not required there is no need for a power cable. Since the temperature (frequency) and flux (amplitude) information is transmitted through the reactor vessel as sound, there is no need for signal cables either. The sensor exploits the energy-rich environment in the core to generate the heat that produces the acoustic signals via thermoacoustic processes that are simple and require no moving mechanical parts. The sensors have no temperature or radiation sensitive materials that limits their operation or accuracy in the high temperature and the dense particle flux environments within the core of a nuclear reactor. The gamma-absorbing heat exchangers can be produced economically by 3-D printing in metal. Temperature and energy flux is to be measured using thermoacoustic sensors without the need for electrical power. At the end of Phase I we will complete the design and modeling of the device and be able to move into a fabrication / demonstration prototype for Phase II. Sensor for Nuclear Reactors, Sensors for other industrial applications where avoidance of electrical power is needed or welcome.