The commercial CFD code STAR-CD v4.02 is used as a numerical simulation tool for flows in the supercritical
water-cooled nuclear reactor (SCWR). The basic heat transfer element in the reactor core can
be considered as round rods and rod bundles. Reactors with vertical or horizontal flow in the core can
be found. In vertically oriented core, symmetric characters of flow and heat transfer can be found and
two-dimensional analyses are often performed. However, in horizontally oriented core the flow and heat
transfer are fully three-dimensional due to the buoyancy effect. In this paper, horizontal rods and rod
bundles at SCWR conditions are studied. Special STAR-CD subroutines were developed by the authors to
correctly represent the dramatic change in physical properties of the supercritical water with temperature.
In the rod bundle simulations, it is found that the geometry and orientation of the rod bundle have
strong effects on the wall temperature distributions and heat transfers. In one orientation the square
bundle has a higher wall temperature difference than other bundles. However, when the bundles are
rotated by 90◦ the highest wall temperature difference is found in the hexagon bundle. Similar analysis
could be useful in design and safety studies to obtain optimum fuel rod arrangement in a SCWR.