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

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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

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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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