• integral model
• interface mass transfer
• vapour film dynamics
• Rapid vaporization

In the context of the development of a new prototype of Sodium-cooled Fast Reactor, it is
necessary to solve the important safety issue connected with the explosive reaction that can
happen when sodium comes into contact with water. This aspect does not fall only within the
plant operation, for example for a possible accident of steam generator tube rupture (SGTR),
but it is also connected with maintenance and decommissioning for washing operations of
materials that have been in contact with liquid sodium.
For this reason, it is very important to clarify the phenomenology of sodium-water reaction in
all the complex aspects that concern it. In this regard, the CEA has capitalized a long
experience which consists of a strong experimental part, but also of different
phenomenological models.
In the present work we have focused the attention on the dynamic of rapid vaporization that
happens when a hot material comes into contact with cold water. This phenomenon concerns
also the interaction between sodium and water, because, besides the chemical reaction, the
initial behavior is not so different from a so called “steam explosion”, i.e. an explosive
evaporation accompanied by pressure peaks.
The developed 0D model has highlighted the fundamental parameters of the interaction,
which are the surface temperature of the hot body and the initial thickness of the gaseous film
that surrounds it. The latter parameter is needed to overcome the impossibility of treating the
direct contact between solid and liquid at the initial instant, because of a numerical
singularity; it strongly affects the evolution of the phenomenon, in particular the magnitude of
the first pressure peak and the amplitude of vapour film’s oscillations. The possible presence
of diffusive phenomena inside the film, which surely regards the reaction case because of the
gaseous products, could strongly influence the behavior.
The main limit of the model is the simplicity of the adopted integral approach, that requires
significant approximations, whose reliability has to be verified, especially in view of a
potential development towards the simulation of the actual chemical reaction.