An important proactive life management technique in many CANDU’s is a programme of regular tube removal and subsequent metallurgical evaluation. For instance, examination of removed tubes is a requirement of the Canadian Standards Association (CSA) standard. Such examinations are an important supplement to the NDE inspections and provide confirmation of tube wall condition and an insight into the local operating environment on the tube surface. This is particularly useful for the secondary side tube surfaces that have been exposed to under-deposit conditions (such as in tube sheet sludge piles).

Secondary side internals

The importance of many key internal components to successful long term operation of the SGs, and the relative lack of information on in-service condition, are typical outcomes of the life assessment work. A detailed risk assessment of these non-tube components based on design function and operational experience, leads to identification of those specific internals that should be subject to inspection in a proactive and comprehensive age management programme for life extension. There have been several instances, both in CANDU SGs and those of PWRs, of degradation of internals structures resulting from flow assisted corrosion. This experience indicates that the secondary side internals are an area where some inspection for component integrity is essential for assurance of life extension.