Stakeholder Workshop Report: Application of the Graded Approach in Regulating Small Modular Reactors, Held on November 24, 2017

1. Introduction

The Canadian Nuclear Safety Commission (CNSC) is the federal organization responsible for regulating the use of nuclear energy and materials in Canada. It regulates to protect health, safety, security and the environment, and to implement Canada's international commitments on the peaceful use of nuclear energy. The CNSC also disseminates objective scientific, technical, and regulatory information to the public.

In recent years, novel reactor technologies, such as small modular reactors (SMRs) and advanced reactor technologies have emerged to supply power to smaller electrical grids or remote, off-grid areas with electrical output ranging from less than one megawatt for non-grid-connected sites to several hundred megawatts for grid-connected sites.

2. Background

2.1 File history

Discussion paper DIS-16-04, Small Modular Reactors: Regulatory Strategy, Approaches and Challenges (DIS-16-04) was published on May 31, 2016 and examines key areas with potential licensing challenges.

On September 12, 2016, the CNSC held a targeted question-and-answer session for those who had contacted it about the regulatory framework for SMRs and to provide additional clarity to interested stakeholders prior to submitting comments on DIS 16-04.

In general, commenters confirmed that SMRs could be licensed under the existing regulatory framework; however, they also requested greater clarity as to how the risk-informed and graded approach concepts would be applied to SMR designs, taking into account novel safety features.

The What We Heard Report for DIS-16-04 was published on September 15, 2017 and provided the CNSC’s proposed way forward for some of the topics addressed in the discussion paper.

On November 24, 2017, the CNSC hosted a targeted workshop (appendix A lists the attendees) to discuss how the graded approach could be applied to SMR technologies, specifically in the CNSC’s review of safety cases. This document outlines the results of that workshop.

In keeping with the CNSC's commitment to stakeholder engagement, comments and suggestions on the CNSC’s application of the graded approach are welcome at all times. As part of ongoing efforts to enhance and clarify the CNSC’s regulatory framework, the CNSC will use these comments to inform reviews of its regulatory tools.

2.2 Regulatory requirements

The CNSC’s assessment verifies that an applicant is demonstrating that it fulfills all regulatory requirements and high-level safety objectives, and that the fundamental safety functions, (control,Footnote 1 cool,Footnote 2 containFootnote 3 ), are being met.

Applicants are also expected to demonstrate appropriate defence in depth (DiD)Footnote 4 while maintaining appropriate safety margins to address any possible uncertainties in the safety case and specific hazards over the lifecycle of the facility.

2.3 Graded approach/grading

The graded approach is a method or process by which elements, such as the level of analysis, the depth of documentation and the scope of actions necessary to comply with expectations, are commensurate with the relative risks to health, safety, security and the environment, and with the implementation of international obligations to which Canada has agreed and the specific characteristics of a facility or activity.

Applicants/licensees may apply the graded approach or grade against any expectation as long as it can still achieve all regulatory requirements.

When a graded approach is applied, factors to be considered include:

  • Reactor power
  • Reactor safety characteristics
  • Amount and enrichment of fissile and fissionable material
  • Fuel design
  • Type and mass of moderator, reflector and coolant
  • Utilization of the reactor
  • Presence of high energy sources and other radioactive and hazardous sources
  • Safety design features
  • Source term
  • Siting
  • Proximity to populated areas

2.4 Characteristics of suitable information

For straightforward assessments undertaken by the CNSC, where risks are well known and the rules for addressing them are relatively clear, suitable evidence may be spelled out by the applicable code or may provide for a record of professional judgment, such as a professional engineer’s stamp on a drawing or report.

The evidence needed to support a proposal is commensurate with the uncertainty and safety significance. Suitable information in support of a proposal includes, but is not limited to:

  • Results of research and development, and computer modelling
  • Consideration of operating experience
  • Numerical analysis

All of these types of evidence must be documented, traceable and quality-assured. The evidence must also be demonstrated to be relevant to the specific proposal.

3. Stakeholder workshops

3.1 Material presented by CNSC staff

CNSC staff began the workshop by presenting their approach and considerations regarding the application of the graded approach and how proposals regarding alternatives to regulatory requirements would be addressed.

In their presentation, CNSC staff defined the graded approach (as set out in 2.3 above) and reiterated that grading is not the relaxing of requirements; rather, it allows for requirements to be applied in proportion to the risk associated with the proposed activity. The CNSC also stated that the focus when applying the graded approach is to assess the submission for novelty, complexity and harm. For a reactor, key aspects would include the reactor’s power, type of fuel and its source term, activities and structures surrounding the reactor’s core, and site characteristics.

CNSC staff then reminded participants that the fundamental safety functions are to demonstrate the ability to control, cool and contain radioactive and hazardous sources. After the presentation, workshop attendees participated in two breakout sessions. One pertained to the application of the graded approach to regulatory requirements, high-level safety objectives and the concept of defence in depth, and the second pertained to the fundamental safety functions for nuclear reactors (control, cool and contain).

The sections below provide a summary of the feedback from workshop participants.

3.2 Breakout session 1 summary: Application of graded approach to regulatory requirements, high-level safety objectives and defence-in-depth

3.2.1 Regulatory requirements

Participants agreed that regulatory requirements for SMRs will include all applicable acts and regulations, and the licensing "basisFootnote 5". Stakeholders affirmed that these requirements cannot be lessened; rather, alternatives may be proposed to achieve the desired results.

3.2.2 High-level safety objectives

Participants agreed that mandated high-level safety objectives are in place to protect against radiological and hazardous substances, and worker exposures are kept below the limits prescribed in the Radiation Protection Regulations and as low as reasonably achievable (ALARA). In addition, there was consensus that facilities should be designed and operated in such a way that they take all practicable measures to prevent accidents.

Stakeholders’ comments on high-level safety objectives included:

  • Affirmation that the risks associated with nuclear power generation should be infinitesimally small.
  • Suggestions that SMR designs should meet these high-level safety objectives; however, vendors should be afforded flexibility in selecting alternative methods to achieve these objectives.
  • Development of environmental performance parameters for a generic envelope that would be applicable to many sites in multiple jurisdictions.

3.2.3 Defence in depth

DiD is applied throughout the design process and during the construction and operation of a reactor to provide a series of levels of defence aimed at preventing accidents and ensuring appropriate protection in the event that prevention fails. All reactors must meet all five levels of DiD.

Participants suggested that SMRs possess diverse and overlapping safety provisions and that DiD embedded in the design provides a potential competitive advantage for SMRs when compared to other energy technologies.

3.3 Breakout session 2 summary: Application of graded approach and fundamental reactor safety functions

The second breakout session focused on considering the fundamental safety functions in the application of the graded approach. To help provide context and guide the discussion, participants were asked to consider what is needed to demonstrate to the regulator that shutdown, emergency core cooling system (ECCS) and containment design requirements are being met.

As it relates to the control, cool and contain requirements, participants suggested the following:

  • SMRs designs should be stable throughout process "upsetsFootnote 6". For more serious events, SMRs will automatically shut down safely in a controlled and predictable fashion without the need for operator intervention.
  • Due to the novel nature of SMRs’ normal reactor cooling process, some designs are expected to provide passive protection in an emergency. As a result, an ECCS may not be required.
  • Traditional concrete structures may not be required, as some proposed SMRs have novel features that meet the regulatory requirements for containment.

Participants were of the opinion that the CNSC could consider an application if the proponent could demonstrate that the reactor’s design makes the probability of a loss of cooling, control, and containment so remote and the consequences so low that no nuclear worker or member of the public would receive a dose above normal levels, and no off-site contamination would occur.

To demonstrate this capacity, stakeholders proposed requiring that the vendor/applicant/licensee:

  • Identify all phenomena or hazards, define failure modes and all postulated accident scenarios, and consider potential unknown phenomena.
  • Conduct deterministic and probabilistic analyses of all identified phenomena or hazards.

The results of the analysis could be validated through the vendor design review (VDR) process, research and development, modelling, small-scale experiments and/or prototypes. Stakeholders suggested that the CNSC could consider the cool, control and contain requirements to be met if the vendor/applicant can demonstrate that the risk(s) associated with a phenomenon are found to be very low (thresholds to be defined).

Participants aligned on the type of information that would need to be supplied to the regulator to support an applicant seeking to apply the graded approach. Documentation or evidence submitted to support a graded approach must have the following characteristics:

  • Facts and data are derived from validated and quality-assured (i.e., traceable and repeatable) scientific and engineering processes, such as:
    • Experimental or field-derived data
    • Operating experience
    • Computer modelling
    • Uncertainties are characterized and accounted for
    • Information is demonstrated to be relevant to the specific proposal

4. Other issues raised by participants

The following represents a summary of the other questions or issues raised by stakeholders at the workshop.

  • Would an SMR be required to remove only residual heat generated by the reactor or full heat at 100% power and decay heat? In addition, stakeholders asked about dispersing reactor heat from an event that is in excess of 100% performance or during a supercritical accident.
  • The terms for preventing accident progression and mitigating consequences need to be established.
  • Vendors/applicants should be required to determine the appropriate amount of redundancy, margin and conservatism built into the design of each reactor. This would be validated through the VDR process, research and development, modelling, small-scale experiments and prototypes.
  • SMRs are being designed with new safety features (e.g., underground structures, natural circulation, etc.) prompting participants to ask how they prove to the regulator that these features are reliable.
  • How can stakeholders demonstrate to the regulator that the computer modelling of inherent safety features is close enough to reality that less experimental data or no prototypes are required?

Regarding siting of SMRs, stakeholders suggested the following:

  • Envelopes could be created whereby a reactor built to address a set of established parameters could be approved for other sites that fit within the approved parameters.
  • Vendors and potential licensees should quantify safety as compared to other energy generation options (hydroelectric dam, gas-fired plant) for that geographic area.

Stakeholders also expressed a desire for early agreement on the graded approach as part of the pre-design review. This would provide a measure of certainty during the pre-licensing design review.

5. Next steps

While elements of the graded approach are already woven into the fabric of its regulatory framework, the CNSC will continue to address how a graded approach may be taken (where appropriate) when revising and publishing new regulatory documents. The CNSC will also consider the comments received during this workshop when making any regulatory changes involving the graded approach.

The CNSC welcomes comments on this topic, as well as comments on any regulatory document or discussion paper from the public at all times. Comments on this or any other CNSC document can be submitted by:

  • Email
  • Mail:
    Canadian Nuclear Safety Commission
    P.O. Box 1046, Station B
    280 Slater Street
    Ottawa, ON K1P 5S9
  • Fax: 613-995-5086

To view current regulatory documents and discussion papers posted for consultation, visit the CNSC's Consultation Web page.

Appendix A: Workshop participants

The table below provides a list of organizations and the number of participants who attended the workshop.

Organization Number of participants
Bruce Power 1
Canadian Nuclear Association 1
Canadian Nuclear Laboratories 3
Canadian Standards Association (CSA) Group 1
Candesco Division of Kinectrics 1
CANDU Energy Inc. 2
CANDU Owners Group 1
Department of National Defence 1
EON Consulting 1
Environment and Climate Change Canada 1
Global First Power 1
Government of Ontario, Ministry of Energy 1
Hitachi-GE Nuclear Energy, Ltd. 1
MeV200 Consulting Inc. 1
Natural Resources Canada 1
Ontario Power Generation 1
SaskPower 1
Terrestrial Energy Inc. 2

Appendix B: List of acronyms

as low as reasonably achievable
anticipated operational occurrences
Canadian Nuclear Safety Commission
CSA Group
emergency core cooling
emergency core cooling system
International Atomic Energy Agency
megawatts electric
nuclear power plants
Nuclear Safety and Control Act
Nuclear Security Regulations
safety and control areas
Shut Down System 1
Shut Down System 2
small modular reactor
structures, systems and components
vendor design review


Footnote 1

The function or power or (usually as controls) means of directing, regulating or restraining, IAEA Safety glossary – Nuclear Safety and Security – International.

Return to footnote 1 referrer

Footnote 2

Removal of heat from the reactor and from the fuel, IAEA Safety Standards No. SSR-2/1, Safety of Nuclear Power Plants: Design – Requirement 4

Return to footnote 2 referrer

Footnote 3

A method or physical structure designed to prevent or control the release of nuclear or hazardous substances, REGDOC-3.6, Glossary of CNSC Terminology.

Return to footnote 3 referrer

Footnote 4

Defence in depth (DiD) is a hierarchical deployment of different levels of diverse equipment and procedures to prevent the escalation of AOOs. Its goal is to maintain the effectiveness of physical barriers placed between a radiation source or radioactive material and workers, members of the public or the environment in operational states and, for some barriers, in accident conditions.

Return to footnote 4 referrer

Footnote 5

Licensing Basis Objective and Definition INFO-0795, regulatory documents, industry codes and standards, proponent or licensee-produced documents.

Return to footnote 5 referrer

Footnote 6

Deviation from normal system processes.

Return to footnote 6 referrer

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