This work presents the development of two optical sensors designed to measure real-time chemical impurity concentrations in molten sodium and molten salt systems. Key aspects of each sensor, including design, functionality, and test results, are discussed in detail in the respective sections.
Molten Sodium Impurity Sensor: An optical sensor that can monitor changes in dissolved sodium oxide levels (< 10 parts per million) in molten sodium is presented in this section. Sodium is used as a coolant in some of the Generation IV nuclear reactors known as Sodium Fast Reactors (SFRs), where isolating the metal from oxygen is paramount to safe and reliable operation. The sensor presented here provides a significantly improved response time compared to the well-established plugging meter technique used in molten sodium systems for measuring dissolved oxygen concentrations of a few ppm. The sensing approach presented is promising as it can overcome several critical limitations of the plugging meter, such as equipment size, measurement time, and power consumption. It can also be a valuable tool in understanding impurity precipitation, deposition, and growth mechanisms in molten sodium.
Chapter one provides an overview of molten sodium systems and highlights the pressing need within the industry for advanced sensors capable of real-time impurity detection. It introduces the design concept developed during this work and details several attempts made toward building a functional prototype.Chapter two describes a working prototype of the molten sodium sensor fabricated using custom optical fibers. It presents the results from testing the sensor in a sodium loop along with traditional diagnostic tools such as the plugging meter and the cold trap.
Molten salt Probe: Molten salts, as an advanced heat transfer fluid, have attracted significant research attention in recent years due to their potential in addressing global energy challenges. This report outlines the development of an optical probe that can be integrated with high temperature molten salt systems to monitor changes in dissolved species using UV-VIS-NIR absorption spectroscopy. The probe offers safe optical access into salt melts through chemically compatible viewports built within rigid tubing that can be easily integrated with salt reservoirs with minimal modifications to test setups. This marks a significant step towards real time optical sensing in molten salts to study salt chemistry and corrosion of structural components under dynamic conditions. Several steps involved in designing, fabricating and testing the probe prototype in molten fluoride melts (FLiNaK – 46.5% LiF-11.5% NaF-42% KF) are presented along with test results on estimating composition of multi-species salt mixtures over short and long duration tests.
Chapter Three discusses the growing interest in molten salts across various applications and provides an overview of Molten Salt Reactor (MSR) systems. It outlines the design requirements considered in developing a real time sensor and discusses several steps involved in coming up with a probe concept. Chapter Four provides a detailed description and the working principles behind the Molten Salt Probe and elaborates on its design and implementation in salt mixtures with multiple impurities over short and long duration tests. Chapter Five presents selected measurements obtained using the optical probe in a FLiBe (LiF 66%–BeF2 34%) test setup conducted at Kairos Power, our industrial collaborator for this project.