Bubbly flows occurring in nuclear power plants remain a major limiting phenomenon for the analysis of operation and safety. Therefore, the choice was made to investigate these complex flows with a multifield approach, considering the gas phase as two separated fields. In so doing, the small and spherical bubbles are considered as parts of the dispersed field whereas the distorted bubbles are simulated with an interface locating method. The flow motion is followed using the two-fluid model of Ishii [1975, Thermo-fluid dynamic, theory of two-phase flow, Eyrolles] extended to n-phases. Nevertheless, this model is known to spread numerically large interfaces, which results in a poor accuracy in the calculation of the local flow parameters such as curvature. Therefore, this paper is focused on the accurate simulation of the large scale interfaces. The implementation of an artificial interface sharpening equation is detailed to limit the interface smearing. The activation criteria are also described. Special attention is given to mass conservation. All these steps are illustrated with test cases of isothermal, incompressible and laminar separated two-phase flows. A final validation is proposed with the simulation of the Bhaga's rising bubble problem.