ANALYSIS OF MIXING PROCESSES IN VVER-440 ROD BUNDLE WITH RANS METHOD
17th Symposium of AER on VVER Reactor Physics and Reactor Safety (2007, Yalta, Crimea (Ukraine, back then))
CORE SURVEILLANCE AND MONITORING. CFD ANALYSIS
Detailed knowledge of the flow and the heat transfer is very important in the case of fuel rod bundles of nuclear reactors from the design and safe operation point of view. Investigations of the thermal hydraulic processes in VVER-440 fuel assemblies are in progress at the Institute of Nuclear Techniques, Budapest University of Technology and Economics using the code ANSYS CFX 11.0 1. In the present work, one single subchannel was investigated in order to reach the necessary resolution of the optimal mesh at first. Models of a subchannel (triangular array, P/D=1.35) were built and comprehensive mesh sensitivity study was performed. The mesh study showed that relatively high mesh density was needed to reach the grid independent solution. Suitable mesh was chosen and turbulence model study was accomplished using the k-epsilon, SST, SSG Reynolds Stress and BSL?Reynolds Stress models. Results of the predictions were compared to measurement published by Trupp and Azad 2. The best results were obtained with use of BSL Reynolds Stress model. Distributions of the Reynolds Stresses and the turbulent kinetic energy were in good agreement with Trupp and Azad?s measurement. Based on the experience of the study two further models of a 250 mm long rod bundle section were developed that contained six rods. One of these models involved a spacer grid to investigate its effects on the flow. Using these models calculations were carried out in order to investigate the mixing effects. In both cases the development of secondary flows were observed but convective mixing occurred between adjoining subchannels only in the case of the model with spacer grid.