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
Temperature dependence of liquid viscosity and applies over a large temperature and viscosity range: where "T" is absolute temperature in kelvins, formula_26 is the kinematic viscosity in centistokes, formula_27 is the zero order modified Bessel function of the second kind, and "A" and "B" are liquid specific values. This form should not be applied to ammonia or water viscosity over a large temperature range. For liquid metal viscosity as a function of temperature, Seeton proposed: Temperature dependence of liquid viscosity The temperature dependence of liquid viscosity is the phenomenon by which liquid viscosity tends to decrease (or, alternatively, its "fluidity" tends to increase) as its