Temperature Effect on Fiber Optical Sensors for Dry Cast Storage Health Monitoring

The increasing number, size, and complexity of nuclear facilities deployed worldwide are increasing the need to maintain readiness and develop innovative sensing materials to monitor important to safety structures (ITS). Assessing and supporting next generation nuclear materials management and safeguards for future U.S. fuel cycles with minimum human intervention is of paramount importance. Technologies for the diagnosis and prognosis of a nuclear system, such as dry cast storage system (DCSS), can improve verification of the health of the structure that can eventually reduce the likelihood of inadvertently failure of a component. In the past decades, an extensive sensor technology development has been used for structural health monitoring (SHM). Fiber optical sensors have emerged as one of the major SHM technologies developed particularly for temperature and strain measurements. However, the fiber optical sensors and sensing system has not been developed with adequate solutions and guideline for DCSS applications. This paper presents an experimental study of temperature effect on fiber Bragg grating (FBG) sensors. The reflective spectrum of FBG sensors on the structure was measured with a tunable laser source. The shift of FBG reflective spectrum reflected the thermal expansion on the structure. The shift of the spectrum due to the temperature effect was correlated to the temperature changes. In addition, the FBG sensing methodology including high frequency guided ultrasonic waves (GUW) under different temperatures were also performed to check the performance of high frequency, small strain sensing. The potential of FBG sensors for DCSS applications was explored. The paper ends with conclusions and suggestions for further work.