ML111990346

Meeting Presentation, Prairie Island Nuclear Generating Plant - Failure to Maintain the Train a and B Direct Current Electrical Power Subsystems Operable

ML111990346
Person / Time
Site:	Prairie Island
Issue date:	07/28/2011
From:	Xcel Energy
To:	NRC/RGN-III
References
EA-11-110
Download: ML111990346 (46)

Text

Prairie Island Nuclear Generating Plant NRC Region III Regulatory Conference Failure to Maintain the Train A and B Direct Current Electrical Power Subsystems Operable July 28, 2011

Agenda Opening Remarks - Mark Schimmel Sequence of Events - Kevin Davison Causes and Corrective Actions - Kevin Davison Regulatory Significance - John Bickel Operator Actions - Darrell Lapcinski Conclusion - Mark Schimmel Closing Remarks - Dennis Koehl 2

Opening Remarks Xcel Energy takes its obligation to protect the health and safety of the public very seriously Violation Failure to maintain the Train A and B direct current electrical power subsystems operable Agree with the performance deficiency and violation Disagree with the significance More than adequate time to diagnose charger lockup 3

Sequence of Events Kevin Davison - Plant Manager 4

Sequence of Events 1994 / 95 1997 1999 2005 Oct 2010 Feb 2012 Battery Follow up Test 12 Battery TS 3.8.1.B Unit 2 chargers testing of procedure Charger mod Entered for battery installed Unit 1 revised to cancelled D2 EDG; chargers to battery remove 12 Exigent TS be replaced chargers Battery change Charger approved 1994 1997 2000 2003 2006 2009 2012 June 2010 Site staff 1996 2002 enters 12 May 2011 12 Battery 1999 Improved Battery Unit 1 Charger Battery Standard Charger battery lockup charger mod Tech Spec testing issues chargers during ISI requests implemented into CAP replaced 5

Causes and Corrective Action A root cause analysis was performed to identify the direct cause and the organizational and programmatic breakdowns that led to failure to correct battery charger lockup.

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Causes and Corrective Actions Root Cause - Direct The organization had developed a blind spot to this issue.

Over several years, multiple opportunities surfaced to identify and correct the condition 7

Causes and Corrective Actions Root Cause - Programmatic RC-1: Equipment issues become long-standing when C severity level CAPs are allowed to be closed to a secondary work process deliverable, which may be canceled or extended beyond the original CAP due date.

Root Cause - Organizational RC-2: Behaviors necessary to drive long-standing equipment issues to timely resolution are neither modeled, nor required by Plant Health Committee (PHC).

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Causes and Corrective Actions Corrective Action - Equipment Implemented compensatory actions for all battery chargers Obtained an Exigent Technical Specification change Replaced and retested Unit 1 Battery Chargers (1R27)

Scheduled replacement of Unit 2 Battery Chargers (2R27)

Procurement of Spare and Unit 2 chargers in progress.

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Causes and Corrective Actions Corrective Action - Process For C severity level CAPs, to ensure all open equipment issues remain captured in the corrective action process.

Establish a PHC Charter and changed behaviors that incorporates the knowledge gained from benchmarking industry leaders and make it available to System and Programs Engineering.

PHC needs to be defined as the champion of projects for presentation to PRG.

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Causes and Corrective Actions Corrective Action - Process Implement a periodic PHC roll-up to evaluate effectiveness of resolving equipment Legacy Issues Plan 11

Conclusion Station had multiple opportunities to identify Corrective actions have focused on:

Replacement of chargers Changing behaviors of PHC members Process changes to assure sustainability 12

Regulatory Significance Scenarios & Risk Evaluation John Bickel - PRA Consultant Engineer Operator Actions Darrell Lapcinski - Shift Manager 13

Regulatory Significance - Scenarios LOOP event with EDG D1 failed and 12 Battery Charger Lockup Scenario is most limiting time available prior to battery depletion Plant emergency lighting powered from the 12 battery Minimum design voltage on 12 battery will be reached in three hours Most risk significant sequence from the PINGP PRA evaluations Noted by the NRC to be significant risk contributor Failure of the EDG D1 would cause the operators to perform additional actions LOOP event with 11 and 12 Battery Charger Lockup EDG D1 successfully operates Scenario is not as limiting in time as scenario listed above Plant emergency lighting powered from the AC source (EDG D1 operates).

Minimum design voltage on 11 battery reached in six and a half hours.

Minimum design voltage on 12 battery reached in seven and a half hours.

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Regulatory Significance - Scenarios LOOP, EDG D1 Failure & 12 Battery Charger Lockup T< 1 T=180 T=0 T<1 T<60 Time for Operators to Diagnose, Cross-tie Buses & Reset Charger LOOP Occurs DG Start Signal 12 Battery Reaches EDG Minimum Design loaded & Voltage Failed; Charger Timeline in minutes lockup 15

Regulatory Significance - Scenarios LOOP, 11 & 12 Battery Charger Lockup T< 1 T=390 T=450 T=0 T<1 T<60 Time needed for Operators to Diagnose

& Reset Charger LOOP Occurs DG Start Signal 11 Battery 12 Battery EDG Reaches Reaches loaded; Minimum Minimum Charger Design Design lockup Timeline in minutes Voltage Voltage 16

Operator Actions - Immediate Immediate Actions Following LOOP Event (memorized actions) 1E-0 Reactor Trip or Safety Injection Step 1: Verify Reactor trip Step 2: Verify Turbine trip Step 3: Verify Both Safeguards Buses - Energized Lead Reactor Operator (RO) will recognize that EDG D1 has failed and Bus 15 is deenergized.

Response Not Obtained: IF one bus deenergized, THEN initiate action to restore power to deenergized safeguards bus per 1C20.5 AOP1, REENERGIZING 4.16KV BUS 15.

Step 4: Check if SI is Actuated Operators will transfer to 1ES-0.1, Reactor Trip Recovery No Safety injection 17

Operator Actions - Trip Recovery Transition to 1ES-0.1, Reactor Trip Recovery Control Room Supervisor (CRS) will restore normal alarm response protocol per FP-OP-COO-01 Conduct of Operations, Attachment 1 Alarm Response.

Crew Brief will be performed.

CRS will direct the ROs to perform a board walkdown and report any alarms that are unexpected for the LOOP/reactor trip.

Operators are trained to look at electrical sources following LOOP event. Pattern of annuciators will also be evident.

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Operator Actions - Emergency Plan Shift Manager Assumes Role of Emergency Director Within 15 minutes, Emergency Planning classification is required To determine escalation criteria, Shift Manager will evaluate alarms on electrical power panel Multiple people through multiple proceduralized paths give many opportunities to diagnose lockup of a battery charger.

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Operator Actions - Control Room Unit 2 Unit 1 20

Operator Actions - Control Room Control Room from the Unit 1 side. The electrical power annunciator 21 panel is shown between Unit 1 and Unit 2 Control Rooms where it can be easily seen and monitored by both units operators.

Operator Actions After the plant is stabilized the operators will walk the panels.

During a LOOP, the power panel will be a priority.

The difference in the pattern for Unit 1 and Unit 2 Annunciators will be quickly identified.

Operators are trained to identify discrepancies to the norm.

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Unit 2 G-Panel Alarms Unit 1 G-Panel Alarms 23

Operator Actions - Restore Bus 15 Per 1E-0, Step 3 RNO:

IF one bus deenergized,THEN initiate action to restore power to deenergized safeguards bus per 1C20.5 AOP1, REENERGIZING 4.16KV BUS 15.

Unit 1 SS will instruct Unit 1 Lead RO to enter 1C20.5 AOP1 per 1E-0.

Dispatch outplant operator to locally check EDG D1.

Per 1C20.5 AOP1, it would be determined that no lockout exists on Bus 15 and is available for repowering Due to LOOP event and D1 EDG failure, Bus 15 will be reenergized via bus-tie breakers per 1C20.5 AOP4.

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Operator Actions - Charger Restart Cues Available To Operator 12 DC System Trouble Alarm (47024-1105) 12 DC Panel Undervoltage Alarm (47024-1204)

Alarm Response Procedures (ARP) will instruct operator to review battery data indication on the Emergency Response Computer System (ERCS).

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Operator Actions - Charger Restart Operators are trained to use all available indication. The Emergency Response Computer System (ERCS) will be initiated to determine 26 status of the batteries. This screen is available on the power panel and would continue to have power during a LOOP.

27 28 29 30 31 Operator Actions - Charger Restart Procedure Instruction to Restart Battery Charger ARP will also refer operator to 1C20.9 AOP4: Failure of 12 Battery Charger.

1C20.9 AOP4 (Attachment B) - Rev 10, provides instruction to restart battery charger.

Outplant operator required.

Outplant Operators Available to Respond Two Turbine Building (TB) Operators per Unit (4 total).

Two of the operators (one per unit) perform immediate actions of 1ES-0.1, Attachment J.

Two TB Operators available to respond to EDG D1 failure and 12 Battery Charger.

In addition, although not credited in the PRA analysis, Auxiliary Building (AB) operator (2 total) can be available to respond to TB issues since this scenario would not require outplant actions in the AB.

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Operator Actions - Charger Restart Complexity of Task and Time To Complete Action Simple action, open and close AC Input Breaker on front panel.

Both the control room and outplant action times were confirmed during two simulator case studies.

Approximate time to complete Bus 15 repower and restart of 12 battery charger actions based on two simulator case studies: less than 60 minutes 33

Operator Actions The only manual action required to physically reset the battery charger is to switch the AC Input breaker shown above on the left from the Off to the On position. 34

Operator Actions - Conclusion T-0 LOOP w/ D1 Failure AOP to Restore 1E-0 Trip and SI Bus 15 Bus 15 Restored 1ES-0.1 Trip Recovery 12 DC Trouble Alarm 12 DC Panel UV Alarm Operator Cues Computer alarms / indications EAL Escalation Criteria ARP & AOP Failure of 12 Procedures Battery Charger Simple Action Response Directed by Procedure Battery Charger Reset T-60 35

Risk Evaluation Key Risk Significance Question:

Do operators have enough time to detect and reset tripped battery charger, before batteries become unavailable ?

Xcel HEP analysis: HEP=8.9E-4 (EPRI HRA Calc.)

NRC analysis: HEP=2.2E-2 (SPAR-H) 36

Risk Evaluation RASP Manual Vol.3 Section 2.3 requires:

Technical reviews. Check whether a knowledgeable specialist reviewed the reasonableness and acceptability of the results of the thermal hydraulic, structural, or other supporting engineering bases that were used to justify the success criteria. (SC-B5)

Fidelity to as-built design:

For CCF of Battery Chargers scenario with both diesels running (no emergency lighting loads on battery) - 7.5hr battery capacity For D1 diesel failure and 12 Charger trip - 3hr battery capacity 37

Risk Evaluation RASP Manual Vol. 1, Section 6.3.1 requires considering following in the recovery analysis:

Demonstration that the action is plausible and feasible for the scenarios to which recovery/repair action are applied (HLR-HR-H).

Availability of procedures, operator training, cues, and manpower (HR-H2).

Relevant scenario-specific performance shaping factors in the HRA (HR-H2 and HR-G3).

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Risk Evaluation 39

Risk Evaluation To obtain HEP=2.2E-2, NRC SPAR-H treatment omits consideration of available time With common cause charger failure and D1/D2 operable: 7.5 hrs available for recovery With D1 failing and lighting transferred to battery: 3 hrs available for recovery Per the SPAR-H model:

1hr to detect/reset 3hr batteries (expansive time) 1.5hr to detect/reset 3hr batteries (expansive time) 1.5hr to detect reset 2.5hr batteries (extra time) 40

Risk Evaluation 41

Risk Evaluation Peer Review of SPAR-H model Page I-17 of NUREG/CR-6883states:

We do reduce the HEP for at-power situations where there is extra or expansive time available, beyond a certain time minimum corresponding to interpretation of the THERP diagnosis curves.

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Risk Evaluation In conclusion, if NRC were to consider:

As-built, As-operated battery capacity Time available for resetting tripped charger for the dominant sequences of interest Per SPAR-H process there is Extra/Expansive time Risk significance is GREEN.

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Conclusion Mark Schimmel - Site Vice President 44

Closing Remarks Dennis Koehl - Chief Nuclear Officer 45

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