## 1 Introduction
Recently, 3D analysis codes for analyzing water vapor and hydrogen behaviors in NPP containments have been developed using various approaches. A typical method is to add special physical models to general-purpose CFD tools such as FLUENT [7], CFX [8], and STAR-CCM+ [9]. In-house codes developed especially for containment thermal hydraulics analysis include GASFLOW [10], GOTHC [11], and TONUS [12]. Recently, research has been conducted to develop models and solvers optimized for containment analysis based on open-source CFD platforms such as OpenFOAM [13]. There are still not many cases where hydrogen behaviors in an NPP containment have been simulated using 3D codes. [PERSON] et al. [14] performed the first full-3D analysis of hydrogen behavior in an NPP containment using the GASFLOW code. The GASFLOW code was upgraded for parallelized computation recently [15] and applied to other NPPs such as Qinshan-II [16]. [PERSON] et al. [17] used CFX by adding water vapor condensation, heat transfer, and hydrogen flame characteristics evaluation models to evaluate flammability and the deflagration-to-detonation transition (DDT) characteristics of hydrogen mixture in Westinghouse and KWU NPPs. Afterward, the KWP NPP was simulated again using GOTHC to study hydrogen mitigation by PAR [18]. [PERSON] et al. [19] also used GOTHC to three-dimensionally simulate hydrogen distribution in the VVER-1000 containment. [PERSON] et al. [20] used FLUENT to study hydrogen distribution in 220 MWe PHWR containment with a user-supplied wall condensation model. [PERSON] et al. [12] used TONUS developed by CEA and IRSN for hydrogen risk analysis in the EPR containment, where there is no information about PAR modeling in the containment. [PERSON] et al. [21] developed a new 3D containment analysis code for hydrogen and carbon monoxide mitigation based on OpenFOAM, but no papers have yet been found on its application to actual NPP containment analysis. The hydrogen recombination rate correlation obtained from PAR performance experiments is easy to implement in the LP-based codes. On the other hand, in order to apply it to a 3D code, additional efforts of model multi-dimensionalization, grid generation, parallelization, etc., are required because each PAR reacting zone may have multiple cells of a containment mesh. Modern CFD codes rely on parallel computing to enhance computing performance. A PAR module of 3D codes requires sophisticated numerical schemes for parallelization of the PAR model. Recently a turbulence-resolved CFD code, contain3D, has been developed for a hydrogen safety analysis in an NPP containment for best estimation [22; 23]. In this paper, we introduce the analytic models implemented in the code, with a particular focus on an enhanced PAR model that accounts for the pressure drop across the porous catalyst and the heat transfer between the catalyst body and the exhaust gas. The PAR and wall vapor condensation models are validated through benchmark test simulations. To streamline the time-consuming process of placing multiple PARs in the containment digital geometry model, we developed and applied a Python program to generate the APR1400 mesh. The contain3D code is used to study hydrogen behavior influenced by water vapor condensation and hydrogen recombination by PARs installed in the APR1400 containment [24]. Through these analyses, the hydrogen removal performance of PARs in the containment building is evaluated, along with the assessment of any uneven or stratified distribution of hydrogen.