The main components which constitute reactor structure include: Calandria vessel, end shields, Calandria supports, end-shield ring, dump tank (RAPS, MAPS, Pickering A), ring thermal shield and ion chamber mountings and if applicable inaccessible piping like that of moderator.

Extensive analysis and studies of HWR reactor structures have already been completed, including an IAEA TECDOC that specifically covers CANDU reactor assemblies [1.5]. Typically, a comprehensive PLiM life assessment or a life cycle management plan specific to the individual plant’s reactor structure is completed and factored into the in-service inspection and maintenance to ensure plant life attainment. These plans are updated periodically as part of the plant life management programme for this component.

No known degradation mechanisms have been identified (Exeption is RAPS 1 End Shield crack at location suspected to have high residual stress due to a local repair in the carbon steel calandria side tube sheet. The design and material of construction has been changed in all units from MAPS2 for PHWRs in India) that will limit the life of the critical (non-replaceable) calandria and end shield assembly to less than 60 years. No problems specific to CANDU 6 operating units requiring repairs or replacements have been identified. Problems at the older CANDU units in Ontario are not likely to occur at CANDU 6 or at current PHWR design employed in Indian units because of design changes incorporated.

There is no significant concerns are seen for life attainment. Additional inspections/assessments may be required for long term operation.

CANDU Nuclear Plant Life Assurance Programme (NPLA) reports were prepared for reactor structures at the Bruce and Pickering sites in the early 1990s, that identified plausible ARDMs and some areas of uncertainty, which required further investigation (e. g. Pickering A shell — shield supports).

I.4. OTHERS