CFD Analyses of the Rod Bowing Effect on the Subchannel Outlet Temperature Distribution
26th Symposium of AER on VVER Reactor Physics and Reactor Safety (2016, Helsinki, Finland)
Nuclear applications of computational fluid dynamics
Abstract
CFD ANALYSES OF THE ROD BOWING EFFECT ON THE SUBCHANNEL OUTLET TEMPERATURE DISTRIBUTIONKaroliina Ekström. Timo ToppilaFortum Power and Heat Ltd, FinlandABSTRACTIn the Loviisa 1 and 2 nuclear power plants, the subcooling margin of the hottest subchannel is monitored during normal operation. The temperature of the coolant in the hottest subchannel of the fuel assembly is limited to the saturation temperature. In this work the effect of bent fuel rods to temperature of the coolant in the hottest subchannel is studied.Bending of the rods occurs during normal operation due to differences in the heat profiles in the rods. Due to the bending of the rods the flow area of the subchannels varies. The coolant temperature will rise more in the subchannel with smaller flow area and this has to be taken into account in the safety margin of subchannel enthalpy rise. The maximum bow of rods in a normal fuel assembly in Loviisa NPP has been estimated based on visual observations. Computational Fluid Dynamics (CFD) simulations are used to estimate how much the estimated maximum bow of a rod affects the temperature rise of the subchannel.The quantitative uncertainty of the predicted enthalpy rise in fuel bundle subchannel is estimated based on the uncertainty of modelling of mixing between subchannels. The measured turbulence quantities from LDA measurements of cold test assembly made in 1990s in Fortum are compared with CFD results to give uncertainty estimation for turbulence, which is further used for quantitative uncertainty estimation of mixing and simulated subchannel enthalpy rise.26th Symposium of AER on VVER Reactor Physics and Reactor Safety 47 10 – 14 October 2016, Helsinki, Finland