[en] A robust and fast-running numerical method is presented for multidimensional two-phase flows. It is based on a semi-implicit method, where the momentum equation is solved explicitly and the pressure equation is derived by combining the momentum and continuity equations. The energy equation is decoupled from the pressure equation so that the coefficient matrix of the pressure equation is symmetric. The finite volume method with an unstructured grid is used for the discretization of the governing equations for a complex geometry. The present method is verified through a set of conceptual problems and applied to the analysis of the small-break loss of coolant accident of an integral-type reactor. (author)