Velocity distribution in the peripheral subchannels of the CANDU-type 19 rod bundle

Measurements of the detailed flow velocity and turbulent intensity in the peripheral subchannels of a non-wrapped CANDU-type 19-rod test bundle were performed by Laser Doppler Anemometry in a water loop. The bundle consisted of rods, 1.905 cm in diameter and 62.28 cm long, positioned by two 3 mm thick end-plates. The test housing was an 11 cm ID transparent pipe.The transverse velocity was negligible (0.002 m/s) and the turbulence intensity uniformly distributed (7%) throughout all the channel areas. The axial flow patterns for the peripheral subchannels are given, and show velocity gradients and average and peak velocities higher in the subchannels facing triangular channels than in subchannels facing square channels, even though they have the same cross-sectional areas.Experimental results show excellent agreement with COBRA-IIIC computer code calculation of flow distribution in CANDU-type reactors if the bundle is well-aligned and well-centered. The average and peak velocities of a off-centered bundle are also given.