Thermal analysis of baffle jetting in fuel rod assembly

Baffle jetting plays a significant role when it comes to safe operation of nuclear power plants. The baffle jetting phenomenon is the generation of horizontal flow impingement on fuel/control rods during the outward flow of the primary coolant into a nuclear reactor. To understand the flow and heat transfer characteristics under the baffle jetting conditions, large eddy simulations (LES) of flow around a 6 × 6 fuel rod assembly were conducted. Three Reynolds numbers based on jet width and inlet velocity were considered 5010, 10 000, and 20 000. A temperature difference of 5°C between the inlet fluid and the heated rods was considered to analyze the heat transfer characteristics within the assembly under baffle jetting. Various flow parameters were computed such as pressure coefficients along different rods, mean and fluctuating forces, Strouhal number, local and averaged Nusselt numbers. LES results were validated against experimental measurements and other numerical data. It was observed that the effect of the baffle jet was more significant on the first stream-wise row of rods with the stagnation points at the lower part of these rods. Furthermore, the averaged Nusselt number was found to be higher on rods in the stream-wise direction of the jet, rather than at other locations.