ML15224A289

Forwards Preliminary ASP Evaluation for Oconee Event Which Ocurred in December 1992 Re Inoperability of Emergency Power from Keowee Hydrostation Due to Potential Reduced Dc Voltages During Loss of Power Scenarios

ML15224A289
Person / Time
Site:	Oconee
Issue date:	08/03/1993
From:	Wiens L Office of Nuclear Reactor Regulation
To:	Hampton J DUKE POWER CO.
References
NUDOCS 9308200166
Download: ML15224A289 (25)

Text

August 3, 1993 Docket Nos. 50-269, 50-270 DISTRIBUTION and 50-287

[FT6ke-tFi-iD L.Berry NRC/Local PDRs L.Wiens Mr. J. W. Hampton PDII-3 Reading OGC, 15B18 Vice President, Oconee Site S.Varga ACRS (10), P-315 Duke Power Company G.Lainas G.Holahan, MNBB9112 w/o enclosure P. 0. Box 1439 D.Matthews Seneca, South Carolina 29679 E.Merschoff, RH

SUBJECT:

PRELIMINARY ACCIDENT SEQUENCE PRECURSOR (ASP) ANALYSIS FOR AN OCONEE EVENT Enclosed is a preliminary ASP evaluation for an Oconee event which occurred in December 1992. The event was the inoperability of emergency power from the Keowee hydrostation due to potential reduced DC voltages during loss of power scenarios. We previously provided, for your information and comment, the preliminary ASP evaluations for three other events which occurred on the Oconee units. Your comments on these events were provided by your letters of March 10 and June 24, 1993.

Your review and comment on the analysis of this additional event would be appreciated. In particular, comments on the characterizations of possible plant response given the event occurrence are sought. We are also interested in comments concerning whether the individual analyses reasonably represent plant safety equipment configurations and capabilities which existed at the time of the events. Lastly, comments on the analyst's assumptions regarding equipment recovery probabilities are also sought.

As discussed with Mr. Mark Patrick of your staff, we are requesting that your comments be provided by August 27, 1993. We will review your.comments and revise the final ASP analyses as appropriate. If you have questions regarding this matter, contact me at (301) 504-1495.

This requirement affects fewer than ten respondents, and therefore, it is not subject to Office of Management and Budget review under P.L.96-511.

Sincerely, Leonard A./sWiens, Project Manager Project Directorate 11-3 Division of Reactor Projects -

I/II Office of Nuclear Reactor Regulation

Enclosure:

Preliminary ASP Analysis cc w/encl sure:

See next page LA:PDII

-3 D.

I Ber y PLW ens/cdw D atthews IAL RECORD CO/

3

'93 DOCUMENT NAME: G:\\OCONEE\\ASPLTR 9308200166 930803 PDR ADOCK,05000269 s

PDR SjFo

tgREGu UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 August 3, 1993 Docket Nos. 50-269, 50-270 and 50-287 Mr. J. W. Hampton Vice President, Oconee Site Duke Power Company P. 0. Box 1439 Seneca, South Carolina 29679

SUBJECT:

PRELIMINARY ACCIDENT SEQUENCE PRECURSOR (ASP) ANALYSIS FOR AN OCONEE EVENT Enclosed is a preliminary ASP evaluation for an Oconee event which occurred in December 1992. The event was the inoperability of emergency power from the Keowee hydrostation due to potential reduced DC voltages during loss of power scenarios. We previously provided, for your information and comment, the preliminary ASP evaluations for three other events which occurred on the Oconee units. Your comments on these events were provided by your letters of March 10 and June 24, 1993.

Your review and comment on the analysis of this additional event would be appreciated. In particular, comments on the characterizations of possible plant response given the event occurrence are sought. We are also interested in comments concerning whether the individual analyses reasonably represent plant safety equipment configurations and capabilities which existed at the time of the events. Lastly, comments on the analyst's assumptions regarding equipment recovery probabilities are also sought.

As discussed with Mr. Mark Patrick of your staff, we are requesting that your comments be provided by August 27, 1993. We will review your comments and revise the final ASP analyses as appropriate. If you have questions regarding this matter, contact me at (301) 504-1495.

This requirement affects fewer than ten respondents, and therefore, it is not subject to Office of Management and Budget review under P.L.96-511.

Si cerely, Leonard A. Wiens, Project Manager Project Directorate 11-3 Division of Reactor Projects -

I/II Office of Nuclear Reactor Regulation

Enclosure:

Preliminary ASP Analysis cc w/enclosure: See next page

Mr. J. W. Hampton Duke Power Company Oconee Nuclear Station cc:

Mr. A. V. Carr, Esquire Mr. M. E. Patrick Duke Power Company Compliance 422 South Church Street Duke Power Company Charlotte, North Carolina 28242-0001 Oconee Nuclear Site P. 0. Box 1439 J. Michael McGarry, III, Esquire Seneca, South Carolina 29679 Winston and Strawn 1400 L Street, NW.

Mr. Alan R. Herdt, Chief Washington, DC 20005 Project Branch #3 U. S. Nuclear Regulatory Commission Mr. Robert B. Borsum 101 Marietta Street, NW. Suite 2900 Babcock & Wilcox Atlanta, Georgia 30323 Nuclear Power Division Suite 525 Ms. Karen E. Long 1700 Rockville Pike Assistant Attorney General Rockville, Maryland 20852 North Carolina Department of Justice Manager, LIS P. 0. Box 629 NUS Corporation Raleigh, North Carolina 27602 2650 McCormick Drive, 3rd Floor Clearwater, Florida 34619-1035 Mr. G. A. Copp Licensing -

ECO50O Senior Resident Inspector Duke Power Company U. S. Nuclear Regulatory Commission P. 0. Box 1006 Route 2, Box 610 Charlotte, North Carolina 28201-1006 Seneca, South Carolina 29678 Regional Administrator, Region II U. S. Nuclear Regulatory Commission 101 Marietta Street, NW. Suite 2900 Atlanta, Georgia 30323 Mr. Heyward G. Shealy, Chief Bureau of Radiological Health South Carolina Department of Health and Environmental Control 2600 Bull Street Columbia, South Carolina 29201 Office of Intergovernmental Relations 116 West Jones Street Raleigh, North Carolina 27603 County Supervisor of Oconee County Walhalla, South Carolina 29621

PRELIMINARY 0.1 LER Number 269/92-018 Event

Description:

Emergency Power Unavailable Date of Event:

December 2, 1992 Plant:

Oconee 1, 2, and 3 0.1.1 Summary With all three Oconee units at 100% power, both emergency power sources, Keowee Hydro Units I and 2 (Keowee I and 2), were determined to be inoperable.

Implementation of a modification to the anti-pump relays in the Westinghouse-type DB breakers at Keowee did not consider the reduced control circuit DC voltage which would exist following a loss of offsite power (LOOP), when the battery chargers are not supplying the DC buses. During emergency start testing six days after the modification was complete (which simulated a LOOP), Keowee breakers did not close when required. Both Keowee units were unavailable for 15 d. The conditional core damage probability estimated for this event is 3.1 x 10'. The relative significance of this event compared to other postulated events at Oconee is shown in Fig. 1.

IER 269/92-018 1E-7 1E-6 1E-1E-4 1E-3 1E-2 I

I IDFW + 1I MRE

-360k EFW

• clades potefnial us of frustrnWr CT-5 for VIey Fig. 1.

Relative event significance of LER 269/92-018 compared with other potential events at Oconee.

0.1.2 Event Description On January 29, 1992, Keowee 2 failed to start during a routine attempt to supply power to the grid. The failure to start was caused by a mechanical failure of the "X" relay (anti-pump relay) in a Westinghouse LER NO: 269/92-018 1

PRELIMINARY

PRELIMINARY type DB circuit breaker. Corrective actions included the replacement of the existing electromechanical anti-pump scheme with an electrical anti-pump scheme in a number of breakers.

During the design review prior to the modification, Westinghouse expressed a concern that the closing coil could be damaged if it remained energized for too long a period of time. Because of this concern, each DB breaker was individually time-tested before and after the modification to ensure that the new anti-pump scheme would maintain the closing coil energized for the same time as the old anti-pump scheme. The modification was completed for Keowee 1 on July 19, 1992 and for Keowee 2 on November 18, 1992.

On November 24, 1992, the annual Keowee emergency start test was performed for both units. This test differed from the post-modification testing described above in that a loss of auxiliary AC power was also simulated. With no output from the battery charger because of the unavailability of auxiliary AC power, DC voltage (supplied only by the battery) was lower than during the post-modification testing. While attempting to tie Keowee 2 to the overhead path (one of the two power paths from Keowee to Oconee),

the Keowee 2 auxiliary power alternate feeder breaker (ACB-8) could not be closed after the normal feeder breaker (ACB-6) was opened. The auxiliaries for both units were placed in a dedicated alignment which would not require breaker operation during an emergency, pending further breaker testing.

On December 1, 1992, voltage regulator problems required Keowee 1 to be shut down and declared inoperable. Testing later in the day demonstrated that Keowee I auxiliary power alternate feeder breaker (ACB-7) failed to close at low DC voltages.

On December 2, 1992, the standby buses were energized from a Lee gas turbine as a precaution, since Keowee I was inoperable and the breaker problem had the potential for affecting Keowee 2. At 1605 hours0.0186 days <br />0.446 hours <br />0.00265 weeks <br />6.107025e-4 months <br />, Keowee 2 locked out due to an indicated ground fault during operability testing. At about the same time, testing of the control circuitry for the DB circuit breakers was completed. This testing indicated that the available DC voltage was inadequate to ensure closure of the breakers. Keowee 2 was declared inoperable.

The utility stated that, under reduced DC voltage situations, the closing mechanism moves more slowly, and therefore has less momentum. This reduced momentum is inadequate to complete the breaker travel.

In addition to the auxiliary power breakers, the problem affected the field and field supply breakers, which made both units inoperable. The problem was corrected by increasing the time that the closing coils were energized.

A faulty voltage error card in the Keowee I voltage regulator was found and replaced on December 2, 1992.

Keowee I was restored to an operable status at 0835 on December 3, 1992, following the modification to increase the time that the DB breaker closing coils are energized. (Also on December 3, 1992, and prior to returning either Keowee unit to operable status, Oconee I was taken off line in preparation for a scheduled refueling outage.)

On December 4, 1992, modifications to increase the time that the Keowee 2 closing coils are energized were completed. The cause of the Keowee 2 lockout (a short circuit that occurred during an inspection that was unrelated to the closing coil problems described herein) was also found, and Keowee 2 was returned to service just before midnight.

LER NO: 269/92-018 2

PRELIMINARY

PRELIMINARY 0.1.3 Additional Event-Related Information The Keowee Station is located approximately three-fourths of a mile east-northeast of the Oconee Nuclear Station. It consists of two hydroelectric generators rated at 87,500 kVA each, which generate at 13.8-kV.

The two units serve the dual functions of generating commercial power to the Duke Power system grid through the Oconee 230-kV switchyard and providing emergency power to the Oconee Station. When a Keowee unit is generating to the grid and an emergency start occurs, it is separated from the 230-kV switchyard and continues to run in standby until needed.

Upon loss of power from an Oconee generating unit and 230-kV switchyard, power is supplied from both Keowee units through two separate and independent paths. One path is a 4000 ft underground 13.8-kV cable feeder to transformer CT-4 which supplies power to the 4160 V standby buses. The underground power path is connected at all times to one hydro unit on a predetermined basis through locked-closed breakers. The underground power path and associated transformer are sized to carry full engineered safeguards auxiliaries of one Oconee unit plus auxiliaries for safe shutdown of the other two units. If a Keowee unit is to provide power to an Oconee unit through the underground power path (required by Technical Specifications if one of the Keowee units is out of service), then due to the limited capacity of CT-4, loadshed of non-essential loads occurs. The second path from Keowee is a 230-kV transmission line through breakers ACB-1 or ACB-2, via the Yellow Bus, to each Oconee unit's startup transformer.

Keowee auxiliary power is required for the AC hydraulic oil pumps, along with other loads. These pumps are used to pressurize the air pre-loaded accumulators that provide hydraulic oil pressure to the governor which controls the position (depending on load) of the wicket gates on the Keowee water turbine. The length of time that the Keowee units can run without AC auxiliaries is limited by the changing load for which the governor must respond. The utility has indicated in several LERs that one hour is the expected maximum time period of Keowee operation without AC auxiliaries.

A Standby Shutdown Facility (SSF) is located in a separate building on the Oconee site. This facility, which is not normally manned, is capable of providing limited high-pressure injection for reactor coolant system makeup and reactor coolant pump (RCP) seal cooling (provided an RCP seal LOCA does not occur) and limited steam generator makeup. The facility includes a separate diesel generator which can power SSF loads in the event of a station blackout.

SSF systems consist of single trains, and are therefore not single-failure-proof.

A more detailed description of the Oconee emergency power system is included in the precursor analysis for LER 270/92-004, "Loss of offsite power with failed emergency power."

0.1.4 Modeling Assumptions The event has been modeled as a postulated LOOP from the time both Keowee units became unavailable (November 18, 1992) until the standby buses were energized from the Lee gas turbine (December 2, 1992), approximately 360 h. A probability of 0.34 (ASP Recovery Class R2) was assumed for failure to recover a Keowee unit in the short term.

LER NO: 269/92-018 3

PRELIMINARY

PRELIMINARY Two calculations were performed: one to address postulated plant-centered LOOPs, and another to address other postulated LOOPs (grid-and severe weather-related). The frequency of LOOP and the probability of not recovering offsite power was estimated as described in ORNL/NRC/LTR-89/1 1, Revised LOOP Recovery and PWR Seal LOCA Models, August 1989.

During a postulated plant-centered LOOP, the Central Switchyard was assumed to be available as an alternate source of emergency power. A probability of 0.12 (ASP Recovery Class R3) was assumed for failing to recover emergency power in the short-term from the Central Switchyard via transformer CT-5. The use of CT-5 is described in the Oconee procedures, but the need for manual load shedding is not addressed.

During a postulated grid-or severe weather-related LOOP, the Central Switchyard was assumed to be unavailable. AC power was assumed to be recoverable in - 1 h using the Lee combustion turbines.

For this analysis, a probability of 0.12 was assumed for failing to recover AC power in the long term (prior to battery depletion). No short-term emergency power recovery was assumed to be possible via CT-5.

The frequency and probability values used in the calculations follow:

Plant-Centered LOOP Other LOOPs LOOP frequency 1.3 x 10^/hr 2.8 x 104/hr PNREC (LOOP) 0.15 0.66 PNREC (Emerg Power) 0.34

• 0.12 0.34 PNREC (AC power prior to battery 0.25 0.74

• 0.12 depletion)

The results of these calculations were combined to yield an overall core damage probability estimate for the event:

p(core damage) =

Loop

• duration * [p(core damage I plant-centered LOOP and emergency power failed) - p(core damage I plant-centered LOOP)] + X& wo.

• duration * [p(core damage I other LOOPs and emergency power failed) - p(core damage I other LOOPs)].

0.1.5 Analysis Results The conditional core damage probability estimated for the event is 3.1 X 10". This conditional probability is applicable to each of the three Oconee units. The dominant core damage sequence, highlighted on the event tree in Fig. 2, involves a postulated LOOP with failure of emergency power, and failure to recover AC power before battery depletion.

The conditional probability estimate is strongly influenced by assumptions concerning the potential for recovery of the Keowee units and the likelihood of providing power from the Lee gas turbines or the Central Switchyard via transformer CT-5. It is also possible that the breakers may have operated at some battery voltages which could exist following a LOOP. In this case, the above analysis is conservative.

LER NO: 269/92-018 4

PRELIMINARY

PRELIMINARY IRT PR/PR/PV LOOP L

EP AFW S

SEAL EPREC HPI HPR SEO END CHA(

REEAT OCA (LONG)

NO STATE OK OK 41 CO 42 CO OK OK 43 CO 44 CD 45 CD OK 46 CD 47 Co 48 CD OK 49 CD 50 CD OK 51 CD 52 CD 53 CD OK 54 CD 55 CD 40 ATWS Fig. 2.

Dominant core damage sequences for LER 269/92-018.

The use of the SSF as an alternate source of RCS and steam generator makeup for the station blackout scenarios was not considered in the above analysis. This was done for consistency with other precursor analyses. Assuming a combined operator and equipment failure probability of 0.2 for the SSF results in a revised conditional probability estimate of 6.2 x 10'.

LER NO: 269/92-018 5

PRELIMINARY

PRELIMINARY CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier:

269/92-018 Event

Description:

Emergency power unavail (plant cent LOOP, EP failed)

Event Date:

12/02/92 Plant:

Oconee 1 INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP 1.5E-01 SEQUENCE CONDITIONAL PROBABILITY SL4S End State/Initiator Probability CD LOOP 1.6E-03 Total 1.6E-03 ATWS LOOP 0.OE+0C Total O.OE+00 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)

Sequence End State Prob N Rec**

54 LOOP -rt/oop EMERG.POWER *afw/emerg.power -porv.or.srv.chatt -

CD 1.4E-03 6.1E-03 seat.loca EP.REC 49 LOOP -rt/loop EMERG.POWER -afu/emerg.power porv.or.srv.chatt -

CD 1.2E-04 6.1E-03 pory.or.srv.reseat/emerg.power -seal.loca EP.REC 55 LOOP -rt/loop EMERG.POWER afw/emerg.power CD 1.DE-04 2.1E-03

• • non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)

Sequence End State Prob N Rec**

49 LOOP -rt/loop EMERG.POWER -afu/emerg.power porv.or.srv.chatl -

CD 1.2E-04

6. E-03 porv.or.srv.reseat/emerg.power -seat.loca EP.REC 54 LOOP *rt/Loop EMERG.POWER -afu/emerg.power -poev.or.srv.chaLt

• CD 1.4E-03 6.1E*03 seat.loca EP.REC 55 LOOP -rt/loop EMERG.POWER afw/emerg.power t.0E-04 2.1E-03

• • non-recovery credit for edited case SEQUENCE MODEL:

c:\\asp\\19891purdseat.cep BRANCH MODEL:

c:\\aspl19891oconeel.s(T PROBABILITY FILE:

c1ssp\\1989\\pr tbs1.pro No Recovery Lieft BRANCH FREQUENCIES/PROBABILITIES Event Identifier: 269/92-018 LER NO: 269/92-018 6

PRELIMINARY

PRELIMINARY Branch System Won-Recov Opr Fall trans 6.4E-05 1.DE+OO..

LOOP 1.6E-05 > 1.3E-05 2.4E-01 > 1.5E-0 Branch Mode(:

IMITOR Initiator Freq:

1.6E-05 1.3E-05 Loca 2.4E-06 4.3E-01 rt 2.&E-04 1.2E-O1 rtf loop O.OEIOO 1.GE+OO EEGPER2.5E-03

> 1.OE.OO 8.OE-O1 > 4.1E!0 Branch Model:

• • F.

Train 1 Cond Prob:

5.06-02 > Failed Train 2 Cond Prob:

5.OE-02 > Failed ONw 3.8E-04 2.6E-01 afw/emerg.power 5.OE-O12 3.4,E-01 mfw 2.GE-01 3.4E-01 pory.or.srv~chatt 8.06-02 1.06.00 porv.or.srv~reseat 1.0E-02 1.1E-02 porv..srv.s~atamerg.power 1.06-02 1.OE.00 seal.toca 0.06.00 1.06+00 ep.rec(sl) 0.06.00 1.06.00 EP.REC 4.5E-01 > 2.5E-01 1.06.00

&ranchi Model:

1.0F.1 Train I Cond Prob:

4.5E-01 >.5E-01 hpi 3.06-04 8.4,E-01 hpi~f/b) 3.06-04 8./+E-01 I.O0E-02 hpr/-hpi 1.5E-0.4 1.06.00 1.06-03

• branch model file.

forced Event Identifier: 269/92-018 LER NO: 269/92-018 7

PRELIMINARY

PRELIMINARY CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier: 269/92-018 Event

Description:

Emergency power avait (plant cent LOOP,. base case)

Event Date:

12/02/92 Plant:

Oconeel..

INITIATING EVENT MO-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP1.E0 SEQUENCE CONDITIONAL PROBABILITY SLIS End State/Initiator Probability CD LOOP 7.9E-05 Total 7.9E-05 ATIJS LOOP 0.OE +OO Total 0.OE.0G SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)

Sequence End State

.Prob W Rec*

54 LOOP -rt/toop emerg.power -afwlemero.power -porv.or.arv.chatt CD 6.8E-05 t.ZE-01 sealt.oca EP.REC 49 LOOP -rt/loop emerg.power -afwl/imerg.power porv.or.rychalL CD 5.8E-06 1.2E-01 porv.or.arv. reseatlemer;.power -seat loca EP.REC 55 LOOP -rt/Loop emerg.pawer afw/euaerg.power CD 5.1E-06 4.1E-02 n n-recovery credit f or edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)

Sequence End State Prob N Rec**

49 LOOP -rt/loop emerg.power -afv/emerg.po4.er porv.or.srv.chalL CD 5.8E-06 1.2E-01 pv.or.srv.resotemer.power -seat.toca EP.REC 54 LOOP -rt/toop emerg.power -afw/emerg.power -pory.or.srv.chatt Co 6.BE-05 1.2E-01 seal.toca E.E 55 LOOP -rt/loop emerg.power afw/emerg.power CDS.1-06 4.1E-02

-~non-recovery cred~it for edited cae SEQUENCE NWEL:

c I:\\ap0989\\pwtdseel.cmp BRANCH MODEL:--

c.\\sp1989\\ocne*.t.st1 PROBABILITY FtLEt t*\\sp\\1989\\pwrbst1.pr*

No Recovery Liat BRANCH.REQUENCIES/PROKBI~LITrE.

Event Identifier: 269/92-018 LER NO: 269/92-018 8

PRELIINARY

PRELIMINARY Branch System Kort-Recov Opr Fail trams 6.4E-05 1.OE+00 LOOP 1.6E-05 >1.3E-05 2.4,E-01 > 1.5E-0 granch Model:

IIJTOR Initiator Freq:

1.6E-05 > 1.3E-05 toc-a 2.4E-06 4i.3E-01 rt 2.8E-04 1.2E-01 rtftoop O.0E400 1.0E400 emerg.power 2.5E-03 8.OE-OI afhd 3.8E-04 2.6E-01 afw/emergpowe.-

5.OE-02 3.4E-01 mfw 2.OE-O1 3.4E-01 porv.otr.srv.catt 8.OE-OZ 1.OE+0O porv.or.srv.reseat 1.OE-02

.1E-02 porv.or.arv. reseat/ererg~oe

.E0

.E0 seal.1ocH O.GE400 I.GE+OO ep.rec(st)

O.0E4'OO 1.OE'OO EP.REC 4.5E-01 > 2.5E-01 1.DE+00 Branch #ode(:

1.OF.1 Train 1 Cond Prob:

4.5E-01 > 2.5E-01 hpi 3.08-04 8.48E-01 hpi~f/b) 3.OE-04 8.4E-01 1.08-02 hpr/-hpi 1.5E-04 1.08.00 1.08-03

• branch model file forced Event Identifier: 269/92-018.

LER O: 29/92-018 9

PRELEMNARY

PRELIMINARY CONDITIONAL CORE DAMAGE PROBABILITY CALCULATIONS Event Identifier* 269/92-018 Event

Description:

Emergency power taiavait (other LOOPs, EP fail ed)

Event Date:

12/02192 Plant:

Oconee 1 INITIATING EVENT NO-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP 6.6E-01 SEQUENCE CONDITIONAL PROBABILITY SUIMS End State/Initiator Probability CD LOOP 2.*.

.4E-02 Total 2.4E-02 ATIJS LOOP O.OE+00 Totsl O.OE.OG SEQUENCE CONDITIONAL PIROBAB1LITIES (PROBABILITYODR Sequence End State Prob N Rec**

54 LOOP -rt/toop EKERG.POE

-afw/.ewra~power -pwo.or.arv.chatt CD I.SE-O2 2.2E-01 seal.toca EP.REC 55 LOOP -rt/loop ENERG.POWER afwlemerg.po.er CD 3.8e-03 7.6E-02 49 LOOP -rt/toop EMERG.POWER -afw/emrg.power porv.or.srv.chatL -

CD 1.6E-03 2.2E-01 parv. or. srv. reseatfemerg.power -seatl toca EP. REC non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)

Sequience End State Prob N Rec**

49 LOOP -rt/Ioop ENERG.POIWER -afw/einerg.power porv.or.srv.diall CD 1.6E-03 2.2E-0t porv.or.srv.rese~atemerg.powder -seat.tc. EP.fEC 54 LOOP -rt/Loop, ENERG.POIIER -afi./eegpwr-ovosvch1.

C SE0 22-1 seet.tca aEP.REC................r~iaL-C....18-2 LEO 55 LOOP -rt/Loop, EMERG.POWER afw/emer.powier-CD3.-03 7.6e-02

'n rn-recovery credit for edited case SE@JUCE MODEL:

c:\\asp1989\\pmrdseaL.cP BRANCH MODEL:

c:\\aap\\1989\\oconeet.at1 PROBABILITY, FILW.

ctasp\\1989\\.pwrbs1.pro No Recovery Limt BRACH FREQUENCIESPROABILITIE Event Identifier: 269/92-018 LER NO: 269/924018 10 PRELIMINARY

PRELIMINARY B ranch System Non-Recov Opr Fall trans 6.4E-05 1.OEOO LOOP 1.6E-05 > Z.8E-06 2.4E-01 > 6.6E-0 Branch Model:

INITOR Initiator Freq:

1.6E-05S 2.8E-06 Loca 2.4.E-06 4.3E-01 rt 2.8E-04 1.2E-01 rtfloop O.OEeOO0 1.OE40 ENEUG.POWER 2.5E-03 >.OE+OO B.OE-O1 >.E0 Branch Model:

1.OF.2..

Train 1 Cond Prob:

5.OE-OZ > Failed Train 2 Cond Prob.

5-OE-02 Fale afe 3.8E-04...:>.>

2.6E-01 afw/emerg.power 5.OE-02 3.4,E-01 mfw 2.OE-01 3.4E-01 porv.or.arv.chall 8.OE-02 1.OE+OO porv.or.srv.reseat 1.OE*02 1.1E-02 Porv.or.srv.resoatemerg.power 1.DE-02 1.0E4OO sest.toca O.OE+OO 1.OE+0O ep.rec(st)

O.OE+OO 1.OE+0O EP.REC 4.5E-01 > 8.9E-02 1.OE+0O.

Oraech Model:

1.OF.1 Train I Cond Prob:

4.5E-01 >8.9E-02 hpl 3.OE*O4 8.4E-01 hpi(f/b) 3.OE-04 8.AE-01 1.GE-OZ hpr/-hpi 1.5E-04 1.GE.OO 1.OE-03

• branch model file forced Event Identifier: 269/92-018 LER NO: 269/92-018 11 PRELIMINARY

PRELIMINARY CONDITIONAL CORE DAM4AGE PROBABILITY CALCULATIONS Event Identifier:

269/92-018 Event

Description:

Emergency power unayalit (other LOOPs, base ease)

Event Date:

12/02/92 Plant*

Oconee 1.

INITIATING EVENT NON-RECOVERABLE INITIATING EVENT PROBABILITIES LOOP 6.6E-01 SEQUENCE CONDITIONAL PROBABILITY SL1S End State/Initiator Probability CD LOOP 1.4E-04..

Total 1.4E-04 ATVS LOOP

.E0 Total

.E0 SEQUENCE CONDITIONAL PROBABILITIES (PROBABILITY ORDER)

Sequence End State Prob NI Rec" 54 LOOP -rt/toop emerg.poweie -afw/emerg.power -porvor.arv.chatt CD 1.1E-04 S.ZE-O seatltoca EP.REC 55 LOOP -rt/Loop emerg.power afwlemerg.power CD 2.2E-05

.1.&E-01 49 LOOP -rt/Loop emerg.power -afwfemerg.power porv.or.srv.chatL -

CD M.E-06 5.2E-01 porv.or. srv. reseatfemerg.power -seat. toca EP.REC non-recovery credit for edited case SEQUENCE CONDITIONAL PROBABILITIES (SEQUENCE ORDER)

Sequence End State Prob N Rec**

49 LOOP -rt/Loop emerg.power -afwlierg.power pory.or.trv.chati CD M.E-06 5.2E-01

.or.or.

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~'forced Event Identifier: 269192-018 LER NO: 269/92-018 13 PRELIMEINARY

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1PAGE 13 FAILITY NAME 11 05000 269 1 OF 9

Oconee Nuclear Station, Unit 1 TITLEi41 Design Deficiency Results In The Inoperability of Oconee Emerreflcv Electrical Pover Source-_______

EVENT DATE f5)

LER NUMBER (61 1 REPORT NUMBER 7c OTHER FACILITIES INVOLVED 81 CA..f NAME DOCKET NUMBER

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TO COMPLY Wirh THIS INFORMATION COLECTION REQUEST:

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COMMENTS REGAR0 BURDEN ESTIMATE TO rME 0FORMATION AND RECORDS MANAGEMENT UOANCM ANGS 7'IJI Uj.S. NUCLEAR TEXT CONTINUATIIN REGULATORY COMMISSION.oWASuoGTON. oC 2c5500.

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BACKGROUND The Keowee Emergency Power System [EIIS:EK) consists of two hydroelectric generators which provide an emergency onsite power source for the Oconee Nuclear Station via two separate and independent paths, one of which is the underground feeder through transformer CT4 and the standby buses [EIIS:EB and the second is the overhead path through the 230 KV switchyard

[EIIS:FKI.

One unit is required to be connected to the underground path at all times.

Each Keowee Hydro (KH) Unit is provided with a separate 125V DC Power System consisting of one battery and charger, which is powered from the lX or 2X load centers.

On a loss of power to the charger. the battery will supply loads necessary for unit starting. The loads on the DC system include the Generator Field and Supply Breakers, which are required to operate on an emergency start.

Each KH Unit is provided with its own automatic start equipment.

Both units undergo a simultaneous automatic start and run in standby on a loss of the grid. an engineered safeguards actuation on any of the three Oconee Units, or an extended loss of voltage on any unit's main feeder buses.

On an emergency automatic startup, the unit connected to the underground feeder supplies that path while the other unit, remaining in standby, is available to supply the overhead transmission line. If there is a grid disturbance, this unit is automatically connected to the Oconee 230 KV switchyard yellow bus only after the yellow bus is automatically isolated from the grid. Therefore, in the event of a Loss of Coolant Accident and the simultaneous loss or degradation of the grid, emergency power is available from either Keowee Unit through the underground feeder and/or the overhead transmission line.

The field, supply. and field flashing breakers are closed to provide DC to the field, which will allow the generator to produce electricity. The "X" relays are the anti-pump relays used in Westinghouse type DB breakers. The anti-pump circuitry prevents the breaker from cycling back and forth between closed and tripped when a close and trip signal are both present.

The "X" relay is operated by a coil which is energized on the close signal.

if power to the Oconee units is not available from the grid or the KH units. power can be made available to the standby power buses from the Central Switchyard or one of the Lee Steam Station Combustion turbines (CT).

The power is provided through a 100 Ky transmission line from the Lee CT's via the Central switchyard to Oconee's CT-5 transformer. if an emergency occurs that would require the use of this 100 KV line it can be isolated from the balance of the transmission system in order to supply

NRC 0~M366 U.. NULEA REULAORY OMMSSIN V APPROVED BY 0MIB NO. 3150-0104 SFO2:

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FACILITY NAME fiI DOCKET NUMBER I2t LEn NUMBER I)

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YERSEQUENTIA.

IREVSCoN YEAR NUMBER NUMBER Oconee Nuclear Station, Unit 1 05000 269 9

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power to Oconee. One of the Lee CT's can be started and supply power within one hour.

Technical Specification (TS) 3.7.2 allows one Keowee unit to be out of service for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> provided the other unit is verified to be operable within one hour. This is verified by starting the Keowee Unit and energizing the standby power bus.

TS 3.7.3 requires that if certain conditions are not met within the time specified in TS 3.7.2, except as noted in TS 3.7.4 and 3.7.7, the reactor shall be placed in a hot shutdown condition within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. If these requirements are not met within an additional 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />, the reactor shall be placed in the cold shutdown condition within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

TS 3.7.4 allows Oconee unit operation for an additional 45 days (beyond the 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> provided for in TS 3.7.2) with one KH Unit unavailable, under certain conditions.

TS 3.7.7 requires that if both Keowee units become unavailable for unplanned reasons, the reactor shall be permitted to remain critical for periods not to exceed 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> provided the 4160 volt standby buses are energized within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> by the Lee gas turbine through the 100 KV transmission circuit and it shall be separate from the system grid and all offsite non-safety related loads.

EVENT DESCRIPTION On January 29, 1992 at 2104 hours0.0244 days <br />0.584 hours <br />0.00348 weeks <br />8.00572e-4 months <br />, Keowee Hydro (KH) Unit 2 failed to start during a routine attempt to supply power to the grid. The failure of KH Unit 2 to start was caused by a mechanical failure of the "X" relay. This event was reported in LER 269/92-02. Corrective actions included a Nuclear Station Modification (NSM) 52917, which replaced the existing electromechanical anti-pump scheme with an electrical anti-pump scheme.

The design process of the modification included a review by Westinghouse.

Westinghouse identified a concern with keeping the closing coil energized too long, potentially damaging the coil.

They did not have a concern with maintaining the coil energized long enough to ensure breaker closure. As a result of Westinghouse's concern every DB breaker was individually time tested before and after the modification to ensure the new anti-pump scheme would maintain the closing coil energized as long as the old anti-pump scheme.

This was documented in the calculations.

The NSM for KH Unit 1 was completed and tested successfully on July 19, 1992. The NSM for KH Unit 2 was completed and successfully tested on November 18, 1992.

IC

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OFFICE OF MANAGEMENT AND BUDGET. WASMINGTON. DC 2003.

FA d" N A M E st III DO C K T N U M S ER 021 LEYE AER4 1PA 9 3 SF UENTtA..

EV1Siot' YEARE NUMBIER 05000 269 04 OF 09 Oconee Nuclear Station, Unit 192-18 00 TE (I mI.ore soe a

eawem as seawerw coes or MAC Faem eemJ (17)

On November 24, 1992, the annual KH Emergency start test was being performed for both KH units. One feature of this test, which differed from the post modification testing performed earlier, was that it assumed and simulated, a loss of auxiliary AC power as part of the emergency condition.

Therefore, the DC battery charger was not assisting the battery during the test. While attempting to tie KM Unit 2 to the overhead power path, it was discovered that after opening the KM Unit 2 Auxiliary Power Normal Feeder Breaker (ACB-6), the KM Unit 2 Auxiliary Power Alternate Feeder Breaker (ACB-8) could not be manually closed.

Engineering Supervisor A suspected this failure was due to a voltage problem in ACB-8's closing coil. The problem was attributed to a possible wiring or connection problem. since the breaker closed in the test position after failing in the operate position.

Both KM Units auxiliaries were placed in a dedicated alignment so they would be available if they were needed during an emergency, since they were already in their closed position. Under this alignment the suspect circuit would not have been challenged during a Design Basis Event.

It was decided that further testing would be performed.

At 1201 hours0.0139 days <br />0.334 hours <br />0.00199 weeks <br />4.569805e-4 months <br /> on December 1, 1992, KM Unit 2.

was generating to the grid when voltage swings and a loss of field alarm occurred due to problems with a voltage regulator.

KM Unit 1 was shutdown manually and declared inoperable.

An investigation was initiated to find the cause. A 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> Limiting Condition for Operation (LCO) was entered under Technical Specification (TS) 3.7.2 and KM Unit 2 was operability tested within one hour and subsequently every eight hours as required by TS.

Since KM Unit 1 was inoperable, no testing of breakers could be performed on KM Unit 2 at this time.

Later that day TM Station's spare breakers and KM Unit l's Auxiliary Power Alternate Feeder Breaker (ACB-7) were tested and a potential problem was identified. This testing showed that KH Unit l's ACB-7 failed to close at low voltages. The results of the testing raised a question about-the test equipments accuracy and speed. since ACB-7 had been known to close at lower voltages than those measured during the test.

It was determined that high speed measuring equipment would be required to adequately test the breakers. This equipment was located of f site and would be on-site the next day.

Also during this period of time, the investigation into Unit l's voltage regulator problem continued.

At approximately 1000 hours0.0116 days <br />0.278 hours <br />0.00165 weeks <br />3.805e-4 months <br /> on December 2, 1992. Engineering Supervisor A met with the NRC Resident and Station Management during a routine weekly meeting to discuss the status of problems at Keowee. During this meeting he notified them of the possibility of breaker problems and the need to do further testing.

After this meeting, Station Management decided to take

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FACILIT NAME #I I

DOCKET NUMBER (21 j

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REVISr, 05100 2 9NUMBER NUMBER 05000 2-05 OF09 Oconee Nuclear Station, Unit 1 92 2918 00 09 TEXT t mwe sene ae e

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of MRC FoM a" (117) further compensatory actions by energizing the Standby Buses from a Lee Gas Turbine. This action was taken as a precautioIn, due to the fact that KH Unit 1 was already inoperable and the breaker problem had the potential for affecting KH Unit 2.

At 1605 hours0.0186 days <br />0.446 hours <br />0.00265 weeks <br />6.107025e-4 months <br /> on December 2, 1992 with KH Unit 1 already inoperable, KH Unit 2 locked out due to an indicated generator ground fault during operability testing as required by TS 3.7.2. !An investigation was initiated into the generator ground fault. At approximately this same time testing of the control circuitry for DB-50 breakers utilizing the high speed measuring equipment was completed. Test results indicated that available DC voltage may be inadequate to close the breakers. At this time KH Unit 2 was declared inoperable due to inadequate DC voltage to close the DB-50 breakers. This affected the field and field supply breakers which made the Unit inoperable. At this time, all three Oconee Units were placed in a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> LCO under TS 3.7.7.

An investigation revealed that with reduced DC voltages the closing mechanism moves slower, therefore has less momentum. Under reduced voltage situations the close coil becomes deenergized in the travel such that the available momentum is not adequate to complete the breaker travel. To correct this problem, a Minor Modification was implemented. This modification added a time delay to increase the amount of time the closing coil is energized. This increased time compensates for the effects of decreased voltage, and ensures breaker closure.

On December 2, 1992 at approximately 2121 hours0.0245 days <br />0.589 hours <br />0.00351 weeks <br />8.070405e-4 months <br />, it was discovered that KM Unit 1's voltage regulator problem was due tola faulty voltage error card.

This was repaired but KH Unit 1 remained inoperable due to the breaker problems.

At 0129 hours0.00149 days <br />0.0358 hours <br />2.132936e-4 weeks <br />4.90845e-5 months <br /> on December 3, 1992, Oconee Unit 1's Turbine Generator was taken off line in preparation for a scheduled Refueling Outage. The reactor was shutdown, and the Unit entered cold shutdown at 2324 hours0.0269 days <br />0.646 hours <br />0.00384 weeks <br />8.84282e-4 months <br /> on December 4, 1992.

A Minor Modification was completed on KH Unit 1 and the unit was restored to an operable status at 0835 hours0.00966 days <br />0.232 hours <br />0.00138 weeks <br />3.177175e-4 months <br /> on December 3, 1992.

At this time TS 3.7.7 was exited and TS 3.7.2 was reentered with approximately 27 hours3.125e-4 days <br />0.0075 hours <br />4.464286e-5 weeks <br />1.02735e-5 months <br /> of the 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> remaining.

At 1201 hours0.0139 days <br />0.334 hours <br />0.00199 weeks <br />4.569805e-4 months <br /> on December 4, 1992, Oconee Uni ts 2 and 3 entered TS 3.7.4.d due to one unit of KH being unavailable for more than the 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> provided for in TS 3.7.2.

The NRC was notified.

During the notification it was stated that Oconee Units 2 and 3 would be considered to have been under TS I~a

_____O

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FORWARD LICESEE VEN REPRT (ER)COMMENTS REGAPDWG BURDIEN ESTIMATE TO TME INFORMATION TEXT CONTINUATION NCLA TEXT ONTINATIONAND RECORDS MANAGEMENT BRANCH luNB 714 U.S. NUCLEAR THE PAPERWORK REDUCTsON PROjECT 315"041). opCE OF MANAGEMENT ANO eUDGET. WASmINGTON. DC 2003.

FACILrf NAME (1)

DOCKET NUMBER (2)

LER NUMBER isi PAGE (31 SEQUENTtA.

REVISION NUMBER NUMBER 05000 269 06 OF 09 Oconee Nuclear Station, Unit 1 92 -

18 00 TEDT fit moe sac a reamua We secoone.cases of MAIC Form Jat (t) 3.7.3, rather than TS 3.7.4.d, if KH Unit 2 could be repaired and declared operable by 0001 hours1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> on December 5th.

A Minor Modification was completed on KH Unit 2 at approximately 1700 hours0.0197 days <br />0.472 hours <br />0.00281 weeks <br />6.4685e-4 months <br /> on December 4, 1992. The investigation into the cause of KH Unit 2's lockout continued.

At 2100 hours0.0243 days <br />0.583 hours <br />0.00347 weeks <br />7.9905e-4 months <br /> on December 4. 1992, the cause of KH Unit 2's lockout, which occurred on December 2 was discovered. As part of a corrective action for an earlier identified problem. Station Instrument and Electrical (I&E) personnel had implemented a Configuration Control Inspection. The inspection is verifying that safety related cabinets' internal wiring agrees with the as-built drawings. On December 2, at approximately 1100 hours0.0127 days <br />0.306 hours <br />0.00182 weeks <br />4.1855e-4 months <br />, I&E technicians were replacing a coverplate on the Voltage Regulator Control Cabinet as part of this inspection. Unknowingly, a screw from the coverplate had penetrated the insulation of a wire associated with the Voltage Regulator circuitry, thus creating a ground and causing the unit to lockout. The wire was replaced. An operability test was performed satisfactorily at 2300 hours0.0266 days <br />0.639 hours <br />0.0038 weeks <br />8.7515e-4 months <br />.

At 2336 hours0.027 days <br />0.649 hours <br />0.00386 weeks <br />8.88848e-4 months <br /> on December 4, 1992. KH Unit 2 was restored to operable status.

The NRC Regional Office was notified at 2348 hours0.0272 days <br />0.652 hours <br />0.00388 weeks <br />8.93414e-4 months <br /> on December 4th.

As stated in the earlier notification it was considered that Oconee Units 2 and 3 had been operating under provisions of TS 3.7.3 from 1201 hours0.0139 days <br />0.334 hours <br />0.00199 weeks <br />4.569805e-4 months <br /> until 2336 hours0.027 days <br />0.649 hours <br />0.00386 weeks <br />8.88848e-4 months <br /> when, KH Unit 2 was declared operable. TS 3.7.4 was never entered.

CONCLUSIONS A design deficiency in the anti-pump relay scheme on DB-50 breakers associated with Keowee Hydro (KH) Units 1 and 2 Supply and Field Breakers resulted in both KH Units being inoperable. This design problem also affected both KH Unit's Air Circuit Breakers (ACB) 5, 6, 7 and 8. The breaker operation is such that, upon receiving the close signal, the breaker close coil is energized through the "X" relay. As the breaker mechanism travels to the closed position, the "X" relay is deenergized before the breaker is fully closed. This removes power from the breaker's closing coil, but by then the closing mechanism has moved far enough in it's travel, allowing the breaker to travel to it's fully closed position by inertia. Under the original design the "X" relay was opened by a mechanical action associated with the breaker closing mechanism, which mechanically opened the "X" relay as it traveled to the closed position.

Under the new design, the "X" relay is opened by breaker auxiliary contacts which operate as the breaker mechanism travels to the closed position.

Time testing of the breakers was performed as part of the modification to Nac FORM S Ws-ea

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OFFCE OF MANAGEMENT AND BUOGET. WASHINGTON. CC 20503 FACILITY NAME 1)

DOCKET NUMBER f2)

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PAGE (3)

YERSEQUENTiX REVISION NUMBER NUMBER 05000 269 070F 09 Oconee Nuclear Station, Unit 1 92 18 00 TEXT (Un Ore sPace a 1ep4 we aaen Wes a NRC Fom 3

( 17) ensure the closing coil remained energized in the new design as long as it did under the original design. The results of the testing indicated that the time in which the closing coil remained energized was compatible with the original design. This appeared to indicate that as the closing coil mechanism traveled to the fully closed position, the "X" relay dropped out at relatively the same location on the closing travel range in the new and old design.

Although attempts were made to ensure that the new design allowed the close coil to remain energized to the same point in the breaker mechanism's travel as the original design did, it appears that the threshold of operability at reduced DC voltages was raised. It is not known if the same breakers would have closed with the original design under the worst case DC voltage conditions.

It is apparent that the design process did not anticipate that low control circuit voltage could prevent breaker closure.

Therefore, the root cause of this event is Design Deficiency (Unanticipated Interaction of System or Components -

Design Oversight).

A review of previous events involving KH, that have resulted from a root cause of design deficiency - unanticipated interaction of systems or components, revealed two LERs (269/92-11 and 269/92-16). Neither of these previous events involved DB-50 breakers, therefore this event is considered non-recurring.

This event did not involve actual equipment failure and therefore was not NPRDS reportable. There were no releases, radiation exposures, or injuries associated with this event.

CORRECTIVE ACTIONS Immediate

1)

Both Keowee Hydro units were declared inoperable, a Lee Gas Turbine was in operation, aligned to the standby bus and a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> Limiting Condition for Operation was entered.

Subsequent

1)

All Westinghouse DB type breakers at Keowee were modified to permit the closed coil to remain energized for a longer period to ensure breaker closure when operating with a degraded DC system voltage.

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OM8 NO. 3150.0104 TEXTIRE CONTIUATIO ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH THIS iNFORMATION COLLECTION REQUEST: S.-,( aS.

FORWARO LICENSEE EVENT REPORT (LER)

COM S REGARDING BURDEN ESTIMATE TO THE INFORMATION AND RECORDS MANAGEMENT BRANCH fuN68 77 1 i u.S. NUCLEAR IWREGULATORY CuuSSION. WASINGTON. DC 2055.0001. AND TO THE PAPERWORK REDUCTION PROJECT (5o0410d.

OFFICE OF MANAGEMENT AND BUDGET. WASMINGTON. DC 20503 FACUJTY NAME III DOCKET NUM&ER 21IV LEM NUMBER (61 PAGE 13 YEAR rSEQUENTLA.

REVISION YEA0 NUMBER NUMBER Oconee Nuclear Station, Unit 1 92 18 0

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Planned

1)

Complete the Design Basis Document for Keowee's 125 VDC Power System.

SAFETY ANALYSIS Keowee Hydro (KH) Station provides an emergency power source to Oconee Nuclear Station for scenarios which involve a Loss of Offsite Power (LOOP).

In this event, the design deficiency produced a common mode failure that could have made both KH Units and the associated emergency power paths inoperable. If both KH Units are inoperable an alternate power alignment for emergency offsite power is through the 100 KV transmission line from Lee Steam Station's gas turbines within 60 minutes. An alternate power alignment is from the Duke grid via the Central Switchyard.

Final Safety Analysis Report (FSAR) 15.8.3 addresses a simultaneous LOOP event on all three units. This analysis shows that natural circulation of the reactor coolant system (EIIS:AB]. turbine driven emergency feedwater system [EIIS:BA). condenser circulating water gravity induced flow, and gravity insertion of the control rods [EIIS:ROD] are among the design features provided to ensure the removal of decay heat for the reactor coolant system without offsite power being available. Additionally, FSAR Section 15.8.3 states that "Each reactor can sustain a complete electrical power loss without emergency cooling for about 23 minutes before the steam volume in the pressurizer is filled with reactor coolant" and that "beyond this time reactor coolant will boil off, and an additional 83 minutes will elapse before the boil off will start to uncover the core."

Therefore, the 106 minutes given in the FSAR for core uncovering is well beyond the 60 minutes required for establishing emergency power from the Lee gas turbines.

The Standby Shutdown Facility (SSF) is a separate seismically qualified building which houses the systems and components necessary to provide an alternate and independent means to achieve and maintain hot shutdown conditions for one or more of the three Oconee Units. The SSF was designed to resolve the safe shutdown requirement for fire protection, turbine building flooding, and physical security. The SSF has the capability of maintaining hot shutdown conditions on all three units for approximately three days following a loss of normal AC power.

In the event that a Loss of Coolant Accident (LOCA) occurs simultaneously with a LOOP and power cannot be restored in a reasonable period of time, the emergency core coolant flow would have been delayed beyond what was assumed in the accident analysis. FSAR 15.14.3.3.6 assumes 48 seconds for

i

-RC FCIM 366A U.S NUCLEAR REGULATORY COMMISSION APPROVED BY OM8 NO. 3150-0104 EXPIRES 5/31/95 ESTIMATED BURDEN PER

RESPONSE

TC COMPLY wi1 THIS INFORMATION COuECTION REQuEST 5C.0 MS FORWARD LICENSEE EVENT REPORT (LER)

COMMENTS REGARDING BURDEN ESTIMATE TO TE INFORMATION AND RECORDS MANAGEMENT BRANCM #MNGB T7141. U.S. NuCLEAA TEXT CONTINUATION ouRAnWY COMMsSN wasMONC 2050so. ANo TO THE PAPERWORK REDUCTION POJEC' si10aiadi. OFFICE OF MANAGEMENT AND BUDGET. WASMtNGTON. DC 20503.

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the loss of Transformer CT4.

If this happens, fuel damage could occur whichwilst rsulth i aadioac e

a ethe containment building.

The SARstaes hatwithut eacor uilingSpray [EIIS:BE] and Reactor BuildinCoo Sytemsr [ES:

be ueiactor lding pressure would not exced he esin pessre or he ontinmntfollowing the LOCA.

Given the 0 mnut tie fame o rstoe pwer itis expected that the reactor n

nt wod ntr p te analysis rate, but dose rates may be higher due to a loss of filtered ventilation until power is

e.

gA tn contament oespons evaluation has shown that equimen qulifcaton ondtios wuldnotbe exceeded in under two hours for the expected temperature and pressure resulting from this event.

Therefore, reactor building equipment would be operable when unit power is restored.

This event did not lead to the release of radioactive material, exposure to radiation, or personnel injury. It did not compromise the health and safety of the public.