## 3 Results
### Validation of the Models
#### 3.1.2 Simulation of PAR Experiments  
Internationally, many commercial PARs have been developed and used in nuclear power plants (NPPs). Because PARs are passive hydrogen mitigation devices, their performances depend on the thermal hydraulic conditions surrounding them. The PAR operation can change thermal distribution in a containment and conversely, thermal hydraulic conditions in the containment affect the performance of the PARs. Therefore, it is important to conduct thermal hydraulic experiments related to PARs and verify and improve the PAR model based on the experimental data. The PAR model implemented in the contain3D code has been applied to simulations of THAI HR tests [36] and SPARC SP tests [37]. In the THAI-1 project, experiments were conducted to evaluate hydrogen recombination characteristics under various thermal and hydraulic conditions using the PARs from AREVA, NIS, and AECL. In this paper, we describe the analysis results of the HR2 test using the AREVA PAR and the HR14 test using the NIS PAR. Figure 7 shows the geometric models and analysis meshes for the HR2 and HR14 tests. Among the features of the HR test facility is that a cylinder is installed in the test vessel to simulate an annular compartment inside a PWR containment, and the PARs are installed adjacent to the outer wall of the inner cylinder. From the figure, it can be seen that the shapes of the PAR housings of AREVA and NIS are very different. In the HR tests, hydrogen was injected through 56 holes in the pipe ring installed above the sum  
Figure 5: Comparison of pressure change over time for the TOSQAN ISP-47 test [35]. Figure 6: Distribution of water vapor concentration in the radial direction: (**a**) at 6000 s; (**b**) at 16,000 s.  
as shown in the figure. The meshes used for the analyses were well generated to resolve the important geometric features of the PAR, inner cylinder, and nozzle and to resolve the wall condensation rate appropriately. A simple mesh dependency test was conducted by doubling the mesh size and it was found that there is little difference in the prediction of the PAR recombination rates. In the HR tests, hydrogen concentration, gas temperature, pressure, etc., were measured at several measuring points, and the measured values were integrated into the volume of the test vessel to predict the amount of hydrogen remaining in the vessel after being removed by the installed PAR over time. The hydrogen recombination rate of the PAR was obtained using the values measured through sensors installed at the inlet and outlet of the PAR housing. The hydrogen mass and recombination rates were reported in the reference [36]. Figure 8 compares the hydrogen masses remaining in the test vessel and the hydrogen recombination rates obtained from the experiments and numerical simulations. In Figure 8a, the rapid rise in the hydrogen recombination rate at 5640 s is due to hydrogen combustion induced by the PAR. Excluding this, it is thought that the PAR model implemented in the contain3D code well simulates hydrogen recombination characteristics of the AREVA and NIS PARs. APR1400 adopts KNT PARs as a hydrogen mitigation system. The correlation for the hydrogen recombination rate, which is supplied by KNT, is included in Table 1. To evaluate the hydrogen recombination characteristics of the KNT PAR according to the thermal hydraulic conditions, we performed the SP8 and SP9 experiments using the SPARC test facility. Figure 7: (**a**) Geometry modeling of the THAI HR2 test; (**b**) mesh for HR2 simulation; (**c**) geometry modeling of the THAI HR14 test; (**d**) mesh for HR14 simulation. A feature of the tests is that to minimize errors in integrating the remaining hydrogen mass due to the non-uniform distribution of hydrogen while the hydrogen was being released into the SPARC vessel, a plate-type gate was installed at the inlet of the PAR housing and a fan was operated while the hydrogen jet was mixed well. Figure 9a shows the KNT PAR installed in the vessel.