An implicit finite difference method has been developed and incorporated into the ICECO code for analyzing hydrodynamics in the above-core region induced by the upper internal structure, and sodium spillage through penetrations and ruptured seals resulting from slug impact on the reactor cover. Eulerian description is employed so that flow through coolant passageways, large material distortions, two-dimensional sliding interfaces, flow around corners, and out-flow boundary conditions can be easily treated. In the analysis, the upper internals and the reactor cover are considered as perforated structures. A control-volume technique is utilized for deriving equations for the conservation of mass, momentum, and energy. The basic idea is to use actual fluid volume and actual flow areas in the mathematical formulation. Several modified Poisson equations are obtained, which govern the hydrodynamic pressures in the vicinity of the perforated structures. Sample problems are provided to illustrate the code capabilities in assessing the effect of the upper internal structure on the containment response and in estimating the amount of coolant ejected from the primary containment.