Thermal-Hydraulic analysis of A 7-Pin Sodium fast reactor fuel bundle with a new pattern of helical wire wrap spacer

Thermal-hydraulic analysis was conducted of a 7-pin fuel bundle by using CFD. Currently, wire-wrapped spacers are wound on the fuel pins in the same direction. Counter flow is predicted to occur in all subchannels due to this pattern. This flow was confirmed in this work as well as previous research. Complicated flow formed locally around the wire-wrapped pins. A new type of arrangement for wire- wrapped spacers, called the U-pattern, is presented to provide favorable flow for coolant mixing. In this pattern, 7 pins are designated as one group, the center pin has no wrapping, and the pins surrounding the center pin have alternate winding directions. Superior mixing effect and ideal flow pattern were confirmed in CFD analysis. The maximum temperature in the 7-pin fuel bundle was about 30° cooler than that of the ordinary wire-wrapped fuel bundle. Pressure drop for the U-pattern was reduced by approximately 10% compared with the ordinary pattern. CFD results show that U-pattern could satisfy the requirements for heat transfer enhancement and reduced pressure drop simultaneously.