The Fukushima nuclear disaster was partly caused by the tsunami triggered by the nearby earthquake. The generator room that supplied power for monitoring and cooling was located in a basement which flooded. Without monitoring and cooling , several of the reactors overheated and generated gases which exploded causing major damage to the reactor buildings. There is some evidence that the cores of several of the reactors may have melted through the bottom of the containment vessels and penetrated into the earth, threatening the ground water.
Researchers from Penn State University presented a new idea for nuclear reactor monitoring at the Annual meeting of the Acoustical Society of America in late October. They suggest the creation of something they call a thermoacoustic standing wave engine inside a fuel rod. Sound is created by variations in air pressure when the air pressure rises and falls in a repeating pattern. Thermoacoustics has to do with the interaction of sound and heat. In a thermoacoustic system, there are variations of heat in a repeating pattern in some material that is related to sound waves traveling through the material. It is possible to create heating systems, cooling systems and engines which generate sound from heat differences with the thermoacoustic effect. One benefit of a thermoacoustic device is that it can be built with no moving parts.
The Penn State researchers created a nuclear fuel rod that incorporates a thermoelectric engine. The engine would resonate at a frequency based on the temperature of the fuel rod. In addition, heat would be distributed more evenly in the fuel rod which would make it more efficient as an energy source. The device was constructed from a stack of ceramic plate full of a parallel pores that was originally made for catalytic converters in car exhaust systems. The stack transfers heat to a resonator full of gas and sound is generated by temperature differences. With this device, the temperature of the fuel rod is measured and signaled without the need for external power making the whole system less vulnerable to accidents.
The thermoacoustic effect will circulate gas between the fuel and the steel shell of the rod and transfer heat out into the surrounding liquid increasing efficiency. The sound generated by the thermoacoustic engine in the fuel rod will travel out of the rod and into the surround fluid. The sound can then be detected by microphones that are some distance from the rod.
The Idaho Nuclear Laboratory has been working in conjunction with the Penn State researchers to extend the use of the thermoelectric effect to monitor microstructural changes in the fuel rods, measure the composition of gas mixtures and to act as a failsafe device in case of emergencies.
Hopefully, utilization of such advanced techniques as thermoacoustic engines can help make future generations of nuclear reactors safer, simpler and more efficient.
Diagram of Penn State Thermoacoustic standing wave engine:
