Best-estimate simulations of condensation-inducedwater hammer in horizontal pipes with the system analysis code athlet

A newly developed hybrid heat transfer coefficient module has been developed, based on two individual surface renewal theory models and implemented into the German thermal-hydraulic system analysis code ATHLET (which stands for analysis of thermal hydraulics of leaks and transients). The new model is based on mechanistic assumptions and does not require special parameter tuning, thus increasing the predictive capabilities of the system analysis code. This model was validated against a full set of 33 experiments performed at the PMK-2 facility for the analysis of condensation-induced water hammer phenomena in a horizontal test section. The integral thermal-hydraulic experimental facility has a similar design to the main steam line of a WWER nuclear power plant.