05000280/LER-2011-001, Regarding Reactor Trip on Both Units Due to Loss of Offsite Power

Regarding Reactor Trip on Both Units Due to Loss of Offsite Power

ML11178A032
Person / Time
Site:	Surry
Issue date:	06/14/2011
From:	Gerald Bichof Virginia Electric & Power Co (VEPCO)
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
11-312 LER 11-001-00
Download: ML11178A032 (8)

LER-2011-001, Regarding Reactor Trip on Both Units Due to Loss of Offsite Power

Event date:
Report date:
Reporting criterion:	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)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
2802011001R00 - NRC Website

text

1 0CFR50.73 Virginia Electric and Power Company Surry Power Station 5570 Hog Island Road Surry, Virginia 23883 June 14, 2011 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D. C. 20555-0001 Serial No.:

SPS:

Docket No.:

License No.:

11-312 JSA 50-280 50-281 DPR-32 DPR-37

Dear Sirs:

Pursuant to 10CFR50.73, Virginia Electric and Power Company hereby submits the following Licensee Event Report applicable to Surry Power Station Units 1 and 2.

Report No. 50-280, 50-281/2011-001-00 This report has been reviewed by the Station Facility Safety Review Committee and will be forwarded to the Management Safety Review Committee for its review.

Very truly yours, Gerald T. Bischo Site Vice President Surry Power Station Enclosure Commitment contained in this letter: None j~Aim)

cc: U.S. Nuclear Regulatory Commission, Region II Marquis One Tower, Suite 1200 245 Peachtree Center Ave., NE Atlanta, GA 30303-1257 NRC Senior Resident Inspector Surry Power Station

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES 10/31/2013 (10-2011)

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

3. PAGE Surry Power Station, Unit 1 05000- 280 1 OF 6

4. TITLE Reactor Trip on Both Units Due to Loss of Offsite Power

5. EVENT DATE

6. LER NUMBER

7. REPORT DATE

8. OTHER FACILITIES INVOLVED SEQUENTIAL REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR NUMBER NO.

MONTH DAY YEAR Surry Unit 2 05000- 281 04 16 11 2011 -

001 00 06 14 11 FACILITY NAME DOCKET NUMBER 0 01 05000

9. OPERATING MODE

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR 4: (Check all that anP/v)

NJ 20.2201(b)

EJ 20.2203(a)(3)(i) 50.73(a)(2)(i)(C)

[]

50.73(a)(2)(vii)

N

[]

20.2201(d)

[]

20.2203(a)(3)(ii)

[]

50.73(a)(2)(ii)(A)

[]

50.73(a)(2)(viii)(A)

EJ 20.2203(a)(1)

EJ 20.2203(a)(4) 50.73(a)(2)(ii)(B)

E] 50.73(a)(2)(viii)(B)

_ _ 20.2203(a)(2)(i) 11 50.36(c)(1)(i)(A)

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

10. POWER LEVEL

[:

20.2203(a)(2)(ii) 50.36(c)(1)(ii)(A)

[] 50.73(a)(2)(iv)(A)

EJ 50.73(a)(2)(x)

[J 20.2203(a)(2)(iii) i]

50.36(c)(2)

EJ 50.73(a)(2)(v)(A)

El 73.71(a)(4) 100%

fJ 20.2203(a)(2)(iv)

[]

50.46(a)(3)(ii) 50.73(a)(2)(v)(B)

EJ 73.71(a)(5) 20.2203(a)(2)(v) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(C)

OTHER Specify in Abstract below

___U 20.2203(a)(2)(vi)

L]

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

[

50.73(a)(2)(v)(D) or in NRC Form 366A

12. LICENSEE CONTACT FOR THIS LER FACILITY NAME TELEPHONE NUMBER (Include Area Code)

B. L. Stanley, Director Safety and Licensing (757) 365-2003CAUSE SYSTEM COMPONENT MANU-REPORTABLE

CAUSE

SYSTEM COMPONENT MANU-REPORTABLE FACTURER TO EPIX FACTURER TO EPIX C

FK BU various Y

14. SUPPLEMENTAL REPORT EXPECTED

15. EXPECTED MONTH DAY YEAR Dl YES (If yes, complete 15. EXPECTED SUBMISSION DATE)

NO DATE ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)

On April 16, 2011, at 1849 hours0.0214 days <br />0.514 hours <br />0.00306 weeks <br />7.035445e-4 months <br />, with Surry Power Station Unit 1 at 100% reactor power and Unit 2 at 98.3% reactor power, an automatic reactor trip occurred on Unit 1 and on Unit 2 due to the loss of offsite power resulting from damage inflicted in the switchyard from a tornado. All automatic safety systems, including Emergency Diesel Generators, performed as designed. The loss of offsite power resulted in violating several Technical Specifications including unavailability of independent offsite power. Following the unit trips, Pressurizer/Pressurizer spray temperature difference and Pressurizer heatup rate were also exceeded. A Notification of Unusual Event was declared at 1855 hours0.0215 days <br />0.515 hours <br />0.00307 weeks <br />7.058275e-4 months <br /> due to loss of offsite power to both emergency busses on both units. This event is reportable pursuant to 10CFR50.73(a)(2)(iv)(A) since the event resulted in automatic actuation of reactor protection systems, 10CFR50.73(a)(2)(i)(B) for operation or condition prohibited by Technical Specifications, and 10CFR73.71(a)(4) for delayed implementation of compensatory measures for loss of power to one source of surveillance equipment.

1.0 DESCRIPTION OF THE EVENT On Saturday April 16, 2011, a Tornado Watch was issued by the National Weather Service (NWS) from 1217 hours0.0141 days <br />0.338 hours <br />0.00201 weeks <br />4.630685e-4 months <br /> until 2100 hours0.0243 days <br />0.583 hours <br />0.00347 weeks <br />7.9905e-4 months <br /> EDT for Southeastern Virginia including Surry County, Virginia. NWS issued a Tornado Warning at 1811 hours0.021 days <br />0.503 hours <br />0.00299 weeks <br />6.890855e-4 months <br />.

At 1849 hours0.0214 days <br />0.514 hours <br />0.00306 weeks <br />7.035445e-4 months <br />, with Surry Power Station Unit 1 at 100% reactor power and Unit 2 at 98.3% reactor power, automatic reactor trips occurred on both units due to a loss of offsite power (LOOP) resulting from damage inflicted in the switchyard from a tornado. Damage to the switchyard resulted in a loss of power to the Reserve Station Service Transformers (RSSTs) [EIIS-EA-XFMR] and Station Service Buses [EIIS-EA-BU].

The operating teams promptly initiated the appropriate emergency operating procedures and completed the immediate actions with no discrepancies. Both teams initiated the abnormal procedure for the loss of power and transitioned to the Natural Circulation Cooldown procedure. A natural circulation cooldown was necessary due to loss of all Station Service Buses.

The plant responded to the reactor/turbine trip as designed. Emergency Diesel Generators (EDGs) [EIIS-EK-DG] auto started and loaded, and the Anticipated Transient Without Scram Mitigation System Actuation Circuitry (AMSAC) armed and initiated. Due to the station blackout signal, the Circulating Water outlet motor operator valves (MOVs) throttled closed to approximately 25% open and the Station Blackout Diesel (AAC) automatically started. Auxiliary Feedwater (AFW) pumps [EIIS-BA-P] started as designed. All three Emergency Service Water Pumps [EIIS-BI-P] were started per procedure to control intake canal level. The common emergency diesel generator, EDG #3, automatically loaded onto the Unit 1 J Emergency bus [EIIS-EB-BU] leaving the Unit 2 J Emergency bus de-energized as designed. At 1917 hours0.0222 days <br />0.533 hours <br />0.00317 weeks <br />7.294185e-4 months <br />, EDG #3 was transferred to the Unit 2 J bus and the AAC diesel generator was aligned to the Unit 1 J bus, providing power to all emergency buses at 1922 hours0.0222 days <br />0.534 hours <br />0.00318 weeks <br />7.31321e-4 months <br />.

Following the reactor trips, Unit 1 RCS cooled down below the nominal temperature of 5470F to a minimum of 517 0F, and Unit 2 RCS cooled down below the nominal temperature of 5470F to a minimum of 5040F. The cooldowns were due to the loss of RCPs, the transition to natural circulation, and the coincident AFW flow. Unit 2 experienced further cooldown due to the inability to throttle AFW flow with the Unit 2 J bus initially de-energized.

A Notification Of Unusual Event (NOUE) was declared at 1855 hours0.0215 days <br />0.515 hours <br />0.00307 weeks <br />7.058275e-4 months <br /> due to loss of offsite power to both emergency busses on both units.U. S. NUCLEAR REGULATORY COMMISSION (10-2011)

LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE YEAR SEQUENTIAL REV YEA NUMBER NO.

Surry Power Station 05000 - 280 N

3 of 6 2011 001 00 At 2236 hours0.0259 days <br />0.621 hours <br />0.0037 weeks <br />8.50798e-4 months <br />, shift personnel made a four-hour report pursuant to 10CFR50.72(b)(2)(iv)(B) due to valid automatic actuation of Reactor Protection Systems and an eight-hour non-emergency report pursuant to 1 OCFR50.72(b)(3)(iv)(A) due to automatic actuation of the Auxiliary Feedwater System and Emergency Diesel Generators.

At 2352 hours0.0272 days <br />0.653 hours <br />0.00389 weeks <br />8.94936e-4 months <br />, both A and B RSSTs were energized by offsite power. Offsite power was restored to the Unit 1 J emergency bus and the AAC diesel was secured on April 17, 2011 at 0035 hours4.050926e-4 days <br />0.00972 hours <br />5.787037e-5 weeks <br />1.33175e-5 months <br />. Offsite power was also restored to the Unit 2 H emergency bus at 0153 hours0.00177 days <br />0.0425 hours <br />2.529762e-4 weeks <br />5.82165e-5 months <br />, and EDG #2 was secured at 0241 hours0.00279 days <br />0.0669 hours <br />3.984788e-4 weeks <br />9.17005e-5 months <br />.

Offsite power was restored to the two remaining emergency buses, Unit 1 H and Unit 2 J, on April 17, 2011 at 1803 hours0.0209 days <br />0.501 hours <br />0.00298 weeks <br />6.860415e-4 months <br /> and 2109 hours0.0244 days <br />0.586 hours <br />0.00349 weeks <br />8.024745e-4 months <br />, respectively, and EDG

1. 1 and EDG #3 were secured.

A one hour notification was made to the NRC on April 17, 2011 at 0250 hours0.00289 days <br />0.0694 hours <br />4.133598e-4 weeks <br />9.5125e-5 months <br /> pursuant to 1 OCFR73.71 (b) for the delayed implementation of compensatory measures for the loss of power to one source of surveillance equipment for unattended openings (UAO). Power was lost to the equipment on April 16, 2011 at 1849 hours0.0214 days <br />0.514 hours <br />0.00306 weeks <br />7.035445e-4 months <br /> and compensatory measures were not established until 0010 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> on April 17, 2011. All physical security barriers remained intact.

At 0515 hours0.00596 days <br />0.143 hours <br />8.515212e-4 weeks <br />1.959575e-4 months <br /> on April 17, 2011, one RCP on each unit was returned to service to facilitate placing both units in Cold Shutdown. Pressurizer pressure control was challenged because adequate Pressurizer Spray flow was not available with only the A RCP in service. This condition required Operators to use auxiliary spray from the Chemical and Volume Control System (CVCS) as a means of Pressurizer pressure control. During RCS cooldown and Residual Heat Removal (RHR) heatup, the Unit 1 and Unit 2 Pressurizer temperature and charging/auxiliary spray temperature exceeded the difference limit of 320°F as allowed by Technical Specification (TS) 3.1.B.3.

Unit 2 achieved Cold Shutdown on April 17, 2011 at 1853 hours0.0214 days <br />0.515 hours <br />0.00306 weeks <br />7.050665e-4 months <br />, Unit 1 achieved Cold Shutdown on April 18, 2011 at 0203 hours0.00235 days <br />0.0564 hours <br />3.356481e-4 weeks <br />7.72415e-5 months <br /> and TS 3.0.1 action statements were exited. The NOUE was exited on April 19, 2011 at 0745 hours0.00862 days <br />0.207 hours <br />0.00123 weeks <br />2.834725e-4 months <br /> after necessary repairs were completed to the switchyard.

On April 20, 2011 at 0211 hours0.00244 days <br />0.0586 hours <br />3.488757e-4 weeks <br />8.02855e-5 months <br />, while performing a Unit 1 RHR system operability test, Unit 1 RHR letdown was isolated per procedure, resulting in a Pressurizer insurge. When letdown flow was restored, Pressurizer level decreased from 40%

to 32% over a 15 minute period, and the Pressurizer liquid space temperature increased over a one hour period from 279°F to 425°F which exceeded the TS 3.1.8.3 Pressurizer heatup rate of less than 100°F per hour.U. S. NUCLEAR REGULATORY COMMISSIONU. S. NUCLEAR REGULATORY COMMISSION (10-2011)

LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE YEAR SEQUENTIALI REV YER NUMBER NO.

4o Surry Power Station 05000 - 280 4 of 6 2011 001 00 This report is being submitted pursuant to:

10CFR50.73(a)(2)(iv)(A) as an event that resulted in the automatic actuation of engineered safety features and the reactor protection system; 1 0CFR50.73(a)(2)(i)(B) for operation prohibited by TSs; Less than the minimum number of operable/operational RCS loops as required by TS 3.1.A.1.c Less than two emergency buses energized on Unit 1 and Unit 2 when the RCS is greater than 350'F and 450 psig as required by TS 3.16.A.2 and 3 Less than the minimum number of operable physically independent circuits from the offsite transmission network to energize the 4,160V and 480V emergency buses as required by TS 3.16.A.4 Less than 2 circulating water pumps per unit operable when the RCS is greater than 350OF and 450 psig as required by TS 3.14.A.3 Less than the required number of component cooling pumps operable when the reactor coolant system is greater than 350°F and 450 psig as required by TS 3.13.B The Unit 1 and Unit 2 RCS Pressurizer temperature and spray temperature exceeded the difference limit of TS 3.1.B.3 Unit 1 RCS Pressurizer exceeded the heatup rate specified by TS 3.1..B.3 10CFR73.71(a)(4) for the failure of a safeguard system that could have allowed unauthorized or undetected access to a protected area for which compensatory measures have not been employed within the required timeframe of one hour.

2.0

SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS

Automatic safety systems, including EDGs, performed as designed. Appropriate operator actions were taken in accordance with emergency operating procedures.

Operating teams initiated the abnormal procedure for the loss of power and transitioned to the Natural Circulation Cooldown procedure that was necessary due to loss of all Station Service Buses. The units were brought to a stable condition.

There were no radiation releases due to these events. Therefore, the health and safety of the public were not affected at any time during this event.U. S. NUCLEAR REGULATORY COMMISSION (10-2011)

LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE YEAR SEQUENTIAL REV YEA NUMBER NO.

Surry Power Station 05000- 280 N

5 of 6 2011 001 00 The risk of this event was assessed considering the dual unit shutdown and the duration when offsite power was not available to power the RSSTs. The conditional core damage probability was estimated to be moderate, but the equipment required for accident mitigation in the scenarios considered remained available throughout the event. The performance of the EDGs and timely recovery of offsite power reduced the significance of this event. Physical security barriers remained intact during power loss to surveillance equipment and the Pressurizer had no adverse consequence due to exceeding Pressurizer spray line differential temperature.

3.0

CAUSE

The root cause of the LOOP and resultant dual unit trip was determined to be wind damage inflicted by a tornado that passed directly through the Surry switchyard.

The transmission lines and switchyard components were not designed to withstand the wind force generated by the tornado.

The preliminary cause of the Unit 1 and Unit 2 Pressurizer and Pressurizer spray line differential temperature in excess of the TS 3.1..B.3 limit on April 17, 2011 was insufficient procedural guidance to ensure compliance with the 320'F TS limit.

The cause of the April 20, 2011 Unit 1 Pressurizer heatup rate exceeding the TS 3.1.B.3 limit was a human performance event involving operator failure to recognize the challenge of reinitiating letdown flow following conclusion of the RHR system operability test.

The preliminary cause of the untimely implementation of compensatory measures after the loss of power to UAO security equipment was conflicting prioritization of resources following the onsite tornado event.

4.0 IMMEDIATE CORRECTIVE ACTION(S)

Following the reactor trips, control room operators acted promptly to place the units in a safe, shutdown condition in accordance with emergency operating procedures.

Immediate restoration of offsite power was initiated to allow restarting an RCP on each unit, starting circulating water pumps, securing emergency service water pumps, providing offsite power to one emergency bus for each unit, and securing the AAC and EDG #2. Offsite power was restored to the two remaining emergency buses, Unit 1 H and Unit 2 J, on April 17, 2011 at 1803 hours0.0209 days <br />0.501 hours <br />0.00298 weeks <br />6.860415e-4 months <br /> and 2109 hours0.0244 days <br />0.586 hours <br />0.00349 weeks <br />8.024745e-4 months <br />, respectively.U. S. NUCLEAR REGULATORY COMMISSION (10-2011)

LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE YEAR SEQUENTIAL REV IEA NUMBER NO.

Surry Power Station 05000- 280 N

6 of 6 2011 001 00 5.0

ADDITIONAL CORRECTIVE ACTIONS

Tornado generated debris from the switchyard that was deposited in the intake canal was removed prior to startup of Unit 1.

The procedure for RCS and Pressurizer heatup/cooldown verification has been revised to enhance monitoring of critical parameters necessary to prevent exceeding the Pressurizer spray line differential temperature limit. An Apparent Cause Evaluation (ACE) is reviewing both Unit 1 TS 3.1.B.3 violations and corrective actions from the ACE will be implemented. An evaluation of exceeding the Pressurizer spray line differential temperature limit was performed and concluded there was no adverse consequence to the Pressurizer, and the Pressurizer is capable of performing its design function.

Following the loss of power to the UAO post related security equipment, interim actions were implemented to ensure the timely implementation of compensatory measures. An ACE will be completed and corrective actions will be implemented to ensure unattended access openings remain protected.

Operators involved with managing the thermal limits when the April 20, 2011 Unit 1 Pressurizer heatup rate exceeded the TS 3.1.B.3 limit were removed from licensed duties for remediation.

6.0 ACTIONS TO PREVENT RECURRENCE To minimize the complications from recurrence of a similar event, an evaluation will be completed to look for enhancements to the switchyard.

7.0

SIMILAR EVENTS

None 8.0 MANUFACTURER/MODEL NUMBER None 9.0

ADDITIONAL INFORMATION

Unit 1 was brought online at 1952 hours0.0226 days <br />0.542 hours <br />0.00323 weeks <br />7.42736e-4 months <br /> on April 23, 2011. Unit 2 commenced the scheduled refueling outage.