Experimental investigations of single and two-phase flow in a heated rod bundle

Within the frame of the coordinated project "Modeling, simulation and experiments for boiling phenomena in pressurized water reactors" (BMBF FZK 02NUK010) an experimental facility for the study of boiling flows in a 3 · 3 rod bundle geometry was setup. The bundle resembles in essential geometrical parts the geometry in a pressurized water reactor fuel element. The facility is operated with a refrigerant fluid. Beside Standard instrumentation for temperature, pressure and flow rate we employed particle image velocimetry for single phase flow studies, gamma ray densitometry for integral gas fraction measurement sand ultrafast X-ray tomography for the study of the void Dynamics in the cross-section. Moreover extensive thermo-Instrumentation allows axial rod surface temperature measurements for the central heated rod. First experimental results have been achieved and will be introduced and discussed in this article.