ML13218B227
| ML13218B227 | |
| Person / Time | |
|---|---|
| Site: | McGuire, Mcguire  |
| Issue date: | 08/06/2013 |
| From: | Duke Energy Corp, Duke Energy Carolinas |
| To: | Office of Nuclear Reactor Regulation |
| Paige Jason, 415-5888 | |
| References | |
| Download: ML13218B227 (37) | |
Text
McGuire Nuclear Station Vital Battery Replacement LAR 384
LAR Background The proposed LAR would revise the McGuire TS 3.8.4, DC Sources - Operating, Condition A.
to allow replacement of the existing shared 125 VDC vital batteries while at power.
The battery replacement cannot be accomplished within the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> Completion Times currently allowed by TS 3.8.4 due to the number of activities, inspections, and tests.
Battery replacement cannot be performed during a single unit refueling outage either since the batteries are shared between two units.
The proposed LAR would extend the Completion Time to 14 days for each battery channel replacement.
This proposed LAR would be applicable one-time for each of the four shared battery channels.
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LAR Background D
During i eachh vital it l battery b tt replacement, l t th the associated i t d DC channel h l will ill remain i energized i d bby bbeing i
cross-tied (bus tie with breakers) to another operable DC channel as allowed by TS 3.8.4 Condition A.
In addition, a temporary battery will be available as an additional, backup DC power supply.
The batteries were last replaced in 1997 under a risk based one-time TS change.
McGuire originally g y submitted this as a risk based LAR on August g 9,, 2012.
This revised LAR supersedes the risk based LAR withdrawn from NRC consideration on January p
17,, 2013. For this revised LAR,, McGuire has replaced the risk based evaluation with a more deterministic engineering justification.
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Tech Spec 3.8.4 DC Sources-Operating LCO 3.8.4 The four channels of DC sources shall be OPERABLE.
APPLICABILITY: MODES 1, 2, 3, and 4.
ACTIONS CONDITION REQUIRED ACTION COMPLETION TIME A. One channel of A.1 Restore channel of DC source to OPERABLE status. 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> DC source inoperable. OR A.2.1 Verify associated bus tie breakers are closed between DC channels. 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> AND A.2.2 Restore channel of DC source to OPERABLE status. 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> 4
Vital Battery 60 GNB NCN-27 NCN 27 Flooded Lead Calcium (1944 AH)
Class 1E cells, procured g Nuclear Logistics, through g ,
Inc. (NLI).
Recent tests indicate that three batteries are greater than 100% capacity, the fourth is at 99%.
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Battery History In May of 2006, positive post seal nut and jar lid cracking on the battery cells was discovered.
NLI evaluated the phenomenon for McGuire and determined it to be nodular corrosion.
The safety function of the post seal components is to prevent the release of acid to the atmosphere, they have no structural role.
Long term effects of post seal cracking is increased creep corrosion on the posts and straps 6
Battery History The jar cover prevents foreign material from entering the cell and provide structural integrity of the battery cell.
The jar covers are reinforced via vertical ribs on the underside of the jar.
In all cases the cracks run adjacent to, but not across, reinforcement ribs. The crack will be constrained by the reinforcing ribs and the battery cell cover will remain seismically intact.
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Need for Replacing Batteries Approximately 50% of the cells are currently affected by this phenomenon.
Even though all McGuires McGuire s vital battery banks are operable from a capacity standpoint standpoint, physical degradation will eventually start to accelerate as a result of the nodular corrosion phenomenon.
GNB advertises a service life of 20 years years, industry operating experience indicates that 15 to 18 years is a much closer approximation.
Consequently Consequently, replacing all four vital batteries prior to the end of their 20 year service life is a conservative and prudent decision.
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125VDC Vital Instrumentation & Control Power System (EPL)
Th The EPL system t provides id power tto nuclear l safety f t related l t d I &C lloads d requiring i i an uninterrupted i t t d power source.
McGuire's EPL system consists of four batteries, chargers and distribution centers shared between both units.
The loads served from these distribution centers are unitized, providing a 125 VDC power panelboard and inverter for each unit.
Sharing of the 125 VDC I&C power system between Units was reviewed and approved by the NRC and documented in the McGuire Safety Evaluation Report (SER) Supplement 1 dated June 6, 1978.
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125VDC Vital Instrumentation & Control Power System (EPL) Equipment Oneline EVCS EVCB EVCC EVCD EVCA Charger Charger Charger Charger Charger Battery Battery Battery Battery EVCA EVCB EVCC EVCD Disconnect Switch K
EVDA EVDB EVDC EVDD 125V DC Panel 1EVDA 2EVDA 1EVDB 2EVDB 1EVDC 2EVDC 1EVDD 2EVDD Boards Static Inverters 1EKVA 120V AC Panel 2EKVA 2EKVA 1EKVA 2EKVA 1EKVA 2EKVA 1EKVA Boards 10
125VDC Vital Instrumentation & Control Power System (EPL)
Train Channel Main Equipment The EPL system consists of four independent Designation Designation and physically separate load channels. A Train A Channel EVCA battery EVCA charger EVDA bus/distribution center Channels A and C are associated with Train A.
C Channel EVCC battery EVCC charger Channels B and D are associated with Train B B. EVDC bus/distribution center B Train B Channel EVCB battery Train A and B loads are concentrated on EVCB charger Channels A and D respectively respectively. EVDB bus/distribution center D Channel EVCD battery EVCD charger Channels C and B supply mainly channel EVDD bus/distribution center related loads.
loads 11
Vital Battery Sizing The Vital Batteries are sized in accordance with IEEE 485-1983.
Design inputs for sizing include:
1.11 temperature correction factor for 60o F 1.25 Aging factor for 80% end of life capacity 1.15 Load growth factor Inverter DC load is calculated from the AC output current with an assumed input voltage of 100VDC plus internal losses measured during inverter factory acceptance testing.
Each battery is sized to carry the accident loads of one unit plus the safe shutdown loads of the other unit for one complete train, assuming a loss of offsite power.
A Train is used for sizing analysis due to carrying the heaviest loads.
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Battery Room Since the EPL system is Class 1E, safety related it is located in the Auxiliary (Aux) Building The Aux Building is a Category 1 structure, able to withstand the most severe natural t l phenomena h (t (tornadoes, d
hurricanes, earthquakes, floods, and Battery RM external missiles).
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Battery Room Each battery is separately housed in a ventilated room apart from its charger, distribution centers and other batteries by 3-hour rated fire barriers.
These smaller battery rooms are contained inside a larger battery room area which separates the equipment from other areas of the plant by 3-hour rated concrete walls and fire doors.
Each battery room is supplied with redundant ventilation to prevent the buildup of hydrogen to dangerous levels.
The general area of the battery room and each of the smaller rooms contain smoke detectors which alarm and annunciate in the control room.
Manual hose stations and portable fire extinguishers are in the area provided for fire suppression.
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EPL Normal Operation The batteries are floated on the buses and assume load without interruption upon loss of a battery charger or AC power source.
Battery chargers provide DC power to their respective distribution centers and maintain their respective batteries at 132V The 125 VDC distribution centers supply power to their respective 125 VDC power panelboards and the 120 VAC power inverters.
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Normal Operation Train A EVCS EVCB EVCC EVCD EVCA Charger Charger Charger Charger Charger Battery Battery Battery Battery EVCA EVCB EVCC EVCD Disconnect K Switch EVDA EVDB EVDC EVDD 125V DC Panel 1EVDA 2EVDA 1EVDB 2EVDB 1EVDC 2EVDC 1EVDD 2EVDD Boards Static Inverters 1EKVA 120V AC Panel 2EKVA 2EKVA 1EKVA 2EKVA 1EKVA 2EKVA 1EKVA Boards 16
EPL Loss Of Offsite Power Operation During a LOOP on one or both trains, the essential motor control centers feeding the Vital I&C battery chargers associated with the affected train will be load shed by the Emergency Diesel Generator (EDG) load sequencer.
Within eleven seconds after the diesel generator start signal, the affected essential motor control centers and battery chargers will be reloaded onto the essential bus by the sequencer.
During the time period that the affected essential motor control centers and battery chargers are de-energized, the batteries feed the vital instrumentation and control loads.
If for some reason both of one units EDGs fail, two chargers can be manually aligned to the opposite units EDGs 17
Battery Crosstie If one battery and/or its charger is removed from its bus REQUIRED ACTION statement A.2.1 of Technical Specification 3.8.4 is invoked by closing tie breakers between DC channels, ensuring normal loads are still energized by a full capacity charger and battery of the same affected ff t d ttrain.
i For this alignment (cross-tied), one battery is serving two channels on one train.
The other train, two batteries are serving two channels, while assuring train independence at all times.
All four vital batteries, are sized to independently carry full normal and emergency loads of their respective trains.
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A Train Crosstie (EVCA out of service)
EVCS EVCB EVCC EVCD EVCA Charger Charger Charger Charger Charger Battery Battery Battery Battery EVCA EVCB EVCC EVCD Disconnect Closed Crosstie K Switch Breakers EVDA EVDB EVDC EVDD 125V DC Panel 1EVDA 2EVDA 1EVDB 2EVDB 1EVDC 2EVDC 1EVDD 2EVDD Boards Static Inverters 1EKVA 120V AC Panel 2EKVA 2EKVA 1EKVA 2EKVA 1EKVA 2EKVA 1EKVA Boards 19
Crosstie Frequency Crosstying two vital channels is a regularly performed evolution at McGuire. In an 18 month period Ops will crosstie two channels eight times for normal preventative maintenance and testing.
Every 18 month cycle each battery is taken out of service for a modified performance test, which requires 48-54 hours of crosstie time.
Once per year each battery is taken out of service for its annual inspection which takes about one shift.
Each channels crosstie is also loaded every 18 months when its respective charger is removed from service for testing and maintenance. EVCS charger is aligned through the crosstie breaker to take the place of the out of service charger.
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EVCS Charger (SPARE) Aligned to EVDA Bus through Crosstie EVCS EVCB EVCC EVCD EVCA Charger Charger Charger Charger Charger Battery Battery Battery Battery EVCA EVCB EVCC EVCD Disconnect K Switch EVDA EVDB EVDC EVDD 125V DC Panel 1EVDA 2EVDA 1EVDB 2EVDB 1EVDC 2EVDC 1EVDD 2EVDD Boards Static Inverters 1EKVA 120V AC Panel 2EKVA 2EKVA 1EKVA 2EKVA 1EKVA 2EKVA 1EKVA Boards 21
OVERVIEW OF BATTERY REPLACEMENT EVOLUTION The replacement vital batteries will be identical to the existing batteries; GNB Type NCN-27.
From discussions regarding the nodular corrosion phenomenon with battery vendors, other nuclear stations, and industry experts there is currently no permanent solution to the issue as the batteries age.
As indicated by the performance tests, the McGuire NCN-27 Batteries have shown minimal capacity loss for their age.
Prior to installation, each new vital battery bank will receive a commissioning charge followed by a Modified Performance Test (MPT) per IEEE 450-1995 22
Installation Evolution After a battery is removed from service, old cells and connectors are disconnected and transported from the battery room to the Service Building through controlled access doors via a roller rack.
New cells are transported into the battery room from the Service Building using the same route as above and are installed into the battery rack.
Once 60 new cells are installed in the battery rack, McGuire's craft personnel torque all battery electrical connections (with new intercell connectors and intertier jumpers) and battery rack connections to the appropriate specifications.
After the battery has passed all required Tech Spec Surveillances (SG readings, cell voltages, capacity, cell connection resistance) it is realigned to the Vital DC bus.
Each battery replacement will take approximately 14 days 23
Defense in Depth, Temporary Battery For the unlikely scenario where the vital battery supporting the cross-tied channels is lost or disabled; the temporary battery would be utilized to recover a DC channel and associated loads.
Th The temporary t battery b tt bank b k will ill bbe llocated t d iin Room 700 of the McGuire Service Building (shared load center room) due to space Temp limitations in the battery room in the Auxiliary Battery Building.
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Defense in Depth, Temporary Battery Th The Service S i Building, B ildi which hi h iis located between the Unit 1 and 2 Turbine Buildings, is not a Seismic Category structure and the temporary battery will not be seismically mounted.
The temporary battery bank will remain disconnected via a disconnect box but available if needed 25
Defense in Depth, Temporary Battery The temporary battery bank will be tied to the DC side of the standby battery charger (EVCS) via EVDS Distribution Center.
Operations can perform the required connections within 60 minutes. It will not be credited for operability of the associated DC channels.
With more than one DC channel inoperable, McGuire would enter TS 3.8.4 Condition B. This would require both Units to be in Mode 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and Mode 5 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />.
The temporary battery is a full capacity, bank of NCN-27 cells and sized in accordance with IEEE Standard 485-1983.
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Defense in Depth, Temporary Battery Voltage drops from the temporary battery to each distribution center has been accounted for in the temporary battery sizing, such that existing voltage drop analysis from the Vital DC distribution centers (EVDA, EVDB, EVDC and EVDD) to their respective loads remains b di bounding.
A temporary charger will be installed to maintain the temporary battery at 132VDC. The temporary charger will have a disconnect to electrically isolate it from the temporary battery and the vital DC bus.
The temporary battery will be subject to regular weekly, quarterly and annual TS surveillances, including a MPT prior to the first vital battery replacement.
All applicable TS surveillances will continue to be performed during periods of battery replacement.
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A Train Crosstie, Defense in Depth Measure EVCS EVCB EVCC EVCD EVCA Charger Charger Charger Charger Charger Battery Battery Battery Battery EVCA EVCB EVCC EVCD Temp Battery K
EVDA EVDB EVDC EVDD Temp Charger 125V DC Panel 1EVDA 2EVDA 1EVDB 2EVDB 1EVDC 2EVDC 1EVDD 2EVDD Boards Static Inverters 1EKVA 120V AC Panel 2EKVA 2EKVA 1EKVA 2EKVA 1EKVA 2EKVA 1EKVA Boards 28
SUMMARY
OF DETERMINISTIC JUSTIFICATION All four vital batteries have been sized to carry the load duty cycle during LOCA and LOOP conditions for their respective bus/train while maintaining battery terminal voltage in a cross-tied alignment.
Due to this robust design, the safety functions of the 125 VDC I&C system are preserved.
Cross-tying two channels to one battery is a normal alignment that Operations performs approximately eight times in an 18 month operating cycle to accommodate battery discharge testing and annual inspection for each of the four batteries.
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SUMMARY
OF DETERMINISTIC JUSTIFICATION The proposed LAR does not introduce a new accident or transient since no new equipment is installed, existing equipment is not operated in a new manner, and thus no new accident initiator is introduced.
The temporary battery remains disconnected via a disconnect box but available if needed.
The 125 VDC I&C power system is not an initiator of any analyzed design basis events, therefore, the proposed LAR does not increase the likelihood of an accident or transient.
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SUMMARY
OF DETERMINISTIC JUSTIFICATION Since the 125 VDC I&C power system is a Class 1E system (safety related), all related equipment (including the vital batteries and cross-tie features) is located in the Auxiliary Building.
The Auxiliary Building is classified as a Category 1 structure, as such, is designed to withstand, without loss of function, the most severe natural phenomena (e.g., tornadoes, hurricanes, earthquakes, floods, and external missiles).
Exiting hatch doors and fire stops would prevent a fire in the area of the temporary battery (Room 700 of the service building) from spreading into the battery room.
During a battery replacement security is stationed at the hatch door as long as it is open and is able to close the door as needed.
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SUMMARY
OF DETERMINISTIC JUSTIFICATION Important equipment will be protected and compensatory measures will be in place to minimize potential common cause failures.
These measures will include avoiding (to the extent possible) severe weather conditions and periods of system grid instability during the proposed TS Completion Time extension.
Appropriate measures will be taken to preserve defenses against potential common cause failures and no new common cause failure mechanisms will be introduced.
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Protected Equipment During Each Battery Replacement McGuire Switchyard Unit 1 and 2 main step-up transformer yard Unit 1 and 2 6.9kV switchgear room Standby Shutdown facility and associated equipment (SSS)
Emergency Diesel Generators (EDG)
Component Cooling water trains (KC)
Nuclear Service Water trains (RN)
Motor driven Auxiliary Feedwater (CA) pumps Unit 1 and 2 Turbine driven CA pumps Diesel powered Instrument Air (VI) compressors Three vital batteries not beingg replaced p
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SUMMARY
OF DETERMINISTIC JUSTIFICATION A
As additional dditi l ddefense-in-depth, f i d th M McGuire G i was ddesigned i d with ith a St Standby db Sh Shutdown td S System t (SSS) to meet 10 CFR 50 Appendix R (Fire Protection Program) and 10 CFR 50.63 station blackout (SBO) requirements.
The SSS is designed to mitigate the consequences of certain postulated fire, sabotage incidents and SBO events by providing capability to achieve and maintain hot standby conditions by controlling and monitoring vital systems from locations external to the control room room.
The proposed change will not allow plant operation in a configuration outside the design basis.
The requirements regarding the vital batteries credited in the accident analysis will remain the same.
As previously discussed discussed, a comparable temporary battery bank and the Standby Shutdown System will also be available for loss of DC power recovery and accident mitigation.
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SUMMARY
OF DETERMINISTIC JUSTIFICATION M
McGuire G i hhas reviewed i d NUREG NUREG-0800, 0800 B Branchh TTechnical h i lP Position iti (BTP) 88-8,8 O Onsite it andd Off Offsite it Power Sources Allowed Outage Time Extensions, and has incorporated the recommendations and guidance of BTP 8-8 where applicable.
This activity does not modify the plant design or the design criteria applied to the relevant systems, structures, or components (SSCs). The 125 VDC I&C power system was designed licensed to be operated in the proposed (cross-tied)
(cross tied) manner.
manner Compliance with the applicable GDCs and other regulatory requirements will not be affected.
The new 125 VDC batteries are identical in design and function to the existing batteries, thus McGuire will continue to meet the applicable regulatory requirements.
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Precedents Six other NRC approved TS Completion Time extension LARs needed to replace batteries were reviewed. This submittal was originally modeled after these.
Two other TS Completion Time extension LARs that were originally submitted as risk based LARs then re-submitted with a more deterministic justification were also reviewed (Browns Ferry and Oconee).
McGuire has modeled this LAR after these also.
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