05000483/LER-2014-006, Regarding Main Generator Excitation Transformer Faulted to Ground, Causing Turbine and Reactor Trip

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Regarding Main Generator Excitation Transformer Faulted to Ground, Causing Turbine and Reactor Trip
ML15033A215
Person / Time
Site: Callaway 
Issue date: 02/02/2015
From: Cox B
Ameren Missouri, Union Electric Co
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
ULNRC-06178 LER 14-006-00
Download: ML15033A215 (7)
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LER-2014-006, Regarding Main Generator Excitation Transformer Faulted to Ground, Causing Turbine and Reactor Trip
Event date:
Report date:
Reporting criterion: 10 CFR 50.73(a)(2)(iv)(A), System Actuation
10 CFR 50.73(a)(2)(i)
10 CFR 50.73(a)(2)(vii), Common Cause Inoperability
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)(x)
10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor
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
4832014006R00 - NRC Website
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text

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WAmeren MISSOURI Callaway Plant February 2, 2015 ULNRC-06178 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Ladies and Gentlemen:

10 CFR 50.73 DOCKET NUMBER 50-483 CALLAWAY PLANT UNIT 1 UNION ELECTRIC CO.

FACILITY OPERATING LICENSE NPF-30 LICENSEE EVENT REPORT 2014-006-00 MAIN GENERATOR EXCITATION TRANSFORMER FAULTED TO GROUND, CAUSING REACTOR TRIP The enclosed licensee event report is submitted in accordance with 10CFR50.73(a)(2)(iv)(A) to report a reactor protection system actuation while critical and an auxiliary feed water system actuation due to a plant trip caused by a ground fault in the main generator excitation transformer.

This letter does not contain new commitments.

DRB/nls Enclosure Sincerely, k~~

Barry Cox Senior Director, Nuclear Operations PO Box 620 Fulton, MD 65251 AmerenMissouri.com

ULNRC-06178 February 2, 2015 Page2 cc:

Mr. Marc L. Dapas Regional Administrator U.S. Nuclear Regulatory Commission Region IV 1600 East Lamar Boulevard Arlington, TX 76011-4511 Senior Resident Inspector Callaway Resident Office U.S. Nuclear Regulatory Commission 8201 NRC Road Steedman, MO 65077 Mr. Fred Lyon Project Manager, Callaway Plant Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Mail Stop 0-8B 1 Washington, DC 20555-2738

ULNRC-06178 February 2, 2015 Page 3 Index and send hardcopy to QA File A160.0761 Hardcopy:

Certrec Corporation 4150 International Plaza Suite 820 Fort Worth, TX 76109 (Certrec receives ALL attachments as long as they are non-safeguards and may be publicly disclosed.)

Electronic distribution for the following can be made via LER ULNRC Distribution:

F. M. Diya D. W. Neterer L. H. Graessle B.L.Cox T. E. Herrmann S.M. Maglio T. B. Elwood Corporate Oversight Corporate Communications NSRB Secretary Performance Improvement Coordinator Resident Inspectors (NRC)

STARS Regulatory Affairs Mr. John O'Neill (Pillsbury Winthrop Shaw Pittman LLP)

Missouri Public Service Commission

NRCFORM366 (01-2014)

U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 01/31/2017 LICENSEE EVENT REPORT (LER)

(See reverse for required number of digits/characters for each block)

Estimated burden per response to comply with this mandatory collection request: ao hours. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regardi~ burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53),

U.S. Nuclear 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-1 0202, (3150-01 04), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

1. FACILITY NAME Callaway Plant Unit 1
2. DOCKET NUMBER 05000483
13. PAGE 1 OF 4
4. TITLE Main Generator Excitation Transformer Faulted to Ground, Causing Turbine and Reactor Trip
5. EVENT DATE
6. LER NUMBER
7. REPORT DATE
8. OTHER FACILITIES INVOLVED YEAR 'SEQUENTIAL I REV MONTH FACILITY NAME DOCKET NUMBER MONTH DAY YEAR NUMBER NO.

DAY YEAR FACILITY NAME DOCKET NUMBER 12 03 2014 2014 -

006 -

00 02 01 2015

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

D 20.2201 (b)

D 20.2203(a)(3)(i)

D 50.73(a)(2)(i)(C)

D 50.73(a)(2)(vii) 1 D 20.2201 (d)

D 20.2203(a)(3)(ii)

D 50. 73(a)(2)(ii)(A)

D 50. 73(a)(2)(viii)(A)

D 20.2203(a)(1)

D 20.2203(a)(4)

D 50.73(a)(2)(ii)(B)

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

D 20.2203(a)(2)(i)

D 50.36(c)(1)(i)(A)

D 50.73(a)(2)(iii)

D 50.73(a)(2)(ix)(A) 1-1-0

.-P-O_W_E_R_L_EV_EL-~D 20.2203(a)(2)(ii)

D 50.36(c)(1)(ii)(A) 181 50.73(a)(2)(iv)(A)

D 50.73(a)(2)(x)

D 20.2203(a)(2)(iii)

D 50.36(c)(2)

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

D 73.71 (a)(4)

D 20.2203(a)(2)(iv)

D 50.46(a)(3)(ii)

D 50. 73(a)(2)(v)(B)

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

D 50.73(a)(2)(i)(A)

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

D OTHER D 20.2203(a)(2)(vi)

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

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

Specify in Abstract below or in

4.

ASSESSMENT OF SAFETY CONSEQUENCES

I SEQUENTIAL I NUMBER 006 REV NO.

00 3

OF 4

The trip occurred without complications, and safety systems responded as required. Appropriate action was taken to restore the required flow to the "D" Steam Generator after the associated failure of ALHV0005 to throttle closed.

This event was evaluated with the Callaway PRA model. The evaluation determined the increase in core damage frequency of this event was less than 1E-6; therefore, this event was of very low risk significance. Use of the PRA model to evaluate the event provides for a comprehensive, quantitative assessment of the potential safety consequences and implications of the event, including consideration of alternative conditions beyond those analyzed in the FSAR.

5.

REPORTING REQUIREMENTS

This LER is submitted pursuant to 10 CFR 50.73(a)(2)(iv)(A) to report a reactor protection system actuation while critical and an auxiliary feedwater system actuation.

Specifically, 10 CFR 50. 73(a)(2)(iv) states in part, "The licensee shall report:

(A) Any event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph (a)(2)(iv)(B) of this section...

(B) The systems to which the requirements of paragraph (a)(2)(iv)(A) ofthis section apply are:

(1) Reactor protection system (RPS) including: reactor scram or reactor trip....

( 6) PWR auxiliary or emergency feed water system."

The RPS was actuated at 00:22 on December 3, 2014, during normal power operations (from 100% power). This fulfills the reporting requirement of 10 CFR 50.73(a)(2)(iv)(A) by actuation of the system specified in 10 CFR

50. 73(a)(2)(iv)(B)(l ).

A valid auxiliary feedwater system actuation was received as a direct consequence of the turbine and reactor trip. This also fulfills the reporting requirement of 10 CFR 50.73(a)(2)(iv)(A) by actuation of the system specified in 10 CFR

50. 73(a)(2)(iv)(B)(6).
6.

CAUSE OF THE EVENT

The root cause of the transformer failure was inadequate design and material selection during the manufacture of the transformer.

The design was inadequate due to critical cables being routed precariously above the transformer core, and the material selected was inadequate because it relied upon low-grade nylon cable ties for restraint.

7.

CORRECTIVE ACTIONS

The corrective action to prevent recurrence is to add lacing to supplement the cable ties used to restrain the jumper cables inside the XMBO 1 transformer enclosure.

The root cause team determined that the use of lacing would prevent the jumper cable from dropping on the transformer core and causing an electrical short. The lacing would have a high temperature rating and would not require periodic replacement. Lacing is scheduled to be installed during the next refueling outage, planned for the spring of2016.

It should be noted that as a remedial action, all nylon cable ties have been replaced with Tefzel cable ties which are designed for higher operating temperatures and a longer life expectancy.

8.

PREVIOUS SIMILAR EVENTS

6. LER NUMBER I

SEQUENTIAL I NUMBER 00?

REV NO.

00

3. PAGE 4

OF No electrical plant events have occurred due to failed cable ties at Callaway. However, in 2003, severely embrittled and broken cable tie wraps were discovered in the diesel generator room. These tie wraps were on a power feed, but the cable was not displaced. Corrective actions included the use of heavy duty aqua-blue (Tefzel) safety-related cable ties.

Recent significant industry events include an age-related failure of plastic cable ties at Palo Verde Unit 1, which allowed a shield conductor to contact a 13.8kv bus. This resulted in catastrophic failure of a 480 volt AC load center as well as a reactor power cutback from 100% to 60% and declaration of an Unusual Event. 4

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