Despite the excellent record at CANDU6 NPPs, it is well known that steam generators provide challenges for the assurance of continued good health, through to design life and particularly for a significant period of extended operation. This includes components other than the tube bundle, which typically has been the most-inspected component to date. Many important secondary side internal components are very difficult to inspect and as a result, little is known about their current condition. However, as the SGs age there have been several instances of secondary side component degradation, typically support plates which are most readily inspected and therefore most likely to be so, which can have significant impact on tube bundle life. Subtle changes to plant operation, especially chemistry control, may have a significant impact on the tubing corrosion potential under deposits that have built up, and in crevices between the tubing and support structures.

As an outcome of the SG work at a number of CANDU plants, it has been concluded that each plant and its steam generators have unique aspects that could impact on life attainment or extended operation. The Life Assessment recommendations typically focus on specific aspects of chemistry control, proactive inspection and monitoring and periodic cleaning. While the prognosis for life attainment and for extended operation of CANDU 6 Steam Generators is good, it has also been found that this conclusion is very dependent upon implementation of the recommended programme enhancements of inspections, effective maintenance, good chemistry control and detailed assessment of the future field data. It is also dependent on assumptions about the condition of un-inspected components, particularly those on the secondary side of the SG.

From the studies undertaken to date, a typical proactive SG age management strategy for life extension would include the following elements.