Stratified flows in horizontal piping of passive emergency core cooling systems

In passive cooling systems of advanced light water reactors outside coolant enters the cold leg by gravity and flows towards the core. This coolant is at a substantially lower temperature and thus is heavier than the liquid in the reactor. The warmer liquid may intrude into the cold leg in the form of a wedge against the flow of the coolant. Such a flow system is analyzed here using the momentum conservation principle. The analysis results in an integral. Upon numerical integration, the length and shape of the wedge can be computed as a function of the specific weights of the fluids and the depth and flow rate of the heavier liquid. The flow system is also investigated experimentally using a brine-water system. The test loop and measurements are described. The laboratory data validates the analytical results. (authors)