The traditional design methodology for pressure reinforcement of openings in pressure vessels is usually accomplished utilizing the equivalent area replacement. This methodology is specified in Divisions 1 and 2, Section VIII of the ASME B&PV code. It is found that in some cases the stresses at the nozzle shell junctions exceed the allowable limits for stress, even though the code requirements of area replacement rules are met. A parametric study was carried out to arrive at simplified formula for stress concentration factor in thin radial nozzle shell junctions under internal pressure loading. An axisymmetric method equivalent to 3D Finite Element Analysis (FEA) was used. Simplified formula for stress concentration factor is expressed in terms of non-dimensional parameters. It is derived based on data generated for maximum membrane stress intensity at the junction. The proposed formula provides a good approximation of the membrane stress intensity at the nozzle shell junction and allows the designer to incorporate the FEA results in the initial design stage.