dc Load Shedding OverviewFukushima Mitigation Strategy

U.S. EPRTMDesign Centered Working Group

January 15, 2013 - Rockville, Maryland

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AAREVA

Agenda

Io Purpose and Background

lo Existing EUPS

io Methodology / Strategy

Oo Key Inputs and Assumptions

Op Results

No Modifications

Oo Summary

Oo Questions

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Purpose

lo Present the AREVA design approach to extend the EUPSbattery capacity to lengthen the FLEX Phase 1 time period.After FLEX Phase 1, the transition phase (FLEX Phase 2) isinitiated to maintain or restore the key safety functions usingportable on-site equipment.

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Background -Recommendation 4.2Loss of All AC

Oo NTTF Recommendation 4.2 is Tier 1 and resulted in Order EA-12-049. Licensees must enhance mitigation capabilities forbeyond design basis external hazards.

Order requires a three phase approach:" Phase 1: Initial phase requires use of installed equipment and resources to maintain or restore core

cooling, containment and spent fuel pool (SFP) cooling capabilities." Phase 2: Transition phase requires providing sufficient, portable, onsite equipment and consumables

to maintain or restore functions until they can be accomplished with resources brought from off site.* Phase 3: Final phase requires obtaining sufficient offsite resources to sustain functions indefinitely.

Implement strategies in all modes

Implement strategies assuming simultaneous loss of all ACpower [LOOP + loss of EDGs + loss of alternate AC source] + lossof ultimate heat sink

Provide reasonable protection of mitigating equipment fromexternal events assuming all units on a site are affected

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Existing EUPS

Pl The U.S. EPR TM design includes several battery systems:

Class 1 E Emergency Uninterruptible Power Supply (EUPS)

Non-Class 1 E Uninterruptible Power Supply (NUPS) System, and

12-Hour Uninterruptible Power Supply (12UPS) System.

Po The EUPS distributes UPS-backed ac and battery-backed dcpower to safety-related loads and to select non-safety relatedloads.

OP The EUPS system provides:

uninterruptible dc control power for safety-related switchgear and loadcenters

uninterruptible dc and ac power for safety-related I&C systems

uninterruptible ac motive power for safety-related motor-operated valves

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Existing EUPS I

No Four EUPS divisions are provided in the U.S. EPR TM design.

10 Each EUPS division includes one 250 Vdc battery, two 100%capacity battery chargers, and a dc distribution bus.

OP The dc distribution bus powers inverter BRU01, which in turnpowers motor control center BRA and panel boards BLB01and BGA01.

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FLEX Phase 1 Mitigation Strategy I

No When the ELAP condition is recognized:

Shed non-ELAP Loads

Division 3 EUPS and Division 4 EUPS are removed fromservice

lo When Divisions 1 and 2 are near depletion, Divisions 3 and4 batteries are placed in service.

lo Portable power is provided for EUPS support beforeDivisions 3 and 4 are depleted. This is the transition toFLEX Phase 2.

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Evaluation Method

Oo The loads required by the FLEX strategy were identified.

lo Categorization of loads and sizing calculations wereperformed using the methods described in IEEE Std 485-1997, Sizing Lead-Acid Batteries for Station Applications,with the following clarifications:

Duty cycle load steps were based on actual expected operation times

The specified minimum cell voltage was 1.75 Vdc.

lo Vendor rating tables provide the available cell amperes atspecific times for the cell type when discharged to a finalvoltage of 1.75 Vdc at 77°F.

Results were adjusted from "standard" electrolyte temperature (770 F) toapproximately 620F.

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Key Inputs and Assumptions

No An Extended Loss of ac Power (ELAP) condition will beidentified shortly after the EDGs and Station Blackout (SBO)Diesel Generators (DGs) have failed to connect to theEmergency Power Supply System (EPSS) buses.

lo Load shedding is assumed to take 60 minutes to complete.

A design modification will allow the operators to efficiently load shedeach EUPS bus and open the EUPS battery disconnect

1P An overlap in discharge duration of 20 minutes is assumedwhen switching from an inservice EUPS division to an out-of-service EUPS division.

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Key Inputs and Assumptions(continued)

li Assumed that ALL of the I&C cabinets supplied by theconverters (24 Vdc I&C Power Supplies) are powered forELAP.

No Assumed ALL inner containment isolation valves operate attime=0 seconds. Exceeds NEI 12-06 para. 3.2.1.11requirement.

lo Aging factor of 1.25 was used consistent with IEEE Std 485-1997 para. 6.2.3.

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Results I

lo The modified EUPS design allows for an extended duty cycleof at least 6 hours and 30 minutes.

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Extended Loss of ac Power (ELAP)Discharge Duration

/ EUPS divisions EM divisions EUPS divisionsEUPS divisions1, 2,3,and 4disctwrge(N mnuties) ~ 7 l ' 1& &2discharge 7 I-,2,3,and4 4> ( 3- H4 discharge(hrs 30min) disnharge (2 hrs 30min)

I I I I I I Ii i i i i i E- MI

TIK--O

-LOOP- inner cortainment isolaion valves dose*EDGstart ater pt*open brealcr to Ahd switear andloa center lbads prior to EDG loAsewwjg

ITllE: 15 seconds.EDslftostart

TIME= 10 mints90OGs eltostartor

comectotheeEPSSbuses*ELAP condition is idenedActions strted to remoe frm sricEUPS divisions 3 and4

.Actions started to shed non-ELAP loads

TIMEz70 minutes-All nonRA loads shed fromEUPS divisions I thn 4

.EUPS divisions 3 and 4 removedfom service

IlIME z 3 hours 40 minutes-ELPS divisions 3 &4returned to service

ITIME :4 hours-EUPS divisions I &2

removed from service

I I.TIME = 6 hours 30 minutes- End of analyzed duration

Note: Time periods not to scale

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Modifications

lo The ELAP-required and non-ELAP-required loads will beseparated to allow shedding the non-ELAP required loads inone step.

lo Ac operated valves which are repositioned in the mitigationstrategy must reside on the only 480V ac powered bus, EUPSbus BRA. Some of these valves are presently powered fromthe Emergency Power Supply System (EPSS) BNB bus, andwill be moved to bus BRA.

Io Connections will be added to transition to Phase 2.

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ModificationsEUPS Division 1 (typical for other 3 buses)

EUPS

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Summary

l The EUPS battery capacity for FLEX Phase 1 can beextended to at least 6 hours and 30 minutes.

lo The EUPS design will be modified to facilitate timely operatoraction.

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