This paper analyzes the geometrical effect of coolant channels in the tightly packed fuel rods assembly (TA) which works at operating pressures of supercritical-pressure light water cooled fast breeding reactor (Super FBR), PWR and BWR. It is well known that high breeding by light water coolant is very challenging due to its high moderating property. The TA is good for high breeding because of the small area fraction of coolant to fuel (less than 0.1). However, with the reduction of coolant area, thermal hydraulic characteristics become more limiting. By ameliorating the geometry of the coolant channel, it is expected to improve the performance on thermal hydraulics. In this study, three types of coolant channel geometry are analyzed: geometry A is circular; geometry B is triangle-like shape with rounded-corner; geometry C is also triangle-like shape but with sharper corner. A CFD code STAR-CCM+ is used to carry out the simulations for each geometry at each operating pressure. Assessments are based on the thermal hydraulic parameters such as cladding temperatures, pressure drop and CHF. It is found that geometry B is superior to others at all operating pressures because of the broad design area of power, cladding temperature and pressure drop, and is able to meet the thermal hydraulic requirements in design of high breeding reactors.
