Investigations into natural circulation driven heat removal systems

Passive safety systems can make an important contribution to decay heat removal in existing and next Generation NPP. Two-phase natural circulation systems have under certain circumstances instabilities which have to be analysed in detail. For this reason the test facility GENEVA has been constructed and commissioned at the TU Dresden. The experiments described in the experimental matrix will be started this year. First experimental data showed flow instabilities e.g. flashing as expected. Generic studies are necessary to examine two-phase flow and especially two-phase flow instabilities in further detail. The influence of subcooling and the diameters of downcomer and riser are of particular interest. These will help to evaluate the system behaviour of passive heat removal systems as well as their safety and reliability for nuclear reactors. (orig.)