This is the second edition of CSA N285.0.1, Commentary on CSA N285.0-17, General requirements for pressure-retaining systems and components in CANDU nuclear power plants. It supersedes the previous edition published in 2016.

This Commentary is based on the document titled Explanation of requirements in the CSA N285 series for CANDU nuclear power plants, which was written by Geoff Legg (AECL) and published in 1998 for members of the N285A Technical Committee only. The discussion provided in this Commentary is directed towards the requirements in CSA N285.0-17 and does not address the amendments released since 2017. This Commentary also does not address CSA N285.6, Material standards for reactor components for CANDU nuclear power plants, which was released in conjunction with CSA N285.0. This Commentary does not provide formal interpretations of CSA N285.0 and should be viewed only as an informative annotation of portions of CSA N285.0. It has been written in informative (non-mandatory) language and is not intended to be adopted by users of CSA N285.0 or regulatory authorities as additional requirements. Significant changes between editions of CSA N285.0 are outlined, along with rationale for the changes, where needed.

Note: CANDU (CANada Deuterium Uranium) is a registered trademark of Atomic Energy of Canada Limited (AECL).

This Commentary responds to questions and comments raised by those who have participated in developing and implementing CSA N285.0. It provides a context and explanation for the structure and content of CSA N285.0, and outlines the governing principles and requirements. The Commentary does not cover the entire content of every clause of CSA N285.0.

The intent is to update this Commentary after the publication of each new edition of CSA N285.0 so as to incorporate information associated with amendments to published editions and new editions, and to expand the Commentary as additional needs are identified.