Two-dimensional calculation of sodium boiling in sub-assemblies

The geometrical differences between interior and peripheral subchannels affect the flow and temperature fields inside a subassembly. In the case of a loss of flow without scram, these effects are enhanced after boiling has started in the hottest region, due to an internal flow distribution. In order to compute this process in a prototypic small size bundle as well as in a full size subassembly, the control volume retained for discretization of the balance equations is coarser than a subchannel. In the present stage of the BACCHUS code, where axial symmetry is assumed, it consists of an hexagonal ring containing both coolant channels and solid structures. After derivation of the macroscopic balance equations and an insight in the numerical techniques used, results are given for steady state boiling. This is indeed a good approximation in case of a slow flow decay as in the reference accident for Creys-Malville