Properties of concentrated aqueous lithium nitrate solutions and applications to fusion reactor design

Aqueous solutions of Li-containing compounds have been proposed to serve as the combined tritium breeding material and coolant for fusion reactors. The salt used for the TITAN-II reversed-field-pinch reactor design is LiNO3, which was chosen for its good neutronics properties, relatively good corrosion characteristics, and for its high solubility in water. An extensive literature survey has shown that the physical and thermal properties of high-temperature, concentrated aqueous LiNO3 solutions are markedly different from the pure water properties at similar conditions. These changes alter the heat transfer performance of the coolant, and the critical heat flux is estimated to rise for sub-cooled flow boiling, while the heat transfer coefficient for forced convection falls. Another important result is the elevation in boiling point, which may allow the operating pressure of the primary coolant to be reduced to a value below that of the secondary steam circuit, preventing leakage of the tritiated coolant into the steam circuit. Further research is needed into corrosion and radiolysis issues, but the available data imply that careful control of the coolant chemistry can minimize the problems.