High Temperature Alloy-Interface Characterization in Molten Salt Reactors by Radiation Resistant Fiber Optic Sensors

For clean, compact, molten salt nuclear reactors, MSRs, and small modular reactors to offer continuous energy to bridge inevitable gaps in intermittent renewable energy sources, their safety and reliability must be ensured. MSRs have highly corrosive salts making the structuralmaterials prone to corrosive damage. In-situ characterization of their structural integrity, preferably continuously, and without system shut-downs, is therefore essential. High- temperature- and radiation-resistant transducers, such as optical fiber sensors, are required for continuously monitoring corrosion levels in reactor conduits. Our team, which includes corrosion science and guided ultrasound experts, proposes to complete our in-situ ultra-high-temperature conduit corrosion detection system development for MSRs and other SMRs during this Phase-IIA. We propose to continue building upon our successful results and ongoing tests towards high-temperature transduction of ultrasound launch and detection, as well as studies on corroded specimens to complete the autonomous in-situ MSRs structural monitoring system. Other MSR alloys, including Hastelloy-N, will also be tested in Phase-IIA. Permanently mounted distributed fiber optic sensors will, for the first time, also allow long-term corrosion measurements at MSR temperatures. In Phase-I and Phase-II, we analyzed sensor responses of several MSR-specific corroded alloy pipes provided by our national laboratory partner. Changes in the properties due to static molten salt interactions have been measured by guided ultrasound, and fiber optic sensors recorded pipe ultrasound responses. Our team developed numerical models for our test facility’s thermal con- vection loop. In Phase-II, we designed, and are testing, the components of our field-usable prototype system to measure real-time corrosion effects in MSR-materials. Data analysis techniques for automated analysis in a continuously operating mode are being developed. This complete hardware and data-analysis software prototype system is being integrated. Ongoing tasks to reach and exceed our Phase-II goals include: detecting and validating molten salt corrosion levels in benchtop studies to enable automated analysis; launching guided modes in a thermal convection loop, at high temperatures has been demonstrated for transmission over a long range and around a bend. This leads the wayto system integration for 800 ºC tests; implementing a control algorithm for automated response detection at corrosion-prone locations with high-temperature fiber-bonding materials, under changing temperature; enabling high sensitivity and improved data analysis; and determining evolving MSR pipe material changes with autonomous ultrasound response acquisition, over several hours of operation at 800 °C, in the thermal convection loop. The continued completion (testing,improvements,andbeta-testing)of oursystem operating at MSR temperatures is proposed for this Phase-IIA. Applications of our high-performance, cost-reducing automated pipe structural health monitoring system are increasing safety and predicting remaining useful life of alloy structures in molten salt reactors and other advanced small modular reactors. Our business model extends structural health monitoring to corrosion-prone pipes in conventional nuclear reactors and other industries’ infrastructure operating at high-temperatures.