A Review on Sodium Boiling Phenomena in Reactor Systems

Sodium boiling phenomena in nuclear reactors have been reviewed in the context of the renewed interest in sodium-cooled fast reactors. This paper presents all properties that influence sodium boiling behavior, including thermodynamic and transport properties, as well as the typical composition of reactor-grade sodium, the surface wetting, radiative heat transfer properties, and noncondensable behavior. Starting from these properties, the tendency for high superheat is explained, together with the reasons that the problem of superheat can be neglected for reactor systems. The peculiar boiling behavior of sodium in assemblies is explained on the basis of the temperature profile. This leads us to conclude that a typical slug flow pattern prevails for sodium boiling. The boiling heat transfer for pool film boiling is also given, deducing that the critical heat flux phenomena for sodium boiling in reactor systems is mainly related to dryout and not to the departure from nucleate boiling. The correlations that exist for the minimum film-boiling temperature are discussed in light of their applicability to liquid sodium. Although there are already a large amount of data, gaps in the current understanding of sodium are highlighted.