Summary An experimental setup was designed and constructed to investigate the detailed pressure distribution data of a wire‐wrapped fuel assembly and to evaluate the friction factor correlations. The test section was a wire‐wrapped 19‐pin fuel assembly manufactured with polymethyl methacrylate, and the working liquid was deionized water. A secondary circuit supplying chilled water was built to minimize the changes in the physical properties of the working liquid induced by temperature fluctuation. Eighteen axial differential pressure drops and twelve transversal differential pressure drops with Reynolds number in the range of 3750 to 16 250 were measured. The relation between the friction factor and Reynolds number was analyzed. The results showed that the axial pressure in the edge subchannels varied periodically similar to a helical pitch. The direction of rotation and height of the wire‐wrap spacers in the subchannels have a significant effect on the transversal pressure distribution, especially in the zones where the wire‐wrap spacers cross. Besides, the Rehme correlation and Cheng and Todreas Detailed (CTD) correlation showed the best fit with the experimental data. The critical Reynolds number, where the shift from the transitional to turbulent flow regions occurs, is approximately 11 700, and the difference between the experimental data and the value predicted by the CTD correlation was approximately 8.33%. The experimental data of the pressure distribution in the wire‐wrapped fuel assembly could complement the existing database, which supports the development of fast reactors.

China initiative Accelerator Driven System (CiADS) combines a linac, spallation target and a Lead-cooled Fast Reactor (LFR) together, which is designed to transmute nuclear waste and accelerate the progress of China’s energy technology research towards the goal of carbon neutrality. A LFR uses helical wire-wrap spacers as positioning components to enhance crossflow mixing in the reactor core. To study the velocity distribution and crossflow characteristics in wire-wrapped rod bundle channels, a 2 : 1 magnified scale 7-pin bundle fuel assembly model was fabricated using polymathic methacrylate. Particle image velocimetry (PIV) and computational fluid dynamics (CFD) simulations were used to investigate the velocity distribution in the 7-pin bundle flow channels at Reynolds number of 1250~5000 in the x z plane and Reynolds number of 1500 and 2500 in the x y plane. The deviation between CFD simulation results and PIV experimental data was small, and the Reynolds Average Navier-Stokes model could accurately simulate the flow characteristics of the wire-wrapped fuel rod bundle channels. The maximum crossflow velocity caused by helical wires was about 40% of the axial bulk velocity. The normalized crossflow velocity at the subchannel interface varied approximately sinusoidally with the axial height. As the Reynolds number increased, the velocity distribution trend and the loss rate of axial velocity in flow channels remained essentially constant while the peak value of crossflow velocity increased. The contour images of velocities with different axial heights were obtained from the x y plane, and their velocity distribution had a certain periodicity. The axial velocity loss rate in each subchannel caused by wire-wrap spacer resistance was between 7.35% and 38.51%, and the axial velocity loss rates in inner subchannels were usually higher than those in edge subchannels.