A Study on the Fluidelastic Stability of a Hybrid Layout Array in Two-Phase Flow

Abstract An experimental test program was carried out to investigate the stability behavior of the SG tube bundle in the APR1400 nuclear reactor design. The SG has a unique tube bundle geometry. In the vertical legs of the tube bundle, the tube array has a triangular tube geometry. In the upper U-bend, this geometry gradually changes such that at the upper (horizontal) region of the U-bend, the triangular geometry is replaced by a rotated square geometry. The U-bend itself is rectangular in shape (as opposed to the more common semi-circular form). The rectangular form of the U-bend results in a section of the U-bend where the array geometry is a ‘hybrid mixture’ at the transition from rotated triangle to rotated square geometry. The test section design allows tests to be performed under partial admission conditions where the U-bend tube legs are immersed in water for both the single phase (water) and two-phase (air-water) tests. The transverse and streamwise stability behavior is investigated by limiting the number of tube supports to two in the vertical tubes sections. Tests for this supporting condition show that the SG tube bundle is highly stable. The transverse stability is expected in view of the positive support action in this direction. The tube bundle is also found to be fully stable in the streamwise direction, for flow velocities well above the SG operating flow velocity (dynamic pressure) conditions.