Cfd simulation of flashing boiling flow in the containment cooling condenser system of kerena reactor

The KERENA™ reactor is a generation III+ BWR concept, which was originally proposed by AREVA and is currently being developed jointly by AREVA and German utility E.ON (AREVA, 2010). It aims to achieve a cost competitive plant with enhanced safety features and an optimal BWR balance of active and passive safety systems. The containment cooling condensers (CCC) belong to such kind of passive features, which require neither electric power nor switching operations to begin functioning. The CCC unity is connected to a shielding/storage pool, which is located above it, via an inlet to the lower end and a discharge line at the upper end. In case of overpressure or overtemperature, steam in the containment will condense at the outside wall of the condensers. Heat released by steam will be transferred to the cooling water inside the tubes. As it is heated, the cooling water will remove heat from the containment to the water of the shielding/storage pool through a natural circulation.

The performance of the complete CCC system has been investigated experimentally on the full-scale INKA test facility of AREVA in Karlstein (Leyer and Wich, 2012). During the experiment, strong flow instability or water hammer caused by the formation and subsequent destruction of steam bubbles inside the discharge line was observed. In other words, the formation of steam will have a significant influence on the safety operation and heat removal capacity of the system, which requires further investigation. In this case, the mechanism of phase change from water to steam is different from that of the traditional boiling as a result of wall heating. Due to the elevation difference between the CCC and the upper end of the discharge line, which is about 12 m, the drop of hydrostatic pressure along the discharge line exceeds 1bar. The formation of steam is a result of depressurization instead of wall-heating, which is called flashing boiling in contrast to the traditional boiling.