Wireless in-core acoustic telemetry and self-powered sensing

A promising wireless telemetry infrastructure based on acoustic transmission of in-pile measurements (information) is being developed at the Idaho National Laboratory for use in nuclear reactors. In this paper, we will demonstrate an approach to telemetry and sensing that exploits a reactor core's energy-rich environment to generate acoustic telemetry signals from self-powered telemeters that produce sounds. These sounds propagate through the reactor's coolant, whether it is gas, water, or liquid metal, through its mechanical structures (e.g., lattice work, pressure vessel, and piping), and can be detected outside the reactor. A thermo-acoustic (TAC) sensor was designed to be geometrically indistinguishable from the other Training Research Isotopes General Atomics (TRIGA) fuel elements in the Breazeale reactor's core. Heat was produced by fission of two Pathfinder ²³⁵UO₂ fuel pellets contained within a finned heat exchanger. The acoustic signals from the TAC sensor can be picked up by hydro-phones and accelerometers anywhere in the reactor pool and from structures that penetrate the pool. Most of the signals we acquired had sufficient signal-to-noise ratios even with both the ¹⁶N diffusion pump and the pool coolant pump operating. The TAC sensor was tested during eight irradiation runs in the Breazeale Nuclear Reactor over the span of a week. We were able to show that the frequency of the thermo-acoustically generated sound provides an accurate determination of the reactor's coolant temperature. Such a sensor strategy might have provided useful information in a reactor accident like that which destroyed the Fukushima complex in March 2011