[en] KOPEC has been developing a two-phase thermal hydraulic solver for the safety analysis of nuclear power plants. The pilot code adopts the multi-dimensional, three field governing equations, which are spatially discretized using a general unstructured polyhedral mesh system. Several numerical schemes, such as collocated, staggered, semi-implicit, and implicit schemes, have been tried so far. Among the various numerical solution schemes implemented in the pilot code, the staggered mesh semi implicit scheme will be described in detail in this paper. In addition, some of its application results, such as manometric oscillation and simplified direct vessel injection tests, will be presented