scope:

The purpose of this Commentary is to provide background information for specific clauses and requirements in the CSA N285.6 Series. This background information can help the user to clarify the context of the CSA N285.6 Series requirements. Also, this Commentary refers to sources of material that were used during the formulation of some of the requirements in the CSA N285.6 Series.

This Commentary focuses on the CSA N285.6 Series and is organized as follows:

a) the original intent of the CSA N285.6 Series;

b) the rationale for requirements; and

c) the evolvement of the CSA N285.6 Series through significant changes in various editions.

This Commentary addresses requirements relating to the manufacture and properties of materials for reactor components for CANDU nuclear power plants. It does not address requirements for the design and construction of pressure-retaining systems and components that are covered in CSA N285.0. Standards that relate to periodic inspection of pressure-retaining components are not addressed. Also, the requirements of other interfacing Standards and ASME Boiler and Pressure Vessel and Piping Code (BPVC), Section III, Division 1 are not addressed in this Commentary.

The discussion provided in this Commentary is directed towards the requirements of the 2017 edition of CSA N285.6 Series and does not address the amendments released since 2017.

Although this Commentary can be read by itself, a better understanding of the Commentary will be obtained if a copy of the 2017 edition of the CSA N285.6 Series is available for reference. Many of the requirements in the CSA N285.6 Series are described in this Commentary. However, the Standards must always govern since they provide the formal requirements.

Note: ASME has published a companion guide to the ASME BPVC, which provides the criteria and a commentary on selected aspects of ASME BPVC.

Where this Commentary might not align with ASME, the differences are only applicable to materials covered and governed by the CSA N285.6 Series.

Scope of the N285.6 Series

The N285.6 Series is a set of individual standards numbered N285.6.x, each with their own specific scope. There is no overall identified scope for the N285.6 series. The preface of N285.0-17/N285.6 Series-17 indicates that as of 2008 the N285.6 series is co-published with the N285.0 Standard, and this may sometimes be misinterpreted that they share the same scope. Whereas N285.0 is expressly concerned with the requirements for pressure retaining systems and components (the pressure boundary aspects) of the CANDU plant, the scope of the N285.6 Series is broader, encompassing materials for pressure boundary items as well as non-pressure boundary items that are unique to the CANDU design and/or are outside the scope of the ASME BPVC. This is reflected in the differences in the titles, with N285.0 explicitly identifying "pressure retaining" and the N285.6 Series being for "Material Standards for reactor components for CANDU nuclear power plants". Although N285.0 has a specific definition of "component" related to the pressure boundary, its use in the N285.6 series is not as strict, often intending the more generic dictionary sense of the term. Material specifications are included for items outside the immediate jurisdiction of the pressure boundary rules (for example, guide tubes for reactivity control units). This is to ensure a standardized, referenceable source for items unique to the CANDU design and important to safety, of appropriate quality and integrity.