05000461/LER-1917-010, Regarding Division 1 Transformer Failure Leads to Instrument Air Isolation to Containment Requiring a Manual Reactor Scram

Regarding Division 1 Transformer Failure Leads to Instrument Air Isolation to Containment Requiring a Manual Reactor Scram

ML18040A463
Person / Time
Site:	Clinton
Issue date:	02/05/2018
From:	Stoner T Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
U-604402 LER 17-010-00
Download: ML18040A463 (5)

LER-1917-010, Regarding Division 1 Transformer Failure Leads to Instrument Air Isolation to Containment Requiring a Manual Reactor Scram

Event date:
Report date:
Reporting criterion:	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)(ix)(A) 10 CFR 50.73(a)(2)(iii) 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)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(i)
4611917010R00 - NRC Website

text

Clinton Power Station 8401 Power Road Clinton, IL 61727 rl

~ Exelon Generation U-604402 February 5, 2018 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555-0001

Subject:

Clinton Power Station, Unit 1 Facility Operating License No. NPF-62 NRG Docket No. 50-461 Licensee Event Report 2017-010-00 10 GFR 50.73 SRRS 5A.108 Enclosed is Licensee Event Report (LER) 2017-007-00: Division 1 Transformer Failure Leads to Instrument Air Isolation to Containment Requiring a Manual Reactor Scram. This report is being submitted in accordance with the requirements of 1 O CFR 50.73.

There are no regulatory commitments contained in this report.

Should you have any questions concerning this report, please contact Mr. Dale Shelton, Regulatory Assurance Manager, at (217) 937-2800.

Respectfully, Theodore R. Stoner Site Vice President Clinton Power Station KP/cac Attachment: License Event Report 2017-010-00 cc:

Regional Administrator - Region Ill NRG Senior Resident Inspector-Clinton Power Station Office of Nuclear Facility Safety -

Illinois Emergency Management Agency

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 03/31/2020 (04-2017)

, the httg://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3D NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. PAGE Clinton Power Station, Unit 1 05000461 1 OF 4

4. TITLE Division 1 Transformer Failure Leads to Instrument Air Isolation to Containment Requiring a Manual Reactor Scram

5. EVENT DATE

6. LER NUMBER

7. REPORT DATE

8. OTHER FACILITIES INVOLVED I

SEQUENTIAL I REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR NUMBER NO.

MONTH DAY YEAR 05000 FACILITY NAME DOCKET NUMBER 12 09 2017 2017 -

010

- 00 02 05 2018 05000

9. OPERATING MODE

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

D 20.2201 (bl D 20.2203(a)(3)(i)

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

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

D 20.2201 (dl D 20.2203(a)(3)(ii)

~ 50.73(a)(2)(ii)(B)

D 50.73(a)(2)(viii)(B) 1 D 20.22os(aJ(1J D 20.22os(aJ(4l D

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

D 20.22os(aJ(2Hil D 50.36(c)(1)(i)(A)

~ 50. 73(a)(2)(iv)(A)

D 50.73(a)(2)(x)

10. POWER LEVEL D 20.22os(aJ(2Hiil D 50.36(c)(1)(ii)(A)

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

D 1s.11(aJ(4l D 20.22os(aJ(2)(iiil D 50.36(c)(2)

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

D 1s.11 (aH5l D 20.2203(a)(2)(iv)

D 50.46(a)(3)(ii)

~ 50.73(a)(2)(v)(C)

D 1s.11(a)(1 l 097 D 20.2203(a)(2)(v)

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

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

D 1s.11(aJ(2Hil D 20.2203(a)(2)(vi)

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

D 50.73(a)(2)(vii)

D 1s.n(aJ(2Hiil

?

..,<)(;.!

...... *-~***....

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

D OTHER Specify in Abstract below or in

C. Cause of the Event

A phase to ground fault was identified on the B Phase of the 480V transformer 1A (1AP11 E). The cause of the transformer failure is currently under investigation and will be provided in a supplemental Licensee Event Report.

D. Safety Consequences

The trip of 4160V circuit breaker and the failure of the 480V transformer placed the station in a potential scram condition due to loss of instrument air to the containment and scram pilot air header. Manual operator actions were taken to shut down the reactor prior to an automatic scram and place the plant in a safe and stable condition. The loss of 480 volt power caused the Fuel Building Ventilation System to isolate resulting in positive secondary containment pressure. Operators placed the Division 2 SGTS in service to restore secondary containment negative pressure. All Division 2 and Division 3 Emergency Core Cooling Systems remained operable and available throughout this event for accident mitigation if required. No plant safety limits were exceeded and no Emergency Core Cooling System actuations occurred.

E. Corrective Actions

On December 14, the faulted transformer was replaced and the plant returned to Mode 1 operations on December 15. Additional corrective actions will be determined following completion of the causal evaluation.

F. Previous Similar Occurrences LEA 2013-008-01 Failure of Division 1 Transformer Leads to Isolation of Instrument Air Supply to Containment, Lowering Scram Pilot Air Header Pressure, and Manual Reactor Scram On December 8, 2013 at 2026 hours0.0234 days <br />0.563 hours <br />0.00335 weeks <br />7.70893e-4 months <br /> with the plant in Mode 1 at 97.3 percent reactor power, operators received multiple alarms due to the trip of 4160 volt 1 A 1 breaker which resulted in a loss of power to two Division 1 480 volt unit substations. Operators were immediately dispatched and found a 4160/480 volt stepdown transformer A 1 (OAP05E) failed. Many Division I components lost power. The loss of power caused an instrument air (IA) containment isolation. The loss of IA affected various containment loads, including the scram pilot air header, the main steam isolation valves and the reactor water cleanup system. At 2036 hours0.0236 days <br />0.566 hours <br />0.00337 weeks <br />7.74698e-4 months <br />, the scram pilot air header low pressure alarm was received and in response to an anticipated automatic reactor scram, operators immediately initiated a manual reactor scram. All control rods fully inserted into the core.

SEQUENTIAL NUMBER 010 REV NO.

00 The cause of the transformer failure was a turn to turn failure of the high side windings due to insulation breakdown over time, prior to its expected end of life. An installed spare was connected to replace the failed Division 1 transformer.

G. Component Failure Data

Component Description: I-T-E Dry Type Transformer; 4160V/480V; 750KVA Manufacturer: GOULD-BROWN-BOVERI Page _4_ of _4_