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

In order to deploy clean, affordable, domestic energy sources of the future, the United States must improve their safety and reliability. Engineering materials for service in nuclear reactors, such as the higher efficiency molten salt reactors, need to be developed that will extend their safe operating lifetimes while achieving long-term energy security. Molten salt nuclear reactors (MSRs) typically have a molten salt temperature between 500 and 800 C, and continuous, in-situ characterization of the structural integrity of their conduits is essential. However, for temperatures beyond 300 C, commercial structural sensors based on electrical transducers (piezo-electric or magnetostrictive) are unreliable. Alternative high-temperature transducers are desired that survive the MSR conditions while monitoring the infrastructure and containment vessels. High melting point (> 1500 C) fused silica optical fibers provide such an alternative. Innoveyda proposes to develop structural diagnostic technology for the in-situ monitoring of MSRs and the highly corrosive molten salts effects on alloy metal containers/tubes by fiber optic sensors that are radiation- and high- temperature-resistant. Structural material changes in alloys containing the molten salts will be measured via ultrasound guided waves in alloy pipes that are detected by radiation and high-temperature capable fiber optic sensors. The integrity of MSR conduit materials is critical for the reliable operation of nuclear reactors with corrosive liquids. The proposed high-temperature sensor based diagnostics are also applicable to other industrial sectors including thermal solar energy generation. Distributed fiber optic sensors will measure ultrasound responses in leached and corroded alloys, under high temperature conditions, to locate structural changes. Pre-corrosion and post-corrosion structural models for MSR-specific alloy pipe sections will be compared to benchmark analysis of ultrasound response data. Changes in material properties due to molten salt interactions will be measured in-situ by ultrasound scattered at corroded alloy interfaces. The diagnostic data obtained from these measurements are expected to assist in the selection of (i) less corrosion-prone alloys and/or (ii) salt mixtures for improving the safe operating lifetimes of high-temperature MSRs presently under development. In Phase-I, MSR-specific alloy samples will be provided by corrosion expert Dr. Bruce Pint of Oak Ridge National Laboratory. The ultrasound responses of the samples will be measured by fiber optic sensors for two conditions: pre- and post-corrosion (induced by MRS fluoride slats), and compared with models to demonstrate feasibility of locating structural weaknesses in the metal alloys. This shall form the basis of a diagnostic system that will measure in-situ alloy material changes at the high MSR operating temperatures. A prototype of this complete diagnostic system will be developed in Phase-II with hardware and dedicated data analysis software. Upon achieving material/geometry-specific mathematical modeled response data that provide a better understanding of pipe guided waves and effect of cracks / damage detected by fiber transducers, the proposed project will enable commercialization of the high performance, cost-effective automated pipe structural health monitoring system. The final goal is to predict remaining useful life of alloy structures. The business model incorporates structural health monitoring for oil, gas, and refinery operation pipelines, for alternative energy solar thermal power plant conduits where corrosive salts are used for heat storage, as well as for corrosion-prone pipes in nuclear reactors that use corrosive fluoride salts.