05000259/LER-2011-006, For Browns Ferry, Unit 1, Regarding Loss of Safety Function (HPCI) Due to Primary Containment Isolation

For Browns Ferry, Unit 1, Regarding Loss of Safety Function (HPCI) Due to Primary Containment Isolation

ML11203A019
Person / Time
Site:	Browns Ferry
Issue date:	07/19/2011
From:	Polson K Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LER 11-006-00
Download: ML11203A019 (10)

LER-2011-006, For Browns Ferry, Unit 1, Regarding Loss of Safety Function (HPCI) Due to Primary Containment Isolation

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
2592011006R00 - NRC Website

text

Tennessee Valley Authority, Post Office Box 2000, Decatur, Alabama 35609-2000 July 19, 2011 10 CFR 50.73 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Browns Ferry Nuclear Plant, Unit 1 Facility Operating License No. DPR-33 NRC Docket No. 50-259

Subject:

Licensee Event Report 50-259/2011-006-00 On May 20, 2011, while preparing to vent the Unit 1 High Pressure Coolant Injection (HPCI) discharge piping, Operations personnel opened the normally closed HPCI Injection Valve, which rapidly pressurized the HPCI System discharge and suction piping to near reactor pressure. Seat leakage past the HPCI System Testable Check Valve, a primary containment isolation valve (PCIV), caused the increase in piping pressure.

To satisfy PCIV Technical Specifications, primary containment was maintained for the HPCI System penetration flow path by closing and de-activating the HPCI Injection Valve.

Once this valve was de-activated, the HPCI System was rendered incapable of performing its accident mitigation safety function.

The Tennessee Valley Authority is submitting this report under 10 CFR 50.73(a)(2)(v)(D),

as any event that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.

U.S. Nuclear Regulatory Commission Page 2 July 19, 2011 There are no new regulatory commitments contained in this letter. Should you have any questions concerning this submittal, please contact J. E. Emens, Jr., Nuclear Site Licensing Manager, at (256) 729-2636.

Respectfully, K. J. Poison Vice President

Enclosure:

Licensee Event Report 259/2011-006 - Loss of Safety Function (HPCI) Due to Primary Containment Isolation cc (w/ Enclosure):

NRC Regional Administrator - Region II NRC Senior Resident Inspector - Browns Ferry Nuclear Plant

Enclosure Browns Ferry Nuclear Plant Unit I Licensee Event Report 25912011-006 Loss of Safety Function (HPCI) Due to Primary Containment Isolation See Attached

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150-0104 EXPIRES 10/13/2013 (10-2010)

, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. PAGE Browns Ferry Nuclear Plant Unit 1 05000259 1 OF 7

4. TITLE Loss of Safety Function (HPCI) Due to Primary Containment Isolation

5. EVENT DATE

6. LER NUMBER

7. REPORT DATE

8. OTHER FACILITIES INVOLVED MO YEAR SEQUENTIAL REV MONTH DAY YEAR FACILITY NAME DOCKET NUMBER MOT DY YER YER NUMBER NO.

N/A, 05000 FACILITY NAME DOCKET NUMBER 05 20 2011 2011 -

006 -

00 07 19 2011 N/A 05000

9. OPERATING MODE

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply)

[1 20.2201(b)

[I 20.2203(a)(3)(i)

[I 50.73(a)(2)(i)(C)

[I 50.73(a)(2)(vii)

[1 20.2201(d)

[] 20.2203(a)(3)(ii)

[I 50.73(a)(2)(ii)(A)

[I 50.73(a)(2)(viii)(A) 1E 20.2203(a)(1)

El 20.2203(a)(4)

[I 50.73(a)(2)(ii)(B)

El 50.73(a)(2)(viii)(B)

I] 20.2203(a)(2)(i) 0l 50.36(c)(1)(i)(A)

El 50.73(a)(2)(iii)

El 50.73(a)(2)(ix)(A)

10. POWER LEVEL El 20.2203(a)(2)(ii)

[I 50.36(c)(1)(ii)(A)

El 50.73(a)(2)(iv)(A)

El 50.73(a)(2)(x)

El 20.2203(a)(2)(iii)

El 50.36(c)(2) 0l 50.73(a)(2)(v)(A)

El 73.71(a)(4)

El 20.2203(a)(2)(iv)

E] 50.46(a)(3)(ii)

[I 50.73(a)(2)(v)(B)

El 73.71(a)(5) 023 El 20.2203(a)(2)(v)

El 50.73(a)(2)(i)(A)

[I 50.73(a)(2)(v)(C)

[E OTHER S20.2203(a)(2)(vi)

El 50.73(a)(2)(i)(B)

[

50.73(a)(2)(v)(D)

Specify in Abstract below or in

1. PLANT CONDITION(S)

On April 27, 2011, severe weather in the Tennessee Valley Authority (TVA) service area caused grid instability and a loss of all 500-kV offsite power sources that resulted in scrams of all three Browns Ferry Nuclear Plant units.

On May 20, 2011, at 2215 hours0.0256 days <br />0.615 hours <br />0.00366 weeks <br />8.428075e-4 months <br /> Central Daylight Time, Unit 1 was in Mode 1 at approximately 23 percent power.

I1. DESCRIPTION OF EVENT A. Event:

On May 20, 2011, Unit 1 was in Mode 1 and preparing for ascension to full reactor power operation following recovery from the April 27, 2011, severe weather event.

At 2100 hours0.0243 days <br />0.583 hours <br />0.00347 weeks <br />7.9905e-4 months <br />, Operations personnel entered Technical Specification (TS) Limiting Condition for Operation (LCO) 3.5.1 actions due to not completing High Pressure Coolant Injection (HPCI) System [BJ] TS Surveillance Requirement (SR) 3.5.1.7 procedure 1-SR-3.5.1.7(COMP), HPCI Comprehensive Pump Test. This rendered the HPCI System inoperable. Operations personnel were making an effort to re-establish operability of the HPCI System by venting the HPCI discharge piping in accordance with 1-SR-3.5.1.1(HPCI), Maintenance of Filled HPCI Discharge Piping.

At 2215 hours0.0256 days <br />0.615 hours <br />0.00366 weeks <br />8.428075e-4 months <br />, Operations personnel opened the normally closed HPCI Injection Valve, 1-FCV-073-0044, which, unexpectedly, rapidly pressurized the HPCI System discharge and suction piping. Some components in the lower design pressure suction piping leaked, some equipment in the HPCI Room was sprayed with water, and room flood level alarms were received in the Main Control Room. Approximately one minute later, Operations personnel closed the HPCI Injection Valve, and pressure decreased.

Leakage was stopped after the HPCI Condensate Storage Tank (CST) Suction Valve, 1-FCV-073-0040, was closed. Seat leakage past the HPCI System Testable Check Valve, 1-FCV-073-0045, a primary containment isolation valve (PCIV), caused the increase in piping pressure.

At 2338 hours0.0271 days <br />0.649 hours <br />0.00387 weeks <br />8.89609e-4 months <br />, to satisfy TS LCO 3.6.1.3 action, PCIVs, primary containment was maintained for the HPCI System penetration flow path by closing and de-activating the HPCI Injection Valve. Once this valve was de-activated, the HPCI flow path was isolated and the HPCI System was rendered incapable of performing its accident mitigation safety function.

B. Inoperable Structures, Components, or Systems that Contributed to the Event:

None C. Dates and Approximate Times of Maior Occurrences:

April 27, 2010, at 1636 hours0.0189 days <br />0.454 hours <br />0.00271 weeks <br />6.22498e-4 months <br /> Severe weather caused grid instability and a loss of all 500-kV offsite power sources that resulted in scrams of all three units.

April 28, 2011, at 1337 hours0.0155 days <br />0.371 hours <br />0.00221 weeks <br />5.087285e-4 months <br /> Unit 1 was in Mode 4 and HPCI was no longer required to be TS operable.

NRC FORM 366 (10-2010)

May 20, 2011, at 0430 hours0.00498 days <br />0.119 hours <br />7.109788e-4 weeks <br />1.63615e-4 months <br /> at 0900 hours0.0104 days <br />0.25 hours <br />0.00149 weeks <br />3.4245e-4 months <br /> at 2100 hours0.0243 days <br />0.583 hours <br />0.00347 weeks <br />7.9905e-4 months <br /> at 2215 hours0.0256 days <br />0.615 hours <br />0.00366 weeks <br />8.428075e-4 months <br /> at 2216 hours0.0256 days <br />0.616 hours <br />0.00366 weeks <br />8.43188e-4 months <br /> at 2338 hours0.0271 days <br />0.649 hours <br />0.00387 weeks <br />8.89609e-4 months <br /> May 24, 2011, at 0810 hours0.00938 days <br />0.225 hours <br />0.00134 weeks <br />3.08205e-4 months <br /> May 30, 2011, at 0350 hours0.00405 days <br />0.0972 hours <br />5.787037e-4 weeks <br />1.33175e-4 months <br /> May 30, 2011, at 0535 hours0.00619 days <br />0.149 hours <br />8.845899e-4 weeks <br />2.035675e-4 months <br /> May 31, 2011, at 0358 hours0.00414 days <br />0.0994 hours <br />5.919312e-4 weeks <br />1.36219e-4 months <br /> As part of unit startup, Operations personnel verified that HPCI was operable prior to exceeding 150 psig reactor vessel pressure.

Per general operating instruction, 1-GOI-100-1A, Unit Startup, performance of 1-SR-3.5.1.7(COMP) is required by 2100 hours0.0243 days <br />0.583 hours <br />0.00347 weeks <br />7.9905e-4 months <br />. The GOI states that, if not previously performed, HPCI must be proven operable within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> after reaching 950 psig, but prior to exceeding 1040 psig reactor pressure.

HPCI was declared inoperable due to not performing the TS SR.

To restore HPCI to operable status, Operations personnel began to vent the HPCI discharge piping in accordance with 1-SR-3.5.1.1(HPCI) by opening the HPCI Injection Valve.

Operations personnel recognized the system pressure increase and closed the HPCI Injection Valve. HPCI System leakage stopped after the HPCI CST Suction Valve was closed.

Because the HPCI System Testable Check Valve is a PCIV, the PCIV TS LCO action was met by closing and de-activating the HPCI Injection Valve.

HPCI System Testable Check Valve was verified closed by Operations personnel.

Operations personnel entered TS LCO 3.0.5 action for the HPCI System Testable Check Valve. Because it was not operable, the applicable action in TS LCO 3.6.1.3 is to isolate the affected penetration flow path. The HPCI Injection Valve was closed and de-activated to satisfy the PCIV TS LCO action. In preparation for performance of 1-SR-3.5.1.1(HPCI) and 1-SR-3.5.1.7(COMP), the HPCI Injection Valve was activated under the allowance of LCO 3.0.5.

Following satisfactory completion of necessary tasks and completion of 1-SR-3.5.1.1(HPCI),

Operations personnel declared the HPCI System Testable Check Valve operable and exited the applicable TS LCO actions.

Based on the review of the completed tasks and with all acceptance criteria met during the performance of 1-SR-3.5.1.7(COMP), Operations personnel declared HPCI operable.

NRC FORM 366 (10-2010)

D. Other Systems or Secondary Functions Affected

None

E. Method of Discovery

The event was self-revealing after Operations personnel opened the isolation valve and HPCI System suction piping components developed leaks.

F. Operator Actions

In response to HPCI System leakage, Operations personnel closed the HPCI Injection Valve. Leakage was stopped after the HPCI CST Suction Valve was closed. Since the HPCI System Testable Check Valve is a PCIV, the PCIV TS LCO action was met by closing and de-activating the HPCI Injection Valve.

G. Safety System Responses:

None Ill.

CAUSE OF THE EVENT

Root Cause A cause analysis determined that the failure of the HPCI System Testable Check Valve to close was due to the misalignment of the valve and operator parts. The main contributor to the misalignment was the linkage between the actuator and the valve. This was identified during the troubleshooting work order. When the linkage between the actuator and the valve was removed, the valve stroked successfully with ease. The actuator linkage was removed and corrective actions are in place to correct the misalignment to allow the valve to operate as designed.

Extent of Condition Units 1, 2, and 3 have the same Atwood & Morrill HPCI System Testable Check Valve installed in their respective HPCI Systems. Unlike the Unit 1 valve, there is no history of binding of the actuator or swing arm on the Unit 2 and Unit 3 valves. Historically, the inspections, refurbishing, and functional/stroke tests performed on the Unit 2 and Unit 3 valves have been successful. Further, the Unit 2 and Unit 3 valves have been in operation almost a decade longer than the Unit 1 valve.

The Reactor Core Isolation Cooling (RCIC) [BN] System has similar testable check valves installed on all three units. The RCIC System Testable Check Valves, 1/2/3-FCV-071-0040, are of the same Atwood & Morrill design, with the only difference being that these valves are a 6-inch version, as opposed to the 14-inch version installed in the HPCI system. No similar issues with these valves were identified.

Contributing Factors A contributing factor to the misalignment of the valve and operator parts was the use of the generic maintenance instruction procedure for swing check valves instead of the valve-specific maintenance procedure for the HPCI and RCIC System Testable Check Valves.

NRC FORM 366 (10-2010)

IV. ANALYSIS OF THE EVENT

TVA is submitting this report under 10 CFR 50.73(a)(2)(v)(D), as any event that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.

Design and Operation of the HPCI System Testable Check Valve The Unit 1 HPCI System Testable Check Valve is an Atwood & Morrill Seismic Class I and American Society of Mechanical Engineers (ASME)Section III Code Class 2 equivalent valve. This valve is a PCIV; its safety functions include primary containment isolation and reactor coolant pressure boundary. This 14-inch valve was supplied with an air operated actuator, which is used to cycle the valve disc open and closed for testing during cold shutdown conditions.

Evaluation of Plant Systems/Components Following the opening of the HPCI Injection Valve, the HPCI System discharge and suction piping pressure increased above the design values. Some components in the lower design pressure suction piping leaked, some equipment in the HPCI Room was sprayed with water, and room flood level alarms were received in the Main Control Room.

The pressure increase was bounded on the suction side of the booster pump by the condensate supply check valve, suppression pool outboard suction valve, and the gland seal condenser water side. The suction piping design pressure is 150 psig. The momentary pressure increase was evaluated to be at a maximum of 1020 psig. The elevated pressure lasted for approximately one minute.

Mechanical and instrumentation components that were exposed to greater than design pressures were inspected and either replaced or evaluated for continued use. Those items potentially subjected to water spray (i.e., junction boxes, control panels, control valves, switches, motors, turbine) were inspected, functionally checked, calibrated, and/or tested and replaced, as necessary. The HPCI Turbine oil was inspected and found to be acceptable. Visual observations of the HPCI System during performance of 1-SR-3.5.1.7(COMP) ensured there was no leakage or signs of obvious distress. No other significant, related, post-event failures or issues were identified prior to returning the HPCI System to operable status.

Evaluation of Personnel Performance Operations personnel performance following the event was reviewed and evaluated and found acceptable. Reactor coolant pressure boundary was restored approximately one minute after the event by closing the HPCI Injection Valve. HPCI System leakage stopped after the HPCI CST Suction Valve was closed.

Past Operability Evaluation Since the HPCI System had been in service on five different occasions since the April 27, 2011, severe weather event, there is no question regarding the system's ability to meet reactor pressure vessel injection and pressure relief (steam through the turbine).

TVA evaluated the potential that this condition may have resulted in past inoperability of the HPCI System's ability to maintain primary containment.

NRC FORM 366 (10-2010)

With respect to primary containment isolation, the past operability evaluation included reviews of the most recent HPCI System Testable Check Valve leak test, reviews of observations or records of any pressure spikes in the HPCI discharge or booster pump suction piping, reviews of monthly venting results, and temperature data comparisons and trending.

Based on the performance of these reviews and the absence of any past operability issues, there is reasonable evidence that the Unit 1 HPCI System completely fulfilled its primary containment isolation function.

V. ASSESSMENT OF SAFETY CONSEQUENCES

The HPCI System is one of the most important risk-significant systems. Loss of HPCI limits the capability for the unit to respond to an accident or transient. For this event, Unit 1 was in Mode 1 and at approximately 23 percent power.

When the HPCI System Testable Check Valve was discovered inoperable, primary containment was promptly maintained by closing and de-activating the HPCI Injection Valve in accordance with the applicable TS LCO 3.6.1.3 action. Due to the action above, the HPCI System was rendered incapable of performing its accident mitigation safety function.

TS LCO 3.5.1 action was entered and required that the RCIC System remain operable and the HPCI System be restored to operable status within 14 days. Per the TS LCO 3.5.1 Bases, the Automatic Depressurization System [SB] function of six safety/relief valves in combination with the low pressure coolant injection mode of the Residual Heat Removal System [BO] and the Core Spray System [BM] provide backup if HPCI fails. These systems/functions were operable at the time of the event, and the HPCI System was returned to operable status within 11 days.

Based on the prompt Operations personnel actions taken, the availability of designated HPCI backup systems/functions, and the restoration of the HPCI System within the required TS LCO completion times, this event was of minimal nuclear safety significance.

VI. CORRECTIVE ACTIONS

Corrective actions are being managed within TVA's Corrective Action Program.

Immediate actions taken to support the primary containment isolation function included:

Closing and de-activating the HPCI Injection Valve, and Restoring the HPCI System Testable Check Valve by removal of the lever arm to eliminate the possibility of the valve actuator interfering with the closing and proper seating of the valve disc.

Corrective actions taken to restore the HPCI System to operable status included:

" Evaluation of components affected by the event:

o Mechanical and instrumentation components exposed to greater than design pressures were inspected and either replaced or evaluated for continued use, o

Items potentially subjected to water spray (i.e., junction boxes, control panels, control valves, switches, motors, turbine) were inspected, functionally checked, calibrated, and/or tested and replaced, as necessary, and o

The HPCI Turbine oil was inspected and found to be acceptable.

Visual observations of the HPCI System during performance of 1-SR-3.5.1.7(COMP)

NRC FORM 366 (10-2010)

ensured there was no leakage or signs of obvious distress.

Corrective actions planned to address the component failure and contributing factors include the following:

" Disassemble and inspect the HPCI System Testable Check Valve at the next available outage, including a thorough inspection and replacement of any degraded parts with new vendor components and correction of the misalignment of the actuator and/or calibration of the associated limit switches. If this inspection reveals new information material to this LER, a revised LER will be submitted.

" Review work orders for use of specific testable check valve procedure and address with work planners. Document and discuss issues with the HPCI System Testable Check Valve maintenance procedure to be used and the importance of issuing the correct procedures for specific valves, which may include the recording of tolerances and clearances measured that are not included in the generic procedure.

Review and revise, if required, the mechanical maintenance procedure to align with the vendor manual requirements.

Revise 1-SR-3.5.1.1(HPCI) to require that, prior to venting, the HPCI System Testable Check Valve is verified closed.

VII. ADDITIONAL INFORMATION

A.

Failed Component:

HPCI System Testable Check Valve B.

Previous LERS or Similar Events:

A search of LERs for Units 1, 2, and 3 for approximately the past three years did not identify any similar issues involving the HPCI System Testable Check Valve.

A search of Problem Evaluation Reports (PERs) in the corrective action program database for approximately the past three years did not identify any similar issues involving the HPCI System Testable Check Valve or the RCIC System Testable Check Valve.

C.

Additional Information

The corrective action document for this report is PER 372659.

D.

Safety System Functional Failure Consideration:

This event is a safety system functional failure in accordance with NEI 99-02.

E.

Scram With Complications Consideration:

This event did not include a reactor scram.

VIII. COMMITMENTS

None NRC FORM 366 (10-2010)