Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf
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Buoyancy driven mixing studies of natural circulation flows at the ROCOM facility using ANSYS CFX
Höhne, T.; Kliem, S.; Weiß, F.-P.
Coolant mixing in the cold leg, downcomer and the lower plenum of pressurized water reactors is an important phenomenon mitigating the reactivity insertion into the core. Therefore, mixing of the de-borated slugs with the ambient coolant in the reactor pressure vessel was investigated at the four loop 1:5 scaled ROCOM mixing test facility. Thermal hydraulics analyses showed, that weakly borated condensate can accumulate in particular in the pump loop seal of those loops, which do not receive safety injection. After refilling of the primary circuit, natural circulation in the stagnant loops can re-establish simultaneously and the de-borated slugs are shifted towards the reactor pressure vessel (RPV). In the ROCOM experiments, the length of the flow ramp and the initial density difference between the slugs and the ambient coolant was varied.
From the test matrix an experiment with 2% density difference between the de-borated slugs and the ambient coolant was used to validate the CFD software ANSYS CFX. To model the effects of turbulence on the mean flow a Reynolds stress turbulence model was employed and a hybrid mesh consisting of 3.6 million nodes and 6.4 million elements was used.
The experiment and CFD calculation show a stratification in the downcomer. The less dense slugs flow around the core barrel at the top of the downcomer. At the opposite side the lower borated coolant is entrained by the colder safety injection water and transported to the core.The validation proves that ANSYS CFX is able to simulate appropriately the flow field and mixing effects of coolant with different densities.
Keywords: CFD; ROCOM; boron dilution; PWR
Contribution to proceedings
Annual Meeting on Nuclear Technology 2006, 16.05.-18.06.2006, Aachen, Germany
Annual Meeting on Nuclear Technology 2006, 16.05.2006, Aachen, Germany