Surface vortices occur at pump intakes, when the water-level sinks below a critical value. They can affect the intake flow in a disadvantageous manner. Pump disturbances may be initiated and the mass flow may be decreased or completely interrupted. The determination of the critical value to avoid surface vortices is an important part of safety analyses of postulated abnormal operations and accidents in Light Water Reactors. The vortex formation phenomena are investigated within the research project "Generic numerical determination of the critical submergence at pump intakes to avoid gas entrainment" sponsored by the German Federal Ministry of Economics and Technology. In this project a coupled numerical-analytical method has been developed to calculate the critical submergence. The method is based on the results of two-phase numerical CFD simulations and on the analytical vortex model of Burgers and Rott. It allows an efficient investigation of various influence parameters, which affect the critical submergence. The results of the method are compared with the experimental results from Jain et al. and Moriya and show a very good agreement. The present paper describes the performed CFD simulations as well as some validation results.

Condensation induced water hammer (CIWH) are caused by contact of steam and subcooled water. Thus, modeling the direct contact condensation is a crucial step towards the simulation of condensation induced water hammer with 1D pressure surge codes. Therefore, also the TÜV NORD SysTec GmbH & Co. KG inhouse pressure surge code DYVRO has been equipped with a new contact condensation model. The validation of DYVRO against an experiment dealing with CIWH is presented in this contribution.