The design of engineered safety systems is primarily based on analytical predictions of the behavior of a reactor under accident conditions and on the result of relevant small-scale experiments. Within this frame, the analytical simulation of two-phase flows plays an important role. It serves as a model law for the extrapolation of small-scaled experimental results over magnitudes of scaling as well as for the detailed interpretation of involved physical processes. A careful description of the technical conditions of an experiment is mandatory for making two-phase flow analytical simulations a successful tool for transforming small-scale experimental results into design decisions for large power reactor systems.