05000315/LER-2003-001, From Cook, Unit 1 Regarding Turbine & Reactor Trip Due to Main Transformer Fault & Fire

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From Cook, Unit 1 Regarding Turbine & Reactor Trip Due to Main Transformer Fault & Fire
ML030850133
Person / Time
Site: Cook 
Issue date: 03/17/2003
From: Bakken A
Indiana Michigan Power Co
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
AEP:NRC:2573-03 LER 03-001-00
Download: ML030850133 (6)
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LER-2003-001, From Cook, Unit 1 Regarding Turbine & Reactor Trip Due to Main Transformer Fault & Fire
Event date:
Report date:
Reporting criterion: 10 CFR 50.73(a)(2)(iv)(A), System Actuation
3152003001R00 - NRC Website
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text

Indiana Michigan Power Company 500 Circle Drive Buchanan, Ml 49107 1395 INDIANA MICHIGAN POWER March 17, 2003 AEP:NRC:2573-03 10 CFR50.73 Docket No. 50-315 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Mail Stop O-P1-17 Washington, DC 20555-0001 Donald C. Cook Nuclear Plant Unit 1 LICENSEE EVENT REPORT 315/2003-001 -00 UNIT 1 TURBINE AND REACTOR TRIP DUE TO MAIN TRANSFORMER FAULT AND FIRE In accordance with the criteria established by 10 CFR 50.73 entitled Licensee Event Report System, the following report is being submitted:

LER 315/2003-001-00: "Unit 1 Turbine and Reactor Trip Dueto Main Transformer Fault and Fire."

There are no new commitments identified in this submittal.

Should you have any questions, please contact Mr. Brian A. McIntyre, Manager of Regulatory Affairs, at (269) 697-5806.

Sincerely, A. Christopher Bakken, III Senior Vice President, Nuclear Operations RAM/jen Attachment te;e

U. S. Nuclear Regulatory Commission AEP:NRC:2573-03 Page 2 c:

L. Brandon - Michigan Department of Health K. D. Curry - AEP Ft. Wayne J. E. Dyer - NRC Region III J. T. King - MPSC MDEQ - DW & RPD NRC Resident Inspector Records Center - INPO J. F. Stang, Jr. - NRC Washington DC

NR or 6

Abstract

On January 15, 2003, at approximately 2010 hours0.0233 days <br />0.558 hours <br />0.00332 weeks <br />7.64805e-4 months <br />, a fault occurred in the Unit 1 main transformer.

The fault caused the current differential relays to actuate resulting in an automatic trip of the main transformer. A sudden internal fault within the main transformer ruptured the transformer oil tank resulting in a loss of oil and a fire.

The loss of the main transformer precipitated an automatic trip of the main generator and an immediate turbine and reactor trip. The main transformer fire was extinguished within 35 minutes of the event with one minor reflash, which was promptly controlled and extinguished by onsite fire brigade members.

One minor personnel injury occurred requiring offsite medical attention. An Unusual Event was declared based on a fire of more than 15 minutes in duration within the protected area. All safety-related components functioned properly and no significant discrepancies in equipment time responses were noted.

In accordance with 10 CFR 50.72(b)(2)(iv)(B), 10 CFR 50.72(b)(2)(xi), and 10 CFR 50.72(b)(3)(iv)(A), all applicable event (EN#39513) and emergency plan required notifications were completed in a timely manner. As such, this LER is being submitted in accordance with the requirements of 10 CFR 50.73(a)(2)(iv)(A) for a condition resulting in an automatic actuation of the reactor protection system.

A one-hour report was completed at 2105 hours0.0244 days <br />0.585 hours <br />0.00348 weeks <br />8.009525e-4 months <br /> and the remaining three reports were completed by a single notification at 2339 hours0.0271 days <br />0.65 hours <br />0.00387 weeks <br />8.899895e-4 months <br />. The apparent cause of the event was a sudden internal fault within the main transformer.

Corrective actions included replacement of the main transformer. Other non-safety related components damaged by the resultant fire were either repaired or replaced.

NRC FORM 366 (7-2001)U.S. NUCLEAR REGULATORY COMMISSION (7-2001)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION

6. LER NUMBER
3. PAGE YEAR SEQUENTIAL REVISION Donald C. Cook Nudear Plant Unit 1 05000-315 NUMBER NUMBER 2 of 4 2003 00
17. TEXT (If more space Is required, use additional copies of NRC Form (366A)

Conditions Prior to Event

Unit 1 -

Mode 1, 100 percent power Unit 2 -

Mode 1, 100 percent power

Description of Event

On Wednesday, January 15, 2003, at approximately 2010 hours0.0233 days <br />0.558 hours <br />0.00332 weeks <br />7.64805e-4 months <br />, a fault occurred in the Unit 1 main transformer (Manufacturer: VA Tech Elin, Model Number: TDQ11GA2OD9K-99)

(ELI.

The fault caused the current differential relays to actuate, resulting in automatic trip of the main transformer.

A sudden internal fault within the main transformer ruptured the transformer tank and resulted in a loss of oil and a fire.

The loss of the main transformer precipitated an automatic trip of the main generator MTB] and an immediate turbine [TA] and reactor trip [JD].

The main transformer fire was extinguished within 35 minutes of the event with one minor reflash, which was promptly controlled and extinguished by onsite fire brigade members.

One minor personnel injury occurred requiring offsite medical attention.

An Unusual Event (UE) was declared, based on a fire of more than 15 minutes in duration within the protected area.

The UE was terminated at 2220 hours0.0257 days <br />0.617 hours <br />0.00367 weeks <br />8.4471e-4 months <br />.

In accordance with 10 CFR 50.72(b) (2)(iv) (B), 10 CFR 50.72(b)(2)(xi), and 10 CFR 50.72(b)(3)(iv)(A), all applicable event (EN#39513) and emergency plan required notifications were completed in a timely manner.

The notifications included:

  • a four-hour report for offsite notification of an oil spill, and.
  • an eight-hour notification for the automatic actuation of an emergency safety features system (auxiliary feedwater) [BA].

The one-hour report was completed at 2105 hours0.0244 days <br />0.585 hours <br />0.00348 weeks <br />8.009525e-4 months <br /> and the remaining three reports were completed by a single notification at 2339 hours0.0271 days <br />0.65 hours <br />0.00387 weeks <br />8.899895e-4 months <br />.

As such, this LER is being submitted in accordance with the requirements of 10 CFR 50.73(a)(2)(iv)(A) for a condition resulting in an automatic actuation of the RPS.

Written notification of the oil spill was transmitted to the NRC via letter AEP:NRC:2401-03, Non-PCB Transformer Oil Spill National Pollution Discharge Elimination System And Groundwater Discharge Authorization Notification.

All safety-related components functioned properly and no significant discrepancies in equipment time responses were noted.

The auxiliary feedwater system actuated due to low steam generator levels as expected.U.S. NUCLEAR REGULATORY COMMISSION (7-2001)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION

6. LER NUMBER
3. PAGE YEAR SEQUENTIAL REVISION Donald C. Cook Nuclear Plant Unit 1 05000-315 NUMBER NUMBER 3 of 4 2003
- l 001 00
17. TEXT (if more space is required, use additional copies of NRC Form (366A)

Cause of Event

The Unit I main transformer experienced a sudden internal fault, with no prior indication, that resulted in a phase-to-phase flashover.

Donald C. Cook Nuclear Plant (CNP) is conducting a formal root cause investigation into the failure of the Unit 1 main transformer.

This root cause investigation is ongoing and includes hardware failure analysis with support from the vendor.

In accordance with the guidance established in NUREG-1022, Revision 2, "Event-Reporting Guidelines," Part 5.1.5, "Supplemental Information and Revised LERs," CNP will issue a supplement to this LER when the final root cause determination has been completed.

Analysis of Event

On Wednesday, January 15, 2003, at approximately 2010 hours0.0233 days <br />0.558 hours <br />0.00332 weeks <br />7.64805e-4 months <br />, a fault occurred in the Unit 1 main transformer.

The fault caused the current differential relays to actuate resulting in an automatic trip of the main transformer.- A sudden internal fault within the main transformer ruptured the transformer tank and resulted in a loss of oil and a fire.

The transformer yard fire protection system actuated as designed and extinguished the fire.

The main transformer and main generator protection circuitry performed as designed and the appropriate reactor protection and safeguards equipment functioned correctly.

The reactor was shut down and the unit stabilized in Mode 3 as designed with all normal and emergency cooling systems available.

This event did not adversely impact the plant's ability to mitigate the consequences of an accident and, therefore, had minimal safety significance.

The change in risk with respect to core damage and large early release frequency as a result of the transformer failure and subsequent plant trip have been qualitatively assessed and judged no different than any other unplanned reactor trips with the main condenser available.

This assessment is based on the following considerations:

  • The automatic plant trip functioned properly.

The automatic trip features also functioned dependably, resulting in a safe and stable plant configuration.

  • Transformer fires are well understood and the plant design features include an installed fire suppression system and the dividing walls (concrete and steel) to mitigate the consequences of the fire.

Additionally, the transformer is located outside the plant structures, away from any risk-significant equipment, and does not have an effect on any safety function.

Therefore, the fire did not degrade any system used to prevent core damage, assure containment integrity, or maintain defense-in-depth and safety margins.

NKC F-OKM 366A (7-2001)

U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION l

1. FACILITY NAME Donald C. Cook Nuclear Plant Unit 1
17. TEXT (if more space Is required, use additional copies of NRC Form (3664A)
  • The subsequent fire suppression water and oil run-offs did not challenge any accident mitigation function.

In addition, the main transformer does not provide any accident mitigation capability, nor is it modeled in CNP's Probabilistic Risk Assessment.

  • The transformer failure does not directly contribute to the increased likelihood of any initiators, other than transients that result in a reactor trip.

Additionally, this event did not have an effect on the function of any emergency diesel generator.

Corrective Actions

Corrective actions included replacement of the main transformer and repair and/or replacement of other non-safety related components damaged by the fire.

Previous Similar Events

In 1995 with Unit 1 shut down, the main transformer experienced a high side (345kv) phase to ground and phase to bushing fault while back energized from the switchyard.

The fault did not result in a unit trip, unit transient, or emergency safety features actuation.

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