Abstract
A numerical study on fuel rod surface temperature distributions in liquid metal cooled sub-channel flow is presented in this paper. There are two kinds of accident analysis. First is normal case, liquid metal is arranged to flow through triangular sub-channels in rather compact fuel rod lattice. Another accident is eccentric case, it is focused on the effects of misaligned central fuel rod in typical fuel rod cluster geometries. Numerical models based on FLUENT, a Computational Fluid Dynamics (CFD) commercial software, are developed to model steady state fuel thermal conductions, fully-developed turbulent convective flows, and local flow mixing. In normal case, the numerical results show the temperature distributions in the azimuthal direction are non-uniform. One could imagine that such situations will be more apparent when one has eccentric geometry in a misaligned fuel lattice. Numerical results show that fuel rod surface temperatures are higher for surfaces facing the narrow gap of the sub-channel. Situations are worse for cases where misaligned fuel rods exist in tightly packed fuel rod clusters. Even for a small amount of rod center deviation, such temperature differences can be as high as 54 K around a fuel rod whose diameter is only 4.7 mm. The situations could be very serious and might generate unnecessary thermal stresses and cause fuel failure.