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Canadian Nuclear Utility Principles for Beyond Design Basis Accidents
IAEA-J4-TM-46463 TM for Evaluation of Design Safety
Mark R Knutson P Eng.
Director of Fukushima Projects
Ontario Power Generation
Overview of Presentation
• Canadian Nuclear Utility Principles for Beyond Design Basis Events
• 1 Objective
• 9 Principles
• Supporting actions planned or taken by the utilities
• Our Commitment
• Summary
2
Canadian Nuclear Utility Principles for Beyond Design Basis Events
• Developed and agreed to by the 3 Utilities
• Provide guidance for utility decision making to maintain consistency
• Intended to position Canadian utilities at the forefront of the Post Fukushima Response
3
Objective of the Principles
Practically eliminate the potential for societal disruption due to a nuclear incident by maintaining multiple and flexible barriers to severe event progression
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Principle 1 – Event Progression Defences
Actions and defences will focus on stopping accident progression prior to a severe accident.
• Maintaining adequate fuel cooling prevents fuel failures.
• Severity of consequences escalates with event progression.
• Prevention should receive the majority of the actions and focus from the utilities.
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Principle 1 - OPG Event Progression Defences Actions
• Robustness of OPG stations confirmed for beyond design basis (BDB) seismic events
• BDB wind analysis completed for Pickering 5-8 and Darlington – Resulted in revisions to P5-8 Emergency Operating Procedures
• BDB wind analysis in-progress for Pickering 1-4 – TCD Dec 31, 2013
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• BDB flooding analysis completed for Pickering and Darlington – Installed flood barriers around
essential systems at both sites
Principle 2 – Multiple Barriers Multiple barriers to event progression and multiple means to supply water or electricity will be used to ensure adequate defence
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Principle 2 - OPG Multiple Barriers Actions
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• Procured diesel driven pumps and generators
• Sufficient number (N+1) of pumps and generators to supply all units at a site simultaneously
• Multiple different connection points
• Design in progress to simplify connections
CANDU
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Principle 3 – Early Fuel Cooling
Methods and actions to initiate heat transport system (HTS) cool-down and maintain fuel cooling will be a primary and early priority
• Rapid cooldown is achieved by opening Steam Release Valves (SRVs) – Increases margin to fuel failures (lower temperature).
– Allows for EME to inject additional water into a depressurized steam generators.
• Actions to open SRVs need to be simple and reliable.
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Principle 3 - OPG Early Fuel Cooling Actions
• Procedures
– Load shedding strategies
• Training
– Initiation of early cool-down of the HTS
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• Design
– Seismic capacity of Class II battery banks
– Portable Uninterruptable Power Supplies (PUPS)
Principle 4 – Containment Integrity
Actions to maintain Containment integrity will be utilized to minimize radioactive releases
• Control pressure – Containment Cooling
– Containment Venting (Principle 5)
• Control hydrogen – Minimize generation
– Effective removal
• Control water inventory to minimize flooding – Water injection and recovery
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Principle 4 - OPG Containment Integrity Actions Design
Larger generators as part of Phase 2 EME to repower most Emergency Power System loads, including, – Vault and boiler room air cooling units (condense steam)
– Post Accident Containment Filtered Venting System
– Emergency Water Systems to cool safety-critical loads
– Reactor water recovery and recirculation
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Principle 4 - OPG Containment Integrity Actions
Design (continued) – Water make-up to moderator and shield
tank to arrest accident • Provide fuel cooling
• Minimize generation of hydrogen
– Shield tank integrity assessed for severe accidents • Additional shield tank overpressure relief
committed for Darlington
• Current overpressure relief confirmed adequate for Pickering
– Additional filtered venting system (beyond phase 2 EME) • Committed as part of Darlington refurbishment
• Under evaluation for Pickering
– Passive Autocatalytic Recombiners for hydrogen removal – 6 of 10 Units complete
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Principle 4 - OPG Containment Integrity Actions
• Procedures
• Severe Accident Management Guidelines developed
• Improved through multiple iterations
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• Training
• Classroom
• Practice deploying actual EME equipment
• SAMG Drills with EME deployment
• 2 one-day drills for each of PA and PB in 2013
• 1 two-day drill planned for Darlington (August 2013)
Principle 5 – Filtered Venting
Containment venting will be controlled through a filtered system
• With a functional containment, decisions can be made when to vent and for how long.
• Controlled filtered venting will minimize radioactive releases and their potential impact on the environment.
• The ability to delay when containment will be vented allows for short lived material to be reduced through decay.
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Principle 5 – OPG Filtered Venting Actions
• Both Pickering and Darlington have Post Accident Containment Filtered Venting Systems
– Repowered as part of Phase II EME
– Additional filtered venting capacity to be installed as part of Darlington Refurbishment. • Pickering is under review, decision by end of 2013.
• Post accident procedures are available and trained
• Installed remote radiation monitoring system
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Principle 5 – OPG Filtered Venting Actions
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• Installed near boundary automated gamma monitoring at Pickering and Darlington • Provide early indication of impact of venting
Principle 6 – Equipment Integrity
Necessary systems, structures and components will be confirmed to survive rare yet credible conditions for external hazards
• Review Level Conditions (RLCs) established for rare yet credible conditions.
e.g., seismic Design Basis ~1,000 yr; RLC ~10,000 yr
• Provides assurance that the EME will meet its objectives for Beyond Design Basis Events
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Principle 6 – OPG Equipment Integrity Actions
• Seismic Margin Assessment completed:
– Passive water supply to Steam Generators (Dearator)
– Class II batteries and rack
• EME Quick connects designed to meet system requirement
• Analyzed impact of seismically induced fires and floods at Pickering and Darlington.
– No significant incremental impact on station risk.
• Instrumentation and Equipment Survivability Assessment is in progress for Pickering and Darlington
• Diversity and independence of EME connection points included in plan to address extreme external hazards.
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Principle 7 – Spent Fuel Cooling
Irradiated Fuel Bay (IFB) water levels will be maintained sufficiently above the top of the fuel to mitigate high radiation fields, hydrogen production, and fuel damage
• The time required to respond to a loss of IFB cooling is typically quite long.
• The volume of water in the IFB should be maximized within normal water levels to the extent practicable.
• EME to supply water to account for leakage and steaming.
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Principle 7 – OPG Actions
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• IFB time to boil > 72 hrs
• EME deployment time < 4 hours • Procedures developed for
EME deployment
• Seismic / Thermal Analysis confirmed leakage plus evaporation << EME water make-up capacity
• Design in progress for portable measurement of level and temperature
Principle 8 – Readily Deployed
Emergency Mitigating Equipment will be robust, readily available, easily deployable within required timeframes, and have adequate redundancy • Stored at higher elevation, away from station, close enough for timely
deployment and accessible following BDBE
– Pre-staging is an option for predictable events (e.g., severe weather)
• Deployable by diverse work groups, supported by procedures, training and practice and validated by drills
• More than one method for deployment (trucks, tractors, security vehicles)
• Reliability of EME supported by using proven technology, preventative maintenance and routine testing
• On-site fuel supplies adequate for > 72 hour run time, with provisions for refueling in place.
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Principle 8 – OPG “Readily Deployed” Actions
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Principle 8 – OPG “Readily Deployed” Actions
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Principle 8 – OPG “Readily Deployed” Actions
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Principle 9 - Common Philosophy
Canadian utilities will utilize a common philosophy for the prevention of a Beyond Design Basis Accident (BDBA)
• Interaction between utilities gives a larger perspective and experience base
– Encourages challenging and learning
– Improves capability to respond and to provide mutual assistance
– Provides credibility
– Facilitates regulatory concurrence.
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Principle 9 - Common Philosophy Actions
COG - Candu Industry Integration Team Bi-weekly domestic meetings
Monthly CNO meetings
Quarterly international meetings
COG Severe Accident Joint Project Technical Reports Shutdown and Low Power
Multi-unit Station
Technical Basis Document and SAMG Update
Containment Integrity
In-Vessel Retention
Instrument Survivability
Habitability
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Principle 9 – OPG Common Philosophy Actions
COG Emergency Preparedness Work Shop III June 3&4,
Diverse participation including CNSC, Health Canada and provincial agencies.
WANO SOER 13-2 corrective action plans
Developed cooperatively
WANO Peer Review at Pickering June 10-21
“Strength” awarded for Fukushima response.
Mutual Aid Agreement in effect
Regional Emergency Response Support Centre
Conceptual design report under review
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Our Commitment
We are committed to these principles in order to protect against Beyond
Design Basis Events such as the one that occurred at Fukushima
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