Why is sodium used for cooling reactors?
Sodium is used as coolant in fast nuclear reactors where nuclear fission is primarily performed by fast neutrons. Accordingly, water is not usually used as coolant in these reactors as it will act also as moderator to neutrons (due to the low atomic number of its constituents of hydrogen and oxygen). Sodium is more efficient as coolant for fast nuclear reactors due to its relatively higher atomic and mass numbers (atomic number 11 and mass number 23) and consequently fast neutrons will not be slowed significantly on collision with Sodium nucleiSodium also has the advantage of having a high boiling point (883 0 C or 1621 0 F) which is higher than the nuclear reactor operating temperature. So, it does not need pressurization as the case with using water as coolant in nuclear reactors. Its melting point (97.72 0 C or 207.9 0 F) is below reactor operating temperature.In addition to the above sodium is available, not expensive, and is of single isotope.The main disadvantage of sodium is its chemical reactivity, which requires special precautions to prevent and suppress fires. Sodium explodes when it comes into contact with water and it burns when it comes into contact with air.