Replacement of a cracked pressure tube in Bruce G.S. Unit 2

Leaking fuel channels in a CANDU reactor can be readily identified, removed and replaced by station maintenance staff using relatively simple tools. The leaking fuel channel removed from Bruce G.S. Unit 2 has been examined and the cause of the crack is delayed hydride cracking, the same phenomenon which caused the cracks found in Pickering Units 3 and 4 in 1974/75. Since there was no prior thermal cycle to reorient a significant number of hydrides into the radial direction during the period when the residual stresses were high, we do not expect there to be a significant number of cracked pressure tubes in Bruce A. In all reactors built since Bruce G.S. A, changes have been made in the rolled joint design to reduce the residual stress levels below that at which cracks can initiate by delayed hydride cracking