Molten salt reactor's fuel is dissolved in fluoride coolant salt typically consisting of some of lithium, beryllium, sodium or potassium fluorides. Composition is chosen according to desired properties like viscosity or melting point (the mixture has lower melting point than a single salt).

    This mixture has not only low reactivity with air and water but it’s also very stable under intense irradiation moreover it allows high operating temperatures (up to 1000°C) at very low pressure (near atmospheric). Boiling point always reaches more than 1200°C. High operating temperatures leads to higher thermal efficiency. From temperatures above 600°C the simple Brayton cycle is more effective than the steam Rankine cycle [1]. Since fluoride salts possess outstanding heat transfer properties, they can be used in various high temperature applications.