A 7 cm length of ~4 mm diameter garter spring. The garter springs are used in CANDU reactors to maintain a spacing between the pressure tube and the calandria tube. They are made from square cross-section wire and have been made from several different alloys. The cross-sectional diameter varies from the ~4 mm diameter shown here from a test unit to almost 8 mm used on some channels at the Nuclear Power Demonstration (NPD) reactor.
A wide variety of garter spring sizes have been used on different CANDU reactors. Two alloys, Zr-Ni-Cu and Inconel X-750, have been the main materials used for their manufacture. The number used for each fuel channel has increased over time from two to four.
Also of note is the fact that the earlier versions were “loose-fitting”. However, over time it was found that vibrations would cause them to move away from the design or optimum positions and later designs of CANDU implemented tight-fitting springs which were effectively fixed in position.
