An in-situ multipoint optical fiber temperature sensor with applications to small modular reactors and thermal energy storage systems

A novel multipoint optical fiber temperature sensor architecture has been proposed to address temperature measurement problems often encountered in SMRs (small modular reactors) and thermal energy storage (TES) systems. This new sensor can be submerged into working fluids to acquire reliable in-situ temperature measurements for multiple locations simultaneously. The spatial resolution of the measurement locations can be controlled by the spacing of Fiber Bragg Gratings (FBGs). This multipoint sensor utilizes interlaced conductor-insulator-conductor sheath design to provide high speed of response and reduce probe-induced thermal smearing. This sensor is particularly suited for capturing nonuniform temperature distributions during transient operations of an SMR and a TES, which thermocline needs to be accurately monitored. This paper describes the principle of the sensor design, thermal and heat transfer analysis by finite element analysis, and experimental evaluation using wax to create a phase change environment to mimic properties of molten salts often found in advanced SMRs and TES. Both numerical analysis and experimental investigation have confirmed that the proposed multipoint optical fiber sensor can achieve reliable and accurate in-situ temperature measurements in environments where traditional temperature sensors, such as thermocouples, are cumbersome to be used.