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

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

2 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

3 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

4 Sequence of Events Kevin Davison - Plant Manager

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

6 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.

7 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

8 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).

9 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.

10 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.

11 Causes and Corrective Actions

Corrective Action - Process

Implement a periodic PHC roll-up to evaluate effectiveness of resolving equipment

Legacy Issues Plan

12 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

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

14 14 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.

15 Regulatory Significance - Scenarios LOOP, EDG D1 Failure & 12 Battery Charger Lockup LOOP Occurs 12 Battery Reaches Minimum Design Voltage T=0 T< 1 DG Start Signal T<1 EDG loaded &

Failed; Charger lockup T=180 Timeline in minutes T<60 Time for Operators to Diagnose, Cross-tie Buses & Reset Charger

16 Regulatory Significance - Scenarios LOOP, 11 & 12 Battery Charger Lockup LOOP Occurs 11 Battery Reaches Minimum Design Voltage T=0 T< 1 DG Start Signal T<1 EDG loaded; Charger lockup T=390 Timeline in minutes T<60 Time needed for Operators to Diagnose

& Reset Charger T=450 12 Battery Reaches Minimum Design Voltage

17 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

18 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.

19 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.

20 Operator Actions - Control Room Unit 2 Unit 1

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

22 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.

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

24 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.

25 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).

26 Operator Actions - Charger Restart Operators are trained to use all available indication. The Emergency Response Computer System (ERCS) will be initiated to determine 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 31



32 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.

33 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

34 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.



35 Operator Actions - Conclusion Battery Charger Reset

  

1ES-0.1 Trip Recovery Operator Cues 12 DC Trouble Alarm 12 DC Panel UV Alarm Computer alarms / indications EAL Escalation Criteria Procedures ARP & AOP Failure of 12 Battery Charger

Response

Simple Action Directed by Procedure LOOP w/ D1 Failure 1E-0 Trip and SI AOP to Restore Bus 15 Bus 15 Restored T-0 T-60

36 36 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)

37 37 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 7.5hr battery capacity battery capacity

For D1 diesel failure and 12 Charger trip - 3hr battery 3hr battery capacity capacity

38 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).

38

39 39 Risk Evaluation

40 40 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)

41 41 Risk Evaluation

42 42 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.

43 43 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.

44 44 Conclusion Mark Schimmel - Site Vice President

45 45 Closing Remarks Dennis Koehl - Chief Nuclear Officer

46