All-metal packaged temperature compensation fiber optic Fabry-Pérot strain sensor for high-temperature liquid metal environments

The erosion of critical in-core components by high-temperature flowing liquid metal leads to surface fatigue damage, and its reliable detection represents a significant challenge for nuclear reactor safety. This study introduces a novel approach that employs an all-metal encapsulated fiber-optic Fabry-Pérot (F-P) strain sensor, designed to endure high-temperature and high-pressure conditions, for in situ surface strain monitoring and fatigue damage assessment. The key contributions of this work are as follows: (1) the development of a comprehensive mechanical model that characterizes the strain transfer mechanism of the sensor; (2) the implementation of an innovative temperature self-compensation structure to mitigate cavity length variations under extreme thermal conditions; (3) the design of a composite-cavity configuration that enables simultaneous strain measurement and in situ temperature monitoring, ensuring accurate thermal compensation. The fabricated sensor was thoroughly evaluated through rigorous performance testing, including high-temperature calibration up to 500 °C and validation experiments in liquid metal environments. Experimental results demonstrate the sensor’s performance: stable operation at 500 °C with a strain sensitivity of 2.43 nm/με, accompanied by high measurement accuracy (SSE = 0.0761, Adj R2 = 0.9974, RMSE = 0.0617). These metrics confirm the sensor’s linearity, stability, and reliability under extreme operating conditions. The successful demonstration of this fiber-optic sensing technology in high-temperature liquid metal environments provides a viable solution for real-time fatigue damage monitoring of nuclear reactor components, offering significant potential to enhance reactor safety and operational lifetime.