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What We Heard Report – DIS-14-01

DIS-14-01: Design Extension Conditions for Nuclear Power Plants


Discussion papers play an important role in the selection and development of the regulatory framework and regulatory program of the Canadian Nuclear Safety Commission (CNSC). They are used to solicit early public feedback on CNSC policies or approaches.

The use of discussion papers early in the regulatory process underlines the CNSC’s commitment to a transparent consultation process. The CNSC analyzes and considers preliminary feedback when determining the type and nature of requirements and guidance to issue.


CNSC published discussion paper DIS-14-01, Design Extension Conditions for Nuclear Power PlantsFootnote 1 in August 2014 to summarize the CNSC’s current understanding of design extension conditions (DECs), based largely on CNSC REGDOC-2.5.2, Design of Reactor Facilities: Nuclear Power PlantsFootnote 2. The intent was to stimulate discussion on the subject of DECs. Comments from stakeholders on the discussion paper were invited.

Since the publication of the discussion paper, CNSC staff have begun working with the CSA Group and other stakeholders on the development of a new Canadian Standard, CSA N-290.16, Requirements for beyond design basis accidentsFootnote 3.When published, this new standard will set requirements and provide guidance in the same areas covered by the discussion paper. The drafting team includes representatives of government and regulatory agencies, owners and operators of nuclear facilities, nuclear service industries, and general interest groups. The discussion paper was one of the seed documents used in drafting the proposed standard.

The following summarizes the results of the CNSC consultation on this discussion paper and outlines the CNSC’s next steps for DECs.

Consultation process

The CNSC published DIS-14-01 on August 29, 2014 in both official languagesFootnote 4. The discussion paper was posted on the CNSC website. Visitors to the CNSC website were alerted via the “Latest News” and “What’s New” that the document was posted and linked to the news release. An email was sent to the CNSC’s subscribers’ list alerting recipients that this document had been posted. A consultation notice was also posted on the Government of Canada’s “Consulting with Canadians” website.

While the usual consultation period for discussion papers is 120 days, this period was extended to January 16, 2015, for a total of 142 days.

On January 27, 2015 the CNSC posted comments it received on its website, and issued an invitation to provide feedback on the comments until February 16, 2015. In total, the CNSC received comments from five sources, three from industry representatives and two from other stakeholders.

Summary of stakeholder comments

Stakeholder comments generally supported the concept of DECs, although it was felt that further clarification was required in a number of areas. The CNSC welcomes support for the characterization of DECs in the discussion paper.

Industry representatives indicated they will work with the CNSC and the CSA Group to produce standards, including CSA N290.16, Requirements for beyond design basis accidents. When published, it is anticipated that this document will provide detailed guidance on how to identify DECs and the associated requirements. The CNSC agrees that development of CSA N290.16 is the most effective way to implement the concept of DECs with associated requirements and further guidance.

Comments were raised about the definition of certain terms; in particular, “safety classification” and “reasonable confidence”. The CNSC will bring these comments to the attention of the CSA N290.16 technical committee that is drafting the DEC standard.

The difficulty of predicting the kind of scenarios that may initiate DECs was raised. This necessitates a flexible strategy for restoring fundamental safety functions, and the CNSC agrees with the importance of preparing a flexible approach.

The value of extensive analytical effort with regards to DECs was commented upon. The CNSC agrees it is not possible to have high confidence that all scenarios have been identified. However, CNSC staff believe that a well-chosen set of DEC scenarios should encompass major challenges and allow the designer to identify options to mitigate them. Without an analysis element, the design process has no basis.

A related comment questioned the benefit of undertaking significant research and development work relative to its cost, given the difficulty in identifying the possible scenarios in advance. CNSC staff are aware that the work is costly and therefore supports international collaboration. It is recognized that exact sequences cannot be known in advance and that the emphasis should therefore be on understanding basic phenomena. It is also noted that the majority of research and development spending on severe accidents is by industry.

One stakeholder provided feedback in the second phase of consultation, “feedback on comments”. The input was not a response to comments received in the first phase of consultation and was not directly related to the content of the discussion paper. The concerns expressed were related to the life extension of the Bruce nuclear power plant.   If such an application is made, the CNSC will hold public hearings where it can consider such concerns properly.

Next steps

  1. Consider the stakeholder comments provided on the discussion paper in the CNSC participation in development of CSA standard N290.16, Requirements for beyond design basis accidents, though it is noted that most of the stakeholders are also represented on the CSA Technical Committee responsible for development of the new standard.
  2. The CNSC is not considering publishing a regulatory document dedicated to DECs. The new Canadian Standard, CSA N-290.16, Requirements for beyond design basis accidents, should address DECs to the CNSC’s satisfaction. However, as safety is of paramount importance to the CNSC, this decision may be revisited.  The CNSC reserves the right to develop its own regulatory document should the final standard not meet its expectations.


Footnote 1

CNSC discussion paper DIS-14-01, Design Extension Conditions for Nuclear Power Plants, 2014-08

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Footnote 2

CNSC REGDOC-2.5.2, Design of Reactor Facilities: Nuclear Power Plants, 2014-05

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Footnote 3

CSA N290.16, Requirements for beyond design basis accidents, under development

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Footnote 4

CNSC news release, Comment on Design Extension Conditions for Nuclear Power Plants, 2014-08-29

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