Fuel Channel Annulus Spacers (Garter Springs)

The fuel channel annulus spacer is specific to the design of the CANDU reactor. This spring wound coil is used to separate the outside diameter of the pressure tube from the inside diameter of the calandria tube. The coil is loosely wound to allow for the flow of gas through the annulus.

A Zircaloy tracer wire is strung through the spring which is used to locate the position of the spring along the fuel channel. Once in the core, the location of the spring must be periodically verified.