High resolution two-phase flow structure investigations in tube bundles

Two-phase flow has a variety of different key applications within the nuclear energy sector. The specific focus of the presented work is a severe accident scenario, in which a steam generator tube rupture combined with core damage occurs in a Pressurized Water Reactor (PWR). The latter is accompanied with the release of radioactive aerosols and iodine species from the core (containment bypass). If the secondary side of the steam generator is filled with water, aerosols and iodine may be partially removed by retention processes occurring in the steam generator tube bundle. The test facility TRISTAN was built for the experimental investigation of the hydrodynamics of the described scenarios. TRISTAN is a mockup of a steam generator bundle that is operated at ambient temperature and pressure. The liquid inventory of the flooded steam generator is modeled by demineralized water. In the first phase of the experiments, tests under pool scrubbing conditions, i.e., with only one tube with a break installed inside the facility, were performed to obtain information about the breakdown of the gas jet spreading from the break into the surrounding liquid. Therefore, a single vertical tube with a machined break orifice through which a high velocity gas jet is fed into the facility is installed inside the facility’s vertical square duct of 500 x 500 mm and 6.2 m in height. Two layers of a wire mesh sensor (WMS) are built directly into the test section, which provides high–resolution data on the flow structure. The WMS allows gaining huge variety of information about accompanied phenomena since a single measurement frame covers the whole channel. An air flow rate of 250 kg/h was used in this investigation.