Séminaire de Mécanique d'Orsay

Le Jeudi 30 juin à 14h00 - Salle de conférences du LIMSI

Design, fabrication, and testing of a fission-powered thermoacoustic sensor

Steve L. Garrett
Graduate Program in Acoustics, Penn State, University Park, PA

The core of a nuclear reactor is a particularly harsh environment when functioning properly. When there is a stress event that may include the loss of electrical service, similar to the earthquake and tsunami that struck the Fukushimi Daiichi reactors on 11 March 2011, the need for robust and reliable self-powered sensors becomes acute. A standing-wave thermoacoustic engine with dimensions identical to an ordinary fuel rod was designed to be placed in the core of the Breazeale Nuclear Reactor on Penn State’s campus. Such an engine can produce sound that couples to the surrounding heat-transfer fluid to telemeter the reactor’s operational conditions (as frequency and amplitude) to the exterior of the reactor vessel, without requiring electrical power. In this demonstration, the heat necessary to produce thermoacoustics oscillations was provided by two 10 mm long by 5 mm diameter, 7.5% enriched, 235U fuel pellets. Those pellets were contained within a stainless-steel finned heat exchanger that was fabricated by additive manufacturing (3-D printing). The (mass-controlled) resonator was suspended in the surrogate fuel rod using two six-armed leaf springs (spiders) that centered the resonator in the “slotted tube” and allowed longitudinal vibrations of the entire resonator that coupled the oscillatory momentum of the gas within the resonator to the surrounding light-water reactor coolant. A 2.0 MPa mixture of 25% argon and 75% helium provided a trade-off between dipole radiation efficiency, resonator length, and low onset temperature differential, to produce a frequency that was high enough to be above the dominant noise produced by coolant and 16N diffusion pumps. These trade-offs were optimized using the Los Alamos DeltaEC software. Signals were received on two hydrophones in the coolant and an accelerometer attached to a structure outside the reactor which provided measurement of the coolant temperature and the core neutron flux.