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LER-2016-001, Regarding Reactor Trip Due to a Ground Fault Resulting in a Generator Trip
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded; 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)(v), Loss of Safety Function; 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown; 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications; 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability; 10 CFR 50.73(a)(2)(i)
	3062016001R00 - NRC Website
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Regarding Reactor Trip Due to a Ground Fault Resulting in a Generator Trip
	ML16043A396
Person / Time
Site:	Prairie Island
Issue date:	02/12/2016
From:	Davison K; Northern States Power Co, Xcel Energy
To:	; Document Control Desk, Office of Nuclear Reactor Regulation
References
	L-PI-16-011 LER 16-001-00
	Download: ML16043A396 (6)
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Xcel Energy FEB 12 2016 ATTN: Document Control Desk U S Nuclear Regulatory Commission Washington, DC 20555-0001 Prairie Island Nuclear Generating Plant Unit 2 Docket: 50-306 Renewed License No. DPR-60 L-PI-16-011 10 CFR 50.73 LER 50-306-2016-001-00, Unit 2 Reactor Trip due to a Ground Fault resulting in a Generator Trip Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy (hereafter "NSPM"), encloses Licensee Event Report (LER) 50-306/2016-001-00, Unit 2 Reactor Trip due to a Ground Fault resulting in a Generator Trip.

Summary of Commitme~ts This letter contains no new commitment and no change to an existing commitment.

~~~

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Kevin Davison Site Vice President, Prairie Island Nuclear Generating Plant Northern States Power Company - Minnesota Enclosure cc:

Administrator, Region Ill, USNRC Project Manager, Prairie Island Nuclear Generating Plant (PINGP), USNRC Resident Inspector, PINGP, USNRC Department of Commerce, State of Minnesota 1717 Wakonade Drive East

Welch, Minnesota 55089-9642 Telephone: 651.388.1121

ENCLOSURE LICENSEE EVENT REPORT 50-306/2016-001-00 4 Pages Follow

NRC FORM366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 (11-2015)

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

r* PAGE Prairie Island Nuclear Generating Plant 05000306 1 OF4

4. TITLE Unit 2 Reactor Trio due to a Ground Fault resultina in a Generator Trio

5. EVENT DATE

6. LER NUMBER

7. REPORT DATE

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

MONTH DAY YEAR 05000 FACILITY NAME DOCKET NUMBER 12 17 2015 2016

- 001

- 00 02 12 2016 05000

9. OPERATING MODE

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

D 2o.2201(b)

D 20.2203(a)(3)(i) 0 50.73(a)(2)(ii)(A)

D 50. 73(a)(2)(viii)(A) 1 D 20.22o1(ct)

D 20.2203(a)(3)(ii) 0 50.73(a)(2)(ii)(B)

D 50.73(a)(2)(viii)(B)

D 20.2203(a)(1)

D 20.2203(a)(4)

D 50.73(a)(2)(iii)

D 50.73(a)(2)(ix)(A)

D 20.2203(a)(2)(i) 0 50.36(c)(1)(i)(A)

X 50.73(a)(2)(iv)(A)

D 50.73(a)(2)(x)

10. POWER LEVEL D 20.2203(a)(2)(ii) 0 50.36(c)(1)(ii)(A)

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

D 73.71 (a)(4)

D 20.2203(a)(2)(iii)

D 50.36(c)(2)

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

D 73.71 (a)(5) 100 D 20.2203(a)(2)(iv)

D 50.46(a)(3)(ii)

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

D 73.77(a)(1)

D 20.2203(a)(2)(v) 0 50.73(a)(2)(i)(A)

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

D 73.77(a)(2)(i)

D 20.2203(a)(2)(vi)

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

D 50.73(a)(2)(vii)

D 73.77(a)(2)(ii) 0 50.73(a)(2)(i)(C) 0 OTHER Specify in Abstract below or in NRC Form 366A

12. LICENSEE CONTACT FOR THIS LER LICENSEE CONTACT

~ELEPHONE NUMER (Include Area Code)

Penny S. Oleson 651-267-1750

13. COMPLETE ONE UNE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT

CAUSE

SYSTEM COMPONENT MANU-REPORTABLE

CAUSE

SYSTEM COMPONENT MANU-REPORTABLE FACTURER TOEPIX FACTURER TO EPIX

14. SUPPLEMENTAL REPORT EXPECTED 15.EXPECTED MONTH DAY YEAR 0 YES (If yes, complete 15. EXPECTED SUBMISSION DATE)

XNO SUBMISSION DATE ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines)

On 12/17/2015 at 1234 Central Standard Time (CST) with Unit 2 (U2) in Mode 1 at 100 percent power, the U2 electric generator tripped due to a ground overvoltage protection relay (59/2G) actuation, which resulted in an automatic reactor trip and expected Auxiliary Feedwater System actuation. At 1307 CST a fire alarm was received in the U2 containment.

Personnel were unable to verify the status within 15 minutes and the site declared an Unusual Event, HU2.1, at 1318 CST.

The licensee notified the NRC Resident Inspector, state and local authorities and made an Event Notification to the NRC for the Unusual Event and the U2 reactor trip as required under 10 CFR 50. 72(a)(1 )(i) and 10 CFR 50. 72(b)(2)(iv)(B).

Subsequently, the Unusual Event was terminated on 12/17/2015 at 1450 CST after a containment entry determined there was no smoke or fire. The original Event Notification was updated to cancel the Unusual Event and to add reporting under 10 CFR 50. 72(b )(3)(iv)(A) for the expected Auxiliary F eedwater system actuation. Decay heat removal was via forced circulation with Auxiliary Feed and Steam Dumps providing secondary cooling. Offsite power remained available. The health and safety of the public was not at risk.

A troubleshooting plan was initiated which determined an actual ground fault existed internal to the new U2 electric generator, installed during the Fall 2015 U2 refueling outage, causing a U2 reactor trip and the expected Auxiliary Feedwater actuation. The cause of the ground fault of the U2 electric generator was determined to be foreign material, specifically a hex socket and hex key introduced at the vendor's manufacturing facility during installation of a temporary dust cover on collector end of the generator rotor.

NRC FORM366 (11-2015) U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 (11-2015)

, the NRC may LICENSEE EVENT REPORT (LER) not conduct or sponsor, and a person is not required to respond to, the information collection.

CONTINUATION SHEET

3. LER NUMBER YEAR SEQUENTIAL Prairie Island 05000306 NUMBER 2016

- 001

Event Description

The Prairie Island Nuclear Generating Plant (PINGP) Unit 1 (U1) and Unit 2 (U2) electric generators were supplied by a vendor through a contract awarded on 12/28/2012 with Xcel Energy. The electric generators were fabricated and assembled by a subcontractor at the vendor manufacturing site between April 2013 and June 2015. The electric generators were shipped to PINGP in 2015 fully assembled with the rotor installed in the stator.

The U2 electric generator was installed by the vendor during the fall 2015 U2 refueling outage. The U2 electric generator was successfully tested and synchronized to the grid on 12/13/15. The U1 replacement electric generator remains staged at the PINGP site awaiting installation.

On 12/17/2015 U2 was in Mode 1 running at 100% power. At 1234 CST, the U2 electric generator tripped due to a ground overvoltage protection relay (59/2G) actuation, which resulted in an automatic reactor trip and expected Auxiliary Feedwater System 1 actuation. At 1307 CST a fire alarm was received in the U2 Containment. Personnel were unable to make a containment entry to verify the status of the alarm within 15 minutes, and the site declared an Unusual Event, HU2.1 at 1318 CST.

The licensee notified the NRC Resident Inspector, state and local authorities and made an Event Notification to the NRC for the Unusual Event and the U2 reactor trip as required under 10 CFR 50. 72(a)(1 )(i) and 10 CFR

50. 72(b)(2)(iv)(B). The Unusual Event was terminated on 12/17/2015 at 1450 CST after a containment entry determined there was no smoke or fire. The site updated the Event Notification cancelling the Unusual Event and reporting, under 10 CFR 50.72(b)(3)(iv)(A), the Auxiliary Feedwater System actuated to start the Auxiliary Feedwater pumps, as designed, to provide makeup flow to the steam generators.

Decay heat removal was via forced circulation with reactor coolant pumps and auxiliary feed and steam dumps providing secondary cooling. Offsite power remained available. The health and safety of the public were not at risk.

1 EllS System Code-BA NRC FORM 366 (11-2015)

NRC FORM 366 (11-2015) 2 REV NO.

- 00 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 (11-2015)

, the NRC may LICENSEE EVENT REPORT (LER) not conduct or sponsor, and a person is not required to respond to, the Information collection.

CONTINUATION SHEET

3. LER NUMBER YEAR SEQUENTIAL Prairie Island 05000306 NUMBER 2016

- 001

Event Analysis

The electric generators are expected to operate continuously during normal plant operations. As a result of the U2 electric generator trip, the plant entered an extended forced outage. Until repaired and returned to service, the U2 electric generator is not capable of producing reliable electric power as expected.

A troubleshooting team of PINGP and vendor personnel were put in place to determine the cause of the U2 electric generator trip and apply lessons learned prior to installing the new U1 electric generator currently stored at PINGP awaiting installation in a future outage. The team verified the relay actuation was due to an actual ground fault condition isolated to number 25 Top Stator Coil. Initial visual inspection of the U2 electric generator after the trip did not reveal a cause of the trip. Investigation under warranty work by the vendor indicated foreign material caused wear to the insulation of the stator winding which eventually failed, actuated the relay, and tripped the U2 electric generator. The damage was created by foreign material (FM); specifically, a 1 0-mm socket and hex key.

The vendor conducted a root cause evaluation and states the FM was introduced at the vendor's manufacturing facility. The activity that introduced the FM in the U2 electric generator was part of an assembly sequence that was not used on the U 1 electric generator.

Safety Significance

This event did not represent a significant challenge to nuclear safety and all plant systems responded as designed. The automatic reactor trip occurred as designed because of the turbine trip. Offsite power remained available. There was no radiological, environmental, or industrial impact associated with this event. The health and safety of the public and site personnel were not at risk at any time during this event.

NRC FORM 366(11-2015) 3 REV NO.

- 00 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2018 (11-2015)

, the NRC may

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,._*i' LICENSEE EVENT REPORT (LER) not conduct or sponsor, and a person Is not required to respond to, the information collection.

CONTINUATION SHEET

3. LER NUMBER YEAR SEQUENTIAL Prairie Island 05000306 NUMBER 2016

- 001 Foreign material at the vendor manufacturing facility caused damage to the number 25 Top Stator Coil of the U2 electric generator leading to a ground fault.

Corrective Actions

Foreign material was removed from the U2 electric generator.

An extensive search of the U2 electric generator was performed and no other foreign material was identified.

Replaced the number 25 Top Stator Coil of the U2 electric generator.

Previous Similar Events

There was no event within the last 5 years with the same failure and same root or apparent cause.

NRC FORM 366(11-2015) 4 REV NO.

- 00

Xcel Energy FEB 12 2016 ATTN: Document Control Desk U S Nuclear Regulatory Commission Washington, DC 20555-0001 Prairie Island Nuclear Generating Plant Unit 2 Docket: 50-306 Renewed License No. DPR-60 L-PI-16-011 10 CFR 50.73 LER 50-306-2016-001-00, Unit 2 Reactor Trip due to a Ground Fault resulting in a Generator Trip Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy (hereafter "NSPM"), encloses Licensee Event Report (LER) 50-306/2016-001-00, Unit 2 Reactor Trip due to a Ground Fault resulting in a Generator Trip.

Summary of Commitme~ts This letter contains no new commitment and no change to an existing commitment.

~~~

//) ~V:K:r- "'

Kevin Davison Site Vice President, Prairie Island Nuclear Generating Plant Northern States Power Company - Minnesota Enclosure cc:

Administrator, Region Ill, USNRC Project Manager, Prairie Island Nuclear Generating Plant (PINGP), USNRC Resident Inspector, PINGP, USNRC Department of Commerce, State of Minnesota 1717 Wakonade Drive East

Welch, Minnesota 55089-9642 Telephone: 651.388.1121