The present study proposes the assessment of closing relations related to the RPI (Rensselaer Polytechnic Institute) wall heat flux partitioning model, as well as the assessment of interfacial heat transfer correlations, via CFD (Computational Fluid Dynamics) simulation. Although simulation software provides several correlations to model these parameters, the selection of these closing relations, most of the time, is made in a way that does not consider its applicability and scope, neglecting the effects that might affect the results obtained in two-phase flow simulations and most of them are not completely suitable for the simulations of the operating conditions found in Pressurized Water Reactors (PWRs). In order to assess which sub-models can properly predict the boiling two-phase flow characteristics found in PWRs, an upward subcooled flow boiling in an annulus, with R-134a as the working fluid - which results can be compared to water based on similarity parameters, was simulated based on an Eulerian-Eulerian approach. Formulations for bubble departure diameter and nucleation site density were evaluated and the best combination of models chosen Three interfacial heat transfer sub-models were also analyzed: Ranz-Marshal (1952), Tomiyama (1998) and Hughmark (1967). The saturation pressure ranged from 1.29 MPa to 2.69 MPa, the mass flux from 998 kg/m².s to 999 kg/m².s, heat flux varying from 120.4 kW/m² to 120.7 kW/m² was applied along the annulus, whereas the flow inlet subcooling ranged from 12.4ºC to 8.0ºC. The void fraction radial profile of two-phase flow was attained, analyzed and compared to the benchmark study. This study concluded that the increase of pressure have distinguishable impacts on the performance of the correlations analyzed. For high pressure cases, the formulations by Lemmert and Chawla (1977) for nucleation site density and the Hughmark (1967) interfacial heat transfer equation performed better than the other models available; for low pressure cases, these formulations shifted for Kocamustafaogullaria and Ishii (1995) and Ranz and Marshal (1952), respectively. The Tolubinski and Kostanchuk (1970) equation for bubble departure diameter had the best performance in both cases.