Research on hydrogen co-firing gas turbines is actively progressing to achieve carbon neutrality. This study performed Computational Fluid Dynamics (CFD) analysis on a current F-class gas turbine nozzle to assess the feasibility of hydrogen co-firing and enhance asset utilization. Reynolds-Averaged Navier-Stokes (RANS) simulations were employed to analyze combustion characteristics up to a hydrogen co-firing rate of 70%, using the Flamelet Generated Manifold (FGM) model and GRI3.0 mechanism. The simulations accurately predicted the reaction zone, flame length, flame shape, and changes in the recirculation flow induced by increased hydrogen reactivity. However, discrepancies in Heat Release Rate (HRR) due to adiabatic wall boundary conditions in the simulation led to deviations from experimental results, affecting the flame shape and the length, particularly impacting NO predictions above a 50% hydrogen co-firing ratio. The findings of this study can provide fundamental insights for future demonstrations of hydrogen in existing F-class gas turbine combustors.