Canadian Regulatory Requirements for Safety Analysis of Nuclear Power Plants

Abstract of the technical paper presented at:
The 2nd International Nuclear Energy Congress
Warsaw, Poland
May 22-24, 2012

Prepared by:
J. Kowalski
Canadian Nuclear Safety Commission (CNSC)
Ottawa, Ontario, Canada

Abstract

In Canada, all nuclear power plants are licensed by the Canadian Nuclear Safety Commission (CNSC) which operates under the Nuclear Safety and Control Act (NSCA) [1]. In addition to NSCA, the CNSC establishes lower level expectations in regulatory documents (RDs) that provide regulatory requirements with respect to the NSCA and license conditions. The CNSC also publishes guidance documents (GDs), which clarify the regulatory requirements and provide guidance as to how a licensee can meet these requirements.

It is mandatory that safety analysis be performed in order to license the nuclear power plant for operation. The main purpose of safety analysis is to verify that applicable safety requirements are met in all lifecycle phases of the nuclear power plant and to demonstrate that the reactor has adequate safety margins under normal and accident conditions. The analysis typically involves deterministic safety analysis, a probabilistic safety assessment and hazards analysis.   During the design stage of the nuclear power plant, the safety analysis is carried out in parallel with the design process, with iteration taking place between these two activities.

Over the past several years, the CNSC staff has been working to ensure that it has the appropriate regulatory framework [2-4] and internal processes in place for licensing all types of reactors. The present paper provides a Canadian regulatory perspective dealing with safety analysis used for licensing the nuclear power plants.  Key requirements for deterministic safety analysis are discussed in detail and include: selection of events to be analyzed, acceptance criteria, analysis methods and analysis documentation and the review and updates of safety analysis.

The paper describes the treatment of initiating events, event combination and classification of events. Acceptance criteria that serve as thresholds of safe reactor operation for anticipated operational occurrences (AOOs) and design basis accidents (DBAs) are provided. Dose limits for AOOs and DBAs are also presented.

The selection of safety analysis and assumptions needs to be such that the appropriate level of confidence can be achieved in the analysis results. The main safety analysis methods used in Canada are described including the limit of operating envelope (LOE) method and best estimate and uncertainty assessment (BEAU). The treatment of uncertainties in both methodologies is also discussed.

To demonstrate that the deterministic safety analysis complies with the regulatory requirements, the following rule must be followed:

• Analysis should be performed over accidents, allowable plant configurations, operating conditions sufficient to provide a high level of confidence in safe plant operation.
• Qualified computer codes should be used to perform analysis with adequate representation of the plant and modeling uncertainties.
• The analysis results should be compared against appropriate acceptance criteria and their acceptability confirmed. Adequate safety margins must be demonstrated.
• The analysis should be documented in a manner that is retrievable and the safety analysis report should be reviewed by qualified experts before being submitted to the regulatory body.

In summary, the paper presents Canadian regulatory requirements and perspective in making safety cases for licensing nuclear power plants. Our experience, practices and expectations are provided depending on the scope of analysis acceptance criteria and safety analysis methodology.

References

1. Canadian Nuclear Safety Commission, “Nuclear Safety and Control Act", Ottawa, 2000.

2. Canadian Nuclear Safety Commission, “Safety Analysis of Nuclear Power Plants", Ottawa, 2008.

3. Canadian Nuclear Safety Commission, “Probabilistic Safety Assessment (PSA) for Operating Nuclear Power Plants", Ottawa, 2003.

4. Canadian Nuclear Safety Commission, “Design of New Nuclear Plants", Ottawa, 2008.