CSA N285.0COM/N285.6 SERIESCOM

CSA N285.0COM:24 – Commentary on CSA N285.0:23,

General requirements for pressure-retaining systems and components in CANDU nuclear power plants Preface This is the first edition of CSA N285.0COM, Commentary on CSA N285.0:23, General requirements for pressure-retaining systems and components in CANDU nuclear power plants. It replaces the previous editions published in 2018 and 2016 under the designation CSA N285.0.1. This Commentary is not a consensus product; that is, it is not a Standard and it has not been formally approved by a CSA Technical Committee. 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 CSA N285A Technical Committee only. The discussion provided in this Commentary is directed towards the requirements in CSA N285.0:23 and does not address any amendments released since 2023. 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 is not written in the style typical of a standard, as this Commentary is informative. Instead, 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. This Commentary does not cover the entire content of every clause of CSA N285.0. Where examples are used, they are not exhaustive, and for each example, there are many others that could have been chosen. 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. This Commentary was prepared by Task Forces C & H — Commentary on CSA N285.0/N285.6 Series, under the jurisdiction of the Technical Committee on CANDU Nuclear Power Plant Pressure-Retaining Systems and Components and the Strategic Steering Committee on Nuclear Standards.

Scope

1.1 General

This Commentary was written as an aid for users and to provide background information for specific clauses and requirements in CSA N285.0. This background information can help the user to clarify the context of the CSA N285.0 requirements. This Commentary does not provide supplementary requirements (“shall” or “should”) in the application of CSA N285.0. Rather, it provides commentary on how CSA N285.0 evolved over time. Also, this Commentary refers to sources of material and other publications that were used during the formulation of some of the requirements in CSA N285.0. With the exception of the annexes, the main clause headings and the main clause numbers used in this Commentary correspond to those in CSA N285.0:23. The numbering for subclauses in the Commentary do not necessarily correspond to those in CSA N285.0:23. This Commentary focuses on CSA N285.0 and is organized as follows: a) the original intent of CSA N285.0, including i) the historical development and evolution — how the nuclear industry developed in Canada; ii) the key concepts that the Standard is built on and how they apply; and iii) the differences between ASME Boiler and Pressure Vessel Code (BPVC), Section III, Division 1, and CSA N285.0 CANDU-specific requirements; b) the aim of CSA N285.0, including the provision of i) rules for the design of the CANDU reactors consistent with regulatory requirements; ii) requirements not covered by ASME BPVC, Section III, Division 1; iii) classification requirements; iv) registration requirements, including those for welding procedures; and v) requirements for repairs, replacements, and modifications; c) the rationale for many of the requirements, which are derived from i) industry practice or experience; ii) engineering or safety analysis; iii) research or test programs; iv) other referenced publications; and v) good engineering judgement; and d) the development of CSA N285.0 through significant changes in various editions. This Commentary addresses requirements relating to the design and construction of pressure-retaining systems and components. Standards that relate to periodic inspection of pressure-retaining components are not addressed. Also, the requirements of other interfacing Standards and ASME BPVC, Section III, Division 1, are not addressed in this Commentary. The discussion provided in this Commentary is directed towards the requirements in CSA N285.0:23 and does not address the amendments released since 2023. Generally, the text is presented in the same sequence used in CSA N285.0, tracing the activities during the design, fabrication, and installation of an item. Although this Commentary can be read by itself, a better understanding of the Commentary will be obtained if a copy of CSA N285.0:23 is available for reference. Many of the requirements in CSA N285.0:23 are described in this Commentary. However, CSA N285.0 must always govern since it provides the formal requirements. The following points should be considered when reading this Commentary: a) The commentary makes no attempt to update CSA N285.0 to reflect any new thinking or concepts that have arisen since its last publication in 2023. Any updating, if required, would be the task of the CSA N285A Technical Committee charged with maintaining the Standard. b) This Commentary does not prescribe methods or techniques of implementation. However, in a limited number of cases, it provides examples of implementation to explain the Standard. These examples of implementation, if used, should not be taken as the only way that a requirement can be met and are not an endorsement of those particular methods and techniques of implementation. c) This Commentary creates no new requirements or recommendations above those in CSA N285.0:23. This Commentary discusses the content of the Standard in an informative context using everyday language for added clarity. Note: ASME has published a companion guide to the ASME Boiler and Pressure Vessel and Piping Codes, which provides the criteria and a commentary on selected aspects of ASME Boiler and Pressure Vessel and Piping Codes.

1.2 Historical background

The requirements in CSA N285.0 are based on provincial and federal regulations, practices developed in the design and construction of CANDU nuclear power plants (NPPs), and the proven and widely adopted rules of ASME BPVC, Section III, Division 1. Their fundamental goal is to ensure public safety. Since the first Standard in the CSA N285 series was issued, regulations and best practices have evolved as the industry gained design, construction, commissioning, and operational experience (OPEX). However, the basic pressure boundary requirements have not changed significantly and are based on the long-standing ASME and industrial practices. Where such changes have occurred, they are described in the appropriate sections. The first CSA N285 Standard, a preliminary edition, was issued in 1975 and included both general requirements and specific requirements for Class 1, 2, and 3 components. Because the provincial acts and regulations took precedence over ASME BPVC, Section III, Division 1, the 1975 edition included an appendix that listed the ASME BPVC, Section III, Division 1 paragraphs that were not applicable to NPPs in Canada. These paragraphs dealt with authorization, stamping, and reports. In 1981, the content of CSA N285 was divided between two Standards, with general requirements in CSA N285.0 and specific requirements for Class 1, 2, and 3 systems and components in CSA N285.1. The CSA N285 series was further developed as shown in Table 1.1. The Status column provides the dates of the Standards from the first to the latest edition.

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CSA N285.6 SeriesCOM:24 – Commentary on CSA N285.6 Series:23, Material Standards for reactor components for CANDU nuclear power plants Preface This is the first edition of CSA N285.6 SeriesCOM, Commentary for CSA N285.6:23, Material Standards for reactor components for CANDU nuclear power plants . It replaces the previous edition, published in 2022 under the designation CSA N285.6.0.1. This Commentary is not a consensus product; that is, it is not a Standard and it has not been formally approved by a CSA Technical Committee. The discussion provided in this Commentary is directed towards the requirements in the CSA N285.6Series:23, and it does not address the amendments released since 2023. This Commentary does not address CSA N285.0, General requirements for pressure-retaining systems and components in CANDU nuclear power plants. This Commentary does not provide formal interpretations of the CSA N285.6 Series and should be viewed only as an informative annotation of portions of CSA N285.6. It has been written in informative (non-mandatory) language and is not intended to be adopted by users of CSA N285.6 or regulatory authorities as additional requirements. Significant changes between editions of CSA N285.6 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 N285.6. It provides a context and explanation for the structure and content of CSA N285.6, and outlines the governing principles and requirements. This Commentary does not cover the entire content of every clause of CSA N285.6. The intent is to update this Commentary after the publication of each new edition of CSA N285.6 so as to incorporate information associated with amendments to published editions and new editions, and to expand the Commentary as additional needs are identified. This Commentary was prepared by CSA N285A Task Force C on Materials, under the jurisdiction of the Technical Committee on CANDU Nuclear Power Plant Pressure-Retaining Systems and Components and the Strategic Steering Committee on Nuclear Standards.

Scope

1.1 Purpose

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 NPPs. 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 2023 edition of CSA N285.6 Series and it does not address any amendments released since 2023. Although this Commentary can be read by itself, a better understanding of the Commentary will be obtained if a copy of the 2023 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 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.

1.2 Scope of the CSA N285.6 Series

The CSA 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 CSA N285.6 Series. The preface of CSA N285.0:23/ N285.6 Series:23 indicates that as of 2008, the CSA N285.6 Series is co-published with the CSA N285.0 Standard, so it could be misinterpreted that they share the same scope. Whereas CSA 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 CSA 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 ASME BPVC. This is reflected in the differences in the titles, with CSA N285.0 explicitly identifying “pressure retaining” and the CSA N285.6 Series being for “Material Standards for reactor components for CANDU nuclear power plants”. Although CSA N285.0 has a specific definition of “component” related to the pressure boundary, its use in the CSA 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.