Development of a numerical analysis methodology for the multi-dimensional and multi-phase phenomena of a sodium–water reaction in an SFR steam generator

A numerical approach on the exothermic sodium–water reaction (SWR) in a SFR steam generator is carried out by using a commercial computational fluid dynamics (CFD) code. The applicability of the analysis models and the physical limitations of some codes was investigated to select the most powerful CFD code to simulate a chemically reacting flow with various phases and components. In order to model the phenomena, among the several chemical reaction models studied, the eddy dissipation model (EDM) was employed because the EDM is the proper one when the reaction rate is sufficiently high when compared to the flow transport time. Based on the basic understandings for the characteristics of the SWR phenomena and the capabilities of the CFD codes, the numerical analysis methodology for a SWR was developed and transient analyses up to 0.05 s and 0.1 s with a time step of 0.0001–0.0005 s were carried out with a consideration of the geometric effect. The vapor mass flow rate and the corresponding hydrogen production rate were also calculated and compared with the conventional one-dimensional analysis results. As a result, it was found that the multi-dimensional approach underestimates the hydrogen production rate by 17% when compared to the theoretical values, and the difference is mainly caused by a multi-dimensional effect of the chemical reaction. The analysis performed in this study presents detailed information on each phase and the components of the SWR process and it also reflects the realistic SWR phenomena well. In order to confirm the applicability of the methodology, a multi-dimensional analysis was also carried out for the 49 tube bundle condition, and it was found that the results of the analysis were satisfactory.