Investigation and Development of Optical Fiber Sensors for Small Modular Reactors and Thermal Energy Storage Systems

This dissertation focuses on developing and applying optical fiber sensors (OFSs) in small modular reactors (SMRs) and thermal energy storage (TES) systems, both of which are pivotal for future energy infrastructure. SMRs, especially when integrated with TES to form hybrid systems, offer flexible power generation for diverse applications. However, due to their compact designs compared to conventional reactors, they require new instrumentation and control systems, particularly sensors that withstand tight in-vessel environments posed by unique system configurations and multiple temperature measurements in coolant and other working fluids. A potential solution is multipoint OFSs utilizing optical fiber as the sensing element. After a review of OFS performance in extreme temperature and radiation environments, this research introduces new multipoint OFS probe with high spatial resolution and featuring a thermal conductor-insulator-conductor (CIC) architecture to reduce thermal smearing caused by the sheath. The conceptual design was validated through thermal analysis and computational simulations. Three prototypes were tested under transient and steady-state conditions, demonstrating probe’s capability to accurately measure localized temperatures in non-uniform thermal fields. Crucially, this work introduces a novel method for optimizing the fiber’s path to avoid obstacles while maintaining a safe-bending radius. An effective layout of optical fiber is crucial for efficient mapping of the measurement environment. A fitness function considers factors like bending radius; length; distance from obstacles. Validation on 2D workpiece with sensing points and obstacles demonstrated this method’s superiority over intuition-based layouts. An application of these OFSs in monitoring TES tanks in SMRs is explored, particularly for molten salt reactors. A finite element model of the tank was developed to simulate the melting and phase charging processes of the working fluids. Experimental validation, using a wax mock-up to mimic molten salt phase change, confirmed the sensor's effectiveness in capturing temperature distributions during both transient and steady state operations, where traditional sensors fail. Key contributions of this research include a new sheath design for high-resolution temperature measurements, a novel methodology to optimize an obstacle-free path for cascading OFSs within a specified bending radius, and numerical and experimental investigations demonstrating the feasibility of using multipoint temperature OFSs in SMRs and TES systems. This work significantly advances OFS technology for SMRs and TES system applications, enhancing temperature measurement accuracy, operational control, and safety, all of which are vital to the reliable integration of SMRs and TES systems in future sustainable energy generation.