Development, Testing, and Validation of Fabry-Pérot Cavity Acoustic Sensors for Microreactor Applications

Nuclear microreactors are a unique reactor design that may enable the nuclear energy industry to access unconventional markets, such as remote communities, mining sites, military bases, and disaster relief programs. Additionally, the modularity of microreactors presents some advantages over larger, conventional reactor designs. For nuclear microreactors to be economically viable, online structural health monitoring may be needed to reduce operation and maintenance costs with lower power production. Optical fiber sensors, specifically optical Fabry-Pérot cavities (FPCs), may enable vibrational frequencies of microreactor components to be monitored during operation, allowing the location and severity of potential damage to be identified. In this work, FPCs were designed and fabricated with materials can survive in the extremely harsh environment of nuclear microreactors. The FPCs were bonded to metal test specimens to monitor their vibrational frequencies, along with a reference piezoelectric accelerometer. Euler-Bernoulli theory was used to calculate the fundamental modes and mode shapes for comparison with experimentally measured frequency spectra. The peak frequencies detected with the FPC and piezoelectric accelerometer, as well as the theoretical modes, all agreed well (within 5%) for the first four fundamental modes. Furthermore, when the FPC and accelerometer were colocated on the test specimen, their peak frequencies all agreed within 1%.