05000286/LER-2011-005, Indain Point, Unit 3 Regarding Automatic Actuation of Emergency Diesel Generators and Auxiliary Feedwater Pumps Due to Undervoltage on 480 Vac Vital Buses Due to a Loss of Offsite Power During a Severe Storm
| ML11299A022 | |
| Person / Time | |
|---|---|
| Site: | Indian Point  |
| Issue date: | 10/18/2011 |
| From: | Joseph E Pollock Entergy Nuclear Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NL-11-111 LER 11-005-00 | |
| Download: ML11299A022 (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)(v), Loss of Safety Function |
| 2862011005R00 - NRC Website | |
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.- En tergy 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-11-111 October 18, 2011 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Mail Stop O-P1-17 Washington, D.C. 20555-0001
SUBJECT:
Licensee Event Report # 2011-005-00, "Automatic Actuation of Emergency Diesel Generators and Auxiliary Feedwater Pumps Due to Undervoltage on 480 VAC Vital Buses Due to a Loss of Offsite Power During a Severe Storm" Indian Point Unit No. 3 Docket No. 50-286 DPR-64
Dear Sir or Madam:
Pursuant to 10 CFR 50.73(a)(1), Entergy Nuclear Operations Inc. (ENO) hereby provides Licensee Event Report (LER) 2011-005-00. The attached LER identifies an event where Emergency Diesel Generators and Auxiliary Feedwater Pumps 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-IP3-2011-04045.
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 r1%
cc:
Mr. William Dean, Regional Administrator, NRC Region I Resident Inspector's Office, Indian Point 3 Mr. Paul Eddy, New York State Public Service Commission LEREvents@inpo.org NRC
/S
Abstract
On August 19, 2011, during a severe thunderstorm, Emergency Diesel Generators (EDGs) 32 and 33 automatically actuated and loaded onto 480 volt buses 5A and 6A as a result of undervoltage due to a loss of 138 kV offsite power feeder 95331.
480 volt buses 2A and 3A remained energized from the Unit Auxiliary Transformer (UAT) which is connected to the Main Generator.
As a result of the 480 volt bus undervoltage, the 32 and 33 Auxiliary Feedwater pumps (AFWP) auto started (Non-SI Blackout Logic).
All EDGs and AFWPs operated as designed.
A load reduction to approximately 74 % power was required due to the loss of condenser vacuum caused by the loss of three Circulating Water Pumps.
The direct cause of the event was loss of power to 480 volt safeguards buses 5A and 6A due to a trip of the 138 kV Primary Pilot Wire relay (87L1/138) that isolated the 138 kV feeder 95331 to the Station Auxiliary Transformer.
The root cause was indeterminate.
The most probable cause was lightning induced extraneous voltage on the ground grid due to a potential deficiency with the ground grid.
Corrective actions included restoration of feeder 138 kV 95331 to service and return of 480 volt buses 5A and 6A to normal feeds, re-alignment of EDGs for unit operation and placement in Auto, securing of the 32 and 33 AFWPs and alignment for automatic operation.
The 138 kV Primary Pilot Wire was placed in test with back-up in service.
Testing of the ground grid will be performed by a vendor and results evaluated for any necessary corrective actions.
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 loss of the offsite feeder did not result in the failure of any primary system to function properly.
The last time the 32 CCW pump was tested was during the Appendix R test on July 1, 2011.
During the time of inoperability, the 31 and 33 CCW Pumps were operable therefore, there was no TS violation.
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 Report's (LERs) for the past three years for any events reporting inadvertent EDG or AFWS actuation as a result of a lightning strike.
One LER was identified, LER-2009-009 reported an automatic reactor and turbine trip due to actuation of the generator protection system lockout relay during a severe storm with heavy lightning.
The cause was indeterminate but the ground mat was a possible cause.
A corrective action (CA) was to evaluate the ground grid condition for adequacy requiring testing by a vendor.
The testing is expected to be completed by the end of 2011.
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 alternate 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 were 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 31 BC and 32 BC were unavailable for approximately 57 minutes (discovery at 18:05 hours, restoration at 19:02 hours) 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 />.
When the 32 CCW pump failed to start the 31 and 33 CCW pumps auto started per design during the Non-SI Blackout sequence so there was no loss of CCW.
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 which also functions as the alternate AC power supply operated from outside the Control Room.