Experimental investigations on heat transfer and flow structure during high pressure steam condensation in a single near-horizontal pipe of a passive heat removal system

Passive safety systems are a feature for improved accident control and mitigation in future nuclear power plants. One example of an advanced boiling water reactor with passive safety systems is the KERENA concept (Wagner u. a., 2011). In this concept a two-stage passive heat transfer chain between the reactor and a large water pool outside the containment is foreseen, which is passively activated in case of an accident. The first stage is an emergency condenser, which transfers the heat from the primary circuit to a core flooding pool in the containment. High-pressure steam condensation in the emergency condenser tubes leads to various complicated flow patterns with strong axial and azimuthal inhomogeneity of the flow. This has feed-back on the local heat transfer and is therefore a challenge for accurate prediction, e. g. by system codes. To investigate the details of flow and heat transfer in emergency condenser pipes the experimental facility COSMEA (Condensation teSt rig for flow Morphology and hEAt transfer studies) with extensive special instrumentation has been setup at HZDR’s TOPFLOW facility. Special attention was paid to obtain wall and fluid temperatures and resolve the local flow patterns during the condensation process. Special measurement techniques are a heat flux probe operated at high wall-differential pressure and X-ray tomography for flow scanning.