Determination of the critical submergence at pump intakes in NPP with a new approach combining ANSYS CFX with the analytical vortex model of Burgers &

Rott, P. Pandazis, F. Blömeling, TŰV NORD SysTec GmbH, Germany

23rd Symposium of AER on VVER Reactor Physics and Reactor Safety (2013, Štrbské Pleso, Slovakia)
Nuclear applications of computational fluid dynamics (CFD)


An important issue of safety considerations for nuclear power plants is the determination of
the necessary submergence of pump intakes to ensure a reliable pump operation during postulated abnormal operation and accidents. Surface vortices occur when the water level above
the pump intake is decreased below a critical value. These vortices induce swirling flow and
gas entrainment at the intake which lead to the decline of flow or even pump failures and
damages. Thus, surface vortices must be considered for the determination of the available
amount of cooling water in the reservoir tanks and reactor sump of nuclear power plants. The
prediction of the critical submergence is difficult, because it depends on many geometrical
and fluid dynamical parameters. The critical submergence is generally calculated with universal and conservative easy-to-use correlations, if experimental data is not available. However,
these correlations are only valid within a limited parameter range. An alternative, more detailed approach to calculate the critical submergence is 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. The developed calculation approach is based on the combination of ANSYS CFX
with the analytical vortex model of Burgers & Rott. This paper describes the application and
validation of the improved method against the experiments from Jain et al. Additionally the
applicability and the limitations of the widely-used correlation of the American National
Standards Institute (ANSI) for the calculation of the critical submergence have been investigated by using the improved method.

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