Canadian Nuclear Safety Commission. Suqiang Xu, Technical Specialist Christopher Cole, Director

Transcription

1 SCREENING OF STRUCTURES, SYSTEMS AND COMPONENTS FOR AGING MANAGEMENT AND RELIABILITY PROGRAMS FOR NUCLEAR POWER PLANTS IN CANADA, A REGULATORY PERSPECTIVE Suqiang Xu, Technical Specialist Christopher Cole, Director Canadian Nuclear Safety Commission IAEA Fourth International Conference on Nuclear Power Plant Life Management Lyon, France, 23-27, 2017

2 Canadian Nuclear Safety Commission Regulates the use of nuclear energy and materials to protect the health, safety and security of Canadians and the environment; implements Canada's international commitments on the peaceful use of nuclear energy; and disseminates objective scientific, technical and regulatory information to the public. Regulating Since 1946! 2

3 Presentation Outline Background; Regulatory Requirements; Industrial Implementation; Classification Terminology; and Conclusions. 3

4 Background All structures, systems and components (SSCs) degrade over time, which must be managed for short and long term operation; Not all of SSCs can be treated the same. A graded approach must be used. Classification of SSCs is required; and Classification could be nuclear safety based, power production based or a combination of both. 4

5 Safety Based Approach All SSCs are identified as either important or not important to safety; Systems important to safety are further divided into safety systems and non-safety systems but still important to safety; In Canada, all SSCs important to safety should be covered in an ageing management and maintenance programs governed by CNSC regulatory requirements detailed in REGDOC and RD/GD -210, respectively; Aging management must include long-lived passive SSCs that may not be covered by maintenance programs; REGDOC offers classification guidance based primarily on deterministic methodologies; and RD/GD 98 recommends probabilistic safety assessment to identify systems important to safety. 5

6 Combined Safety and Production Approach Nuclear power plants in Canada have adopted INFO AP 913, the Equipment Reliability Process Description; Equipment reliability program covers maintenance, aging management and RD/GD 98 reliability programs; INPO AP 913 component classification incorporates US NRC maintenance rules and aging management scoping criteria; and When implementing AP 913 in Canada, the criteria must be adjusted. 6

7 A typical Four Tier classification High critical components (Criticality Code 1 CC1); Low Critical Components (Criticality Code 2 CC2); Noncritical Components (Criticality Code 3 CC3); and Run to Maintenance Components (Criticality Code 4 CC4) 7

8 Criticality classification Component classification includes multiple disciplines; Criticality classification must be consistent with safety classification; Criticality classification should be checked against pressure boundary, seismic, environmental, electrical classifications, etc., all of which are safety-based; and Be aware of differences between CANDU and PWR safety classification, particularly terminology. 8

9 CNSC Terminology -Important to Safety Used in REGDOC SSCs important to safety include safety systems; complementary design features; safety support systems; and other SSCs whose failure may lead to safety concerns. The term important to safety used in REGDOC is equivalent to the term safety-related used in CSA N

10 CNSC Terminology -Important to Safety Used in RD/GD-98 In RD/GD-98, systems important to safety are defined as systems of a nuclear power plant associated with the initiation, prevention, detection or mitigation of any failure sequence and that have the most significant impact in reducing the possibility of damage to fuel, the associated release of radionuclides or both. RD/GD-98 adopts the same high level criteria from REGDOC However, in practice, items important to safety for RD/GD-98 are identified using a different approach resulting with a shorter classification list than the list for REGDOC

11 CNSC Terminology Safety-Related The term safety-relatedhas been widely used in historical CNSC documents and CSA standards. Safety-related systems are defined as those systems and their related components and supports that, by failing to perform in accordance with the design intent, have the potential to impact the radiological safety of the public or nuclear power plant personnel. As mentioned above, the term safety-relatedis equivalent to the term important to safety in REGDOC

12 CNSC Terminology Safety System Historically, the term special safety systems has been used in CNSC and CSA documents. Special safety systems in CANDU reactors are shutdown systems, emergency coolant injection systems and containment systems; and CNSC REGDOC adopts the IAEA definition of safety systems as those provided to ensure the safe shutdown of the reactor or the residual heat removal from the core, or to limit the consequences of anticipated operational occurrences and DBAs. 12

13 IAEA Terminology Important to Safety An item important to safety is part of a safety group and/or whose malfunction or failure could lead to radiation exposure of the site personnel or members of the public. Items important to safety include: those structures, systems and components whose malfunction or failure could lead to undue radiation exposure of site personnel or members of the public; those structures, systems and components that prevent anticipated operational occurrences from leading to accident conditions; and those features that are provided to mitigate the consequences of malfunction or failure of structures, systems and components. 13

14 IAEA Terminology Safety Systems The term safety systems is defined the same as in REGDOC The IAEA glossary states that safety systems consist of the protection system, the safety actuation systems and the safety system support features. In Canada, the safety system support features are treated as separate systems from the safety systems, sometimes. 14

15 IAEA Terminology Safety-Related A safety-relateditem is important to safety, but it is not part of a safety system. This definition is rarely used in publications. IAEA Important to Safety = IAEA Safety System + IAEA Safety-Related. CNSC Safety-Related = US NRC Safety-Related + IAEA Safety-Related. 15

16 US NRC Terminology Important to Safety As defined in 10 CFR 50, Appendix A, SSCs important to safetyare those that provide reasonable assurance that the facility can be operated without undue risk to the health and safety of the public. Important to Safety > Safety-Related. 16

17 US NRC Terminology Safety-Related Safety-related SSCs are defined in 10 CFR 50.2 as those that are relied upon to remain functional during and following design-basis events to ensure one of the three most important safety functions: The integrity of the reactor coolant pressure boundary; The capability to shut down the reactor and maintain it in a safe shutdown condition; or The capability to prevent or mitigate the consequences of accidents which could result in potential offsite exposures comparable to the applicable guideline exposures. The term safety systems is synonymous with safety-related systems. Safety-related SSCs represent a subset of SSCs important to safety. 17

18 A Comparison of Terminology All Structures, Systems and Components Important to Safety(ITS), REGDOC Non ITS Safety System (SS) Non SS but ITS CNSC ITS,RD/GD-98 Not ITS Safety Related(SR) Non SR Important to Safety(ITS) IAEA Safety System(SS) Safety Related(SR) Not ITS Important to Safety(ITS) Not ITS NRC SR=SS Non SR but ITS Utilities CC1 CC2 CC3 CC4 18

19 Conclusions Component criticality classification has been an essential element of an equipment reliability program. The classification consists of safety and power production criteria. It must be consistent with safety classification. The list of all SSCs important to safety must be reviewed for completeness and adequacy. When applying international classification criteria, it is important to know the similarities and differences of classification terms used by CNSC, and IAEA and US NRC. Moving forward, clarity and alignment between various agencies terms and definitions would be a positive step in reducing confusion and misinterpretation. 19

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