CFD study on coolant mixing inside VVER-440 fuel rod Bundle

Tellervo Brandt, Fortum Nuclear Services Ltd, Finland

19th Symposium of AER on VVER Reactor Physics and Reactor Safety (2009, Varna, Bulgaria)
Reactor Dynamics, Thermal Hydraulics and Safety Analysis, CFD Analysis


In this article, we study mixing inside TVEL fuel rod bundles used in VVER-440 -type
pressurized water reactors. The computational fluid dynamics (CFD) solver FLUENT 6.3 is
utilized. We are interested in the flow conditions under normal operation where the flow is in
one phase, the average temperature at the end of active fuel is approximately 315?C and pressure
inside the reactor pressure vessel 12 MPa. Our CFD model includes a 30 degree sector of the 2.5
m long fuel rod bundle. In this article the CFD results are presented for both the first and second
generation TVEL fuel assemblies, and some ways to further enhance mixing are studied. The
CFD results are applied in the calibration of certain parameters of the core performance
monitoring system, RESU, used in the Loviisa NPP. In this article, we present comparison
between the CFD and RESU results for both the first and second generation TVEL fuel
assemblies. We conclude that the changes in the geometry of the fuel assembly that have been
made after the year 2000, have only a minor effect on the mixing of the coolant between the

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