Molten salt for advanced energy applications: A review

•Molten salt is used in energy technologies, such as energy production and storage.•Nuclear reactors and hybrid energy systems are examples of molten salt systems.•Molten salt systems involve many radiological and chemistry challenges.•Many unique technologies have been designed for molten salt systems.•The technology readiness level for power cycle coupling is lower for molten salt systems. The primary uses of molten salt in energy technologies are in power production and energy storage. Salts remain a single-phase liquid even at very high temperatures and atmospheric pressure, which makes molten salt well-suited to advanced energy technologies, such as molten salt reactors, or hybrid energy systems. The molten salt cooled reactor is an advanced nuclear reactor concept that utilizes molten salt as either a coolant for solid fuel or as a fuel salt. The liquid phase provides orders of magnitude higher heat capacity per cubic meter than the gas phase. This, coupled with the low-pressure environment required to maintain the liquid phase, provides significant advantages in terms of compact-sized systems constructed with relatively thin walls. The heat from a heat-generating process is transferred to a heat transfer media and can be extracted later using a secondary power cycle. There are several types of facilities that use thermal energy storage with molten salts, such as concentrated solar power plants (CSP plants) or nuclear hybrid energy systems (NHES). A CSP plant is a power production facility that uses a broad array of reflectors or lenses to concentrate solar energy onto a small receiver. Since molten salt remains in the liquid phase, it has excellent heat retention properties, meaning heat from a solar-generation process can be stored for an extended period for later use. A Nuclear Hybrid Energy System (NHES) refers to several energy systems combined to generate energy more efficiently, such as nuclear reactors, renewable energy sources, process heat applications, and energy storage. The selection of a salt type for a nuclear reactor or a thermal storage system requires careful consideration of the chemical and thermodynamic properties of the candidate salts. Different energy technologies will require different salt types, based on temperature and fluid property requirements. Fluoride salts are often the primary candidate salts for nuclear reactor systems. Chloride salts are another category of candidate salt that have been considered for power produc