## 3 Results
### Application to PWR Containment
#### 3.2.1 Containment Mesh Generation and Source Modeling  
An important factor when modeling a containment building is the level of detail that can be resolved. The reference for the detail of the geometry is the characteristic length to resolve flow features with the analysis code. In the case of the APR1400 containment with PARs installed, the hydraulic diameter of the PAR inlet can be the characteristic length. Whether to trim or resolve a geometric shape can be determined by the characteristic length. Another important step in geometry modeling is the placement of the PARs in the containment building. In general, PAR is an accident mitigation facility and can be changed during licensing, so its installation location is not included in the containment drawing but is indicated in the form of a table in the accident management or safety analysis report. A python program was developed to automatically place PARs on the computer drawing of the containment. When a table of PAR locations is input to the python program, it sequentially adds a PAR geometry to the containment drawing by finding the shape that fits the PAR model in a database and copying it to its location listed in the table. Thirty PARs are installed in the APR1400 containment building. Figure 11 schematically shows the process of placing PARs in the digitalized APR1400 containment drawing. The color legend in Figure 11c means the identification numbers of the PARs installed in the containment. Figure 10: Hydrogen mass remaining in the test vessel and recombination rate of: (**a**) the SPARC SP8 test; (**b**) the SP9 test simulation with the KNT correlation. A computational mesh for the APR1400 containment was generated using snappy-HexMesh, which is an automatic mesh generator included in OpenFOAM. The numerical solution may be dependent on the mesh characteristics used, among which the number of cells, mesh skewness, and mesh topology were considered in the study. To evaluate the mesh dependency of the numerical solutions, three meshes were constructed. Figure 12 shows the three meshes tested for solution's mesh dependency. The meshes in Figures 12a and 12c are generated based on a hexahedral background grid and consist of 680,000 and 1,150,000 cells, respectively. As can be expected, the containment outer wall is cylindrical. A cylindrical mesh can be an option. The mesh in Figure 12b is generated based on a cylindrical background grid. This mesh is the coarsest among them because a 0.3 m annular gap between the containment wall and operating deck is easily resolved in the cylindrical background grid. A simple hydrogen injection and PAR recombination test was conducted to check the mesh dependency of the solution. In this study, mesh dependency was evaluated based on the hydrogen mass remaining in the containment at 1000 s. The difference among the meshes is less than 0.1%. So, Mesh A was chosen for the accident analysis because it results in the fastest running time among the three meshes due to its smaller number of cells and better skewness. to apply to debris formed on the core support plate or the lower plenum of the vessel. The MELCOR analyses of the accident scenarios indicate that approximately 500 kg of hydrogen would be produced before pressure vessel failure is reached. The remaining hydrogen mass to satisfy 100% active core oxidation was assumed to be constantly produced in the MELCOR simulation until vessel failure. Figure 13 shows water vapor and hydrogen release rates into the containment during the accident progressions with the assumption of 100% active core oxidation. The total masses released until the vessel failure are summarized in Table 2. As the SBO accident in APR1400 begins, the water vapor is released into the in-containment refueling water storage tank (IRWST) through the safety depressurization valves. When the core exit temperature reaches 650 \({}^{\circ}\)C, the vapor and hydrogen are released into the SG compartment by turning a three-way valve under a severe accident management guide (SAMG).