ML052790615
| ML052790615 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 09/14/2004 |
| From: | Neil Sheehan NRC Region 1 |
| To: | Nelson S Entergy Nuclear Operations |
| References | |
| FOIA/PA-2004-0369 | |
| Download: ML052790615 (7) | |
Text
LNeI Sheehan - Copy of report on Vermont Yankee trans ormner fire Page 1 From:
Neil Sheehan (U/
To:
INTERNET: SNelson@IOEnergy.Com Date:
9114104 11:22AM
Subject:
Copy of report on Vermont Yankee transformer fire
- Susan, Attached is a copy of the report submitted by Entergy to us regarding the June 18th transformer fire at Vermont Yankee.
Please let me know if you have any questions after reviewing it.
Neil Sheehan NRC Public Affairs Officer (610) 337-5331 ran
I I
i V 'Entertgy Entergy Nuclear Northeast Entergy Nuclear Operations, Inc.
Vermont Yankee 185 Old Ferny Rd.
P.O. Box 500 Brattleboro, Vr 05302 Tel 502-257-5271 August 16, 2004 BVY 04-080 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555
Subject:
Vermont Yankee Nuclear Power Station License No. DPR-28 (Docket No. 50-271)
Reportable Occurrence No. LER 2004-003-00 As defined by 10CFR50.73. we are reporting the attached Reportable Occurrence LER 2004-003-00. No Regulatory Commitments have been generated as a result of this event.
Sincerely, Entergy Nuclear Operations, Inc.
Vermont Yankee Kevin Bronson General Manager cc:
USNRC Region I Administrator USNRC Resident Inspector - WNPS USNRC Project Manager - VYNPS Vermont Department of Public Service
NRCO0RM 366 U.S NUCLEAR REGULATORY APPROVED BY OMB NO. 31500104 EXPIRES 7-31004 (7p001)
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- 1. FACILITY NAME
- 2. DOCKET NUMBER
- 4. TITLE Automatic Reactor Scram due to a Main Generator Tri as a result of an Iso-Phase Bus Duct Two-Phase Electrical Fault
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- l.
OTHER FACILTIES INVOLVED FACILLrr NAME DOCKET NUMBER MO DAY YEAR YEAR SEOUENTIAL REV MO DAY YEAR 05000-NUMBER NO WA 04FACILITY NAME DOCKET NUMBER 06 18 2004 2004-003
-00 08 16 2004 WA WCENME S. OPERATING
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Kevin Bronson, General manager (80Qt 257-7711
- 13. COMPLETE ONE UNE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT CAUSE SYSTEM COMPONENT MANU.
REPORTABLE CAUSE SYSTEM COMPONENT MANU-REPORTABLE TO FACTURER TO EPIX I
FACTURER EPIX E
EL FCON P295 Yes E
EL IPBUI P295 Yes E
EL BDUC P295 Yes E
EL LAR G066 Yes
- 14. SUPPLEMENTAL REPORT EXPECTED
- 15. EXPECTED MONTH DAY EAR C1 I YES (If yes, complete EXPECTED SUBMISSION DATE)
No SUBMISSION DATE WA WA W/A t16. ABSTRACT (LUrit to 1400 spaces, I.e., approximately 15 single-spaced typewritten lines)
On 06/18104 at 0640, with the plant at full power, a turbine load reject scram occurred due to a two phase electrical fault to ground on the 22 kV Iso-phase bus. All safety systems responded as designed and the reactor was shutdown without Incident. Offsite power sources and station emergency power sources were available throughout the event. Arcing and heat generated during the fault damaged an area around the Iso-phase bus ducts and Main Transformer low voltage bushings. The electrical faults disrupted an oil line flange between the Main Transformer oil conservator (expansion tank) and the '0 phase low voltage bushing box, and the leaking oil Ignited. Fire suppression systems activated automatically. An Unusual Event was declared at 0650 for a fire lasting greater than 10 minutes. The VY fire brigade and local community fire departments extinguished the oil fire at 0717. At 1245, the Unusual Event was terminated. The electrical grounds that Initiated the event were caused by loose material In the *B" iso-phase bus duct as a result of the failure of a flexible connector. The grounds raised the voltage on the "A7 Iso-phase bus contributing to the failure of the UA7 phase surge arrester. The root causes of the event were determined to be Inadequate preventative maintenance on portions of the Iso-phase bus and failure to monitor age related degradation on the surge arresters. There was no release of radioactivity or personnel injury during this event.
I NRC FORM 366 (7-2001)
- *e I.
1 NRCFORM 366A U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
05000271 2004 -
003 00 2 OF 4
- 17. NARRATIVE (if more space Is required, use addZlnal copies of NRC Form 366A)
DESCRIPTION:
On 06/18/04 at 0640, with the plant operating at full power, a two-phase electrical fault-to-ground occurred on the 22kV System (EIIS=IPBU, BDUC). The "B" phase faulted to ground In the low voltage bushing box on top of the Main Transformer (ElIS=XFMR), and the WA' phase faulted to ground In the surge arrester cubicle of the Generator Potential Transformer (PT) Cabinet through the WA' phase surge arrester (EIIS=LAR).
Within less than one cycle (I 1 milliseconds) of the Initial electrical fault, the Main Generator protective relaying sensed the condition and Isolated the generator from the grid within the following 5 cycles (80 milliseconds). A generator load rejection reactor scram then occurred. Approximately 400 milliseconds following the Initial electrical faults to ground from WA' and "B' phases, arcing and ionization In the "B' phase low voltage bushing box carried over to the "CU phase low voltage bushing box on top of the Main Transformer. The electrical faults disrupted a flange In the oil piping between the Main Transformer oil conservator (expansion tank) and the IC" phase low voltage bushing box. The arcing or heat from the fault Ignited the oil, resulting In a fire. Fire suppression systems activated automatically as expected.
The plant response following the scram was as expected, with the exception that both Recirculation pumps tripped and other AC voltage effects were observed as a result of the voltage transient associated with the high fault current. An safety systems functioned as designed and the reactor was shutdown without Incident.
There was no release of radioactivity and no personnel Injuries.
The VY fire brigade was dispatched at 0641. An Unusual Event was declared at 0650 due to "Any unplanned on-site or In-plant fire not extinguished within 10 minutes". The VY fire brigade Initiated fire hose spray from a nearby hydrant and quenched the fire. Local fire departments began arriving at 0705. The fire was completely extinguished at approximately 0717and re-flash watches were established. Offslte power sources and station emergency power sources were available at all times throughout the event.
slko Qfnfne orf Itfarmernt Hoaw Il,4mncrhirP nrnd 1caahilctts wArP nrnvidnd with Initial notification of the event
.1 NRCJFORM 366A US. NUCLEAR REGULATORY COMMISSION 51.2001)
LICENSEE EVENT REPORT (LER)
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE i SEQUENTIAL REVISION VERMONT YANKEE NUCLEAR YEAR NUMBER NUMBER POWER STATION (VY) 05000271 2004 003 00 3 OF 4
- 17. NARRATIVE (Ifmore space Is required, use additionalcopies ofNRC Form 366) inspecting the flexible connectors was Identified during a recent review of Industry operating experience (OE).
Tibs OE is being included as recommended preventative maintenance for future outages; however, it was not Included In the preventative maintenance inspection performed during RFO-.24.
The 'A! surge arrester failure was the result of the combination of a ground occurring on the "B* Iso-phase bus that caused an increase in voltage on the "A! Iso-phase bus and not performing preventative maintenance necessary to monitor age related degradation of the sAw surge arrester. Industry experience has revealed that surge arrestors degrade over time due to a combination of age, service environment and service conditions.
Periodic Inspection/testing could have detected degradation and allowed replacement prior to failure.
A contributing cause to both of the conditions previously described was Identified by the Investigation team as a failure to effectively use Industry OE to prevent similar events from occurring at VY. Specifically, It was noted that; the actions taken by VY In response to recommendations provided within the INPO Significant Operating Experience Report (SOER) 9001 for "Ground Faults on AC Electrical Distributionr were inadequate. In addition to the SOER, guidance provided within EPRI's Isolated Phase Bus Maintenance Guide' TR-1 12784 (1999) for the 22 kV flexible connectors and periodic Inspections/testing was not utilized.
ASSESSMENT OF SAFEiY CONSEQUENCES:
All safety systems and fire suppression systems responded as designed. The reactor was shutdown without Incident. Offsite power sources and station emergency power sources were available at all times throughout the event. Emergency reponse personnel acted promptly to prevent the fire from significantly damaging or breeching the adjacent turbine building. There was no release of radioactivity or personnel injury during this event. Therefore, this event did not significantly Increase the risk to the health and safety of the public.
CORRECTIVE ACTIONS:
Immediate:
- 1. An Unusual Event was declared at 0650.
- 2. The station fire brigade on scene to combat the fire at 0652. Local fire departments arrived on-site at 0705 to provide assistance. The fire was extiguished at 0717.
- 3. Completed the initial notification to the States of Vermont, New Hampshire and Massachusetts at
...0721.
a- *
-I. ---
- 4. Notifed the NRC Operations Center of the Unusual Event at 0748.
- 5. Secured all affected site and plant areas for personnel safety and Isolated affected equipment as necessary to maintain investigation Integrity.
- 6. Condition Reports were generated for this event and potentially associated Issues as appropriate for entry into the Corrective Actions Program.
- 7. A Root Cause Investigation team was established to assess damage and to secure the area.
- 8. Initial testing was completed on the main transformer, station auxiliary transformer, and main generator with no Indication of damage that would affect the operation of the transformers or generator.
- 9. A Preliminary Nuclear Network Entry was completed to Inform the Industry of the Initial findings and conditions of the event.
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I1 N4RC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER)
- 1. FACILITY NAME
- 2. DOCKET
- 6. LER NUMBER
- 3. PAGE SEOUENmIAL REVISION VERMONT YANKEE NUCLEAR YE NUMBER NUMBER POWER STATION (VY) 05000271 2004-003 00 4 OF 4 NARRATIVE (if more space Is mqAd, Me add inArcopies of NRC Form 36A) (17)
Prior to Plant Start Up:
- 1. The phase A, B, and C 22 kV surge arresters and capacitors were replaced prior to energizing the 22kV bus.
- 2. The phase A, B. and C 22 kV flexible connectors were replaced with an upgraded design supplied by Delta-Unibus prior to energizing the 22kV bus.
- 3. A cleanliness Inspection was performed and documented as part of iso-Phase Bus Duct Modification.
- 4. Maintenance department personnel Inspected the cooler and leads fans for foreign material. Following operation of the fans, an additional Inspection of the fans and coolers was performed.
- 5. Operator Alarm response sheets were revised to enhance operator actions In the event of future ground faults.
- 6. A preventative maintenance schedule was established for Increased sampling of transformer oil for the main, auxiliary, and two startup transformers for four weeks after start-up.
- 7. The Isophase bus duct system was monitored after assembly with the fans running to ensure that vibration levels are acceptable.
- 8. VY discussed this event and associated Issues with the Entergy Fleet and Industry experts as --
necessary to gather Information pertinent to the root cause Investigation and equipment recovery.
Long Term:
I. Include the 22kV surge arresters and capacitors in the preventative maintenance program and define periodic testing requirements.
- 2. Revise the 22kV Isophase bus preventative maintenance program and periodic Inspection requirements as necessary to Improve performance and to prevent recurrence of this event.
- 3. Complete the testing of selected components Involved In the event to validate the initial conclusions of the root cause investigation team, and revise the root cause analysis report If needed.
ADDITIONAL INFORMATION:
No similar events with a related cause have occurred at Vermont Yankee.
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Copy of report on Vermont Yankee transformer fire 9/14/04 11:22AM Neil Sheehan NAS@nrc.gov Recipients Action IOEnergy.Com Transferred SNelson (INTERNET: SNelson@IOEnergy.Com)
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