Zircaloy-2 Pressure Tube Elongation at the Hanford N Reactor

Abstract

The Hanford N Reactor contains 1004 cold-worked Zircaloy-2 pressure tubes made by four different fabrication routes. They operate at 395 to 560°F (475 to 566 K) with a hoop stress of 8400 psi (58 MPa) and a peak neutron flux of 2.2 × 1013 neutrons (n)/cm2/s (>1 MeV). Length measurements on all the tubes after 50 000 h of operation show elongation up to 0.4 percent in proportion to channel power. The highest average elongation (0.35 percent) is observed in tubes fabricated with a high extrusion ratio (29:1) and a high amount of cold work (30 percent). The lowest elongation (0.19 percent) is observed in tubes fabricated with a lower extrusion ratio (13:1) and a lower amount of cold work (17.5 percent). Intermediate elongations (0.26 percent) are observed in tubes fabricated with a high extrusion ratio (29:1) and low cold work (17.5 percent) or a low extrusion ratio (8:1) and high cold work (30 to 35 percent). The elongations and diameter changes are analyzed in terms of two separate components: a stress independent component, irradiation growth, and a stress dependent component, irradiation creep. The magnitudes and signs of the two components depend on texture, dislocation density (cold work), and neutron flux. The analysis correctly predicts the dimensional changes of the four types of tubes from structural data and uniaxial in-reactor creep and growth data obtained from the literature.