05000251/LER-2005-002, Regarding Automatic Reactor Trip Due to Main Transformer Failure
| ML052500483 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 08/25/2005 |
| From: | Jones T Florida Power & Light Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-2005-163 LER 05-002-00 | |
| Download: ML052500483 (6) | |
| 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) 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)(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)(v)(B), Loss of Safety Function - Remove Residual Heat 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 10 CFR 50.73(a)(2)(iv)(B), System Actuation 10 CFR 50.73(a)(2)(iv)(B)(1) 10 CFR 50.73(a)(2)(iv)(B)(6) |
| 2512005002R00 - NRC Website | |
text
- - AUG 2 5 2005 10 CFR § 50.73 L-2005-163 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Re:
Turkey Point Unit 4 Docket No. 50-251 Reportable Event: 2005-002-00 Date of Event: June 27, 2005 Automatic Reactor Trip due to Turkey Point Unit 4 Main Transformer Failure The attached Licensee Event Report 50-251 / 2005-002-00 is being submitted pursuant to the requirements of 10 CFR 50.73(a)(2)(iv)(A) to provide notification of the subject event.
If there are any questions, please call Mr. Walter Parker at (305) 246-6632.
- Very truly yours,
/1b Terry 0. Jones Vice President Turkey Point Nuclear Plant SM Attachment cc:
Regional Administrator, USNRC, Region II Senior Resident Inspector, USNRC, Turkey Point Nuclear Plant an FPL Group company
I I
5 I
NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 06/30/2007 (6.2004)
Estimated burden per response to comply with this mandatory collection request 50 hours5.787037e-4 days <br />0.0139 hours <br />8.267196e-5 weeks <br />1.9025e-5 months <br />. Reported lessons learned are incorporated Into the licensing process and fed back to industry. Send comments regarding burden estimate to the Records and FOIAfPrivacy Service Branch (T.5 F52), U.S. Nuclear Regulatory Commission LICENSEE EVENT REPORT (LER)
Washington, DC 20555-0001, or by Internet e-mail to infocollects~nrc gov, and to the Desk Officer. Office of Information and RegulatoryAfairs, NEOB-10202, (3150 0104), Office of Management and Budget, Washington, DC 20503 If a means used to Impose an Information collection does not display a currently vafid OMB control number, the NRC may not conduct or sponsor, and a person Is not required to respond to, the Information collection.
Turkey Point Unit 4 05000251 1
1 OF 5
- 4. TITLE Automatic Reactor Trip due to Turkey Point Unit 4 Main Transformer Failure
- 5. EVENT DATE
- 6. LER NUMBER
- 7. REPORT DATE
- 8. OTHER FACILITIES INVOLVED FACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEUENTIAL R EOV MONTH DAY YEAR FACIUTY NAME DOCKET NUMBER 06 27 2005 2005 - 002 - 00 08 25 2005 OPERATING MODE THIS(REPORT IS SUBMITEDPURSUANTTTHE REQUIREMENTSOF10CFR§: (Checkallthatapply) ol 20.2201 (b)
[I 20.2203(a)(3)(i 0l 50.73(a)(2)(i)(C)
El 50.73(a)(2)(Vii) 1 0 20.2201(d) 0 20.2203(a)(3)(ii) 0 50.73(a)(2)(ii)(A) 0 50.73(a)(2)(viii)(A) o 20.2203(a)(1) 0 20.2203(a)(4) 0 50.73(a)(2)(ii)(B) 0 50.73(a)(2)(viii)(B)
El 20.2203(a)(2)(i) 0 50.36(c)(1)(i)(A) 0 50.73(a)(2)(iii) 0 50.73(a)(2)(ix)(A)
- 10. POWER LEVEL 0 20.2203(a)(2)(ii) 0 50.36(c)(1)(ii)(A) 0E 50.73(a)(2)(iv)(A) a 50.73(a)(2)(x) o 20.2203(a)(2)(iii) 0 50.36(c)(2) 0 50.73(a)(2)(v)(A) 0 73.71 (a)(4) o 20.2203(a)(2)(Iv) 0 50.46(a)(3)(ii) 0 50.73(a)(2)(v)(B) 0 73.71 (a)(5) 100 0 20.2203(a)(2)(v) 0 50.73(a)(2)(i)(A) 0 50.73(a)(2)(v)(C) 0 OTHER o 20.2203(a)(2)(vI) 0 50.73(a)(2)(i)(B) 0 50.73(a)(2)(v)(D)
Specify in Abstract below I
or In NRC Form 366A
- 12. LICENSEE CONTACT FOR THIS LER NAME TELEPHONE NUMBER (Include Area I
Code)305-246-6454 0 YES (If yes, complete 15. EXPECTED SUBMISSION DATE)
ABSTRACT (LImit to 1400 spaces, I.e., approximately 15 single-spaced typewritten lines)
On June 27, 2005, at 0316, Turkey Point Unit 4 reactor was automatically tripped from 100% power following a turbine trip due to a Main Generator lock out generated from an electrical fault of the Unit 4 Main Transformer. The transformer was recently installed during the refueling outage in Spring 2005. The fault ruptured the transformer tank releasing oil and caused a fire that damaged the transformer and adjacent equipment. At 0327, an Unusual Event was declared based on the fire in the plant protected area lasting longer than 10 minutes. The site fire brigade responded and extinguished the fire. Offsite fire fighting assistance was requested, but was not used to extinguish the fire. The fire was extinguished and the Unusual Event was terminated at 0500. All plant systems functioned as designed during and after the event.
The operating crew controlled and stabilized the plant, and therefore the health and safety of the public was not adversely impacted by this event. The apparent cause of the event was a sudden internal fault on the B phase high side windings of the Main Transformer. A root cause analysis is being conducted. Corrective actions included replacement of the Main Transformer and repair/replacement of components damaged by the resultant fire.
NRC FORM 366(6.2004)
PRINTED ON RECYCLED PAPER NRC FORM 366 (6 2004)
PRINTED ON RECYCLED PAPERU.S. NUCLEAR REGULATORY COMMISSION 7-2001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
DOCKET
______NUMBER(6)___AGE_(3 Turkey PointNUMBER U24 LER NUMBER (6)
PAGE (3)
YEAR ISENTEIAL REVISION Turkey Point Unit 4 05000251 UBR NME Page 2 of 5 2005-002
- - 00 TEXT (if more space Is required, use additional copies of NRC Form 366A) (17)
DESCRIPTION OF THE EVENT Turkey Point Units 3 and 4 were operating at 100% power. On June 27, 2005, at 0316, the Unit 4 experienced a Turbine-Generator trip resulting in an automatic Reactor trip [JD: RCT]. It was found later that the Turbine and Generator [TB] tripped as a result of an internal electrical fault initiated in the Unit 4 Main Transformer [EL:TB,XFMR].
Following the reactor trip, Operations entered 4-EOP-E-0, Reactor Trip or Safety Injection verified the Reactor and Turbine tripped and safety injection was not required. The Operating crew verified that the plant was stable and that the Auxiliary Feedwater System [BA] automatically actuated as designed (for transients that result in Steam Generator narrow range levels less than 10%).
The first indication of the transformer failure reached the control room at 03:16:14 on June 27, 2005. Trip signals were provided from several sets of protective relays. The Main Generator lockout relays [TB: RLY, 86] actuated and tripped the Unit 4 Generator breakers [TB:BRK], 8W65 and 8W88, as well as the Unit 4 Auxiliary Transformer breakers [TB:EB,XFMR,BKR] and caused an automatic fast transfer of the safety related 4160V busses. Both safety related 4160V busses [EB] 4A and 4B, as well as their respective loads, were energized via the Unit 4 Startup Transformer.
The electrical fault initiated a transformer pressure spike that resulted in the rupture of the transformer tank, the release of the transformer insulating oil and a damaging transformer fire. The plant fire team responded to the fire. The transformer deluge system [KP] actuated, slowing the fire down but not extinguishing it completely. At 03:27, the site emergency plan was activated and an Unusual Event was declared based on the fire in the plant protected area lasting longer than 10 minutes. Metro Dade Fire Department (offsite) assistance was requested, but it was not used to extinguish the fire. The fire was ultimately contained and extinguished by the onsite fire brigade in approximately 27 minutes from the beginning of the event. At 0343, the fire had been extinguished and the Hazardous Material Response Team was subsequently activated to control the transformer oil leak. The Unusual Event was terminated at 0500.
This event was reported to NRC (Event #41800) in accordance with 10 CFR 50.72 (a)(1)(i), 10 CFR 50.72 (b)(2)(iv)(B) and 10 CFR 50.72 (b)(3) (iv)(A), and 10 CFR 50.72 (b)(2)(xi).
ANALYSIS OF THE EVENT
The Unit 4 Main Transformer is a three phase type TDQ-805A17D9K-99 transformer and is rated at 850 MVA with a voltage ratio of 22 kV to 245 kV. It was manufactured in 2004 and installed during the Unit 4 Spring 2005 refueling outage. The transformer was in operation for 14 days and it failed suddenly and without any warning. There were no annunciator alarms received prior to the fault occurrence. No evidence of any system, plant or Generator transient could be found occurring at the time of or in the hours before the failure.U.S. NUCLEAR REGULATORY COMMISSION I-2001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
DOCKET LER NUMBER (6)
PAGE (3)
NUMBER (2 YEAR l SEQUENTIAL REVISION Turkey Point Unit 4 05000251 YEA NUBE0UME Page 3 of 5 200 00
=
TEXT (If more space Is required, use additional copies of NRC Form 366A) (17)
Analysis of the plant and switchyard digital fault recorder traces show that the internal fault began as B phase to ground and propagated into a three phase fault after approximately. 1 second (60 cycles).
This was evidenced by the abnormally high current flow into the transformer from both the switchyard and the Main Generator. The switchyard fault current contribution ceased in 4 '/2 cycles when the Generator breakers 8W65 and 8W88 tripped open. However, there is no breaker for isolation between the Unit 4 Main Generator and the Unit 4 Main Transformer. As such, the Main Generator continued to contribute to the fault for an additional 11 seconds while coasting down, until the internal energy stored in the Generator field dissipated. The Generator fault current contribution was in excess of 44,000 Amps.
The pressure relief devices located at the top of the transformer actuated, but could not maintain the integrity of the main tank. The transformer seam at the top of the unit separated across the entire rear of the unit along the cooler banks and across a portion of the unit located under the conservator tank. The bolted flange for cooler bank 1 located on the top of the transformer was also separated, shearing some of the connecting bolts. These tank ruptures resulted in the release of transformer.
insulating oil and contributed to the fire. The Unit 4 Main Transformer was severely damaged and is not repairable. The fire charred the transformer body, the transformer control cables and conduit, and the transformer retaining pit.
Other plant equipment located in the proximity of the Main Transformer was damaged by the fire.
These components included POV-3-4883 (Turkey Point Unit 3 Intake Cooling Water to Turbine Plant Cooling Water Header 'A' Isolation valve) and associated control cables; the 480V cable run between the 4E load center (464106) and the non-vital 4B Motor Control Center (4B0651), as well as the associated conduits and cable tray; the Main Transformer deluge piping and control tubing; the transformer high side conductor A-frame support structures; and the transformer high side conductors. These components were addressed in the corrective action program and were either repaired or replaced prior to the Unit 4 restart. The fire damage did not impact safe shut down (Appendix R) capability.
In addition to the equipment damage, the Unit 4 Main Generator was subjected to abnormal stresses as a result of supplying fault current to the transformer for an extended period of time. The event necessitated a thorough examination of the Unit 4 Main Generator, including the Generator, excitation system, voltage regulator, isophase bus, and neutral bus. A thorough Unit 4 Main Generator inspection was performed. Minor damage, which was observed in the neutral bus, was repaired prior to the Unit 4 restart. The generator was re-certified for its normal service conditions.
Additionally, during the event, the Unit 4 Auxiliary Transformer was electrically connected to and exposed to the fire and subsequent deluge. However, no fault current flowed through the Auxiliary Transformer with the exception of any minor contribution from large motors being powered from the 4A and 4B switchgear at the time of the event. The current flowing through.the Auxiliary Transformer ceased in less than 10 cycles when breakers 4AA05 and 4AB05 opened. Auxiliary Transformer testing was performed including power factor and insulation meggering as a precautionary measure.
All testing was completed satisfactorily prior to Unit 4 restart.U.S. NUCLEAR REGULATORY COMMISSION l-2001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION FACILITY NAME (1)
MDOCKET LER NUMBER (6)
PAGE (3) r YEAR
(
EQUENTIAL OfREVISION Turkey Poinjt Unit 4 05000251 YEAR IS NUMBER RENUVER Page 4 of 5 200
=-002-TEXT (if more space is required, use additional copies of NRC Form 366A) (17)
CAUSE OF THE EVENT
The apparent cause of-the'trip is an internal fault on the B phase high side windings of the Turkey Point Unit 4 Main Transformer. A root cause investigation is being conducted. This investigation is ongoing and includes failure analysis with support from the vendor. Florida Power and Light Company will issue a supplement to this report when the final root cause determination has been completed.
REPORTABILITY
A review of the reporting requirements of 10 CFR 50.72 and 10 CFR 50.73 and NRC guidance provided in NUREG-1022, Revision 2, Event Reporting Guidelines 10 CFR 50.72 and 10 CFR 50.73, was performed for the subject condition. As a result of this review, the condition is reportable as described below.
1 OCFR50.73(a)(2)(iv)(A) states that the licensee shall report any event or condition that resulted in a manual or automatic actuation of any of the systems listed in 1 OCFR50.73(a)(2)(iv)(B). Systems to which the requirements of 1 0CFR50.73(a)(2)(iv)(A) apply include the Reactor Protection System actuation resulting in a automatic trip 10 CFR 50.73(a)(2)(iv)(B)(1). The event is also reportable in accordance with 10 CFR 50.73 (a)(2)(iv)(A), due to automatic AFW system actuation 10 CFR 50.73(a)(2)(iv)(B)(6).
ANALYSIS OF SAFETY SIGNIFICANCE For this automatic reactor trip, the initial conditions were well within the assumed conditions of the Loss of External Electrical Load event analyzed in the Final Safety Analysis Report (FSAR). The plant was operating at 100% power. A 100% loss of load resulted in a reactor trip on turbine trip due to Main Generator Lock out. All plant systems functioned as designed during and after the event. The plant response was well within the FSAR minimum and maximum values compared to the Loss of External Electrical Load event.
The risk with respect to core damage and large early release frequency as a result of the transformer failure and fire have been assessed to be no different from any other unplanned reactor trip, since all automatic plant trip features functioned as designed resulting in a stable plant configuration. The deluge water did not challenge any accident mitigation function and the Main Transformer does not provide any accident mitigation capability. The transformer condition did not have an effect on the function of any Emergency Diesel Generator. The transformer fire did not have any adverse effect.
This event did not adversely impact the plant's ability to mitigate the consequences of an accident and therefore, had minimal safety significance.U.S. NUCLEAR REGULATORY COMMISSIONU.S. NUCLEAR REGULATORY COMMISSIO N (7-2001)
LICENSEE EVENT REPORT (LER)
TEXT CONTINUATION DO:KETr
.E NUBR,)PG 3
FACILITY NAME (1)
O NUMBER (2)__
NUMBR_(6__AE_(3 YEAR SEQUENTIAL IREVISION Turkey Point Unit 4 05000251 NUMBER NUMBER Page 5 of 5 2005-02 00 TEXT (If more space Is required, use additional copies of NRC Form 366A) (17)
CORRECTIVE ACTIONS
Corrective actions included replacement of the Unit 4 Main Transformer and repair/replacement of other components damaged by fire.
ADDITIONAL INFORMATION
EIIS Codes are shown in the format [EIIS SYSTEM: IEEE system identifier, component function identifier, second component function identifier (if appropriate)].
No similar events were identified at Turkey Point.