<p>The China initiative accelerator-driven system (CiADS) holds great promise for transmuting nuclear waste and enhancing nuclear fuel utilization.Therefore, studying the flow characteristics in reactor fuel assemblies is crucial for the design and safety analysis of CiADS. In this study, a visual hydraulic experimental platform was constructed to investigate the flow velocity distribution in a fuel assembly of CiADS, employing polymethyl methacrylate and a 62.932 wt% sodium iodide solution as the material of the test section and a refractive index matching fluid. Particle image velocimetry and FLUENT were used to investigate the axial and transverse velocity distributions within the axial heights of 2.25–3.25 pitches (H) and 3.75–4.75 H in 19-pin wire-wrapped fuel bundle channels. The findings reveal that the shear stress transport <i>k</i>-<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\omega\)</EquationSource> <EquationSource Format="MATHML"><math> <mi>ω</mi> </math></EquationSource> </InlineEquation> model can accurately describe the velocity distribution in a wire-wrapped fuel assembly, and the transverse and axial periodicity of the velocity distribution was one pitch. The flow velocity distribution patterns were unchanged at various Reynolds numbers. The patterns of velocity contour images on gaps 1–5 at 2.25–3.25 H were symmetrical to those at 3.75–4.75 H on gaps 5–1, respectively. The values of the axial velocities and root mean square transverse velocities increased proportionally with increasing Reynolds numbers. The normalized transverse velocity varied as a cosine function, with a maximum value of approximately 40% and a peak occurring slightly behind 3/4&#xa0;H. The cross-flow around the wire-wrap spacers enhanced, and there was a deviation in the velocity direction. These results can help researchers deepen their understanding of the flow velocity distribution in wire-wrapped fuel bundles and advance research on the cross-flow characteristics of lead-cooled fast reactors.</p>