05000317/LER-2011-001, For Calvert Cliffs, Unit 1, Regarding Reactor Trip Due to a Phase-to-Phase Short Circuit on Main Transformer

For Calvert Cliffs, Unit 1, Regarding Reactor Trip Due to a Phase-to-Phase Short Circuit on Main Transformer

ML11297A113
Person / Time
Site:	Calvert Cliffs
Issue date:	10/20/2011
From:	Costanzo C Calvert Cliffs 3 Nuclear Project, Constellation Energy Group, EDF Development
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LER 11-001-00
Download: ML11297A113 (7)

LER-2011-001, For Calvert Cliffs, Unit 1, Regarding Reactor Trip Due to a Phase-to-Phase Short Circuit on Main Transformer

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 10 CFR 50.73(a)(2)
3172011001R00 - NRC Website

text

Calvert Cliffs Nuclear Power Plant CENGSM a joint venture of Constellation e

O Energy-1650 Calvert Cliffs Parkway Lusby, Maryland 20657 CALVERT CLIFFS NUCLEAR POWER PLANT October 20, 2011 U.S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION:

SUBJECT:

Document Control Desk Calvert Cliffs Nuclear Power Plant Unit No. 1; Docket No. 50-317; License No. DPR 53 Licensee Event Report 2011-001, Revision 00 Reactor Trip Due to a Phase-to-Phase Short Circuit on Main Transformer The attached report is being sent to you as required by 10 CFR 50.73.

Should you have questions regarding this report, please contact Mr. Douglas E. Lauver at (410) 495-5219.

Very truly yours, Christopher R. Costanzo Plant General Manager CRC/CAN/bjd

Attachment:

As stated cc:

D. V. Pickett, NRC W. M. Dean, NRC Resident Inspector, NRC S. Gray, DNR KBRk)

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2013 (10-2010)

Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the Records and FOIA/Privacy Section (T-5 F53), U.S. Nuclear LICENSEE EVENT REPORT (LER)

Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to infocollects.resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose (See reverse for required number of an information collection does not display a currently valid OMB control digits/characters for each block) number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. PAGE Calvert Cliffs Nuclear Power Plant, Unit 1 05000 317 1 OF 6

4. TITLE Reactor Trio Due to a Phase-to-Phase Short Circuit on Main Transformer

5. EVENT DATE

6. LER NUMBER

7. REPORT DATE

8. OTHER FACILITIES INVOLVED MNH DY YA FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR I

NUMBER NO.

05000 FACILITY NAME DOCKET NUMBER 08 27 2011 2011

- 001 00 10 20 2011 05000

9. OPERATING MODE

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

[] 20.2201(b)

[1 20.2203(a)(3)(i)

U] 50.73(a)(2)(i)(C)

[I 50.73(a)(2)(vii) 1[3 20.2201(d)

EU 20.2203(a)(3)(ii)

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

[U 50.73(a)(2)(viii)(A)

[I 20.2203(a)(1)

[I 20.2203(a)(4)

Ul 50.73(a)(2)(ii)(B)

Ul 50.73(a)(2)(viii)(B)

E_ 20.2203(a)(2)(i)

EU 50.36(c)(1)(i)(A)

[I 50.73(a)(2)(iii)

[3 50.73(a)(2)(ix)(A)

10. POWER LEVEL

[] 20.2203(a)(2)(ii)

EU 50.36(c)(1)(ii)(A)

ED 50.73(a)(2)(iv)(A)

EU 50.73(a)(2)(x)

[U 20.2203(a)(2)(iii)

EU 50.36(c)(2)

EU 50.73(a)(2)(v)(A)

EU 73.71(a)(4)

EU 20.2203(a)(2)(iv)

[U 50.46(a)(3)(ii)

El 50.73(a)(2)(v)(B)

U 73.71(a)(5) 100 Ul 20.2203(a)(2)(v)

[U 50.73(a)(2)(i)(A)

EU 50.73(a)(2)(v)(C)

U OTHER EU 20.2203(a)(2)(vi)

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

[U 50.73(a)(2)(v)(D)

Specify in Abstract below or in NRC Form 366A

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

C. A. Neyman, Senior Engineering Analyst 410-495-3507CAUSE SYSTEM COMPONENT MANU-REPORTABLE I

CAUSE

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

EL XFMR M380 Y

X EK DG Y

14. SUPPLEMENTAL REPORT EXPECTED 16.SEXPECTED MONTH DAY YEAR SUBMISSION U] YES (If yes, complete 15. EXPECTED SUBMISSION DATE)

[

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

On August 27, 2011, at 2248 eastern daylight time, Unit 1 experienced an automatic reactor trip from 100 percent power. The Reactor Protective System actuated on loss of load. The loss of load occurred due to a phase-to-phase short circuit on the main transformer when main transformer lines were struck by dislodged Turbine Building siding caused by winds associated with Hurricane Irene. Immediately following the short circuit, 14 Containment Air Cooler stopped operating. Shortly after the plant trip occurred, 1A Emergency Diesel Generator was declared inoperable due to a shorted speed switch. The root cause analysis performed to address this event concluded that the Turbine Building Northwest corner siding was not installed per design during original construction. This resulted in a weaker siding connection to the Turbine Building structure, allowing the siding to come off in wind speeds less than design.

At Calvert Cliffs, there have been no recent similar events involving a reactor trip associated with severe weather. This event is being reported pursuant to 10 CFR 50.73(a)(2)(iv)(A) due to Reactor Protective System actuation. Corrective actions include testing and inspection of the main transformer, replacement of B and C phase high line drops to the main transformer and inspection and repair of electrical connectors on the 1A Emergency Diesel Generator.

NRC FORM 366 (10.2013)U.S. NUCLEAR REGULATORY COMMISSION (10-2010)

LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE SEQUENTIAL I REV YEAR NUMBER NO.

Calvert Cliffs Nuclear Power Plant, Unit 1 05000 317 2011 001 00 1 02 of 06 I.

DESCRIPTION OF EVENT

A.

PRE-EVENT PLANT CONDITIONS Unit I was operating at 100 percent of rated thermal power on August 27, 2011.

B.

EVENT On August 27, 2011 at 2248 eastern daylight time, Calvert Cliffs Nuclear Power Plant Unit 1 automatically shut down from 100 percent power on loss of load signal from the Reactor Protective System. The loss of load signal was generated when siding from the Turbine Building became dislodged during high winds from Hurricane Irene and contacted the B and C phase high line drops going to 1XU-25000-12 transformer causing a phase differential. All control rods fully inserted, there was no loss of normal heat removal. Unit 2 remained at full power during the event on Unit 1.

The short circuit resulted in an explosion, which met emergency action level declaration criteria A.U.6.2.2, "Unanticipated explosion within Protected Area resulting in visible damage to permanent structures or equipment." An Unusual Event was declared at 2302. Follow-up investigation determined no fire resulted from the explosion, which was attributed to arc flash.

Following the trip, Emergency Operating Procedure (EOP)-0, "Post Trip Immediate Actions,"

was implemented. All safety functions were met during EOP-0 indicating an uncomplicated reactor trip response, allowing transition to EOP-1, "Reactor Trip," at 2300. During implementation of EOP-1, it was noted that 14 Containment Air Cooler (one of four Containment Air Coolers) had stopped running. An investigation determined the containment air cooler had stopped running due to an instantaneous voltage drop that had occurred on the site distribution system during the phase-to-phase short event. This short duration voltage drop caused the containment air cooler's controller to drop out and secure it. The containment air cooler was restarted without issue.

Once the unit was stable in Mode 3, numerous alarms were received for the 1A Emergency Diesel Generator (EDG) (one of two safety-related EDGs dedicated to Unit 1). Water was intruding down the diesel generator exhaust piping resulting in a DC ground. Based on these indications the 1A EDG was declared inoperable and appropriate Technical Specifications implemented. During the event, there was no demand for the 1A EDG.

Otherwise, plant response was as expected and EOP-1 was exited on August 28, 2011, at 0130. At that time, Operators entered Operating Procedure (OP)-4, for plant shutdown from power operation to hot standby.

On August 28, 2011, at 0755, the licensee exited the Unusual Event condition based on the fact that the affected equipment was inspected in the daylight to determine the extent of the damage.U.S. NUCLEAR REGULATORY COMMISSION (10-2010)

LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE SEQUENTIAL REV YEAR NUMBER NO.

Calvert Cliffs Nuclear Power Plant, Unit 1 05000 317 2011 001 00 03 of 06 This licensee event report (LER) is applicable to Calvert Cliffs Nuclear Power Plant Unit 1 only.

C.

INOPERABLE STRUCTURES, COMPONENTS, OR SYSTEMS THAT CONTRIBUTED TO THE EVENT There were no inoperable structures, components, or systems that contributed to the event.

D.

DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES

The reactor trip occurred on August 27, 2011, at 2248. Operators implemented EOP-0 and performed post-trip immediate actions. The 14 Containment Air Cooler stopped at the time of the reactor trip.

At 2254, a Nuclear Regulatory Commission inspector reported hearing an explosion near the Unit 1 main transformers at the time when the reactor trip occurred.

At 2258, operators exited EOP-0. At 2300, operators entered EOP-1 and performed actions associated with an uncomplicated reactor trip.

At 2302, an Unusual Event was declared for report of an explosion within the Protected Area that affected plant equipment.

On August 28, 2011, at 0000, the 1A EDG was declared inoperable due to receiving several alarms. The 1 B EDG was verified operable and the OC Diesel Generator was verified available.

At 0130, operators exited EOP-1 and entered OP-4, for plant shutdown from power operation to hot standby.

At 0145, the 14 Containment Air Cooler was restarted.

At 0755, the licensee exited the Unusual Event.

On August 29, 2011 at 1030, the 1A EDG was declared operable. Total elapsed time of inoperability was 34.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />.

Inspections were performed on the affected equipment and the reactor was taken critical on August 31, 2011, at 0113.

At 1008, the unit was paralleled to the grid.

At 2319, the unit was returned to 100 percent power.U.S. NUCLEAR REGULATORY COMMISSION (10-2010)

LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE SEQUENTIAL REV YEAR NUMBER NO.

Calvert Cliffs Nuclear Power Plant, Unit 1 05000 317 2011 001 00 04 of 06 E.

OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED

No other systems or secondary functions were affected.

F.

METHOD OF DISCOVERY

The event was self-revealing.

G.

MAJOR OPERATOR ACTION No major operator actions were taken as a result of this condition.

H.

SAFETY SYSTEM RESPONSES The Reactor Protective System operated as required. The 14 Containment Air Cooler stopped at the time of the reactor trip. The 1A EDG was declared inoperable due to receiving several alarms. There were no safety system functional failures.

I1.

CAUSE OF EVENT

The Unit 1 reactor trip is documented in station condition report number CR-2011-008704. The reactor trip occurred due to a phase-to-phase short when main transformer lines were struck by dislodged Turbine Building siding caused by winds associated with Hurricane Irene. Turbine Building Northwest corner siding was not installed per design during original construction resulting in a weaker siding connection to the Turbine Building structure, allowing the siding to come off in wind speeds less than design.

The Turbine Building siding on the Northwest corner was not fastened to the top two support members, the west most panel on the north face was fastened from the inside, and the bottom 18 feet of the west most panel had no fasteners. These connections cannot be seen with the siding installed.

The stoppage of 14 Containment Air Cooler is documented in station condition report CR-2011-008715. An investigation determined the containment air cooler had stopped running due to an instantaneous voltage drop that had occurred on the site distribution system during the phase-to-phase short event. This short duration voltage drop caused the containment air cooler's controller to drop out and secure it. The containment air cooler was restarted without issue.

The inoperable 1A EDG is documented in station condition report number CR-2011-008708.

The penetration around the 1A2 combustion air intake pipe on 80 foot level of the 1A Diesel Generator Building was unable to perform its design function of being leak tight. Dripping water penetrated the 1A EDG 1A2 speed switch connector causing the speed switch circuit to short.

This shorted speed switch caused the 1A EDG field flash circuit to attempt to flash the 1A EDG.

Since the generator was not turning, a field was not established and the field flash circuitU.S. NUCLEAR REGULATORY COMMISSION (10-2010)

LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE SEQUENTIAL I REV YEAR NUMBER NO.

Calvert Cliffs Nuclear Power Plant, Unit 1 05000 317 2011 001 00 05 of 06 protective features were enabled. Because these protective features were enabled, the field flash circuit would not have been available for subsequent EDG starts. Evaluation has determined that the most likely root cause(s) are limited to improper installation, manufacturing defect, or original design considerations.

Ill.

ANALYSIS OF THE EVENT

This event resulted in a valid actuation of the Reactor Protective System. The actuation was not part of a pre-planned sequence during testing or reactor operation. Therefore, this event is reportable in accordance with 10 CFR 50.73(a)(2)(IV)(A). Immediate notification of this event (Event Number 47208) was made on August 27, 2011, at 2327 in accordance with 10 CFR 50.72(b)(2)(iv)(B) and 10 CFR 50.72(a)(1)(i).

The Nuclear Regulatory Commission Performance Indicator for Unplanned Scrams per 7,000 Critical Hours is projected to rise to approximately 0.8 and remain green. No other performance indicators were impacted.

There were no actual nuclear safety consequences incurred from this event. An estimated conditional core damage probability of 2.02E-06 and an estimated conditional large early release probability of 1.72E-07 were calculated for this event.

IV.

CORRECTIVE ACTIONS

A.

ACTION TAKEN TO RETURN AFFECTED SYSTEMS TO PRE-EVENT NORMAL STATUS:

1.

The main transformer was inspected and tested to detect any abnormalities. No abnormal conditions were found.

2.

The B and C phase high line drops going to the main transformer were replaced.

3.

Affected electrical connectors on the 1A EDG were disassembled, inspected, and repaired.

B.

ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE

1.

Perform temporary repair to Northwest Turbine Building corner siding.

2.

Replace Turbine Building corner siding per design requirements.

3.

Repair the combustion air inlet piping penetrations for the 1A EDG to ensure the penetrations are leak tight.

If information is subsequently developed, that would significantly affect a reader's understanding or perception of this event, a supplemental LER will be submitted.U.S. NUCLEAR REGULATORY COMMISSION (10-2010)

LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET

1. FACILITY NAME

2. DOCKET

6. LER NUMBER

3. PAGE I

SEQUENTIAL I

REV YEAR NUMBER NO, Calvert Cliffs Nuclear Power Plant, Unit 1 05000 317 2011 001 00 06 of 06 V.

ADDITIONAL INFORMATION

A.

FAILED COMPONENTS:

1.

The 25 kV to 500 kV step up transformer was manufactured by Mitsubishi Heavy Industries.

2.

The 1A EDG was manufactured by Societe Alsacienne De Constructions Mecaniques De Mulhouse.

B.

PREVIOUS LERs ON SIMILAR EVENTS A review of Calvert Cliffs' events over the past several years was performed. No previous LERs on similar events (reactor trip associated with severe weather) were identified.

C.

THE ENERGY INDUSTRY IDENTIFICATION SYSTEM (EIIS) COMPONENT FUNCTION IDENTIFIER AND SYSTEM NAME OF EACH COMPONENT OR SYSTEM REFERRED TO IN THIS LER:

IEEE 803 IEEE 805 Component EIIS Function System ID Transformer XFMR EL 1A Diesel Generator DG EK 14 Containment Air Cooler CLR BK D.

SPECIAL COMMENTS None