Advancements in High-Temperature Measurement Techniques to Aid the Development and Enhance the Monitoring of Advanced Reactors

This manuscript includes research results focused on high-temperature measurements crucial for characterizing the behavior of advanced reactor components, such as heat pipes, as well as providing online monitoring of advanced reactors that operate at temperatures exceeding 800 °C. The study employs Type II Fiber Bragg Grating (FBG) sensors, systematically testing them with various fiber coating and jacket materials. The results obtained from FBG measurements are compared against conventional type K thermocouple measurements. Temperature transients at various rates, as well as cycled measurements were carried out to shed light on the repeatability, accuracy, and potential hysteretic behavior at high temperature conditions found in advanced reactors. This paper underscores the promising outcomes of this research, positioning both FBG and distributed Rayleigh scattering techniques as invaluable tools. These techniques can not only aid in the development of advanced reactor components, such as sodium heat pipes, but also emerge as integral elements in the instrumentation and control strategy for monitoring the operation of advanced reactors. Of particular significance is the application of these techniques to microreactors, which have potential as enabling technologies for remote reactor operation. Enabling remote operation would set microreactors apart from conventional reactor designs, opening new avenues for low-cost and efficient reactor management. The results show that type-II FBGs are a promising technique for temperature measurements up to 800 °C, here tested with two different sensor packaging designs, showing no appreciable spectral distortions. When the temperature was cycled between 700 °C and 800 °C, however, a hysteretic behavior arose.