[en] A new computational program SERAPHIM (Sodium-watEr Reaction Analysis: PHysics of Interdisciplinary Multi-phase flow) is developed to investigate the Sodium-Water Reaction (SWR) phenomena based on parallel computation technology. A compressible three-fluid (liquid water, liquid sodium and mixture gas) and one-pressure model is adopted for multi-phase calculation. The Highly Simplified Maker And Cell (HSMAC) method considering with compressibility is implemented as the numerical solution. The Message-Passing Interface (MPI) is used for the parallel computation. Two types of reactions are considered for the SWR modeling; one is a surface reaction and the other is a gas phase reaction. The surface reaction model assumes that liquid sodium reacts with water vapor on the surface of liquid sodium. An analogy of heat transfer and mass transfer is applied in this model. Reaction heating vaporizes liquid sodium resulting in the gas phase reaction. The ab initio molecular orbital method is applied to investigate the reaction mechanism and evaluate the reaction rate described by the Arrhenius law. A performance of parallel computation is tested on the cluster-PC (16 CPUs) system. The execution time becomes 17.1 times faster in case of 16 CPUs. It seems promising that the SERAPHIM code is practicable for large-scale analysis of the SWR phenomena. Three-dimensional SWR analyses are also carried out to investigate the characteristics of the thermal-hydraulics with the SWR and an influence of initial pressure (0.2 MPa and 0.6 MPa) on an early stage of the SWR phenomenon. As a result, distribution of a gas region, in which water vapor or product of the SWR such as hydrogen and sodium hydroxide exits, velocity and high temperature region differs by 0.2 MPa and 0.6 MPa conditions. However, the maximum gas temperature has an upper bounding and is almost constant both in the analyses. The reason of the upper bounding is attributed to the fact that a hydrogen gas covers up a liquid-gas interface and thus suppresses the SWR. Sodium hydroxide is a dominant species of the gas at the high temperature region in each case. Heat capacity (=ρ.Cp) of sodium hydroxide is not influenced by pressure resulting in the same value of maximum gas temperature. (authors)