05000247/LER-2011-001, Regarding Automatic Actuations of Emergency Diesel Generators Due to Undervoltage on 480 Vac Vital Buses 5A and 6A Caused by a Loss of Offsite Power During Switchyard Troubleshooting
| ML11130A024 | |
| Person / Time | |
|---|---|
| Site: | Indian Point  |
| Issue date: | 05/02/2011 |
| From: | Joseph E Pollock Entergy Nuclear Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NL-11-042 LER 11-001-00 | |
| Download: ML11130A024 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(1), Submit an LER, Invalid Actuation 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 2472011001R00 - NRC Website | |
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eEntergy Indian Point Energy Center 450 Broadway, GSB P.O. Box 249 Buchanan, N.Y. 10511-0249 Tel (914) 734-6700 J. E. Pollock Site Vice President NL-1 1-042 May 2, 2011 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Mail Stop O-Pl-17 Washington, D.C. 20555-0001
SUBJECT:
Licensee Event Report # 2011-001-00, "Automatic Actuation of Emergency Diesel Generators Due to Undervoltage on 480 VAC Vital Buses 5A and 6A Caused by a Loss of Offsite Power During Switchyard Troubleshooting" Indian Point Unit No. 2 Docket No. 50-247 DPR-26
Dear Sir or Madam:
Pursuant to 10 CFR 50.73(a)(1), Entergy Nuclear Operations Inc. (ENO) hereby provides Licensee Event Report (LER) 2011-001-00. The attached LER identifies an event where Emergency Diesel Generators automatically actuated, which is reportable under 10 CFR 50.73(a)(2)(iv)(A). This condition was recorded in the Entergy Corrective Action Program as Condition Report CR-IP2-2011-01108.
There are no new commitments identified in this letter. Should you have any questions regarding this submittal, please contact Mr. Robert Walpole, Manager, Licensing at (914) 734-6710.
Sincerely, JEP/cbr cc:
Mr. William Dean, Regional Administrator, NRC Region I NRC Resident Inspector's Office, Indian Point 2 Mr. Paul Eddy, New York State Public Service Commission LEREvents@inpo.org
Abstract
On March 1, 2011, Emergency Diesel Generators (EDGs) 21, 22 and 23 automatically actuated as a result of undervoltage on 480 Volt buses 5A and 6A due to a loss of 138 kV offsite power.
480 volt buses 2A and 3A remained energized as 6.9 kV buses 2, and 3 were energized from the Unit Auxiliary Transformer (UAT) which is connected to the Main Generator.
All EDGs operated as designed.
EDGs 21 and 23 were manually loaded onto buses 5A and 6A.
Prior to the event Con Edison personnel were performing troubleshooting in the Buchanan switchyard on a metering circuit for 138 kV feeder 95332.
The direct cause was loss of power to 480 volt safeguards buses 5A and 6A due to isolation of 138 kV feeder 95332 to the Station Auxiliary Transformer.
Feeder 95332 isolated as a result of an arc on the feeder metering circuit current transformer (CT) switch that caused an imbalance.
The CT circuit also supplies the first line pilot wire relay which tripped due to the imbalance.
In accordance with design, the pilot wire relay tripped 138 kV breakers F2 and BT3-4 in the Buchanan switchyard and actuated protective relay 87L/138 which actuated lockout relay 86 STP tripping unit 2 breakers BT4-5 and 6.9 kV breakers 52/ST5 and 52/ST6 thereby isolating feeder 95332.
The apparent cause was a failure of the current transformer (CT) test switch associated with the 138 kV feeder metering circuit to make-before-break.
The test switch did not make-before-break due to corrosion on the contact surfaces.
Corrective actions include closure of the test switch and restoring feeder 95332 to service.
A Con Edison deficiency tag was placed on the switch.
Troubleshooting was performed on the Buchanan switchyard feeder 95332 CT circuit and the test switch replaced.
Con Edison indicated their notification procedure for work impacting the switchyard will be revised.
The event had no significant effect on public health and safety.
(If more space is required, use additional copies of (if more space is required, use additional copies of NRC Form 366A) (17)
The actuation and start of the EDGs due to undervoltage on buses 5A and 6A from the loss of offsite power feeder 95332 meets the reporting criteria.
Because plant shutdown was not completed for TS 3.0.3 as a result of inoperable BC-21 and BC-24, the TS 3.0.3 entry is not reportable under 10CFR50.73(a) (2) (i) (A).
The loss of the offsite feeder did not result in the failure of any primary system to function properly. Therefore, there was no safety system functional failure reportable under 10CFR50.73(a) (2) (v) as the minimum required safeguards components were available.
In accordance with reporting guidance in NUREG-1022, an additional random single failure need not be assumed in that system during the condition.
Past Similar Events A review was performed of Licensee Event Reports (LERs) for the past three years for any events reporting inadvertent EDG actuation as a result of maintenance activities.
No similar LERs were identified.
Safety Significance
This event had no significant effect on the health and safety of the public. There were no actual safety consequences for the event because there were no accidents and the emergency AC power system was available to power required safeguards buses.
Power from both offsite sources and onsite emergency power were available and the actuation circuitry and EDGs performed in accordance with design and minimum safeguards power was available to power safety loads.
All plant parameters responded normally for the transient and remained within operating limits.
There were no significant potential safety consequences of this event.
This event was bounded by the analyzed event described in UFSAR Section 14.1.12 (Loss of all AC Power to the Station Auxiliaries).
The plant is designed for a LOOP and has safety related emergency AC power by EDGs to start on a 480 VAC safety bus undervoltage and power the 480 VAC safety buses (2A/3A, 5A, 6A).
Results of the analysis show that for the loss of offsite power to the station auxiliaries all safety criteria are met.
The Auxiliary Feedwater capacity is sufficient to prevent water relief through the pressurizer relief and safety valves assuring the reactor coolant system (RCS) is not over pressurized.
The analysis also demonstrates that sufficient long term heat removal capability exists by the natural circulation capability of the RCS following reactor coolant pump coast down to prevent fuel or clad damage.
The loss of BCs is an expected condition for a LOOP which results in the motor control centers powering the BCs from bus 5A and 6A to trip and require reset.
There are four BCs and an installed spare in BC-35 which can supply BC loads for one of the 31-34 BCs.
Each battery has been sized to carry its expected shutdown loads for a period of 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> following a plant trip and a loss of all AC power.
All equipment supplied by the batteries are maintained operable with minimum expected voltages at the battery terminals during the 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />.
During this event the 21 was unavailable for 22 minutes and the 24 BC was unavailable for 41 minutes which is within the battery design capability of 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />.
In addition, there is an independent station blackout (SBO)/Appendix R diesel generator and associated switchgear necessary to achieve and maintain cold shutdown conditions independent of the normal safeguards and instrumentation power supplies and to function as the alternate ac power supply operated from outside the Control Room.