ML20099F387
| ML20099F387 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 08/06/1992 |
| From: | Danni Smith PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9208130019 | |
| Download: ML20099F387 (15) | |
Text
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I PHILADELPHIA ELECTRIC COMPANY NUCLEAR GROUP HEADQUARTERS 955-65 CHESTERGROOK BLVD.
W/.YNE, PA 19087 5691 August 6, 1992
)
D. M. 5MITH
)
c: mon vice enssisent wuetsan Docket Nos. 50-277 50-278 License Nos. DPR-44 DPR-56
[
U.S. Nuclear Regulatory Commission Attnt Document Control Desk
. Washington, DC 20555
SUBJECT:
Peach Bottom Atomic Power-Station, Units 2 and 3 Station Blackout Response to NRC Quertions Concerning the Use of the conowingo Hydroelectric Power Station
.as the Alternate AC Power Source
REFERENCES:
(1) Letter from D.
R. Helwig (PECo) to NRC dated April 24, 1991 (2) Letter from J. W.
Shea (NRC) to G. J. Beck (PECo) dated January 28, 1992 (3) Letter from G.
J. Beck (PECo) to NRC dated April 1, 1992 (4) Letter from C. L. Miller (NRC) to D. M. Smith (PECo) dated June 23, 1992 (5) Letter from G. J. Beck (PECo) to NRC dated July ~17, 1992 Dear-Sir -
In Reference (1), Philadelphia Electric Company (PEco) submitted a revised complete Station Blackout (SLO) analysis for Peach Dottom Atomic Power Station (PBAPS),'Unita 2 and 3.
In. Reference (2), the.NRC roquested additional information regarding this analysis.
PECo response to this request was provided in Reference (3).
On'May 15, 1992, we met with NRC representatives and-presented,
.among other issues, a proposal to install a dedicated line from the conowingo Hydroelectric Power Station to the PBAPS onsite distribution system.
Following this meeting, additional telephone discussions between PECo and the NRC were held to discuss the possibility of crediting the conowingo Hydroelectric Power Station as the Alternate AC (AAC) powcr source to meet the requirements of the SBO rule.
As a result of these
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-9200130019 920806 PDR ADDCK-05000277 l
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S. Nucle r R:guletory Commiesion August 6, 1992 PDAPS, Unito 2 and 3 Stetion-Bicekout Racponca Pags 2 discussions, we agreed to identifying the Conowingo Hydroelectric Power Station as the AAC power source. Accordingly, in Reference (4), the NRC
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transmitted 13 questions regarding the conowingo Hydroelectric Power Station line and its use as the AAC power source.
The NRC requested that responses be provided by July 24, 1992.
In Reference (5), we requested that the response date be extended to August 7, 1992, due to personnel resource constraints.
The purpose of this letter is to provide responses to the NRC questions.
In the Enclosure to this letter, each NRC question is restated followed by our response.
If you require additional information, please do not hesitate to contact us.
Sincerel,
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.T.
T. Hartin, Administrator, Region I, USNRC J. - J. Lyash, USNRC Senior Resident Inspect or, PBAPS
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Enclosuro P go 1 i
Peach Sottom Atomic Power station, Units 2 and 3 j
e Response to Questions Regarding Use of l
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Conowingo Line in station Blackout Analysis 1
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1._
-Provide a complete description of the proposed circuit from the r
conowingo station to the Peach Bottom safety buses. One-line diagrams showing.the-hydro units, buses, transformers, breakers, protected transmission line, associated voltage levels and capacities, and extent of protection against weather related events would be acceptable.-
- Responser
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_The proposed line from Conowingo Hydroelectric Power Station (Conowingo) to Peach' Bottom Atomic Power Station (PBAPS) is designed to support the necessary loads (i.e., safe shutdown of both units from
-full _ power operation) during a Station Blackout (SBO). A SBo is defined as. loss of the preferred offsite power supplies and loss of the four-station emergency diesel generators (EDGs). The proposed j
line will function as the alternate AC.(AAC) power supply as defined in. Regulatory Guide (RG) 1.155, " Station Blackout" and NUMARC 87-00,
" Guidelines and> Technical Bases for NUMARC-Initiatives Addressing I
Station Blackout at Light Water Reactors." The'line is designed to support a continuous load of 15HVA. The line is located to take
. advantage of.the highly reliable'and available conowingo generating.
unita.- Attachment -1 provides a' simplified single line of the proposed 4
' design.-
4
-There are 11 generating units at Conowingo..Seven units (Unita 1 through 7) ara' rated at 36MW.
The-remaining four units (Units 8 through:11)'are. rated at 65HW.. Units'3,-4. 5, 6,~ 10 and 11 provide power.directly to thel33kV transmission sydtem via either the E
.Susquehanna' substation No. 10 or No. 12 transformers, each of which is.
irated atm25NVA.- ' Units 1, 2,17, 8 and 9 can:also provide power _to the 33kV system via the 220kV switchyard.-
A' minimum Conowingo startup rp configuration (i.e., assuming loss of offsite power)-will. consist of-
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.one 36MW' unit 1and one 65MW unit. This As different from the d
configuration presented at the May 15,11992 ~ meeting between representatives of_ Philadelphia Electric _ Company.(PEco) and_the NRC.
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'At.that1 meeting,'we stated that any one of.the 11 Conowingo units was sufficientLto3provida7the'needed.AC power to PBAPS, Unita 2 and 3.
Further. analysis determined that.a combination ~of one small unit and
'one large' unit was needed-to provide transientistability during the-
- startfof the Residual Heat Removal"(RHR)'and High Pressure Service.
1 Water?(HPSW)-pump motors..
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nThe proposed:33kV.line will initiate at'the 33kV Susquehanna
. Substation located-at Conowingo, and will.terminato at a 33/13kV-15MVA
' transformer to be located at PBAPS.' -The transformer load side (13kV)
'will'be-connected 2to.the PBAPS'No.12 13hV-startup bus which provides
- power.to
- the 4kV omergency buses via the 2EA transformer (13/4kV).
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.The line will include 33kV circuit breakers at both the 33kV Susquehanna substation and the 33/13kV transformer at PBAPS.
The proposed line will provide a feed to PBAPS Unit 1 and will carry a normal load of approximately 1MVA. A partially loaded line will
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. provide greater reliability than an energized line with no load.
PBAPS Unit 1 will.be the only normal load on this line. No other distribution customers will be fed from this line.
Provisions will be made to disconnect PBAPS Unit 1, as necessary, to provide PBAPS Unita 2'and 3 the full 15HVA.
The. proposed line will be designed to withstand severe weather conditions and will be routed either underground or under the conowingo Dam reservoir.
2.
Confirm that the 33kV line from conowingo and the associated 33kV/13kV transformer and 13kV-bus at Peach Bottom would be continuously energised, and that any unavailability.or-fault on this circuit would be immediately-alarmed in the Peach Bottom control room.
Responset
-The proposed line will-be-normally energized and provide power to PBAPS Unit.1 for building light and power. The line may be taken out of service for periodic testing and/or maintenance.
Anyfplanned or unplanned de-energization of this line will result in an undervoltage/ loss of power annunciation in the PBAPS Unita 2 and 3 contro1' Room.- Priority would be given to placing the line back in aervice expeditious 1y'in order to maintain a high availability.
We' propose-that a" loss of this line.for greater than 15: days will-
= result:in; notification to the NRC providing restoration plans and componsatory actions or precautions to be taken.'.-This notification.
requirement.will-be formalized.in a. Technical specifications'changs-
- Request that we.will. submit to the 'NRC. -
3.-
'DescribeLthe procedures'for assuring restoration'of power to Peach Bottom from the conowingo station given (1) a general system failure including trip of the conowingo units,.and (2) a system'fallure which Edid:not trip:the conowingo units. 'In each case, provide the time' required for-restoration.'
. Response:'
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We plan for-and would~ perform a system restoration following-a system
< blackout in accordancelwith the.PEco System Operations i. vision -
- procedure titled " System Rostoration Following Complete hutdown."-
'At;the onset of aisystem disturbarce, all generating stations are to take' appropriate action to prevent the loss of operating units.
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F Encle uro P g: 3 Conowingo normally has five of its units (Units 3, 4, 7,
9, and 10) running as electrical condensors and are available for generation as spinning reserves.
In this case, the time required for conowingo to provide power to the 33kV system would be about 5 minutes.
The existing governing procedure for restoration of power will be revised to also energize the proposed Conowingo 33kV line to PBAPS, Units 2 and 3.
If Conowingo has no units in cervice, the initial actions required by the conowingo operators as part of the System nestoration Prccedure woulu be to start several of the conowingo units.
Station power to facilitate starting these units is available from one of two "Meuse" generators, one of which is normally running.
Each house unit is rated at 1600kVA. These actions would take an additional 10 minutes so that Conowingo would provide power to the proposed Conowingo 33kV N
line -sithin 15 minutes.
Once the line is energized, DBAPS personnel would close both a 33kV circuit breaker on the high side of the proposed 33/13kV transformer and a 13kV circuit breaner installed on the No. 2 13kV startup bus to energize the 2EA 13//kV transformer, thus providing power to the safeguards 4kV buses. The actions required by Peach Bottom personnel will be incorporated into PBAPS procedure SE-ll, " Station Blackout."
These additional actions will take approximately 15 minuten to perform.
Thus, the time required to energize the safogeards buses at PBAPS from Conowingo following a system blackout would be between 20 minutes to 30 minutes depending on the initial condition of the conowingo units.
4.
Provids the expected overall availability (conkidering both reliability and availability aspects) of the power supply from the Conowingo hydro site at the Peach Bottom 13kV bus.
Provide an estimated breakdown for the separate components (e.g., hydre power, transformers, 33kV cable) including the bases for these est.' mates to the extent that such information is available.
Response
The overall availability of the proposed line from Conowingo to PBAPS is expected to be in excess of the 95% target EDG availability 904.1 provides the total line availability f or the thrce cac;n routing opcions being evaluated.
The availability analyels wau baked upon methodology presented in IEEE Standard 493, " Design of Reliable
. Industrial and Commercial Power Systems." As shown in Attachment 2, the contribution to total line unavailability due to Conowingo generation is approximately 1 hr/yr. This assumes the re"ised configuration of any.one of the seven small units and any one of the four large units.
Because of this small contribution due to generation, it is concluded that any decrease in generation availability resulting from the combination configuration is negligible.
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Enclosuro P003 4 L.
Describe how Peach Bottom's priority for conowingo's power will be implemented.
For example, if the spinning reserve at the conowingo hydro site were not sufficient to supply the SBO load on demand, what would the sequence of events be (communications required, shedding of 33kV load, adding hydro generation, etc.)Y
Response
Hestoration of power to the $3kV system, which will include the conowingo line, is one of the very first actions taken by conowingo operators as part of the system restoration.
The conowingo line will be the initial line energized on the 33kV system.
Any activities needed to support the conowingo line such as load additions or shedding from the 33kV system will be coordinated and directed by the Power System Director as defined in the System Rostoration Procedure.
The Power System Director is the single point of contact for communications and direction following a system blackout.
Communication between the Power System Director and PBAPS will occur via a dedicated load dispatching telephone system. Availability of this telephone system is already verified daily by PBAPS operators.
The Power System Director will have responsibility and authority to ensure that need for power to PBAPS is met as the top priority.
6.
In event of an SBO at Peach Bottom, provide your best and worst case entimates of the time required to energize the safety buses at Peach Bottom fror the conowingo power source. Also, state which of these j
estimated times is used in arriving at your answer to question 7.
t-
Response
The response to Question 3 provides the estimated time for emergency power restoration following a SD0 at PBAPS.
The analysis referred to
.p in Question 7 10 based upon 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> to energize the PBAPS Unita 2 and 3 sagoguards buses.
7.
Your April. 24, 1991, revised response to the 880 Rule provided a coping assesement for an 8-hour SBO assuming one of the existing EDGs
'3 would be available as an AAC source within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, consider each section (i.e., condensate inventory, class 12 battery capacity,.
compresssd air, effects of loss of ventilation, containment isolation,
'raactor inventory, etc.) and state if any changes would be applicable
-to these sections if the conowingo power source were the AAC power source rather than the EDO.
Responses since the time required to energize the safeguards busos at P3APS, l
Units 2 and 3 via the.propoced Conowingo line is lose than 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, the l
referenced coping assessment can be considered bounding.
If the conowingo line is substituted as the AAC power source'in the referenced coping assessment, the'following conclusions can be made.
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4 The operator actions to control EDO 2oads, previously required to q
mainttin the AAC EDG loading below 3000hW, will not be required.
In aadition, the containment analysis performed to demonstrato the
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ab(11ty of each unit to cope with the SB0 evont for the 8-hour period wit'hout containment cooling, bounds the expected results for a SB0 with Conowingo as the AAC power source during the second through the j
eishth hour of the 880 since power for a RHR pump and HP5W pump for s
3
- containment-cooling will become available during this period.
Eo.ch
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specific ~dection of the referenced coping assessment id addressed below.
A.
condanoate_ Inventory _for Decay _leat Removal j
our Aprl1 24, 1991 submittal stateq that a minimum of approximately 100,000 gallons of the 166,713 gallons of makeup water required for each PDAPS unit would be available from the Condensate Storage Tank (CST). With an EDG as the AAC sourew, no contatament cooling wts postulated for either unit durin5 the SB0 duration. The High Pressure Coolant Injection (HPCI) r.nd Reactor Core Isolation Cooling (RCIC) pump suctions were ther> fore transferred back to the CST upon reaching a suppree91on pool temp 6rature of 180*F due to net positive suction head concerns.
K0 wever, with Cenowingo as the AAC source, sufficient power would be available to align a RHR and HPSW pump for containment cooling for each unit aftur the first hour.
If necessary,'in fact, sufficient power would be available to align two containment cooling loops per unit. Therefore, based on the heat generated at-1~ hour into the 8B0 event relative to the existing heat removal capability with;Conowingo as the AAC sourco, it is our
- engineering judgement that the wuppression pool inventory will not increase in temperature to greater than 180*F during the SB0 avent, and transferring HPCI and RCIC pump _ suction back to the CST will' not be required to supply reactor makeup water for safe shutdown.- Fct this reason, with Conowingo as the AAC source, the CST inventory will not need to be credited as a makeup water sourCO.
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2.
Class-IE Battery Capacity This section is unchanged.
The batteries will still be capable L
of providing the required power during the first hour without recharging,.and will be charged ~with power from the conowingo AAC-
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power source after the end of the first hour.
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3.
- compressed Air l
This section l's unaffected by the Conowingo AAC power source.-
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Enclosuro L
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Effects of Loss of Ventilation s
The results of ths analyses in this section are either unchanged with Conowingo as the proposed AAC source, or bounded by the results obtained when the previously proposed EDG was the AAC source.
The analyzed temperatures in che HPCI and RCIC Room, control Room, Ceble Spreading Room, and other plant areas are unchanged by the difference between the previously and currently proposed AAC source. The containment analysis in our April 24, 1991 submittal will bound the conditions that will exist with the it ;
Conowingo AAC source since with an EDG as the AAC Source, no containment cooling was postulated for the entire 0-hour SBo event.
With Conowingo as the AAC source, its greater capacity will allow establishing a RHR and HPSW pump for containment raoling on each unit during the second through eighth hour of the SBO du.9(1Gn.
The conditions analyzed with no containment cooling will therefore bound the conditions which will exist when containment cooling is available.
Due to the available capacity of Conowingo as the AAC source, we may consider an analysis to demonstrate the effects of energizing a non-safeguard bus after the first hour of the SBO event to recover normal control Room ventilation.
Priority would be given
-to recovering this ventilation over opening cabinet doors or removing ceiling tiles to enhance control room cooling.
Recovering normal control room ventilation would obviate the need for these operator actions.
5.
Containment Isolation The list of primary containmenc valves that do not qualify for exclusion as defined by NUMARC 87-00, Section 7.2.5 is not affected by the proposed Conowingo AAC power source.
6.-
Reactor cc.lant Inventory This section is unchanged. The source of.the AAC power after the first hour of the SB0 even* does not affect the ability to maintain adequate reactor coolant system inventory.
7.
Equipment Quality Assurance
-In our April 24, 1991 submittal, we listed the CST and its associated level instrumentation as some of the few components credited in our SBO analysic, but not covored by our-Quality Assurance Program as required by Appendix B of 10CFR50.
Accordingly, we. committed to maintain that equipment in accordance with Appendix A of RG 1.155.
As stated previously, the CST is no longer credited in our 800 analysis and, therefore, will not be maintained in accordance with Appendix A of RG 1.155.
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Enclosurc Pag 3 7 In!our April 24, 1991 submittal we also stated that the 00A19 non-segregated phase 4kV bus would be maintained in accordance with Appendix A of RG 1.155 and that no part of the 13kV system was needed for response to a SB0 evont.
The No. 2 startup bus, which is part of the 13kV system, will now be needed-for response to a-SBO event.._As shown on Attachment 1, the No. 2 13kV startup bus is~where the conowingo line will be, connected to PBAPS. We
. plan to maintain the conowingo generating units, the proposed i
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PBAPS connecting line, the OCA19 bus and the portion of the PBAPS distribution 'ayat em up to but not including the Class 1E breaker, j
Iccated between.the 2EA transformer and the 4kV bus, as non-safety related equipment. The existing equipment of this list has been highly rollable and available.
'We plan to maintain both the existing and the proposed equipment of this list in
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accordance with our standard utility maintenance practices.
We-
-do not commit to' maintaining this;11st of equipment in accordance
- with Appendix A-of.RG 1.155.
This is consistent with the quality assurance: practices currently applied to our preferred offeite
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sources.-
8.~
- Address each item of NUMARC 87-00, Aprendix B (i.e., El through 513)
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'and describe to;what extent the Cnnowingo hydro power scarce to Peach
)
Bottom meets these criteria for AAC power sources.
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1 Respo'nse s
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B.1 :Th's.conowingo-generating units and proposed PBAPS connecting line o" '
are not designed to sneet Class 1E or: safety system requirements.
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- B.2
- The Conowingo: generating un!$s atC croposed PBAPS connecting line I
will not-be protected-against wrf efts;ts:of failure or
- misoperation of: mechanical equipment, including (1)._ fire (11) pipe whip, (iii)-jet impingement,-(iv) wateriepray, (v) flooding i
- from a pipe break, (vi); radiation, pressuriaation, elevated temperature or.ht.midity caused by high'or medium energy pipe.
- break, and,;(vii) missiles resulting_from failure of_ rotating equipment orLhigh energy. systems.
The conowingo generating units
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'and proposed PBAPS connecting line will not be:soismically desigrad.
1B.3' The conowingo line will consist'of the conowingo Hydroelectric l
Power Stationi the substation equipment at Conowingo and.PBAPS
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and the distribution"line. A111of these" components are capable i
A.
.of withstanding the effects of likely weather-related: events.
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- Each:of the!three' cable = touting-options being'avaluated for the i
Eline includes-burying the cable..
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8.4 The C4-nowingo line-_will be physically separated from the PBAPS, 1
Unita 2fand 3 Class;1E power lines and will meet the separation crite la~asidefined in the PDAPS.UPSAR.-
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Pags 8 B.5 Failure of the Conowingo generating units and proposed PBAPS connecting line will not adversely affect any Class lE AC power systema due to the isolation devices incorporated into the design.
B.6 The conowingo line will be connected to the PBAPS Ho. 2 13kV startup buces which are non-safety related; therefore, isolat.on will be provided by the exieting Class lE safeguards 4kV bus breakers and the non-class lE 13kV startup feeder breaker to the Unit 2 emergency auxiliary transformer. See Attachment 1 for a simplified single line diagram of this configuration.
D.7 The conowingo line normally will not be connected to the preferred or on-site Emergency AC Power System for either PBAPS Unit 2 or Unit 3.
Shutdown equipment will not be capable of automatically loading onto the conowingo line.
B.8 Hinimum potential exists for common cause failure of the Conowingo generating units and proposed PBAPS connecting line for the following reasons.
(a) Any required back-up power source for conovingo will be independent f rom PBAVS preferred and Class lE power system.
(b) An air start system is not applicable to the conowingo generating units.
(c) A fuel oil supply is not applicable to the conowingo generating units.
(d) The conowingo line will rely upon hydro generator units, as compared to the PBAPS EDGs.
(e) The conowingo generating units and proposed PBAPS connecting line will be designed to prevent vulnerability to failure from a weather-related event or single active failure that could simultaneously disable the onsite EAC sources and the preferred power source.
(f) The Conowingo generating units and proposed PBAPS connecting line will be capable of operating during and after a SBo event without any support nystems powered from the PBAPS preferred power supply or the PBAPS Class lE power source.
(g) Portions of the conowingo line subjected to maintenance activities will be tested prior to returning the conowingo line to service.
B.9 The conowingo lino will be sized at 15MVA nominal to carry the required shutdown loads for the required a-hour coping duration for PBAPS, Units 2 and 3.
It will be capable of maintaining I
Enclosuro Pego 9 voltage and frequency within limita consistent with established industry standards such that the performance of any components within shutdown systems will not be degraded.
B.10 The conowingo line normally will be energized from the Susquehanna Substation to the No. 2 startup switchgear breaker.
The loss of this source will be annunciated in the Control Room.
The line will be tested approximately once every two years to verify that it can support the required loading.
B.11 The Conowingo generating units and proposed PBAPS connecting line will be maintained according to practices currently in place or as subsequently modified commensurate with a principal function of system restoration for system blackout.
B.12 Upon completion of the modification to permit the use of the conowingo line as the AAC Source, it shall be demonstrated by test to be capable of carrying a load equivalent to the load of the required shutdown equipment within I hour of a station blackout event.
B.13 The conowingo generating units and proposed PBAPS connecting line normally will be operated (i.e., powering PBAPS Unit 1) and will be monitored to an availability goal of 95% of the time the reactor !.e operating.
This is the target availability goal for a normally on-line power system. There is no target for reliability for normally on-line systems.
9.
Describe the testing that will be performed in accordance with 10 CFR 50.63(c)(2) to demonstrate the capability of Cenowingo as the AAC source.
Responses (1) Pre-Operational Testing Prior to placing the conowingo line in service, a pre-operational test will be performed to verify the following.
(a) The capability to establish power to the 4kV emergency buses from the conowingo line within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> of a SBO event.
This includes simulating the start of the required number of Conowingo generators from a condition of no units running.
(b) The capability of.the conowingo line to carry approximately 7000kW in load.
The 7000 kW represent the load required to bring both units to safe shutdown.
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EnclosurO l
Pago 10 (2)
Periodic Testing Testing of the conowingo lina will be done approximately once every two years. The periodic test will verify the capability of the conowingo line to start and carry approximatley 7000kW of load. The capability of the 4kV buses and the SBO required shutdown equipment to energize and start in already demonstrated by existing surveillance tests.
10.
Provide.an estimated implementation schedule for the proposed power feeder from the conowingo Station.
Response
The proposed Conowingo line will be installed and placed in service within two years of NRC issuance of the Safety Evaluation approving the SBO analysis for PDAPS, Unita 2 and 3.
11.
If the allowable outage time (ACT) for an inoperable EDO is incraased from I week to 2 weeks, how would this affect the overall availability (considering both reliability and availability aspects) of the EDG7 Same question if the ACT for an inoperablo EDG is increased from I week to 30 days? Provide the bases for these answers.
2:sponse The intent of the increased allowable outage time is to increase the flexibility should an unexpected condition occur associated with the EDGs.
Actions would be taken to limit the time in any Limiting condition for Operation Technical Specifications Action dtatement and therefore, limit the EDG unavailability.
If all preventive maintenance activities are not completed during existing 7-day AOT, entry into another AOT at a later date would be necessary to complete the activities.
These multiple entries into an AOT would cause an increase in EDG unavailability over that of one longer bst continuous AOT due to the testing and post-maintenance checks that must be performed prior to each time the EDG is returned to service.
If an EDG were removed from service for a two week period, the unavailability would double from the one weak value of 1.9% to 3.8%
per year.
The yearly availability would decrease by only 1.9%, from 98.1% to 96.2%.
Similarly, an increase from one week to one month would result in a 8.3% unavailability, or a 91.7*. availability.
However, availability averaged over several years would be expected to remain about the same or better as additional preventive maintenance activities would be expected to preclude work required at a later date, and thus limiting the duration of future outages.
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Encicouro P g) 11 9
The historical reliability of the EDGs has been e tremely high (e.g.,
99.35%) and would bo expected to remain high roganw ras of the unavailability experienced by the EDGs.
12 Provide the results of PRA analyses that have been performed in aupport of the proposed power faeder from the Conowingo Station.
Responset The current Probabilistic Risk Assessment (PRA) for PBAPS, Units 2 and 3 core damage frequency (CDF) is 5.5E-06/ Reactor (Rx)-yr. The contribution of SBO and Loss of Offsite Power (LOOP) sequences to the CDP is 8.7% and 24.8% respectively. A LOOP sequence is one in which multiple (but not all) EDGs have failed subsequent to a loss of offsite power. The conowingo line would be capable of supplying power with a capacity greater than the combined output of the onsite EDGs to the safeguards 4kV buses. This substantially reduces the need to load manage the available EDG power to succesefully mitigate an accident affecting one or both of the PBAPS units following a LOOP.
The contribution of SBO and LOOP with the installed conowingo line to the i
CDF calculated to be 0.4% and 0.1%, respectively. The total CDP would consequently decrease to 3.7E-06/rx-yr, which represents a 33%
decrease.
13.
Provide historical data on Peach Bottom's EDG unavailability (due to maintenance) during power eporations and during shutdown of one or both units.
Responses-
!!istorical EDG unavailability recorded from 1986 to the present (i.e.,
May,-1992) represents thL most recent, consistent, and applicable collection of data for the PBAPS EDGs and was used to determine the EDG unavailabilities below.
With one or both of the PBAPS units operating, the EDG unavailability
-recorded.in the above time frame averaged 2.3% per EDG per year.
The annual EDG inspection required by the Technical Specifications contributes 1.9% EDG unavailability for each EDG every year. This inspection interval was recently changed to once every 18 months and would result in a drop in EDG unavailability per year by approximately one-third.
For th6 last three yeara, 90% of the unavailability was due to planned outages and 10% due to unplanned outages.
During the approximately 25 months when both PBAPS units were shut down (March 31,-1987 to April 26, 1989), the EDG unavailability averaged 6% per EDG per year. This unavailability was a result of modifications, tests, and lengthened inspection outages. Although the units were not operating, the annual EDG inspections were performed.
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b' TRANS SIMPLIFIED SINGLE LINE EMERGENCY PEACH BOTTOM
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ATTACHMENT 2 PEACH DOTTOM ATOMIC WWER STATION, UNITS 2 AND 3 CONOWINGO LINE JNAVAILAB LITY j
BASED ON EQUIPMENT FAILURE AATES CABLE ROUTING OPTIONS DUCT BANK DIRECT BURIED SUBMARINE Generation (Including Generators and associated equipnent)
I hr/yr 1 hr/yr 1 hr/yr Distribution (Including breakers, transformers, and cables) 131 hr/yr 143 hr/yr 133 hr/yr TOTAL LINE Ui!AVAILAHILITY (excluding maintenance) 132 hr/yr 144 hr/yr 334 hr/yr TOTAL LINE AVAILABILITY 98%
98%
96%
_ _ _