CSA N291COM:24

Preface This is the first edition of CSA N291COM, Commentary on CSA N291, Requirements for nuclear safety-related structures . The discussion provided in this Commentary is directed toward the requirements of the third edition of CSA N291 published in March 2019, and does not address any amendments issued since this initial publication. This Commentary does not provide formal interpretations of CSA N291 and should be viewed only as an informative annotation of portions of CSA N291. It has been written in an informative (non-mandatory) language and is not intended to be adopted by users of CSA N291 or regulatory authorities as additional requirements. Significant changes between editions of CSA N291 that would benefit from commentary along with the rationale for the changes are outlined. This Commentary responds to questions and comments raised by those who have participated in developing and implementing CSA N291. It provides a context and explanation for the structure and content of CSA N291 and outlines the governing principles and requirements. The Commentary does not cover the entire content of every clause of CSA N291. The intent is to update this Commentary after the publication of each new edition of CSA N291 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 the Subcommittee on Commentary on CSA N291 Requirements for Nuclear Safety-Related Structures, under the jurisdiction of the Technical Committee on Concrete Containment and Safety-Related Structures for Nuclear Power Plants and the Nuclear Strategic Steering Committee on Nuclear StandardDetails, and has been formally approved by the Technical Committee. Scope CSA N291 provides requirements for nuclear safety-related structures. The scope of the Standard has somewhat evolved as described below. The first edition (2008) of the Standard included within its scope the structures and components of CANDU NPPs that support, house, or protect nuclear safety systems and are required for the safe operation and shutdown of the reactor. The scope also included the facilities for the storage of irradiated fuel and other radioactive waste material. The intent of this was to be broad and all- encompassing, and to allow for the operating organization to determine the applicability of the Standard to their structure, as agreed by the authority having jurisdiction (AHJ). Clarification of the scope with regards to radioactive waste storage structures was provided in the second edition (2015) to ensure that the users understood that the Standard applies to the storage of wet and dry irradiated fuel. The scope statement in the second edition clarified that the storage of other radioactive waste was to be included for facilities as agreed by the AHJ. In the third edition (2019), the requirement of dry irradiated fuel was refined from a generic inclusion to include those that are required as agreed with the AHJ. Dry irradiated fuel was moved to Item e) of Clause 1.1 and included with other radioactive waste material. The use of "as agreed with the AHJ" means that the AHJ and the operating organization can agree to use other StandardDetails besides CSA N291 for the structures listed in Item e). Notes were added to Clause 1.1 to clarify that not all elements of the structures described in Item e) are considered safety-related, and to provide additional guidance on the storage of other radioactive waste with reference to CSA N292 with respect to "high-level" waste. In the third edition, the scope of the Standard has been broadened to apply to any nuclear safety-related structures, not only those within NPPs.