Study on velocity field in a deformed fuel pin bundle; Influence of pin deformation and wrapping wire on velocity distribution

Sato, Hiroyuki; Kobayashi, Jun ; Miyakoshi, Hiroyuki; Kamide, Hideki 

A sodium cooled fast reactor is designed to attain a high burn-up core in a feasibility study on commercialized fast reactor cycle systems. In high burn-up fuel subassemblies, deformation of fuel pin due to the swelling and thermal bowing may decrease flow rate via change of flow area in the sub-assembly and influence the heat removal capability. A 2.5 times enlarged 7-pin bundle water model was applied to investigate the influence of pin bowing and wrapping wire. The test section consisted of a hexagonal acrylic duct tube and fluorinated resin pins which had the refractive index nearly the same with water and high light transmission rate. This enabled to visualize around the central pin through the outer pins. Velocity distribution was measured by using PIV in sub-channels around the central pin in reference and deformation condition. Velocity distribution around the wrapping wire was measured and the wire influenced to the velocity and RMS in the wide region near the pin surface.