05000247/LER-2009-005, Automatic Reactor Trip Due to a Turbine-Generator Exciter Protective Trip Caused by a Loss of the Generrex Power Supply Monitored Voltage Due to a High Resistance Ground Connection

Automatic Reactor Trip Due to a Turbine-Generator Exciter Protective Trip Caused by a Loss of the Generrex Power Supply Monitored Voltage Due to a High Resistance Ground Connection

ML100120456
Person / Time
Site:	Indian Point
Issue date:	01/04/2010
From:	Joseph E Pollock Entergy Nuclear Operations
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NL-09-159 LER 09-005-00
Download: ML100120456 (6)

LER-2009-005, Automatic Reactor Trip Due to a Turbine-Generator Exciter Protective Trip Caused by a Loss of the Generrex Power Supply Monitored Voltage Due to a High Resistance Ground Connection

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
2472009005R00 - NRC Website

text

~Entergy 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-09-159 January 4, 2010 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Mail Stop O-P1-17 Washington, D.C. 20555-0001

SUBJECT:

Licensee Event Report # 2009-005-00, "Automatic Reactor Trip Due to a Turbine-Generator Exciter Protective Trip Caused by a Loss of the Generrex Power Supply Monitored Voltage Due to a High Resistance Ground Connection" 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) 2009-005-00. The attached LER identifies an event where the reactor was automatically tripped, which is reportable under 10 CFR 50.73(a)(2)(iv)(A).

As a result of the reactor trip, the Auxiliary Feedwater System was actuated and the Main Steam Isolation Valves (MSIVs) were closed which is also reportable under 10 CFR 50.73(a)(2)(iv)(A). This condition was recorded in the Entergy Corrective Action Program as Condition Report CR-IP2-2009-04530.

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. Samuel J Collins, 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 WZ&

Abstract

On November 02,

2009, an automatic reactor trip (RT) was initiated as a result of a turbine-generator protective trip (86P Lockout Relay).

All control rods fully inserted and all required safety systems functioned properly.

The Main Steam Isolation Valves (MSIVs) were closed after reports that one of the four turbine stop valves did not indicate fully closed.

The plant was stabilized in hot standby with decay heat being removed by the Steam Generators (SG) via the Atmospheric Steam Dump Valves.

The Emergency Diesel Generators did not start as offsite power remained available.

The Auxiliary Feedwater System automatically started as expected due to SG low level from shrink effect.

The direct cause was a high resistance connection on the common ground terminal between the Generrex power supplies and alarm cards.

The cause of the event was a poor Original Equipment Manufacturer (OEM) design of the common ground wiring connections on the Generrex power supply distribution block.

Corrective actions

included repairs to the Generrex power supply connection and installation of a second ground connection in the exciter cabinet.

A Generrex system upgrade is planned for the refueling outage 19 in the spring of 2010 which includes upgrading to solid state power supplies and testing the ground wire.

The event had no effect on public health and safety.

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Past Similar Events A review of the past three years of Licensee Event Reports (LERs) for events that involved a RT from a Generrex Main Generator protective trip was performed.

The review identified LER-2006-005 which reported a RT on November 15, 2006, due to a Generrex protective trip.

The cause was determined to be a momentary loss of electrical ground to the alarm cards that monitor the Generrex power supplies.

High resistance connections caused unreliable operation of the Generrex regulator circuit card.

The circuit card has tin plated steel sleeves that mate to connection pins on the main power supply chassis.

The connection pins showed oxidation.

A contributing cause was a loose screw terminal where the grounds are mounted due to mechanical vibration of the Generrex power supply.

Corrective actions included replacement of the #1 power supply circuit card, cleaning and lubricating the pins, providing proper connections for the common ground, checking remaining +/-

15 volt pins and terminal points for proper operation.

The 2006 event recognized the four wire termination but believed it was justified as it complied with the OEM design and was verified for tightness.

Safety Significance

This event had no effect on the health and safety of the public.

There were no actual safety consequences for the event because the event was an uncomplicated RT with no other transients or accidents and the plant safely shut down as designed.

Actuation of the AFWS is an expected reaction to full power reactor trips due to SG shrink effect which causes SG level to drop below a SG level trip set point.

The closure of the MSIVs was in accordance with plant procedures in response to indication that a turbine stop valve did not close.

The stop valve was subsequently determined to be closed and the condition was due to an indicator switch.

The turbine control valve that was not indicating fully closed was determined to have a sheared anti-rotation pin that connects the valve stem to the actuator causing the valve to rotate down and contact the valve seat prematurely.

The control valve was determined to be closed with its valve plug on its seat.

The anti-rotational pin was replaced and the valve spring actuator was adjusted to center.

All required safety systems performed as designed in response to the RT.

There were no significant potential safety consequences of this event.

The RPS is designed to actuate a RT for any anticipated combination of plant conditions including a direct RT on TT unless the reactor is below approximately 20% power (P-8).

The analysis in UFSAR Section 14.1.8 concludes an immediate RT on TT is not required for reactor protection.

A RT on TT is provided to anticipate probable plant transients and to avoid the resulting thermal transient.

If the reactor is not tripped by a TT, the over temperature delta temperature (OTDT) or over pressure delta temperature (OPDT) trip would prevent safety limits from being exceeded.

The generator is protected by the generator protection system (GPS) which is designed to protect the generator from internal and external faults by tripping the output breakers.

During this event the GPS functioned as designed and initiated a TT.

This event was bounded by the analyzed event described in FSAR Section 14.1.8, Loss of External Electrical Load.

The response of the plant is evaluated for a complete loss of steam load from full power without a direct RT and includes the acceptability of a loss of steam load without direct RT on turbine trip below 35 percent power.

The analysis shows that the plant design is such that there would be no challenge to the integrity of the reactor coolant system or main steam system and no core safety limit would be violated.

A low SG water level initiates actuation of the AFWS whose design has adequate capability to provide the minimum required flow.

For this event, rod control was in Auto and all rods inserted upon initiation of the automatic RT.

The AFWS actuated and provided required FW flow to the SGs.

The reactor coolant system pressure remained below the set point for pressurizer PORV and code safety valve operation, and above the set point for automatic safety injection actuation.

Following the RT the plant was stabilized in hot standby.