Differences between PWR and HWR nuclear piping are primarily due to the horizontal CANDU fuel channel design, which requires more extensive piping runs. The feeders are also a design feature specific to HWRs. IAEA TECDOC [III.1.20] addresses ageing of primary piping in PWRs.

Process water in all the’ multi-unit CANDUs is lake water, not seawater as in most of the single-unit HWRs, which leads to different ageing concerns. Degradation mechanisms for single-unit HWRs, generally apply to this section as well.

Transient monitoring programmes were developed as part of the NPLA programme in the 1990s to address thermal fatigue due to process transients in the multi-unit CANDUs. Other factors to include (to be added by OPG and Bruce Power) are listed below:

• Carbon steel — Chromium content

• Feeders — FAC susceptibility

• LBB concept

• Underground piping