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Proposed Alternate Method for Complying With Order EA-12-049, “Order Modifying Licenses with Regard to Requirements for Mitigation Strategies for Beyond-Design-Basis External Events” NRC Technical Meeting Rockville, MD November 8, 2012

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Agenda

Opening Remarks

Requirements/Guidance

Design Comparisons

Alternate Method: The Standby Shutdown Facility (SSF)

Phase II FLEX Deployment

Closing Remarks

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Opening Remarks

Duke Energy continues to work expeditiously to develop FLEX strategies and supporting analyses

We have reviewed the methodologies described in NEI 12-06, “Diverse and Flexible Coping Strategies (FLEX) Implementation Guide,” and are considering an alternate coping method at the Oconee Nuclear Station (ONS)

We have developed a project schedule with milestones to support submittal of the Overall Integrated Plan by February 28, 2013

Insights and fresh perspectives provided by independent oversight, industry benchmarking, and stakeholder input are valued

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Requirements/Guidance

Order EA-12-049, Attachment 2 FLEX strategies must be capable of mitigating a simultaneous

loss of all alternating current (ac) power and loss of normal access to the ultimate heat sink

NRC Interim Staff Guidance JLD-ISG-2012-01 Endorses, with clarifications, the methodologies described in the

industry guidance document, NEI 12-06, “Diverse and Flexible Coping Strategies (FLEX) Implementation Guide”

NEI 12-06 provides one acceptable approach for satisfying the requirements of Order EA-12-049

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Requirements/Guidance

NEI 12-06, Section 1.3 The objective of FLEX is to establish an indefinite coping

capability that addresses both an extended loss of alternating current (ac) power (ELAP) event and the simultaneous loss of access to the ultimate heat sink event (LUHS)

The ELAP event involves the loss of: (1) off-site power, (2) emergency diesel generators, and (3) any alternate ac source as defined in 10 CFR 50.2 but not the loss of ac power to buses fed by station batteries through inverters

NEI 12-06, Section 3.2.1.3 (2) All installed sources of emergency on-site ac power and

SBO Alternate ac power are assumed to be not available and not imminently recoverable

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Requirements/Guidance

NEI 12-06, Section 2.1 While initial approaches to FLEX strategies will take no credit for

installed ac power supplies, longer term strategies may be developed to prolong Phase I coping that will allow greater reliance on permanently installed, bunkered, or hardened ac power supplies that are adequately protected from external events.

NEI 12-06, Section 3.2.1.3 (6) Permanent plant equipment that is contained in structures

with designs that are robust with respect to seismic events, floods, and high winds, and associated missiles, are available.

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Attributes of an ELAP Mitigation Facility

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Maintain Core

covered and cooled

Independent power supply

Decay Heat Removal -

SG

RCS pressure boundary isolation

RCS pressure

control – Pzr heaters

Negative Reactivity Addition

RC Pump Seal

Protection

RCS volume control – RC makeup and

letdown

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Design Comparisons

Typical Pressurized Water (PWR) Reactor: ELAP mitigation strategies typically rely on a turbine driven

emergency feedwater (TDEFW) pumps for secondary side heat removal (SSHR)

Time to core damage is extended in large part by promptly establishing and maintaining SSHR from a protected source

Oconee Nuclear Station: Although the failure probability of the Oconee TDEFW pumps is

commensurate with that of other facilities, they are not located in a hardened structure nor are their suction sources missile protected

ONS has a Standby Shutdown Facility (SSF) that provides additional defense in depth not available at other facilities

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Provides independent source of electrical power for SSF system loads. SSF DG

Provides source of water for OTSG secondary side cooling. SSF Auxiliary Service Water (ASW) system & SSF submersible pump

Provides makeup water for RCS inventory control and for RCP seal cooling. SSF Reactor Coolant Makeup (RCMU) system

Provides instrumentation for monitoring RCS, OTSG, and SSF Systems.

Provides limited RCS pressure control. PZR heaters.

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Alternate Method: The SSF

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“Alternate Method” refers to utilizing the SSF Diesel Driven AC Generator for Phase I coping for some minimum period until implementation of Phase II FLEX

SSF design basis: backup for existing safety systems to provide an alternate and independent means to achieve and maintain MODE 3 conditions for all three units for 72 hours.

The SSF is credited for mitigation of the following events: 1. Fire 2. Turbine Building Flood (internal – seismic induced) 3. Security Event 4. SBO (SSF ASW used when TDEFW Pump is not available) 5. Tornado (which renders FDW & EFW system inoperable)

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Alternate Method: The SSF

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The SSF D/G is provided solely for operation of SSF equipment and is disconnected from normal/emergency electrical distribution system (similar to a diesel/turbine driven pump) Procedures, protective relaying, and interlocks ensure SSF

systems are only supplied from the SSF The SSF Reactor Coolant Makeup system provides Reactor

Coolant Pump (RCP) seal injection and seal cooling independent of High Pressure Injection (HPI)

The SSF Auxiliary Service Water (ASW) system provides auxiliary feedwater flow independent of the main feedwater, emergency feedwater, and station auxiliary feedwater systems

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Alternate Method: The SSF

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The SSF and SSF control room are separate and independent of the main control room

The SSF is a robust structure with respect to PMP flooding, seismic events, high winds, and associated tornado missiles [NEI 12-06, Section 3.2.1.3 (6)] : SSF equipment is protected from design basis flooding

(PMP). Protection provided by the flood wall is well above flooding that could result from PMP at ONS.

SSF equipment is protected from design basis seismic events.

SSF equipment is protected from wind and tornado missiles. Upgrades are part of an open licensing action.

The SSF has a 72 hour mission time.

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Alternate Method: The SSF

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The SSF provides a viable coping strategy: Feeds both steam generators on all three Units in 14 minutes. Prevents RCP seal degradation by providing seal injection in 20

minutes SSF programmatic controls include quarterly operator

proficiency drills, operator training on an SSF simulator, and emergency operating procedure

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Alternate Method: The SSF

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If the TDEFW pump and SSF are assumed lost at T=0, then: A pre-staged portable equipment would need to be installed in a

robust structure, with robust piping from a robust water source to each units SGs

The robust structure would be very similar to the SSF.

In consideration of the diversity offered by SSF’s unique design features, assuming the SSF is available is considered a practical alternative approach for Phase I coping until Phase 2 FLEX is implemented

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Alternate Method: The SSF

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Phase 2 – FLEX Deployment

The FLEX Phase 2 strategy is to deploy portable pumps and electrical equipment as outlined in NEI 12-06

Barring unknowns relative to event duration and debris clearing impacting the actual start of deployment, Oconee is confident that deployment can be accomplished in just a few hours after the event.

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Closing Remarks

Short time frames to establish OTSG feed Not repowering electrical infrastructure Electrical independence Not repowering station pumps Robust facility and system designs Backed by FLEX implementation for Phases 2 and 3 Utilizing the methods described in NEI 12-06 would

require a pre-staged system that mimics all SSF design criteria barring the “Permanently Installed AC Generator.”

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Questions?

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