dc Load Shedding OverviewFukushima Mitigation Strategy
U.S. EPRTMDesign Centered Working Group
January 15, 2013 - Rockville, Maryland
EPRby AREVA
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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U.S. EPR Design Centered Working Group - dc Load Shedding Overview - Fukushima Mitigation Strategy - January 15, 2013 2
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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U.S. EPR Design Centered Working Group - dc Load Shedding Overview - Fukushima Mitigation Strategy - January 15, 2013 3
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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U.S. EPR Design Centered Working Group - dc Load Shedding Overview - Fukushima Mitigation Strategy - January 15, 2013 5
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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U.S. EPR Design Centered Working Group - dc Load Shedding Overview - Fukushima Mitigation Strategy - January 15, 2013 6
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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U.S. EPR Design Centered Working Group - dc Load Shedding Overview - Fukushima Mitigation Strategy - January 15, 2013 7
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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U.S. EPR Design Centered Working Group - dc Load Shedding Overview - Fukushima Mitigation Strategy - January 15, 2013 8
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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U.S. EPR Design Centered Working Group - dc Load Shedding Overview - Fukushima Mitigation Strategy - January 15, 2013 10
Results I
lo The modified EUPS design allows for an extended duty cycleof at least 6 hours and 30 minutes.
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U.S. EPR Design Centered Working Group - dc Load Shedding Overview - Fukushima Mitigation Strategy - January 15, 2013 11
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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U.S. EPR Design Centered Working Group - dc Load Shedding Overview - Fukushima Mitigation Strategy - January 15, 2013 13
ModificationsEUPS Division 1 (typical for other 3 buses)
EUPS
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U.S. EPR Design Centered Working Group - dc Load Shedding Overview - Fukushima Mitigation Strategy - January 15, 2013 14
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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