Experimental Investigation of Coolant Mixing in VVER and PWR Reactor Fuel Bundles by Laser Optical Techniques for CFD Validation

D. Tar, G. Baranyai, Gy. Ézsöl, I. Tóth, KFKI AEKI, Hungary

20th Symposium of AER on VVER Reactor Physics and Reactor Safety (2010, Hanasaari, Espoo, Finland)
Nuclear applications of three-dimensional thermal hydraulics


Nonintrusive laser optical measurements have been carried out to investigate the coolant
mixing in a model of the head part of a fuel assembly of a VVER reactor. The goal of this
research was to investigate the coolant flow around the point based in-core thermocouple; and
also provide experimental database as a validation tool for CFD calculations. The experiments
have been carried out on a full size scale model of the head part of VVER-440/213 fuel
assembly. In this paper first the previous results of the research project is summarised, when
full field velocity vectors and temperature were obtained by particle image velocimetry (PIV)
and planar laser induced fluorescence (PLIF), respectively. Then, preliminary results of the
investigation of the influence of the flow in the central tube will be reported by presenting
velocity measurement results. In order to have well measurable effect, extreme flow rates
have been set in the central tube by applying an inner tube with controlled flow rates. Despite
the extreme conditions, the influence of the central tube to the velocity field proved to be
significant. Further measurement will be done for the investigation of the effect of the gaps at
the spacer fixings by displacing the inner tube vertically, and also the temperature distribution
will also be determined at similar geometries by LIF. The aim of the measurements was to
establish an experimental database, as well as the validation of CFD calculations.

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