IR 05000282/2011010

Prairie Island. Units 1 & 2, Supplemental Information Regarding Inspection Report 05000282/2011010; 05000306/2011010 (EA-11-110)

ML11195A336
Person / Time
Site:	Prairie Island
Issue date:	07/13/2011
From:	Schimmel M A Northern States Power Co, Xcel Energy
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
EA-11-110, ir-11-010, L-PI-11-071
Download: ML11195A336 (43)

Text

XcelEnergy"JUL 1 3 2011 L-PI-1 1-071U S Nuclear Regulatory CommissionATTN: Document Control DeskWashington, DC 20555-0001Prairie Island Nuclear Generating Plant Units 1 and 2Dockets 50-282 and 50-306Renewed License Nos. DPR-42 and DPR-60Supplemental Information Reqarding NRC Inspection Report 05000282/2011010:05000306/2011010 (EA-11-110)By letter dated June 9, 2011 (Agencywide Documents Access and ManagementSystem (ADAMS) Accession Number ML111610249), the NRC transmitted InspectionReport 05000282/2011010; 05000306/2011010 for the Prairie Island NuclearGenerating Plant (PINGP). In the inspection report, the NRC identified one finding andapparent violation related to battery charger performance with a preliminary significanceof White for Unit 1 and a preliminary significance of Green for Unit 2, and provided theopportunity to request a Regulatory Conference. By letter dated June 14, 2011(ADAMS Accession Number ML111662049), Northern States Power Company, aMinnesota corporation, doing business as Xcel Energy (hereafter "NSPM") requested aRegulatory Conference which will be held on July 28, 2011.This letter transmits documents which support the July 28, 2011 RegulatoryConference. Enclosure 1 provides document V.SPA. 11.016, "Simulator Runs forBattery Charger Significance Determination Process". Enclosure 2 provides adocument entitled, "Battery Depletion Calculation Load Profile". Enclosure 3 providesdocument V.SPA. 11.006, "Evaluation of Battery Depletion Differences".If there are any questions or if additional information is needed, please contactMr. Dale Vincent, P.E., at 651-388-1121.* 1717 Wakonade Drive East * Welch, Minnesota 55089-9642Telephone: 651.388.1121 Document Control DeskPage 2Summary of CommitmentsThis letter contains no new commitments and no revisions to existing commitments.Mark A. SchimmelSite Vice President, Prairie Island Nuclear Generating PlantNorthern States Power Company -MinnesotaEnclosures (3)cc: Administrator, Region III, USNRCProject Manager, PINGP, USNRCResident Inspector, PINGP, USNRC ENCLOSURE1V.SPA.11.016SIMULATOR RUNS FOR BATTERY CHARGER SIGNIFICANCE DETERMINATIONPROCESS15 pages follow CXcel EnergyPrairie Island Nuclear Generating PlantProbabilistic Risk AssessmentV.SPA.1 1.016Simulator Runs for Battery Charger SignificanceDetermination ProcessMarch 2011Document Review FormDocument or Analysis Title: V.SPA.11.016- Simulator Runs for Battery Charger SDPRevision of Document or 0Analysis:Date: 3/11/2011Preparer: ,,,t- Date: 3/11/2011Mark A. Brossart ,1Reviewer:Jayne E. RitterDate: 3/11/2011PRA AcceptanceDate: 6/07/2011Ashley Peterman V.SPA.11.016Simulator Runs for Battery Charger Significance Determination ProcessTable of ContentsPage NumberT able of C ontents .............................................................................1.0 P u rp o se ....................................................................................2.0 Simulator Development Process ........................................................3.0 S im ulator R uns ............................................................................3.1 Sim ulator "Initial R un" R esults .....................................................3.2 Simulator "Follow-up Run" Results ..............................................4 .0 C o nclu sio n s ................................................................................5 .0 R e fere nce s ..................................................................................12233.578

Attachments:

Attachment 1 -Simulator Prior Knowledge Statement .................................. (2 pages)Attachment 2 -Simulator Scenario Security Agreement ............................... (2 pages)File Prepared By:Mark BrossartDate: 3/11/2011File Reviewed By:Jayne RitterDate: 3/11/2011V.SPA.1 1.016Simulator Runs for BatteryCharger Significance Determination ProcessPage 1 of 8 V.SPA.11.016Simulator Runs for Battery Charger Significance Determination Process1.0 Purpose:A simulator scenario was developed to support the arguments used in the Significance Determination Processfor the Battery Charger past operability. The results of the scenario will not be used as part of the PRA successstrategy but may be used to demonstrate, in a simulated environment, that there is adequate time withsignificant margin to perform the recovery actions credited in the PRA success strategy. It is intended that sitemanagement may use this information in discussing the site response with the Regulator as a demonstrationthat the PRA recovery strategy assumptions are reasonable.The simulator run will determine the time it takes operators to:1. Diagnose and respond to re-energizing a safeguards 4.16KV bus via the opposite unit bustiebreaker during a LOOP event.2. Perform the actions necessary to restart the battery charger following a lock up.Information pertaining to this calculation folder can be found in the following directory:J:\PRA\Calc Folder Writeups\SPA Folders\ V.SPA.11.016 -Simulator Runs for Battery Charger SDP2.0 Simulator Development Process:1) The simulator scenario is based on the limiting accident sequence developed for the Battery ChargerSDP (Reference 5.3). The scenario includes the following conditions:a. Dual unit LOOP (Initiating Event).b. The 12 Battery Charger experiences a lock up during the load sequencing restoration process.c. The Emergency Diesel generator (EDG) Dl experiences a lockout. As a result of the LOOPand D1 failure, Bus 15 will not be energized. This will cause the emergency lighting totransfer from its normal AC source to the 12 Battery (DC source) resulting in a more rapidbattery depletion and minimizing the allowed operator response time. (Reference 5.1)d. The inverters will fail to the DC source as a result of a known issue with voltage overshootassociated with the D1ID2 voltage regulators. This will result in more rapid battery depletionand minimizing the allowed operator response time.e. The Non-License Operator (NLO) used to restore the battery charger is physically located in alocation that was expected for the scenario (Screenhouse for DDCLP monitoring) but tryingto maximum travel time to the battery rooms.2) Sequence of Events: Dual Unit LOOPBoth units experience a simultaneous LOOP. D1 is locked out causing Bus 15 to not be immediatelyavailable to power safeguards loads. As a result of the 12 Battery Charger's susceptibility to lock up,the DC loads for B Train will be powered from the 12 Battery as 12 Battery Charger locks up duringthe load sequence restoration process. See PRA Calculation Folder V.SPA. 11.003 for details on theimpact on the 12 Battery depletion time. In order to maximize the time for the NLO to respond to thebattery room, the NLO was sent to monitor the Diesel Driven Cooling Water Pumps (DDCLPs) in thePlant Screenhouse.V.SPA.1 1.016 Page 2 of 8Simulator Runs for BatteryCharger Significance Determination Process 3) Expected Crew Responses:a. Enter IE-0 and initiate restoration of Bus 15 at Step 3 per 1C20.5 AOPI (Reference 5.4).b. Perform actions necessary to restore the 12 Battery Charger per the Alarm ResponseProcedure ARP C47024-1105 (Reference 5.5) and 1C20.9 AOP4 (Reference 5.6).4) Positioning of NLO:The decision was made to pre-stage the NLO initially in the Records Room and then upon theannouncement of Reactor Trip dispatch him to monitor the Diesel Driven Cooling Water Pumps.Alternate locations were evaluated but discounted for the following reasons. With a Loss of OffsitePower event the assumption was that the duty crew would dispatch operators to monitor all runningdiesels. If the NLO was doing Attachment J of IESO. I (Reference 5.7), he would have been in closerproximity to make copies of procedures and go to the battery rooms. The D I or D2 rooms wereconsidered but it was determined it would take less time to get to the battery rooms from the Dl or D2rooms considering that the operator would need to make a copy of the procedure and would use thewater treatment office to do so. Remote locations in the auxiliary building were not considered sincethe Turbine Building Operators would not have been utilized or sent to the auxiliary building tasksduring this scenario.5) Two simulator runs were performed:The initial run was performed on March 5th, 2011 and a follow-up run on March 8 h, 2011. Thepurpose of the initial run was to demonstrate that the assumptions made in the PRA success strategyare reasonable with normal Control Room staffing including a Shift Manager (SM), Shift Supervisor(SS) and Shift Technical Advisor (STA). Also included were two Unit 1 Reactor Operators (RO), 1Unit 2 RO and a Unit 1 Turbine Building NLO. Following the initial run for this scenario, it wasdetermined that a more limiting scenario would be to assume that Unit 2 was in a sufficiently complexrecovery that the extra Unit 2 RO would not be available to support the Unit 1 response.Consequently, the follow-up run was performed with a crew of a Shift Manager, Shift Supervisor, twoUnit I ROs and a Unit 1 Turbine Building NLO6) Simulator Run Data Collection:Simulator timing data was collected for both simulator runs. There were three individuals collectingtiming data (PRA Engineer in booth, Operations SM in booth, Engineering Supervisor in the plant).3.0 Simulator Runs3.1 Simulator "Initial Run" Results (March 5th% 2011)The initial simulator run demonstrated the following risk-significant operator actions.a. The restoration of Bus 15 from Bus 25 via bustie breaker per 1C20.5 AOP4 (Reference 5.8)occurred at approximately 24 minutes into the event.b. The restoration of the battery charger per 1C20.9 AOP4 (Reference 5.6) occurred atapproximately 43 minutes into the event.These actions were demonstrated in an initial simulator run performed on March 5, 2011. The crewconsisted of Darrel Lapcinski (SM), Mark Davis (SS), Jim Kapsh (U1 RO), Mark Jenkin (STA), MikeMurphy (U1 Lead RO), Evan Bystrom (UI NLO) and Joe Julian (U2 Lead RO).See Table 1 for a detailed event description and tining for this simulator preliminary run.V.SPA. 11.016 Page 3 of 8Simulator Runs for BatteryCharger Significance Determination Process ThhIA 1-~imsIIAtnr fuRl unit LOOP Fv~nt ~wlth EDfl Dl Lnnk-niit~ ~r~An,~arin ~/fl~/~flhlTime fromTime Start of Event Event/Action q8:50:15 0:00:00 Trigger 1 -LOOP event (Dual-unit) with EDG D1 Lock-out8:50:15 0:00:00 Enter 1E-08:50:45 0:00:30 Unit 1 RX Trip Announced to PlantImmediate Actions per 1 E-0 completed, Bus 15 is de-energized and8:51:15 0:01:00 was reported to the Unit 1 SS.8:52:10 0:01:55 13 Charging Pump startedUnit 1 SS instructed Unit 1 Lead RO to enter 1C20.5 AOP1 per 1 E-0,8:53:10 0:02:55 Step 3 RNO8:53:32 0:03:17 Verified that SI is not requiredUnit 2 Lead RO instructed to perform actions in 1C20.5 AOP1 per8:54:00 0:03:45 Unit 1 SS/Lead RODiscussion of RCS condition between Unit 1 SS and RO (potentialde-pressurization of RCS and LOCA conditions, watch for SI8:55:00 0:04:45 actuation conditions)8:55:45 0:05:30 Transition to 1 ES-0.18:58:30 0:08:15 Dispatch outplant operator to check EDG D1 and D2, locallyCrew Brief, SS restored normal alarm response protocol. Thendirected the ROs to perform a board walkdown and report any alarms8:58:30 0:08:15 that are unexpected for the LOOP/reactor trip.8:59:52 0:09:37 Sump C and RHR pit high level alarms were identified as abnormal.RCDT indicated zero. This was addressed as being caused by the9:00:51 0:10:36 loss of Bus 15.Unit 1 Lead performed board walkdown and reported that Bus 11, 12,9:01:00 0:10:45 13 and 14 are de-energizedPer Step 2.4.2.B of 1C20.5 AOP1, report from outplant operator thatthe Bus 15 Undervoltage signal was lit and Bus 15 was not locked9:01:45 0:11:30 out.A discussion about the 12 battery charger being de-energized with9:02:30 0:12:15 bus 16 available and at power was conducted.9:03:00 0:12:45 Started 122 CR Chiller and fansInstructed Turbine building Operator to investigate 12 battery Trouble9:03:50 0:13:35 alarm.SM announced that Alert was declared. Escalation criteria would9:03:55 0:13:40 occur if Bus 16 was lost.9:06:30 0:16:15 SM makes plant announcement that an Alert was declaredDispatch outplant operator to investigate why 12 Battery isDischarging. Outplant operator was located in the 12 DDCLP room9:08:00 0:17:45 (Screenhouse)Crew Brief. The crew is working through ES-0.1. The inter-unit9:10:40 0:20:25 cross-tie to bus 15 is nearly complete.Report back from TB operator on status of 12 Battery -12 Battery is9:11:30 0:21:15 discharging.TB Operator proceeded to the Water Treatment office to get a copy of9:12:00 0:21:45 1 C20.9 AOP4.9:13:25 0:23:10 U2 RO announced that he was ready to cross-tie bus 15.Unit 2 Bus 25 connected to Bus 15. Bus 15 re-energized per 1C20.59:14:00 0:23:45 AOP 4.V.SPA.1 1.016 Page 4 of 8Simulator Runs for BatteryCharger Significance Determination Process Table 1-Simulator Dual Unit LOOP Event (with EDG D1 Lock-out) Scenario -3/05/2011Time fromTime Start of Event Event/ActionTB operator reported that he is using 1C20.9 AOP4 and investigating9:16:00 0:25:45 12 Battery Charger operation.9:16:26 0:26:11 Announced that bus 15 loads can be restored.9:18:00 0:27:45 Control Room Update: Entered 1 C20.9 AOP4 for 12 Battery Charger9:21:31 0:31:16 Began efforts to restore battery room cooling9:22:34 0:32:19 Swapped charging pump suction from VCT to RWSTIdentified that letdown was not in service. Directed U2 RO to place9:25:04 0:34:49 letdown in service.TB Operator reports back to control room information fromAttachment A of 1 C20.9 AOP4. TB Operator recommendedcompleting action in Attachment B of 1 C20.9 AOP4 (re-starting 129:27:00 0:36:45 Battery Charger)Reported the pressurizer level is 36% and rising with minimum9:28:00 0:37:45 charging.Unit 1 SS directed TB operator to re-start 12 Battery Charger per9:28:00 0:37:45 1C20.9 AOP4, Attachment B.9:30:00 0:39:45 Entered AOP to repower battery room cooling from D3TB operator open AC input breaker for 12 Battery Charger, waited,9:32:00 0:41:45 then reclosed breaker.Report from TB operator that 12 Battery Charger has been restored.Output is 250 amps. At Step 8 of 1C20.9 AOP4 and will continue to9:33:00 0:42:45 monitor.9:33:50 0:43:35 Letdown establishedUnit 1 Lead RO confirmed with ERCS that 12 Battery Charger has9:36:00 0:45:45 been restored.9:39:00 0:48:45 End of simulator run.3.2 Simulator "Follow-up Run" Results (March 8th, 2011)The follow-up simulator run demonstrated the following risk-significant operator actions.a. The restoration of Bus 15 from Bus 25 via bustie breaker per 1C20.9 AOP4 occurred atapproximately 17 minutes into the event.b. The restoration of the battery charger per 1C20.9 AOP4 occurred approximately at 51minutes into the event.These actions were demonstrated in a follow-up simulator run performed on March 8, 2011. The crewconsisted of Steve Ingalls (SM), Doug Larimer (SS), Greg Boek (UI RO), Jack Edwards (U I Lead RO)and Rick Lodermeier (Ul NLO).See Table 2 for a detailed event description and timing for this simulator preliminary run.V.SPA.1 1.016Simulator Runs for BatteryCharger Significance Determination ProcessPage 5 of 8

...Table 2-Simulator Dual Unit LOOP Event (with EDG D1 Lock-out) Scenario -.3/08/2011Time fromTime Start of Event Event/Action15:24 Crew has duty15:35:06 0:00:00 Trigger 1 -LOOP event (Dual-unit) with EDG D1 Lock-out15:35:15 0:00:09 Enter 1E-015:35:31 0:00:25 Unit 1 RX Trip Plant AnnouncementImmediate Actions per 1 E-0 completed, Bus 15 is de-energized, SI15:36:20 0:01:14 not actuated or required.15:36:33 0:01:27 1 E-0, Step 1 Reactor trip verified15:37:21 0:02:15 1 E-0, Step 2 Turbine trip verified1E-0, Step 3, Bus 16 is energized, Bus 15 has Undervoltage alarm15:37:36 0:02:30 and is de-energized Turbine trip verified15:38:00 0:02:54 12 DC System Trouble Alarm actuated on simulatorUnit 1 SS Directs Unit 1 Lead RO to enter 1C20.5 AOP1 (Re-15:38:39 0:03:33 energizing 4.16KV Bus 15) to restore bus 1515:39:00 0:03:54 Charging Pump in operation15:39:03 0:03:57 1E-0, Step 4, Check SI actuated -no. Check if SI is required (RNO)15:40:03 0:04:57 DDCLPs running SATUnit 1 Lead calls turbine building operator to investigate Undervoltageon Bus 15 protective relays per Step 2.4.2.B in 1C20.5 AOP1 (Re-15:40:44 0:05:38 energizing 4.16KV Bus 15)15:40:51 0:05:45 Transition to 1 ES-0.115:40:51 0:05:45 SM reports that all safety functions are GREEN15:41:39 0:06:33 1 ES-0.1, Step 2 entered15:42:42 0:07:36 1ES-0.1, Step 3 entered15:45:00 0:09:54 1ES-0.1, Step 4 enteredTurbine Building operator calls back control room to inform them thatthere are degraded and undervoltage relays on Bus 15 Load15:45:00 0:09:54 Sequencer per 1C20.5 AOP1 Step 2.4.2.B15:46:00 0:10:54 Alert declared, 577 completed15:46:27 0:11:21 1 ES-0.1, Step 5 enteredUnit 1 RO calls turbine building operator to perform 1 ES-0.1,15:46:55 0:11:49 Attachment J (Isolate Unit 1 Moisture Separator Reheaters)15:47:00 0:11:54 SS and Lead RO discuss re-energizing Bus 15 from crosstie15:47:34 0:12:28 1ES-0.1, Step 6 entered15:52:00 0:16:54 Cross-tie between Bus 15 and Bus 25 closed. Bus 15 is re-energizedUnit 1 RO reports that the Reactor Makeup Flow deviation alarm is in.Discussed with Unit 1 SS and it was decided to open the RWST to15:54:00 0:18:54 charging pump suction (MV-32060).15:55:00 0:19:54 MV-32060 is opened.Unit 1 Lead RO is in ARP 47024-1105 for 12 DC System Trouble15:55:00 0:19:54 Alarm15:55:55 0:20:49 1ES-0.1, Step 7 entered15:56:00 0:20:54 Normal alarm response protocol re-established15:56:34 0:21:28 1ES-0.1, Step 8 enteredV.SPA.1 1.016Simulator Runs for BatteryCharger Significance Determination ProcessPage 6 of 8 Table 2-Simulator' Dual Unit;LOOP Event (with EDG D1 L"ck-0ut) Scenario 13/08/2011Time from,-Time Start of Event Event/ActionUnit 1 Lead RO Recognized that 12 Battery is discharging. 12Battery is supplying load. This was discussed with Unit 1 SS andLead RO was told to instruct outplant operator to look at 12 battery15:58:45 0:23:39 charger.Unit 1 Lead RO call outplant operator to investigate 12 battery15:59:21 0:24:15 charger15:59:27 0:24:21 1 ES-0.1, Step 8.b -RO instructed to place letdown into serviceOutplant Operator called from 12 Battery Room -Informationtransmitted to Lead RO was: 0 amps DC output (charger), 117 V DC,16:06:09 0:31:03 Low Voltage Lit, and AC Light ON.12 Battery Charger information from ouptlant operator was discussed16:07:21 0:32:15 with Unit 1 SS16:08:33 0:33:27 Entered 1 C20.9 AOP4 (Failure of 12 Battery Charger)1C20.9 AOP4, Attachment A, dispatched to Turbine Building16:10:00 0:34:54 Operator16:12:27 0:37:21 1ES-0.1, Step 9 entered16:13:57 0:38:51 1ES-0.1, Step 10 entered16:14:55 0:39:49 1ES-0.1, Step 11 entered1 ES-0.1, Step 11.a.RNO.b, RO calls outplant operator to open VC-1 -16:17:21 0:42:15 116:19:49 0:44:43 1ES-0.1, Step 11.C enteredUnit 1 Lead RO instructed outplant operator to restart 12 Battery16:22:00 0:46:54 Charger per 1C20.9, AOP4, Attachment B.Per 1 ES-0.1, Step 11 .C.RNO.C, Unit 1 SS discussed that battery16:23:50 0:48:44 room cooling must be placed in service per C20.16 AOP1.16:24:00 0:48:54 Discussed using TSC support staff for re-start Battery Room Cooling16:26:00 0:50:54 Restarted 12 Battery Charger16:28:00 0:52:54 Used ERCS to confirm 12 Batter Charger was restarted.16:30:00 0:54:54 End of simulator run.4.0 ConclusionsThe purpose of these simulator runs was to demonstrate that the actions assumed in the PRA successstrategy were reasonable given the time available. The limiting depletion time for the 12 Battery for thisevent is just over three hours assuming Bus 15 remains de-energized (PRA Calculation V.SPA. 11.003).The depletion is much slower once Bus 15 is restored and the emergency lights are no longer a load on the12 Battery (PRA Calculation V.SPA.1 1.009). The simulator runs demonstrated that Bus 15 can be re-energized via the bustie breaker in less than 30 minutes during a LOOP event and the battery charger canbe restored in less than an hour. Once the charger is restored the event is over. The assumptions in thePRA success strategy can be concluded to be reasonable.V.SPA.1 1.016Simulator Runs for BatteryCharger Significance Determination ProcessPage 7 of 8 5.0 References5.1 PRA Evaluation V.SPA. 11.003, Prairie Island Batter, Depletion Study PRA LOOP with EmergencyLighting and ISI Steady State Test Loads, Revision 0.5.2 PRA Evaluation V.SPA. 11.009, Prairie Island Batter, Depletion Study PRA LOOP with ISI SteadyState Test Loads, Revision 0.5.3 PRA Evaluation V.SPA. 11.012, Batteny Charger SDP: Accident Sequence Analysis, Revision 0.5.4 1C20.5 AOP1, Re-energizing 4.16kV Bus 15, Revision 12.5.5 1C20.9 AOP4, Failure of 12 Battery Charger, Revision 10.5.7 1ES-0.1, Reactor Trip Recover,, Revision 25.5.8 1C20.5 AOP4, Reenergizing 4.16kV Bus 15 Via Bustie Breakers, Revision 3W.V.SPA.1 1.016 Page 8 of 8Simulator Runs for BatteryCharger Significance Determination Process AfKc6hment Page 1 ofA,-XceIEnergy" IPrior Knowledge StatementSIMULATOR SCENARIO: Scenario performed in support of the Prairie Island Battery Charger SDP conducted on March 8h, 2011 andcommehcing at approximately 1500I confirm that I had no prior knowledge of the details used in the above simulator scenario. Further, I confirm that I had no knowledge of thedetails of the simulator run performed on March 5t, 2011. I understand that had I had prior knowledge of the scenario it would impact thelegitimacy and use of the information gathered in support of the Battery Charger SDP.PRINTED NAME JOB TITLE / RESPONSIBILITY SIGNATURE DATE NOTE2.5.6.7.8.9.10.NOTES:

faPageof 1SXcelEnergy- Prior Knowledge StatementSIMULATOR SCENARIO: Scenario performed in support of the Prairie Island Battery Charger SDP conducted on March 8th, 2011 andcommencinq at approximately 1500I confirm that I had no prior knowledge of the details used in the above simulator scenario. Further, I confirm that I had no knowledge of thedetails of the simulator run performed on March 5t, 2011; I understand that had I had prior knowledge of the scenario it would impactthelegitimacy and use of the information gathered in support of the Battery Charger SDP.PRINTED NAME JOB TITLE / RESPONSIBILITY _VNATURE DATE NOTE2.3.4.5.6.7.8.9.9i0- T_______1___10.NOTNOTES:.j AwIa.cXv~wo 2Z Page 1 of/A -I XceIEnergy SIMULATOR SCENARIO SECURITY AGREEMENTSIMULATOR SCENARIO: Scenario performed in support of the Prairie Island Battery Charger SDP conducted on March 8e, 2011 andcommencing at approximately 1500During the post-critique I agreed that I would NOT discuss any aspects associated with the contents of this simulator run with any other operatoruntil informed that it was acceptable to do so. I understand that violation of the conditions of this agreement may impact the legitimacy and useof the information gathered should subsequent runs of this scenario become necessary.PRINTED NAME JOB TITLE / RESPONSIBILITY SIGNATURE DATE NOTE1. .j _ .T-f)3. 1 t e 1kOA 3/5.6.7.8.9.10._NOTES:--

Page;kofT 4,SXeelEnergyl SIMULATOR SCENARIO SECURITY AGREEMENTSIMULATOR SCENARIO: Scenario performed in support of the Prairie Island Battery Charger SDP conducted on March 8t". 2011 andcommencing at approximately 1500During the post-critique I agreed that I would NOT discuss any aspects associated with the contents of this simulator run with any other operatoruntil informed that it was acceptable to do so. I understandthat violation of the conditions of this agreement may impact the legitimacy and useof the information gathered should subsequent runs of this scenario become necessary.PRINTED NAME JOB TITLE / RESPONSIBILITY SIGNATURE DATE NOTE2.3.4.5.6.7.8.9.10. _NOTES:U ENCLOSURE2BATTERY DEPLETION CALCULATION LOAD PROFILE3 pages follow Batterv DeDletion Calculation Load ProfilePurpose:The purpose of this document is to summarize the basis for the load profile used to determine thebattery depletion time at the Prairie Island Nuclear Generating Plant (PINGP). Battery depletiontime was needed to support the risk assessment of the battery charger lock up condition thatcould occur for the old battery chargers during loss of offsite power and safety injection accidentscenarios. For the purposes of the risk assessment evaluations, battery depletion is defined asthe time for the batteries to reach minimum design voltage when supplying the required loads.Discussion:Although battery depletion is defined as battery voltage reaching minimum design voltage whenthe batteries are supplying required loads, the risk assessment depletion calculations weredeveloped as best-estimate evaluations so that the actual plant and operator responses to theanalyzed events could be realistically evaluated. As a result, use of design-basis inputs for DCsystem loading would not be appropriate. Rather, a load profile based on actual, expectedsystem response was developed. The load profile used in the risk assessment depletioncalculations consists of three parts: a first minute transient portion, a steady state portion, and afinal minute transient portion. Development of each of the load profiles is discussed below.A one hour design-basis battery loading profile is developed in the design-basis battery sizingcalculations to meet the battery sizing requirements in the Updated Safety Analysis Report(USAR). The purpose of the load profile developed to meet the USAR requirements is todetermine a worst case and conservative load profile, thereby resulting in a conservative batterysize and greater battery capability. The load profile developed for the depletion calculations wasmodeled after the design-basis load profile with some adjustments to reflect expected systemresponse.The design-basis load profile developed for the USAR battery sizing requirements contains a firstminute transient portion, a steady state portion, and a final minute transient portion. However, thedesign-basis load profile and calculation contain conservative assumptions to ensure that thecalculation and required battery size has adequate margin to the minimum size required by theUSAR.In the design-basis load profile, the first minute transient portion of the load profile containsvarious changes in the DC load due to multiple breaker operations and device actuations. Thefirst minute profile modeled in the risk assessment battery depletion calculations is the same asthe first minute profile used in the design-basis calculations with a slight adjustment downward forthe inverter loads. The adjusted inverter loading was determined from reviewing historicaloperating data taken during regular inverter surveillances. Use of the adjusted design-basis loadprofile continues to result in a conservative first minute profile in the depletion calculations. Theloading includes many smaller loads that are assumed energized in the calculation which wouldactually de-energize on an event. These are further described below.The steady state portion of the battery depletion load profile was modified from the design-basisload profile. As stated above, the design-basis load profile contains conservative assumptions toprovide additional margin to actual system response. One of the major assumptions whichresults in an overly conservative steady state load in the design-basis load profile is that variousloads such as lights, relays, solenoid valves, etc. are modeled as energized during the entirescenario. While this assumption is appropriate for use in the design-basis evaluations that are todetermine conservative battery sizes, this assumption is overly conservative for an evaluation ofactual expected system response. As a result of these conservatisms, use of the design-basis steady state profile would result in much higher loading than what would be expected in a realevent. This is not consistent with a best estimate evaluation.A review of the major contributors of the steady state load estimated that the actual load would bereduced by approximately 50% or more from the design-basis steady state load values whenactual equipment operation is considered. This review identified various DC system componentsthat are modeled as a constant energized load which would actually de-energize on an event orhave only momentary actuations. For example, solenoid valves which de-energize to their failsafe position are modeled as being energized for the entire scenario. It was also identified thatdual indicating lights (on/off, open/close, etc.) were both included as energized for the entirescenario when only one light would be energized at a time. Reactor protection relays were alsomodeled as energized for the entire scenario when the relays would de-energize on a reactor trip.The Integrated Safety Injection (SI) Test simulates an SI with a Loss of Offsite Power (LOOP).During this test, the various devices which are required to respond to an event are actuated.Correspondingly, the DC load profile during the Integrated SI Test is representative of the loadprofile that would be expected during an actual event. The loading that occurs during theIntegrated SI test was compared to the actual load profile that occurred during a past inadvertentSI event. The two profiles were approximately equal, showing a difference of less than 2 amps.The steady state DC load value observed during the Integrated SI Test also includes additionalloads, such as inverters, that are present on Unit 1 due to operating conditions that are notpresent in the current design-basis calculations. Therefore, use of the worst case best estimatesteady-state load profile from either the Integrated SI Test or the inadvertent SI event provides aslightly conservative but realistic representation of the expected system response to a LOOP orSI event.This steady state load value was then adjusted upward for use in the risk assessment depletioncalculations. This upward load adjustment was to account for swing loads that could be presentin scenarios evaluated in the risk assessment but would not be seen in the Integrated SI Test.The swing loads accounted for an additional load of approximately 4 -6 amps depending on thebattery system being evaluated. An upward adjustment of 7.5% of this adjusted steady state loadwas also added to provide additional conservatism. This percentage increase resulted in anadditional load of approximately 9 amps applied to 11 and 12 batteries, approximately 3 ampsapplied to 21 battery, and approximately 2 amps applied to 22 battery.This worst case scenario was a failure of Train A AC which is the normal power source for theemergency lights. To account for this scenario, an additional adjustment to the steady state loaddescribed above was added to the 12 and 22 batteries to account for the emergency lights. Thisresulted in an increase of 110 amps for the 12 battery and approximately 66 amps for the 22battery at the evaluated voltages. These adjustments result in a final steady state load profilethat is slightly higher than would be expected but that can be used for the best-estimate batterydepletion calculations.The final minute of the load profile in both the design-basis load profile and the battery depletionload profile is a continuation of the steady state load described above with one addition. In thelast minute of the profile, it was assumed that operation of one 4160 VAC circuit breaker would berequired. The breaker operation is a momentary load with a relatively high load demand.Application of this load in the last minute of the profile is conservative as it causes a relativelysignificant drop in battery voltage due to the high current and length of time the battery has beendepleted. Since operation in the last minute is the most conservative time after the first minutedue to the length of time the battery has already been depleted, the modeled momentary load is abounding case for other miscellaneous momentary load operations which may occur. Theassumption of a breaker operation results in a conservative last minute profil Summary:The load profile developed for the battery depletion calculations is a realistic representation of theactual expected system response during a LOOP or SI event. Development of the load profile forthe risk assessment was based on the design-basis evaluation summarized in the USAR withmodifications to remove overly conservative assumptions that are not appropriate for a best-estimate evaluation. Removal of the conservatisms combined information from the design-basiscalculations as well as test data to obtain an accurate and conservative representation of the DCsystem load during an event. This resulted in battery depletion times which are representative ofactual battery capability.References1. PRA Evaluation V.SPA.1 1.006, Rev. 0, "Evaluation of Battery Depletion Differences"2. Calculation 91-02-11, Rev. 2, "PI Battery 11 Calculation"3. Calculation 91-02-12, Rev. 4, "PI Battery 12 Calculation"4. Calculation 91-02-21, Rev. 2, "PI 21 Battery Calculation"5. Calculation 91-02-22, Rev. 2, "PI Battery 22 Calculation"6. PRA Evaluation V.SPA.1 1.003, Rev. 0, "Prairie Island Battery Depletion Study PRA LOOPwith Emergency Lighting and ISI Steady State Test Loads"7. Prairie Island Updated Safety Analysis Report, Section 8, Rev. 31, "Plant Electrical Systems"8. Corrective Action Program Action Request #01270104, "Non conservative assumption in Unit1 Battery Calcs" ENCLOSURE 3V.SPA.11.006EVALUATION OF BATTERY DEPLETION DIFFERENCES20 pages follow Xcel EnergyPrairie Island Nuclear Generating PlantProbabilistic Risk AssessmentV.SPA.1 1.006Evaluation of Battery Depletion DifferencesMarch 2011Document Review FormDocument or Analysis Title: V.SPA.1 1.006: Evaluation of Battery Depletion DifferencesRevision of Document or 0Analysis:Date:Preparer: Robert Flaaen .i Date: ,/0E.Zo ijReviewer Greg Kvamme Date: 3 ' /ibof* " ' ,//,,/PRA Acceptance Review:Jayne E. Ritter Prairie IslandNuclear Generating Plant(PINGP)Evaluation of Battery Depletion Differences Table of Contents1.0 Purpose ................................................................................................... 32.0 Evaluation of DC System Loading .......................................................... 32.1 Comparison of Calculated Load to Observed Load .................................... 32 .1.1 11 D C S yste m ...................................................................................................... ..32 .1.2 12 D C S ystem ...................................................................................................... ..42.1.3 2 1 D C S ystem ...................................................................................................... ..62 .1.4 22 D C S ystem ...................................................................................................... ..72.2 DC Circuit Comparisons ............................................................................. 92 .2 .1 11 D C S ystem ...................................................................................................... ..92.2.2 12 D C S ystem ................................................................................................... ..102.2.3 2 1 D C S ystem ................................................................................................... ..102.2.4 22 D C S ystem .................................................................................................... ..113.0 Evaluation of Loading Used in Battery Depletion Calculations ............. 133.1 Station Blackout (SBO) Depletion Calculation ............................................ 133.2 Safety Injection on Offsite Power (SI) Depletion Calculation ...................... 143.3 Loss of Offsite Power (LOOP) Depletion Calculation ................................ 153.3.1 LOOP with Actual Inverter Loading .................................................................... 153.3.2 LOOP with Actual Inverter Loading and Failure of Opposite Train AC .............. 164.0 Other Influences on Battery Depletion Timing ...................................... 184.1 Minimum Allowable Battery Terminal Voltage ...................................... 185.0 Conclusion ............................................. 186.0 References .......................................................................................... 19 1.0 PurposeThe purpose of this evaluation is to document and provide justification for the differencesin battery depletion times calculated for Probabilistic Risk Assessment (PRA) purposes fora Station Blackout (SBO) scenario, Loss of Offsite Power (LOOP) scenario, and SafetyInjection on Offsite Power (SI) scenario. This evaluation will review the battery loadingthat was assumed in the calculations and describe the differences.2.0 Evaluation of DC System LoadingA battery loading profile of one hour is developed in the design basis battery sizingcalculations (Ref. 6.1, 6.2, 6.3, and 6.4) per requirements stated in the Updated SafetyAnalysis Report (USAR) (Ref 4.10). The design basis load profile is based on assumingworst case loading for loads to develop a conservative load profile. Additionally, otherthan major loads (breaker coils, spring charging motors, inverters), smaller loads (lights,misc relays, solenoids) are assumed on for the entire duration of the analysis oralternating lights and similar components (red/green indicating lights, separate open/closesolenoid valves on the same component, etc.) are assumed as both simultaneously on forthe entire duration of the analysis. This results in a conservative design basis load profileas the devices actually only operate for a short period of time and do not all operatesimultaneously.To obtain the load for these miscellaneous panels which feed such devices as solenoidvalves, relays, etc., the design basis calculation took all of the devices on a circuit andadded up their individual rated loads, whether the individual devices were on or not. Alldepletion calculations used the design basis calculation and design basis load profile as astarting point and modified the load profile as necessary to obtain battery depletion timessuitable for the specific evaluation being performed.A comparison of the design basis steady state DC load to the steady state load observedduring testing follows in Section 2.1. Additionally, some specific example of circuits areincluded in Section 2.2 by evaluating the design basis load and reviewing anticipatedloading on that circuit based on actual operation of devices.2.1 Comparison of Calculated Load to Observed LoadBecause of the conservative load profile used in the calculation, the DC load used inthe calculation is much greater than that experienced while testing simulated LOOP/SIconditions during Integrated SI testing and also experience during an inadvertent SIevent on Unit 2. During these events, the first 30-40 seconds contains a number oftransient periods due to breaker closures, valve and relay actuations, etc. However,after 30 seconds, the DC load settles to a steady state value. The steady state valueshown in the design basis calculations is during the 1 minute to 59 minute time period.When comparing this to steady state DC load values experienced during simulated oractual event conditions, the calculated value is much higher than what is actuallyexperienced. As the steady state load is the major influence on the depletion times,the use of a conservative steady state load values on the batteries can result in aconservative depletion time and would not be representative of actual system load orresponse.2.1.1 11 DC SystemThe design basis calculated load of the 11 DC system at steady state conditionsis approximately 123.5 amps (Ref. 6.1). This value does not include inverterloads based on assumptions within the calculation. The design basis inverterloading on 11 battery is approximately 129.5 amps (Ref. 6.1). From the lastperformance of the Integrated SI test shown below in Figure 1, it can be seen thatPage 3 of 19 the steady state load of the 11 DC system experience during the test isapproximately 115 amps.Unit I Train A 1R26 Data (10/23/2009)300150Time (Seconds)-Battery Float Current -11 Charger Current -DC System Demand (Charger-Float)Figure 1This steady state value from the Integrated SI test is assumed to contain theinverter loads as the inverter loads were not removed from the DC system duringthe event. This is due to a trip of the inverter AC input breaker on the largevoltage overshoot of the EDGs. The basis for this assumption is the differencebetween the pre-event DC load and the steady state load. This difference(approximately 83 amps) closely resembles the actual inverter load. It would beexpected that the steady state load would be approximately equal to or onlyslightly greater than the pre-event DC load due to the lack of the actuation ofloads and generally the same number of operating (running) loads (indicatinglights, continuously energized lights, etc.). This is confirmed by reviewingIntegrated SI test data and actual SI data from Unit 2 in which the inverter loadsdo not remain on the DC system. The comparison of the Unit 2 data showed thatthe steady state load was only a few amps higher than the pre-event load for bothan SI/LOOP and SI loading condition (Ref. Sections 2.1.3 and 2.1.4).The tripping of the inverter AC input breaker on a high voltage has been identifiedto occur on Unit 1 due to the Unit 1 EDG voltage response during transientloading (Ref. 6.6). This issue has been input into the corrective action programand is being evaluated for additional impact (Ref. 6.11).The profile above in Figure 1 does not include transferable DC panels 17 and 19.These panels are normally fed from the 11 DC system (Ref. 6.12) however, aretransferred to their alternate source (21 DC system) during a unit shutdown (Ref.6.13) are then returned to their normal source after a unit startup (Ref. 6.14). Thedesign basis load for these panels on the batteries is approximately 12.4 amps.2.1.2 12 DC SystemThe calculated load of the 12 DC system at steady state conditions isapproximately 201.5 amps (Ref. 6.2). This value does not include inverter loads,Page 4 of 19 but does include emergency lighting. The design basis inverter loading on 12battery is approximately 134.8 amps (Ref. 6.2). The design basis emergencylighting load on 12 battery is approximately 110 amps (Ref. 6.2). From the lastperformance of the Integrated SI test shown below in Figure 2, it can be seen thatthe steady state load of the 12 DC system is approximately 115 amps. Note thatsince the 12 battery charger was not included in the test, it is not shown in thisFigure.12 DC System Data from 1R26 Test (10/23/2009)2C o II II I I I I I l 1 l l I IT , IEb -- 1 1 -I 11 11 11 11I WI iI I + [II III IIII M1 II II I II JM I I I I II isIIIiI i I I Ji tN ISeconds-DC DemandFigure 2This steady state value from the Integrated SI test does not include theemergency lighting, however, it is assumed that the steady state value containsthe inverter loads as the inverter loads were not removed from the DC systemduring the event due to a trip of the inverter AC input breaker on the large voltageovershoot of the EDGs. This is due to the difference between the pre-event DCload and the steady state load. This difference (approximately 92 amps) closelyresembles the actual inverter load. It would be expected that the steady stateload would be approximately equal to or only slightly greater than the pre-eventDC load due to the lack of the actuation of loads and generally the same numberof operating (running) loads (indicating lights, continuously energized lights, etc.).This is confirmed by reviewing Integrated SI test data and actual SI data from Unit2 in which the inverter loads do not remain on the DC system. The comparison ofthe Unit 2 data showed that the steady state load was only a few amps higherthan the pre-event load for both an SI/LOOP and SI loading condition (Ref.Sections 2.1.3 and 2.1.4).The tripping of the inverter AC input breaker on a high voltage has been identifiedto occur on Unit 1 due to the Unit 1 EDG voltage response during transientloading (Ref. 6.6). This issue has been input into the corrective action programand is being evaluated for additional impact (Ref. 6.11).The profile above in Figure 2 does not include transferable DC panels 14 and 18.These panels are normally fed from the 12 DC system (Ref. 6.12) however, arePage 5 of 19 transferred to their alternate source (22 DC system) during a unit shutdown (Ref.6.13) are then returned to their normal source after a unit startup (Ref. 6.14). Thedesign basis load for these panels on the batteries is approximately 8 amps.2.1.3 21 DC SystemThe calculated load of the 21 DC system at steady state conditions isapproximately 113.1 amps (Ref. 6.3). This value does not include inverter loads.The design basis inverter loading on 21 battery is approximately 94.6 amps (Ref.6.3). From the last performance of the Integrated SI test shown below in Figure 3,it can be seen that the steady state load of the 21 DC system is approximately 36amps.Unit 2 Train A 2R26 Data (5/17/2010)200180160140120100806040E i i i i i i i i i i i i i i i ! i i i i 4 " i i i i i i i i i i I i i ! i II I I I I I I I I I I I II I I ¶ II I I I I I I I I I I I ICL11 Ill! I 111111 N 11 W Ill 11111 1MIM 11111111111............-..... .. ........ ..... ...0-20-40-60-80-100-120fl1i iiii i i F.11 Sli iiiiii i~ Ti17lYIT F 1II~.ISecondsi ?U M ý3R1-21 Battery Float Amps -21 Battery Charger Amps -21 DC System Demand IFigure 3Additionally, Unit 2 experienced an inadvertent SI event in 2007. Data taken fromthat event is shown below in Figure 4. From this data it can be seen that thesteady state load of the 21 DC system is approximately 37 amps.Page 6 of 19 4/5/2007 U2 SI Event -Train A DC Loading (1st Minute)Load Step 1 2 3 4 5 6 7110.000090.000080.000070.000060.000050,0000400000tE 30000020.000-200000 V I-300000-400000-50.0000Tlme1- 21 Battery Float -21 Battery ChargerFigure 42.1.4 22 DC SystemThe calculated load of the 22 DC system at steady state conditions isapproximately 155.6 amps (Ref. 6.4). This value does not include inverter loads,but does include emergency lighting. The design basis inverter loading on 22battery is approximately 103.5 amps (Ref. 6.4). The design basis emergencylighting load on 22 battery is approximately 65 amps (Ref. 6.4). From the lastperformance of the Integrated SI test shown below in Figure 5, it can be seen thatthe steady state load of the 22 DC system is approximately 21 amps.Unit 2 Train B 2R26 Data (5/17/2010)250200II I150E o .I II-o 1Seconds1- 22 Battery Roat Amps -22 Battery Charger Amps -22 DC System DemandFigure 5Page 7 of 19 Additionally, Unit 2 experienced an inadvertent SI event in 2007. Data taken fromthat event is shown below in Figure 6. From this data it can be seen that thesteady state load of the 22 DC system is approximately 19.5 amps.4/5/2007 U2 SI Event -Train B DC Loading (lt Min)Load Step 1 2 3 4 5 6 7I9080706050403020 110 L VAo -" ^ -,.,s. V-10-20-30-40-50 .... ....Time1-22 BteyFlot -22 WeryCha~rer]Figure 6Page 8 of 19 2.2 DC Circuit ComparisonsThis section will look at some of the DC system circuits and compare the design basisloading used in the design basis calculation with estimated loading based on actualdevice operation to give some example of the conservatisms that are present in thedesign basis load profile of the batteries. The design basis calculations obtain the DCloading information from the Master DC Load List (Ref. 6.15). However, as statedabove under Section 2.0, the calculations summed up the rated load of each deviceon the circuit within miscellaneous load panels to obtain the panel load and did notconsider device operation. This resulted in a conservative load value.Reference 6.15 also contained information which identified the expected operation ofspecific devices on a circuit. This was done by reviewing equipment operation,drawings, control circuits, etc., to try and determine when and if a device wouldoperate during an event. Using this information, a load value which more accuratelyresembles actual expected load can be estimated. This load value is still slightlyconservative due to the use of worst case loading of individual devices andconservative device load assumptions where specific manufacturer data could not belocated. The following sections will review the design basis load for various panels onthe system based on Attachment J of References 6.1, 6.2, 6.3, and 6.4 and comparethat to estimated load values based on device operation from Reference 6.15.2.2.1 11 DC SystemThe major contributors to the design basis steady state load of the 11 DC systemas shown in Reference 6.1 are panels 13, 15, 17, 19, 151,152, 153, and 191.The design basis load of these panels at nominal DC voltage (125VDC) istabulated in Attachment J of Reference 6.1. The expected steady state load for aHSD condition, such as during a LOOP, can be estimated using the Reference6.15 information of whether the device would operate during the event andactually be a load on the DC system. The different load values are comparedbelow in Table 1.DC Panel Design Basis Load Estimated Expected Load % ReductionFrom Attachment J of From Reference 4.15Reference 4.1 (Amps) (Amps)15 17.64 7.11 60%17 4.84 3.26 33%19 7.22 4.07 44%151 23.54 14.04 40%152 9.44 6.88 27%153 5.67 1.24 78%191 6.77 2.15 68%Total 75.12 38.75 48%Table 1: Comparison of 11 DC System LoadingPanel 13 is not included in the above table since it is not detailed in Reference6.15. Assuming a 48% load reduction for panel 13 to be consistent with the totalload reduction seen by the above panels, panel 13 load can also be consideredas shown below in Table 2.Page 9 of 19 DC Panel Design Basis Load Estimated Expected Load % ReductionFrom Attachment J of From Reference 4.15Reference 4.1 (Amps) (Amps)13 34.56 16.73* 52%15 17.64 7.11 60%17 4.84 3.26 33%19 7.22 4.07 44%151 23.54 14.04 40%152 9.44 6.88 27%153 5.67 1.24 78%191 6.77 2.15 68%Total 109.68 55.48 49%*Assumed Load Reduction of 48%Table 2: Comparison of 11 DC System Loading with Panel 13This shows that the design basis steady state load for the 11 DC system is veryconservative to expected and observed loading and is not reflective of actualsystem performance or loading.2.2.2 12 DC SystemThe major contributors to the design basis steady state load of the 12 DC systemas shown in Reference 6.2 are panels 14, 16, 161,162, 161,181. The designbasis load of these panels at nominal DC voltage (1 25VDC) is tabulated inAttachment J of Reference 6.2. The expected steady state load for a HSDcondition, such as during a LOOP, can be estimated using the Reference 6.15information of whether the device would operate during the event and actually bea load on the DC system. The different load values are compared in Table 3.DC Panel Design Basis Load Estimated Expected Load % ReductionFrom Attachment J of From Reference 4.15Reference 4.2 (Amps) (Amps)14 6.74 2.95 56%16 41.59 8.54 79%18 1.25 1.15 8%161 21.35 3.28 85%162 6.72 2.67 60%163 3.41 0.42 88%Total 81.06 19.01 77%Table 3: Comparison of 12 DC System LoadingThis shows that the design basis steady state load for the 12 DC system is veryconservative to expected and observed loading and is not reflective of actualsystem performance or loading.2.2.3 21 DC SystemThe major contributors to the design basis steady state load of the 21 DC systemas shown in Reference 6.3 are panels 17, 19, 23, 25, 251, 252, and 253. Thedesign basis load of these panels at nominal DC voltage (125VDC) is tabulated inAttachment J of Reference 6.3. The expected steady state load for a HSDcondition, such as during a LOOP, can be estimated using the Reference 6.15information of whether the device would operate during the event and actually bea load on the DC system. The different load values are compared in Table 4.Page 10 of 19 DC Panel Design Basis Load Estimated Expected Load % ReductionFrom Attachment J of From Reference 4.15Reference 4.3 (Amps) (Amps)17 4.84 3.26 33%19 5.13 4.07 21%25 18.23 3.59 80%251 11.85 5.2 56%252 8.63 5.31 38%253 6.33 1.55 76%Total 55.01 22.98 58%Table 4: Comparison of 21 DC System LoadingPanel 23 is not included in the above table since it is not detailed in Reference6.15. Assuming a 50% load reduction for panel 23 to be consistent with the totalload reduction seen by the above panels, panel 23 load can also be consideredas shown below in Table 5.DC Panel Design Basis Load Estimated Expected Load % ReductionFrom Attachment J of From Reference 4.15Reference 4.3 (Amps) (Amps)17 4.84 3.26 33%19 5.13 4.07 21%23 33.1 16.55* 50%25 14.16 3.59 75%251 11.85 5.2 56%252 8.63 5.31 38%253 6.33 1.55 76%Total 84.04 39.53 53%*Assumed Load Reduction of 50%Table 5: Comparison of 21 DC System Loading with Panel 23This shows that the design basis steady state load for the 21 DC system is veryconservative to expected and observed loading and is not reflective of actualsystem performance or loading.2.2.4 22 DC SystemThe major contributors to the design basis steady state load of the 22 DC systemas shown in Reference 6.4 are panels 14, 18, 26, 261, 262, and 263. The designbasis load of these panels at nominal DC voltage (1 25VDC) is tabulated inAttachment J of Reference 6.4. The expected steady state load for a HSDcondition, such as during a LOOP, can be estimated using the Reference 6.15information of whether the device would operate during the event and actually bea load on the DC system. The different load values are compared in Table 6.DC Panel Design Basis Load Estimated Expected Load % ReductionFrom Attachment J of From Reference 4.15Reference 4.2 (Amps) (Amps)14 6.82 2.95 57%18 1.25 1.15 8%26 30.39 5.2 83%261 11.14 2.81 75%262 5.52 0.21 96%263 3.54 0.42 88%Total 58.66 12.74 78%Table 6: Comparison of 22 DC System LoadingPage 11 of 19 This shows that the design basis steady state load for the 22 DC system is veryconservative to expected and observed loading and is not reflective of actualsystem performance or loading.Page 12 of 19 3.0 Evaluation of Loading Used in Battery Depletion Calculations3.1 Station Blackout (SBO) Depletion CalculationOn the occurrence of an SBO, the batteries supply the emergency lights (whereapplicable) and inverters due to a loss of AC power. The SBO depletion calculationused the design basis load profile and modified the inverter (INV) loading to morerealistically resemble actual data by removing the conservatism in the inverter load.The inverter load values that were used were based on actual load readings takenduring surveillance procedures of the DC system. The approximate inverter loadvalues used in the SBO calculation, the difference from the design basis inverter load,as well as the resultant steady state load in the SBO calculation and is shown belowin Table 1. The SBO steady state load includes values with and without theemergency lights (E.L.) where applicable as it was evaluated that during an SBO, theemergency lights are manually shed from the DC system 40 minutes into the eventper emergency procedures. (Ref. 6.5)DC System Approximate Inverter Difference In Approximate SteadyLoad in SBO Inverter Load State Load in SBODepletion Calculation From Design Depletion Calculation(Ref. 6.5) Basis Calculation (Ref. 6.5)11 DC Inverters 97.7 amps 31.8 amps lower 219 amps12 DC Inverters 107.2 amps 27.6 amps lower 305 amps (w/ E.L.)1 1 197 amps (w/o E.L.)21 DC Inverters 89.1 amps 5.5 amps lower 201 amps22 DC Inverters 85.36 amps 18.1 amps lower 239 amps (w/ E.L.)174 amps (w/o E.L.)Table 1This steady state load that was used in the SBO depletion calculations still containsthe conservatisms of various loads being energized during the entire event. Whencomparing the steady state load used in the SBO depletion calculation to the DC loadprofile during the Integrated SI Test in Figures 1-4 under Section 2.1, it can be seenthat the steady state load used in the SBO depletion calculation is above the steadystate load seen under actual conditions and in some cases is above the highest loadexperience during the entire Integrated SI Test when the Emergency Diesel Generator(EDG) is starting up and there is no AC power.DC Maximum DC System DC System Steady Approximate SteadySystem Load During Sequence State Load From State Load in SBOFrom Section 2.1 Figures Section 2.1 Figures Depletion Calculation(ISI Test Data) (includes Inverter andE.L (if applicable))(Ref. 6.5)11 133 amps (2) 115 amps 219 amps12 235 amps (13 115 amps 305 amps (w/ E.L.)197 amps (w/o E.L.)21 113 amps 37 amps 201 amps22 145 amps V) 21 amps 239 amps (w/ E.L.)174 amps (w/o E.L.)Table 2(1) The load value listed here also includes the Inverters and(2) The load value listed includes the Inverters.Emergency Lighting.Page 13 of 19 This shows that the steady state load values used in the SBO depletion calculationwere still very conservative even with the adjustment of the inverter loads. However,the depletion times reached in the calculation were adequate for the evaluation thatwas occurring at the time and therefore, no additional conservatism needed to beremoved.The SBO depletion calculation (Ref 6.5) provided the following results:Battery Depletion TimeBattery 11 165 minutes (2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> 45 minutes)Battery 12 217 minutes (3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> 37 minutes)Battery 21 184 minutes (3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> 04 minutes)Battery 22 239 minutes (3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> 59 minutes)3.2 Safety Injection on Offsite Power (SI) Depletion CalculationThis event occurs on offsite power and therefore, there is no loss of AC power to theemergency lights or the inverters and they remain powered from their respective ACsources. This calculation used the design basis load profile, modified it to representSI sequencing without a loss of offsite power, and removed the inverters and theemergency lighting (as applicable) due to no loss of AC power. Table 3 shows thesteady state load values used in the depletion calculation and compares them tosteady state load values seen from Figures 1 -4 under Section 2.1.DC System Approximate Steady State Approximate SteadyLoad in SI Depletion States Load FromCalculation (Ref. 6.7) Section 2.1 Figures11 124 amps 115 amps 12 93 amps 115 amps 1'21 114 amps 37 amps22 91 amps 21 ampsTable 3(1) The load value listed includes the Inverters.As shown above in the table, the steady state load for 12 DC system from Section2.1.2 is higher than that used in the SI only depletion calculation. The load profileunder Section 2.1.2 is a SI/LOOP condition. As discussed in Sections 2.1.1 and2.1.2, the load profiles for 11 and 12 DC system contained the inverter loads duringthe entire sequence, as well as during the steady state portion of the profile, due tothe inverters' AC input breaker tripping on an EDG voltage overshoot causing them tobe a continuous load on the DC system. The event analyzed under the SI onlydepletion calculation is when offsite power is available. The voltage overshootsexperienced during Unit 1 EDG sequence loading do not occur when sequencing onoffsite power. Therefore, the inverters would not be a steady state load on the Unit 1DC system for this event. If the inverter loads were removed from the profiles underSections 2.1.1 and 2.1.2, the steady state load would be slightly higher than the pre-event load of approximately 30 amps for 11 DC system and 20 amps for 12 DCsystem shown in Figures 1 and 2.Page 14 of 19 The steady state load that was used in the SI only depletion calculations still containsthe conservatisms of various loads being energized during the entire event. Whencomparing the steady state load used in the depletion calculation to the DC loadprofile during the Integrated SI Test in Figures 1-4 under Section 2.1, it can be seenthat the steady state load used in the calculation is very conservative. However, thedepletion times reached in the calculation were adequate for the evaluation that wasoccurring at the time and therefore, no additional conservatism needed to beremoved.The SI only depletion calculation (Ref 6.7) provided the following results:Battery Depletion Time To Design Basis VoltageBattery 11 460 minutes (7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> 40 minutes)Battery 12 710 minutes (11 hours1.273148e-4 days <br />0.00306 hours <br />1.818783e-5 weeks <br />4.1855e-6 months <br /> 50 minutes)Battery 21 515 minutes (8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> 35 minutes)Battery 22 645 minutes (10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> 45 minutes)3.3 Loss of Offsite Power (LOOP) Depletion CalculationThis event was further evaluated into two separate scenarios: (1) LOOP with ActualInverter Loading (Ref. 6.8) and (2) LOOP with Actual Inverter Loading and Failure ofOpposite Train AC (Ref. 6.9).The initial case (1) evaluated the actual response where only the Unit 1 invertersbecome a load on the DC system due to tripping of their AC input breaker on a Unit 1EDG overshoot. Unit 2 inverters were assumed to remain on AC power since it is notexpected that the Unit 2 inverters' AC input breaker will trip due to a lack of significantovershoots during EDG sequencing (Ref. 6.6). This case also modified the steadystate load to match what is seen during the Integrated SI Test or what was seenduring the inadvertent SI event. This removes the conservative assumption in whichvarious loads are continuously energized and more closely resembles actual systemloading and response.The second case (2) used the load profile developed under case 1 in which theinverters were a load on the Unit 1 EDGs and the steady state load matched theactual test or event data. Additionally, this case assumed a failure of the oppositetrain's AC power source. The emergency lighting is fed from Train A AC power andTrain B DC power. By assuming a failure of the Train A AC power, the emergencylights become a load on the Train B DC system during the entire event. This isconsidered the limiting case for DC loading and battery depletion during a LOOPevent.3.3.1 LOOP with Actual Inverter LoadingThis case used the same load profile developed for the SBO calculations exceptthat the emergency lights were removed from the load profile after the EDGsprovided AC power to the bus, the Unit 2 inverters were removed from the loadprofile after the EDGs provided AC power to the bus (the Unit 1 invertersremained on the DC system), and the steady state load was adjusted toapproximately match actual test or event data. The missing panels describedunder Section 2.1 for Unit 1 DC systems were conservatively added to the steadystate load values observed from the tests for both units, plus some additionalmargin.Page 15 of 19 Table 4 shows the steady state load values used in the depletion calculation andcompares them to steady state load values seen from Figures 1 -4 under Section2.1.DC System Approximate Steady Approximate SteadyState Load in Case 1 States Load FromLOOP Depletion Section 2.1 FiguresCalculation (Ref. 6.8)11 130 amps 115 amps12 128 amps 115 amps21 50 amps 37 amps22 30 amps 21 ampsTable 4This steady state load that was used in the Case 1 LOOP depletion calculationsstill contains some margin to actual values but is much more reflective of actualplant conditions and a more realistic load value.The Case 1 LOOP (with actual inverter loading and Steady State Load) depletioncalculation (Ref 6.8) provided the following results:Battery Depletion Time To Design Basis VoltageBattery 11 Greater than 6.5 hour5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />sBattery 12 Greater than 7.5 hour5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />sBattery 21 Greater than 22 hour2.546296e-4 days <br />0.00611 hours <br />3.637566e-5 weeks <br />8.371e-6 months <br />sBattery 22 Greater than 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />s3.3.2 LOOP with Actual Inverter Loading and Failure of Opposite Train ACThis case used the same load profile for the Case 1 LOOP depletion calculationdiscussed in Section 3.3.1, however, due to the assumed failure of the oppositetrain AC power source, the emergency lights (EL) were included as a load on 12and 22 batteries during the entire time period. Table 5 shows the steady stateload values used in the depletion calculation.DC System Approximate Steady State Load in Case 2LOOP Depletion Calculation (Ref. 6.9)11 130 amps z12 238 amps (1)21 50 amps (2)22 96 amps "ITable 5(1) The load value listed here also includes the Inverters and Emergency Lighting.(2) The load value listed includes the Inverters.(3) The load value listed includes Emergency LightingThis steady state load that was used in the Case 2 LOOP depletion calculationsstill contains some margin to actual values but is much more reflective of actualplant conditions and a more realistic load value when the emergency lights wouldbe powered from the DC system due to a failure of the opposite train AC.Page 16 of 19 The Case 2 LOOP (with actual inverter loading and Failure of Opposite Train ACPower) depletion calculation (Ref 6.9) provided the following results:Battery Depletion Time To Design Basis VoltageBattery 11 Greater than 6.5 hour5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />sBattery 12 Greater than 3 hour3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />sBattery 21 Greater than 22 hour2.546296e-4 days <br />0.00611 hours <br />3.637566e-5 weeks <br />8.371e-6 months <br />sBattery 22 Greater than 9 hour1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br />sPage 17 of 19 4.0 Other Influences on Battery Depletion Timing4.1 Minimum Allowable Battery Terminal VoltageThe minimum allowable terminal voltage is specific to each battery and is determinedby the battery sizing calculations (Ref. 6.1 to 6.4). The depletion time for the batteryto reach minimum terminal voltage is largely influenced by the steady state load onthe battery as described above, however, the minimum allowable terminal voltagealso has an affect on the battery depletion time. The minimum allowable terminalvoltage values for each battery is listed in table below.Battery Minimum Allowable Terminal VoltageBattery 11 110.34 Vdc (Reference 6.1 )Battery 12 109.55 Vdc (Reference 6.2)Battery 21 110.61 Vdc (Reference 6.3)Battery 22 110.08 Vdc (Reference 6.4)Given similar loading on each battery, the depletion time will be shorter for a batterywith a higher minimum allowable terminal voltage limit. For example, in Section 3.3.1(LOOP with Actual Inverter Loading), the 11 battery and 12 battery have very similarsteady state loads (130 amps and 128 amps, respectively). However, the depletiontimes for 11 battery and 12 battery are different (6.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> and 7.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />,respectively). The 12 battery depletion time is 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> longer due to the lowerminimum allowable terminal voltage.5.0 ConclusionThe evaluation performed above in Section 2.0 showed that the design basis loadingprofile of the batteries is very conservative when compared to actual data. Whenperforming battery depletion studies to obtain a best estimate depletion time, the use oftest or actual event data represents a more accurate reflection of system performance andloading.As the PRA evaluations progressed, significant initiating events were identified whichrequired re-evaluation of the battery depletion calculations in order to identifyconservatisms. As part of that process, conservatisms were removed from the designbasis load profile to more accurately match real data.Page 18 of 19 6.0 References6.1 Calculation 91-02-11, Rev. 2, "PI Battery 11 Calculation"6.2 Calculation 91-02-12, Rev. 4, "PI Battery 12 Calculation"6.3 Calculation 91-02-21, Rev. 2, "PI 21 Battery Calculation"6.4 Calculation 91-02-22, Rev. 2, "PI Battery 22 Calculation"6.5 PRA Evaluation V.SPA.1 0.013, Rev. 0, "Battery Depletion Calculation"6.6 PRA Evaluation V.SPA.1 1.005, Rev. 0, "Evaluation of Inverter Source Selection DuringEmergency Diesel Generator Loading"6.7 PRA Evaluation V.SPA.1 1.004, Rev. 0, "Prairie Island PRA SI Only Battery DepletionStudy"6.8 PRA Evaluation V.SPA.1 1.009, Rev. 0, "Prairie Island Battery Depletion Study PRALOOP with ISI Steady State Test Loads"6.9 PRA Evaluation V.SPA.1 1.003, Rev. 0, "Prairie Island Battery Depletion Study PRALOOP with Emergency Lighting and ISI Steady State Test Loads"6.10 Prairie Island Updated Safety Analysis Report, Section 8, Rev. 32P, "Plant ElectricalSystems"6.11 Corrective Action Program Action Request #01270104, "Non conservative assumptionin Unit 1 Battery Calcs"6.12 Operating Procedure C20.9, Rev. 29, "Station Battery & DC Distribution System"6.13 Operating Procedure 1C1.3, Rev. 69, "Unit 1 Shutdown"6.14 Operating Procedure 1C1.4, Rev. 51, "Unit 1 Power Operation"6.15 Master DC Load List (File MasterDCLddlst_05-31-01 .xls Dated 05/31-01 at 1:08pm)Page 19 of 19