Fuel rod surface temperature distributions in liquid metal sub-channel flows

A numerical study on fuel rod surface temperature distributions in liquid metal cooled sub-channel flow is presented in this paper. Special interests are 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. Numerical results show that fuel rod surface temperatures are higher for surfaces facing the narrow gap of the sub-channel. The temperature differences are mainly dependent on the fuel pitch-to-diameter ratio, flow patterns, and other flow physical properties. 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. (author)