Modification of multi-dimensional sodium-water reaction analysis code: SERAPHIM and sensitivity analyses on the early stage of leakage

Takata, Takashi; Yamaguchi, Akira; Watanabe, Akira*

Modification of the SERAPHIM code, which was developed to deal with the sodium-water reaction phenomena in a steam generator of the LMFR, has been carried out With regard to the reaction mechanism, the surface reaction model is improved. The hydrated effect on the reaction rate in the gas-phase reaction is estimated and the reaction product in the sodium-water reaction is investigated. The SERAPHIM code is also parallelized using the MPI (Message Passing Interface) method to apply to a large-scale simulation such as over one million nodes with a limited PC resource. The analysis region and the memory needed in the analysis are discrete in the SERAPHIM code. The execution time becomes approximately l7 times faster in case of 16 CPUs. The calculation of one million nodes can be available even in a PC cluster system with 1 GB memory. Sensitivity analyses of the surface reaction model in the beginning of the water vapor leakage are carried out and the following conclusion are obtained. 1)Gas region develops quickly in case of no chemical reaction. The pressure peak is obtained at an early stage of the leakage regardless of the chemical reaction. 2)The difference of the initial pressure strongly affects the development of the gas region and the flow-field. However,It is less influential on the maximum temperature. The maximum temperature depends not only on the chemical reaction characteristics such as the gas region and heat generation but also on the thermal-hydraulics characteristics in the multi-phase flow field. 3)Considering the evaporation of sodium hydroxide (NaOH), the maximum gas temperature of approximately 1200deg is observed in the analysis. In the standard state, the chemical reaction that produces a gas state sodium oxide and hydrogen gas from liquid sodium and water vapor is endothermic. In is concluded that the evaporation of sodium hydroxide is very important phenomena in the sodium-water reaction.