sodium as a coolant in nuclear engineering was introduced and discussed in the last chapter in terms of its ability to deal with the high power densities encountered in fast reactors, an ability that arises from its excellent heat-transport properties. However, it has other desirable qualities also; its boiling point, 882°c (1,620°F), is high, so that it can remove heat at high temperature without having to be kept at high pressure; and its neutron absorption cross-section is relatively low, so that it could be used as coolant in a thermal reactor with only slight enrichment of the fuel. In fact the use of sodium cooling offers the possibility of operating a thermal reactor at atmospheric pressure and at temperatures high enough to produce superheated steam.