The generation of sound by heat has been documented as an acoustical curiosity since 1568 when a Buddhist monk reported in his diary the loud tone generated by a ceremonial rice cooker. Over the last four decades, significant progress has been made in understanding thermoacoustic processes, enabling the design of thermoacoustic engines and refrigerators. Motivated by the Fukushima nuclear reactor disaster, we have developed and tested a thermoacoustic engine that exploits the energy-rich conditions in the core of a nuclear reactor to provide core condition information to the operators without a need for external electrical power. The heat engine is self-powered and can wirelessly transmit the temperature and reactor power level by generation of a pure tone that can be detected outside the reactor. We report here the first use of a fission-powered thermoacoustic engine capable of serving as a performance and safety sensor in the core of a research reactor and present data from the hydrophones in the coolant (far from the core) and an accelerometer attached to a structure outside the reactor. These measurements confirmed that the frequency of the sound produced indicates the reactor’s coolant temperature and that the amplitude (above an onset threshold) is related to the reactor’s operating power level. These signals can be detected even in the presence of substantial background noise generated by the reactor’s fluid pumps.