ML061740010

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

McGuire Nuclear Station Technical Information Meeting Atlanta, GA May 19, 2006 1

Duke Participants Jim Kammer, McGuire Safety Assurance Manager Jeff Thomas, McGuire Regulatory Compliance Manager Eric Henshaw, Duke Safety Analysis Senior Engineer Mike Weiner, McGuire Operations Senior Engineer 2

Agenda Opening Remarks

Background

Unresolved Issues Postulated Event Description Emergency Procedure / UFSAR Changes 10CFR50.59 Rationale Summary 3

Background

10/04 - 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 basis Entered the Operability Determination Process 4

Background

Prompt Corrective Actions 3/4 Enhanced margin by opening refueling canal drain path from upper containment 3/4 Increased Refueling Water Storage Tank (FWST) level Subsequent Corrective Actions 3/4 Revised Emergency Procedures to incorporate alternate SBLOCA swapover sequence for specific SBLOCAs 3/4 Conducted training to enhance awareness 3/4 Completed Operability Evaluation confirms that sufficient water volume exists. Nonconformance with UFSAR identified (3/05) 5

Background

Subsequent Corrective Actions (continued) 3/4 Installed precision containment sump level switches in Unit 2 (8/05) and Unit 1 (10/05) 3/4 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).

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Unresolved Issues

1. Did changes to emergency procedures and/or UFSAR 6.3.2.6 require changes to Technical 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)?

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Unresolved 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?

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Postulated Event Description Overview 3/4 Review of Containment Response Large Break LOCA Small Break LOCA 3/4 Minimum Sump Level SBLOCA evaluations 3/4 Conservative Inputs 3/4 Typical Sequence of Events 3/4 Containment Spray Functions 9

Postulated Event Description Objective of minimum sump level cases (from an analysts perspective) 3/4 Maximize leakage to incore room 3/4 Minimize ice melt 3/4 Avoid containment spray operation Actuation transfers FWST fluid to containment sump Actuation speeds up event time line 10

Postulated Event Description SBLOCA minimum sump level evaluation 3/4 Focus changed from maximizing pressure/temperature to minimizing ice melt 3/4 UFSAR Chapter 6 containment response analyses performed from EOC hot full power conditions, which are conservative for evaluating peak containment pressure & maximum sump temperature.

3/4 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).

3/4 Peak clad temperature (PCT) (UFSAR Chapter 15.6.5) not challenged for breaks that do not actuate containment spray 11

Postulated Event Description Comparison of Conservative Inputs Peak Containment Min Sump Pressure Level Decay heat EOC (max) BOC (min)

FWST temperature TS max TS min ECCS flow rates Min 1 train Max 2 train Ice temperature TS max Min Lower containment ventilation none Max 12

Postulated Event Description Typical Sequence of Events for SBLOCA that does not cause containment spray actuation, including procedural operator actions (preliminary evaluation results) 3/4 Initiated from Hot Zero Power (HZP) 557 oF 3/4 Maximum ECCS flow 3/4 Cold FWST 3/4 Low decay heat (BOC) 3/4 Lower containment non-safety coolers operate 3/4 Start cooldown 60 minutes after Safety Injection 3/4 Operator performs SI reduction sequence 13

Postulated Event Description HZP 0.005 ft2 cold leg nozzle break w/ Max ECCS, 65 oF FWST (preliminary evaluation results) 3/4 Time [min] Description 3/4 0 Break initiation 3/4 n/a Reactor trip 3/4 n/a Turbine trip 3/4 5.2 SI actuation on low RCS pressure 3/4 65.2 Operator initiates cooldown (60 min after SI) 3/4 81.1 Operator trips RCPs on loss of subcooled margin 3/4 84.8 Operator cycles Pzr PORV to obtain 25% Pzr level 3/4 87.4 Operator isolates CLAs (Pzr level > 25% & subcooled margin)

(beginning of recovery) 3/4 114.1 Operator begins SI reduction sequence 3/4 186.6 Hot leg temperature reaches 350 oF (exit Mode 3, RHR initiation setpt) 3/4 299.1 End simulation - Thot reaches 250 oF (@ ~5 hours) 14

Postulated Event Description Summary 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) 3/4 Pzr pressure = 175 psig 3/4 Pzr level = 52%

3/4 Thot = 250 oF 3/4 SM pressure = 13 psig 3/4 FWST has not reached FWST lo-level setpoint 3/4 ~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) 3/4 Total ECCS flow = 347 gpm (1 charging pump) 3/4 RHR flow = 0 gpm 3/4 Containment Spray flow = 0 gpm 3/4 Sump level = 0.23 ft, incore room is full 3/4 94.5% (1.786E6 lbm) of ice remains (initial ice mass = 1.89E6 lbm) 15

Postulated Event Description Functions provided by Containment Spray 3/4 Maintain pressure below containment design.

Containment pressure not a concern for min sump level cases 3/4 Scrub atmosphere to reduce dose Rod ejection provides the limiting SBLOCA source term Containment spray not credited in rod ejection dose analysis 3/4 Remove heat from containment sump via heat exchanger Function performed after FWST reaches lo-lo level setpoint 3/4 After FWST lo-level containment spray operation part of long-term recovery for minimum sump level cases 16

Emergency Procedure / UFSAR Changes Overview 3/4 Normal transfer sequence 3/4 Alternate sequence (procedure changes) 17

Emergency Procedure / UFSAR Changes Swapover Sequence (Pumps Taking Suction From FWST)

Normal Alternate FWST RHR CCP + HHSI Spray RHR CCP + HHSI Spray Off Lo LoLo (Spray off, Low Sump level)

RHR - Low Head SI CCP - Charging SI HHSI - High Head SI 18

Emergency Procedure / UFSAR Changes Normal Transfer to CLR Sequence 3/4 FWST lo-level alarm 3/4 ND pump auto-swap from FWST to containment sump 3/4 Operator manually re-aligns NI/NV pump suction from FWST to RHR pump discharge 3/4 FWST lo-lo level alarm 3/4 Operator stops Containment Spray pumps 3/4 Operator manually re-aligns Containment Spray pump suction from FWST to containment sump 3/4 Operator manually restarts Containment Spray pumps 19

Emergency Procedure / UFSAR Changes Transfer to Cold Leg Recirc Consideration for SBLOCA with Containment Spray off:

3/4 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 the incore 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.

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Emergency Procedure / UFSAR Changes The alternate sequence enclosure of the Emergency Procedure (EP) does the following:

3/4 Ensures proper swap of RHR pumps to sump and confirms that RHR pumps are off 3/4 Ensures Spray pumps cannot start by pulling power fuses 3/4 NV and NI pumps to continue to run with suction on FWST until FWST Lo Lo level is reached 3/4 After FWST Lo Lo level is reached:

The ND pumps are started on sump and NV&NI are aligned to piggy back mode The Spray pumps are aligned to sump Manual start of one Spray pump is performed as needed with TSC concurrence 21

Emergency Procedure / UFSAR Changes Procedural Considerations 3/4 Without additional guidance, NI/NV pumps might be at risk following a Spray pump auto-start 3/4 Mass and energy release to containment decreases as RCS pressure and temperature decrease; GOTHIC analysis would not predict a Containment Spray auto-start 3/4 Engineering judgment leads to conclusion that while not needed, hypothetically Containment Spray auto-start still possible considering the following:

Instrument air in-leakage Loss of non-safety coolers 3/4 Therefore, Containment Spray pump start should be mitigated 22

Emergency Procedure / UFSAR Changes Revised UFSAR 6.3.2.6 to note:

3/4 Credible NC System break locations have been identified that may cause a diversion of coolant inventory to the Incore Instrument Room 3/4 For 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.

3/4 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 inventory is available (and maintained) for sump recirculation to provide adequate core cooling for such SBLOCA events 23

10CFR50.59 Rationale

1. Rationale for why UFSAR and/or emergency procedure changes did not require changes to TS 3.4.15 3/4 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 leakage 3/4 Therefore, the UFSAR and/or emergency procedure changes did not require changes to TS 3.4.15 pursuant to 50.59(c)(1)(i) 24

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 3/4 The intended design function of Containment Spray is not required at the time the power fuses are removed 3/4 Regarding containment pressure response, the plant is in long term recovery where manual operator action can be credited 3/4 Local operator actions during containment pressure recovery are reasonable and confirmed in the control room 3/4 Containment 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 3/4 The changes do not credit manual action in place of an automatic safety limit protection 25

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 type 3/4 Station response to LOCAs previously evaluated in the UFSAR is unchanged 3/4 The frequency of occurrence of LOCAs evaluated in the UFSAR is unchanged 3/4 The changes apply to the mitigation of SBLOCAs from credible break locations that do not initiate Containment Spray during post accident recovery 26

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 result 3/4 No new malfunctions or failure modes 3/4 SSCs important to safety are not prevented from performing their intended design functions as described in the UFSAR 27

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 Evaluation 3/4 The intent of the UFSAR change was to add words 3/4 The act of adding words did not require a change to the TS or adversely affect an SSC design function 3/4 The condition was considered within the licensing basis 3/4 Conclusions unchanged if a 50.59 Evaluation had been performed 28

Summary Complex Issue Conservative Decision Making 3/4 Conservatively evaluated scenarios using most applicable tools 3/4 Considered penalties associated with non-safety equipment operation not currently included in analyses 3/4 Ensured adequate sump level Followed applicable regulatory processes and guidance documents 29

Containment Drawing 180 270 90 RX BLDG VERTICAL 0 SLICE AN VIEW NU US L US AN NU L

BUILDING SPRAY RING HEADER POLAR CRANE AHUs INSULATION BLANKET HYDROGEN RECOMBINER 1B ELEV 841 + 10 HYDROGEN UPPER CONT.

SKIMMER COOLING 1C 1B FAN 1B UNITS REFUELING ICE BRIDGE CONDENSER S/G 1C S/G 1B ICE BASKETS ENCLOSURE ENCLOSURE REFUELING WATER LEVEL LOWER ICE 771 + 4 PZR CONDENSER INLET DOOR AIR RETURN CRD MISSLE SHIELD ELEV FAN 1A 778 + 10 INCORE INST DRIVE ASSEMBLIES (TYP)

MOVABLE FRAME ASSEMBLY CRD MISSLE SEAL TABLE SHIELD GATE ELEV 738 + 3 PRT ELEV 725 + 0 NCDT NCDT NCP 1B NCDT PUMP HX REACTOR VESSEL CONTAINMENT VESSEL STIFFNER INCORE ELEV RING PLATE (TYP) INSRUMENTATION 696 + 11 AREA 30

Acronyms BOC - Beginning of Cycle PCT - Peak Clad Temperature CCP - Charging SI PIP - Problem Investigation Process CLA - Cold Leg Accumulator PORV - Power Operated Relief Valve CLR - Cold Leg Recirculation RCP - Reactor Coolant Pump ECCS - Emergency Core Cooling System PZR - Pressurizer EOC - End of Cycle RCS - Reactor Coolant System EP - Emergency Procedure RHR - Residual Heat Removal FWST - Refueling Water Storage Tank SBLOCA - Small Break Loss Of Coolant Accident HHSI - High Head SI HZP - Hot Zero Power SI - Safety Injection LBLOCA - Large Break Loss Of Coolant Accident SM - Main Steam LOCA - Loss Of Coolant Accident SSC - Structure System, or Component ND - Residual Heat Removal TS - Technical Specification NI - Safety Injection UFSAR - Updates Final Safety Analysis Report NS - Containment Spray VX - Containment Air Return and Hydrogen Skimmer System NV - Chemical and Volume Control 31