Application of unstructured mesh-based numerical method to sodium-water reaction phenomenon analysis code SERAPHIM

When pressurized water or vapor leaks from a failed heat transfer tube in a steam generator of sodium-cooled fast reactors, a high-velocity and high-temperature jet with sodium-water chemical reaction may cause wastage on the adjacent tubes. To evaluate the effect of the reacting jet to the adjacent tubes, a computational fluid dynamics code SERAPHIM, in which a compressible multicomponent multiphase flow with sodium-water chemical reaction is computed, has been developed. The multiphase flow under the tube failure accident is calculated by the multi-fluid model considering compressibility. The chemical reaction between liquid sodium and water vapor is considered under the assumption of an infinite reaction rate. The original SERAPHIM code is based on the finite difference method. In this study, unstructured mesh-based numerical method was developed and introduced into the SERAPHIM code to advance a numerical accuracy for a complex-shaped domain including multiple heat transfer tubes. Validity of the unstructured mesh-based SERAPHIM code was investigated through the analysis of an under-expanded jet experiment, which is a key phenomenon in the tube failure accident. The calculated pressure profile showed good agreement with the experimental data. Numerical analysis of water vapor discharging into liquid sodium was also performed. The calculated temperature field agreed with the existing experimental knowledge. It was demonstrated that the proposed numerical method could be applicable to evaluation of the sodium-water reaction phenomenon. (author)