Heavy liquid metal reactors characteristics

There is one significant difference. Depending upon design, a positive void coefficient is possible with a molten salt coolant. Several other reactor types have this characteristic liquid-metal fast reactors and heavy water reactors. A positive void coefficient implies that if the core looses all coolant, the power level increases. 

Cooling by a liquid metal, such as sodium, has been universally adopted for fast breeder reactors. The main reason is that so many potential coolants are unsuitable because of the need to minimize moderation of the fast neutron spectrum in the core. Water (light or heavy) and organic coolants are therefore eliminated. Consideration has been given to the use of steam or helium as fast reactor coolants, but the heat transfer characteristics of a liquid metal are so much more favorable, particularly for a reactor of high power density, that neither steam nor gas cooling has been adopted for current fast breeder designs. 

---