Preliminary validation of WWER-440 fuel assembly head CFD model

In WWER-440/213 type reactors the outlet temperature of coolant is measured with thermocouples installed above 210 fuel assemblies. These temperatures are fundamental information in on-line core monitoring therefore the accuracy of the temperature measurement is very important. Former CFD calculations have called attention to the fact that the temperature at the thermocouples differs from the average temperature of the coolant of the given fuel assembly. In order to investigate the mixing processes in WWER-440 fuel assembly head a full-scale test facility was built in the Kurchatov Institute and extensive measurements were performed. A CFD model of the head part of the test assembly was developed by our institute employing the code ANSYS CFX 11.0. The model involves the main parts of the test facility from the inactive upper part of the rod bundle up to the PTU plate simulator. Calculations were performed for a selected measurement set. The inlet boundary conditions (normal velocity component, temperature distributions) were determined using COBRA and VERONA subchannel codes. Calculations were accomplished applying these velocity and temperature distributions and their effect on the results was examined. The results of COBRA, VERONA and CFD calculations were compared with measurement data (Authors)