Liquid metal cooled reactor Clementine was the first liquid metal cooled nuclear reactor and used mercury coolant, thought to be the obvious choice since it is liquid at room temperature. However, because of disadvantages including high toxicity, high vapor pressure even at room temperature, low boiling point, producing noxious fumes when heated, relatively low thermal conductivity, and a high neutron cross-section, it has fallen out of favor. Sodium and NaK (a eutectic sodium-potassium alloy) do not corrode steel to any significant degree and are compatible with many nuclear fuels, allowing for a wide choice of structural materials. They do, however, ignite spontaneously on contact
Liquid-liquid critical point a higher percentage of HDL exists while below the critical pressure a higher percentage of LDL is present. The ratio "r" = LDL/(LDL + HDL) of phase amounts is determined according to the thermodynamic equilibrium of the system, which is often governed by external variables such as pressure and temperature. A discontinuity is present in "r" when crossing the liquid-liquid phase transition, which separates the LDL-rich phase from the LDL-poor phase. At any point of the liquid-liquid phase transition, including the associated liquid-liquid critical point, the ratio of LDL to HDL is exactly one ("r" = ½). The liquid-liquid critical