High-Temperature Fiber Optic Sensor Performance for Heat Pipe Instrumentation

Presented in this article are experimental results of an investigation on the performance of distributed fiber optic temperature sensors at temperatures up to $800~^{\circ }$ C. The experimental results produced in this work assess the performance of fiber optic temperature sensors for use in instrumenting liquid metal heat pipes. Distributed fiber optic temperature sensors are capable of providing high spatial and temporal resolution temperature measurements across a wide range of operating temperatures and conditions, making them intriguing candidates for many advanced nuclear reactor technologies. Tests were conducted at high temperature on the prolonged survivability, short-term performance, and high-temperature cycling effects of distributed optical fiber temperature sensors. A quartic fit of the spectral shift produced by the fiber sensors was developed to fit with thermocouple (TC) measurements of the experiment and was compared with fits available in literature. An upper limit of $700~^{\circ }$ C was established for the prolonged use of distributed fiber optic sensors. No significant hysteresis effects were observed when the fiber sensors were cycled at high temperatures. Distributed fiber optic temperature sensors were determined to be viable for instrumenting liquid metal heat pipes under limited operational conditions.