ML061740010

McGuire Nuclear Station Technical Information Meeting

ML061740010
Person / Time
Site:	McGuire, Mcguire
Issue date:	05/19/2006
From:	Duke Energy Corp
To:	Office of Nuclear Reactor Regulation
References
Download: ML061740010 (31)

Text

1McGuire Nuclear StationTechnical Information MeetingAtlanta, GAMay 19, 2006 2Duke ParticipantsJim Kammer, McGuire Safety Assurance ManagerJeff Thomas, McGuire Regulatory Compliance ManagerEric Henshaw, Duke Safety Analysis Senior EngineerMike Weiner, McGuire Operations Senior Engineer 3 AgendaOpening RemarksBackgroundUnresolved IssuesPostulated Event DescriptionEmergency Procedure / UFSAR Changes10CFR50.59 RationaleSummary 4 Background10/04 -McGuire questioned if sufficient sump level would exist to complete transfer to cold leg recirculation following certain small break loss of coolant accidents (SBLOCAs) Issue entered into corrective action program (PIP M-04-5115)Issue considered within the current licensing basisEntered the Operability Determination Process 5 BackgroundPrompt Corrective Actions Enhanced margin by opening refueling canal drain path from upper containment Increased Refueling Water Storage Tank (FWST) level Subsequent Corrective ActionsRevised Emergency Procedures to incorporate alternate SBLOCA swapover sequence for specific SBLOCAsConducted training to enhance awarenessCompleted Operability Evaluation confirms that sufficient water volume exists. Nonconformance with UFSAR identified (3/05) 6 BackgroundSubsequent Corrective Actions (continued)Installed precision containment sump level switches in Unit 2 (8/05) and Unit 1 (10/05) Revised UFSAR to clear the nonconformance and to describe the SBLOCA scenarios in which Containment Spray is not operating and the actions to be taken to mitigate such events (9/05).

7Unresolved Issues 1.Did changes to emergency procedures and/or UFSAR 6.3.2.6 require changes to Tec hnical Specification (TS) 3.4.15, Reactor Coolant System Leakage Detection Instrumentation, per 50.59(c)(1)(i)?

2.Did changes to emergency procedures and/or UFSAR 6.3.2.6 result in more than a minimal increase in the likelihood of a malfunction of a structure system, or component (SSC) important to safety previously evaluated in the final safety analysis report per 50.59(c)(2)(ii)?

8Unresolved Issues 3.Did changes to emergency procedures and/or UFSAR 6.3.2.6 create a possibility for an accident of a different type than any previously evaluated in the final safety analysis report (as updated) per 50.59(c)(2)(v)?

4.Did changes to emergency procedures and/or UFSAR 6.3.2.6 create a possibility for malfunction of an SSC important to safety with a different result than any previously evaluated in the final safety analysis report (as updated) per 50.59(c)(2)(vi)?

5.Should the changes to UFSAR 6.3.2.6 have been evaluated via a 50.59 Evaluation instead of a 50.59 Screening?

9Postulated Event DescriptionOverviewReview of Containment ResponseLarge Break LOCASmall Break LOCA Minimum Sump Level SBLOCA evaluationsConservative InputsTypical Sequence of EventsContainment Spray Functions 10Postulated Event DescriptionObjective of minimum sump level cases(from an analyst's perspective)Maximize leakage to incore roomMinimize ice melt Avoid containment spray operationActuation transfers FWST fluid to containment sumpActuation speeds up event time line 11Postulated Event DescriptionSBLOCA minimum sump level evaluationFocus changed from maximizing pressure/temperature to minimizing ice meltUFSAR Chapter 6 containment response analyses performed from EOC hot full power conditions, which are conservative for evaluating peak containment pressure & maximum sump temperature.Peak containment pressure (UFSAR Chapter 6) not limiting for SBLOCA, and not challenged if minimum sump level is an issue (i.e., little ice melt).Peak clad temperature (PCT) (UFSAR Chapter 15.6.5) not challenged for breaks that do not actuate containment spray 12Postulated Event DescriptionComparison of Conservative InputsTS minTS maxFWST temperature Max noneLower containment ventilation Min TS maxIce temperatureMax 2 trainMin 1 trainECCS flow ratesBOC (min)EOC (max)Decay heatMin Sump LevelPeak Containment Pressure 13Postulated Event DescriptionTypical Sequence of Events for SBLOCA that does not cause containment spray actuation, including procedural operator actions (preliminary evaluation results)Initiated from Hot Zero Power (HZP) 557 o FMaximum ECCS flowCold FWSTLow decay heat (BOC)Lower containment non-safety coolers operateStart cooldown 60 minutes after Safety InjectionOperator performs SI reduction sequence 14Postulated Event DescriptionHZP 0.005 ft2 cold leg nozzle break w/ Max ECCS, 65 oF FWST (preliminary evaluation results)Time [min]Description0 Break initiationn/a Reactor tripn/a Turbine trip5.2SI actuation on low RCS pressure65.2Operator initiates cooldown (60 min after SI)81.1Operator trips RCPson loss of subcooled margin84.8Operator cycles Pzr PORV to obtain 25% Pzr level 87.4Operator isolates CLAs (Pzr level > 25% & subcooled margin) (beginning of recovery)114.1Operator begins SI reduction sequence186.6Hot leg temperature reaches 350 oF (exit Mode 3, RHR initiation setpt)299.1End simulation -Thot reaches 250 oF (@ ~5 hours) 15Postulated Event DescriptionSummary of conditions at 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> (end of simulation) (preliminary evaluation results)Pzrpressure = 175 psigPzr level = 52%Thot = 250 o FSM pressure = 13 psigFWST has not reached FWST lo-level setpoint~2 hours to FWST lo-level & ~6.7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> to FWST lo-lo level (assuming ECCS flow of 350 gpm)Total ECCS flow = 347 gpm (1 charging pump)RHR flow = 0 gpmContainment Spray flow = 0 gpmSump level = 0.23 ft, incore room is full94.5% (1.786E6 lbm) of ice remains (initial ice mass = 1.89E6 lbm) 16Postulated Event DescriptionFunctions provided by Containment SprayMaintain pressure below containment design.Containment pressure not a concern for min sump level casesScrub atmosphere to reduce doseRod ejection provides the limiting SBLOCA source termContainment spray not credited in rod ejection dose analysisRemove heat from containment sump via heat exchangerFunction performed after FWST reaches lo-lo level setpointAfter FWST lo-level containment spray operation part of long-term recovery for minimum sump level cases 17Emergency Procedure / UFSAR ChangesOverviewNormal transfer sequenceAlternate sequence (procedure changes) 18Emergency Procedure / UFSAR Changes Lo LoLoNormalAlternateRHR CCP+HHSI SprayOffFWST(Spray off, Low Sump level)RHR -Low Head SI CCP -Charging SI HHSI -High Head SISwapover Sequence (Pumps Taking Suction From FWST)RHR CCP+HHSI Spray 19Emergency Procedure / UFSAR ChangesNormal Transfer to CLR SequenceFWST lo-level alarmND pump auto-swap from FWST to containment sumpOperator manually re-aligns NI/NV pump suction from FWST to RHR pump dischargeFWST lo-lo level alarmOperator stops Containment Spray pumpsOperator manually re-aligns Containment Spray pump suction from FWST to containment sumpOperator manually restarts Containment Spray pumps 20Emergency Procedure / UFSAR ChangesTransfer to Cold Leg Recirc Consideration for SBLOCA with Containment Spray off:For SBLOCA with Containment Spray off, the volume in the FWST between FWST Lo and Lo Lo level will be left in the tank using the normal swapover sequence. If the break is in theincore room, we need this volume to be pumped into containment. An alternate sequence may be required to use the water between the FWST Lo and Lo Lo level setpoints.

21Emergency Procedure / UFSAR ChangesThe alternate sequence enclosure of the Emergency Procedure (EP) does the following:Ensures proper swap of RHR pumps to sump and confirms that RHR pumps are offEnsures Spray pumps cannot start by pulling power fusesNV and NI pumps to continue to run with suction on FWST until FWST Lo Lo level is reachedAfter FWST Lo Lo level is reached:The ND pumps are started on sump and NV&NI are aligned to piggy back modeThe Spray pumps are aligned to sumpManual start of one Spray pump is performed as needed with TSC concurrence 22Emergency Procedure / UFSAR ChangesProcedural ConsiderationsWithout additional guidance, NI/NV pumps might be at risk following a Spray pump auto-startMass and energy release to containment decreases as RCS pressure and temperature decrease; GOTHIC analysis would not predict a Containment Spray auto-start Engineering judgment leads to conclusion that while not needed, hypothetically Containment Spray auto-start still possible considering the following:Instrument air in-leakageLoss of non-safety coolersTherefore, Containment Spray pump start should be mitigated 23Emergency Procedure / UFSAR ChangesRevised UFSAR 6.3.2.6 to note:Credible NC System break locations have been identified that may cause a diversion of coolant inventory to the Incore Instrument RoomFor SBLOCAs where Containment Spray does not actuate, Emergency Procedures (EPs) ensure ND pumps are off prior to swap to sump if the desired sump level is not confirmed.When FWST lo-level is reached and desired sump level is not indicated at FWST lo-level,EPs provide an alternate swapover (as opposed to the LBLOCA sequence described in Table 6-125) to cold leg recirculation to ensure that adequate sump inventoryis available (and maintained) for sump recirculation to provide adequate core cooling for such SBLOCA events 24 10CFR50.59 Rationale 1.Rationale for why UFSAR and/or emergency procedure changes did not require changes to TS 3.4.15 The changes to the UFSAR and the emergency procedures involved an alternate swap-over sequence and did not affect our ability to detect, and indicate in the control room, reactor coolant pressure boundary leakageTherefore, the UFSAR and/or emergency procedure changes did not require changes to TS 3.4.15 pursuant to 50.59(c)(1)(i) 25 10CFR50.59 Rationale 2.Rationale for why UFSAR and/or emergency procedure changes did not result in more than a minimal increase in the likelihood of a malfunction of a SSC important to safety The intended design function of Containment Spray is not required at the time the power fuses are removedRegarding containment pressure response, the plant is in long term recovery where manual operator action can be creditedLocal operator actions during containment pressure recovery are reasonable and confirmed in the control roomContainment Spray is not required to perform any automatic protective action to correct any abnormal situation before any safety limit is exceeded following removal of the power fuses The changes do not credit manual action in place of an automatic safety limit protection 26 10CFR50.59 Rationale 3.Rationale for why changes to emergency procedures and/or the UFSAR did not create a possibility for an accident of a different typeStation response to LOCAs previously evaluated in the UFSAR is unchangedThe frequency of occurrence of LOCAs evaluated in the UFSAR is unchanged The changes apply to the mitigation of SBLOCAs from credible break locations that do not initiate Containment Spray during post accident recovery 27 10CFR50.59 Rationale 4.Rationale for why changes to emergency procedures and/or UFSAR did not create a possibility for malfunction of an SSC important to safety with a different resultNo new malfunctions or failure modesSSCs important to safety are not prevented from performing their intended design functions as described in the UFSAR 28 10CFR50.59 Rationale 5.Rationale for why the changes to UFSAR 6.3.2.6 were evaluated via a 50.59 Screening instead of a 50.59 EvaluationThe intent of the UFSAR change was to add words The act of adding words did not require a change to the TS or adversely affect an SSC design functionThe condition was considered within the licensing basisConclusions unchanged if a 50.59 Evaluation had been performed 29SummaryComplex IssueConservative Decision MakingConservatively evaluated scenarios using most applicable toolsConsidered penalties associated with non-safety equipment operation not currently included in analysesEnsured adequate sump levelFollowed applicable regulatory processes and guidance documents 30Containment Drawing A N N U L U SELEV778 + 10ELEV 738 + 3ELEV725 + 0ELEV 696 + 11ELEV841 + 10LOWER ICECONDENSERINLET DOOR ICECONDENSERICE BASKETSINSULATIONBLANKET A N N U L U S AHUsBUILDING SPRAYRING HEADERCRD MISSLE SHIELDINCORE INSRUMENTATIONAREAPRTCONTAINMENTVESSEL STIFFNERRING PLATE (TYP)INCORE INSTDRIVEASSEMBLIES(TYP)SEAL TABLE NCDT NCDT HX NCDTPUMPMOVABLEFRAMEASSEMBLYAIR RETURNFAN 1AREFUELINGWATERLEVEL771 + 4CRD MISSLESHIELD GATE180 90VIEW 0 270 RXBLDGVERTICALSLICEHYDROGENSKIMMERFAN 1BHYDROGENRECOMBINER 1BPZRNCP 1BS/G 1BENCLOSURES/G 1CENCLOSUREUPPERCONT.COOLINGUNITS 1C 1BPOLAR CRANEREFUELINGBRIDGEREACTOR VESSEL 31AcronymsNV -Chemical and Volume ControlNS -Containment SprayNI -Safety InjectionND -Residual Heat RemovalLOCA -Loss Of Coolant AccidentLBLOCA -Large Break Loss Of Coolant Accident HZP -Hot Zero Power HHSI -High Head SI FWST -Refueling Water Storage Tank EP -Emergency Procedure EOC -End of Cycle ECCS -Emergency Core Cooling System CLR -Cold Leg Recirculation CLA -Cold Leg Accumulator CCP -Charging SI BOC -Beginning of CycleVX -Containment Air Return and Hydrogen Skimmer System UFSAR -Updates Final Safety Analysis ReportTS -Technical Specification SSC -Structure System, or Component SM -Main Steam SI -Safety Injection SBLOCA -Small Break Loss Of Coolant Accident RHR -Residual Heat Removal RCS -Reactor Coolant SystemPZR -PressurizerRCP -Reactor Coolant Pump PORV -Power Operated Relief Valve PIP -Problem Investigation Process PCT -Peak Clad Temperature