05000286/LER-2015-005

LER-2015-005, Automatic Reactor Trip Due to a Turbine-Generator Trip Caused by the Trip of 345kV Main Generator Output Breaker 3 due to a Failure of South Ring Bus 345kV Breaker 5

Indian Point 3
Event date:	6-15-2015
Report date:	9-14-2016
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(B), System Actuation 10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function
2862015005R01 - NRC Website

LER 15-005-01 for Indian Point 3 RE: Automatic Reactor Trip Due to a Turbine-Generator Trip Caused by the Trip of 345kV Main Generator output Breaker 3 due to a Failure of South Ring Bus 345kV Breaker 5

ML16263A290
Person / Time
Site:	Indian Point
Issue date:	09/14/2016
From:	Vitale A J Entergy Nuclear Operations
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NL-16-102 LER 15-005-01
Download: ML16263A290 (7)

Note: The Energy Industry Identification System Codes are identified within the brackets {}.

DESCRIPTION OF EVENT

On June 15, 2015, while at 100 percent reactor power, an automatic reactor trip (RT) {JC} occurred at 19:20 hours, due to a Main Turbine {TA} Main Generator {TB} trip as a result of a direct generator trip from the Buchanan switchyard. All control rods [AA} fully inserted and all required safety systems functioned properly. The plant was stabilized in hot standby with decay heat being removed by the condenser {SG}. There was no radiation release. The emergency diesel generators {EK} did not start as offsite power remained available. The auxiliary feedwater system {BA} actuated as expected due to steam generator {AB} low level from shrink effect. An investigation into the cause of the event and a post transient evaluation was initiated. The event was recorded in the Indian Point corrective action program (CAP) as Condition Report CR-IP3-2015-03487.

Prior to the RT Control Room operators were informed by the Con Edison District Operator (DO) at 11:43 hours, of an issue on 345 kV feeder W97 {F10. At 16:15 hours, the Con Edison DO reported the issue with feeder W97 which also affected feeder W93 requiring both feeders to be de-energized. The outage for the scheduled work was expected to last approximately one hour and was designated a Category 2 emergency (Equipment is in danger of failure but does not pose an immediate hazard to people or other equipment) in accordance with IP-SMM-OP-104 (Offsite Power and Continuous Monitoring and Notification). The issue concerned a Mylar balloon on the top conductor of feeder W97 just outside of the Millwood 345 kV substation. To Main Generator Output breaker {BKR} (345kV Breaker 1) had to be opened. On June 15, 2015, at 19:16 hours, 345kV Breaker 1 was opened in accordance with 3-SOP-EL- 017 (Operation of 345kV Breakers #1 and #3). Shortly after opening 345kV Breaker 1, South Ring Bus {FK} 345kV Breaker 5 failed causing Main Generator Output Breaker 3 to auto open and the automatic trip of feeders Y88, W98 and W96. In accordance with design, opening of 345kV Breakers 1 and 3 will trip the 86 Primary and 86 Backup lockout relays and initiate a turbine trip which will cause a RT. The following relays were tripped: 1) 345kV Line BU Ground Fault Detected (W96), 2) 345kV Line Backup Phase Fault Detected (A, C), 3) 345kV Line Phase Fault Detected (A, C), 4) 345kV Line Primary Ground Fault Detected.

The Unit 3 High Voltage Electrical Distribution System consists of the following subsystems: 1) 22kV system, 2) 345kV system, and 3) 138kV and 13.8kV system. The Unit 3 Main Generator supplies electrical power at 22kV through isolated phase bus to the two Main Transformers (MT). The MTs increase the voltage of the generator output to 345kV which is transmitted to the Buchanan Substation South Ring Bus via feeder W96. The Buchanan Substation contains two 345kV Ring Buses (North and South) and a 138kv bus. The South Ring Bus is normally supplied by Unit 3 and the North Ring Bus by Unit 2. The South Ring Bus is connected to the Millwood West Substation via two feeders, W97 and W98 and to the Ladentown Substation via feeder Y88. The South Ring Bus consists of four 345kV breakers, numbered 1, 3, 5 and 6.

The 345kV breaker #5 was a Power Circuit Breaker, Te 345GA 25-30, SN 41-39006- 2044, manufactured by ITE Imperial Corporation {I004 yp } in 1971 and installed in 1973. This breaker is owned by Con Edison.

An extent of condition (EOC) investigation determined that the Indian Point Energy Center (IPEC) does not own any 345kV circuit breakers manufactured by ITE. Prior to replacement in 2003, Main Generator Output Breakers 1 and 3 were ITE circuit breakers.

FACILITY NAME (1) PAGE (3) DOCKET (2) LER NUMBER (6) F4-6 Smi W97 I TO

MD

0-0 T ROLLED FROM INDIAN POINT 10.3 1$ SFC; T 5A 5 SECT smEimmimmw...s.

F 70 LADENTOWN TO MiLLMOIX) REST r 1A -J Prior to August 15, 2012, the OE program did not require switchyard and grid OE sharing, IPEC should have formally notified Con Edison of ITE Imperial Type GA breaker unreliability, the detrimental effect failure of the breakers would have on generation and requested Con Edison to take timely action to intensify PM or replace the Buchanan 345 kV breaker 5. Breaker 6 was replaced in 2009.

The Cause of Event Direct cause of the RT was failure of Buchanan 345kV breaker 5 due to age-related degradation of the C phase contacts. This degradation was due to misalignment of the contacts that resulted in a hot spot due to high resistance. Con Edison who owned the breaker, determined the contact support system failed due to repeated cycling (fatigue failure). The failure of breaker 5 activated protective relays that opened the remaining Main Generator Output breaker 3 which initiated a trip sequence that resulted in an immediate Generator Trip, Turbine Trip and RT. The root cause was Indian Point Energy Center did not provide formal notification of industry operating experience (OE) to Con Edison. The specific incident pertains to the OE on ITE Type GA breakers that could impact IPEC generation. The condition was exacerbated by the OE process (EN-0E-100) that did not have a trigger for formal communication of important OE information to external groups that control and own equipment critical to IPEC generation.

IPEC does attend periodic face-to-face meetings with Con Edison to discuss reliability concerns and pending projects in the Buchanan Switchyard which could affect IPEC operation.

Corrective Actions

The following are some of the corrective actions that have been performed under the Corrective Action Program (CAP) to address the causes of this event.

• A detailed inspection and failure analysis of 345kV breaker 5 was performed by Con Edison to identify the specific failure mechanism and root cause. The Con Edison results were discussed with Entergy and a Root Cause Evaluation performed that included the results obtained from Con Edison.

• 345kV Breaker, 5 was replaced by Con Edison.

• Procedure EN-0E-100 (OE Program) was revised by including a new section describing how to initiate formal notification to external groups when OE related to components they own and/or control can affect generation.

• A new IPEC site procedure was prepared (SMM-LI-126) that formalizes the process for notifying external groups of operating experience that can affect generation at IPEC.

Event Analysis

The event is reportable under 10CFR50.73(a)(2)(iv)(A). The licensee shall report any event or condition that resulted in manual or automatic actuation of any of the systems listed under 10CFR50.73(a)(2)(iv)(B). Systems to which the requirements of 10CFR50.73(a)(2)(iv)(A) apply for this event include the Reactor Protection System (RPS) including RT and AFWS actuation. This event meets the reporting criteria because an automatic RT was initiated at 19:20 hours, on June 15, 2015, and the AFWS actuated as a result of the RT. On June 15, 2015, at 20.15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br />, a notification was made in accordance with 10 CFR 50.72: a 4-hour non-emergency notification for an actuation of the reactor protection system {JC} while critical under 10 CFR 50.72(b)(2)(iv)(B), and an 8-hour notification under 10CFR50.72(b)(3)(iv)(A) for a valid actuation of the AFW System (Event Log #51156).

As all primary safety systems functioned properly there was no safety system functional failure reportable under 10CFR50.73(a)(2)(v).

Past Similar Events

A review was performed of previous Licensee Event Reports (LERs) in the past three years reporting a RT as a result of a high voltage breaker failure. No LERs were identified.

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 reactor trip with no other transients or accidents. Required primary safety systems performed as designed when the RT was initiated. The AFWS actuation was an expected reaction as a result of low SG water level due to SG void fraction (shrink), which occurs after a RT and main steam back pressure as a result of the rapid reduction of steam flow due to turbine control valve closure.

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.

This event was bounded by the analyzed event described in FSAR Section 14.1.8 (Loss of External Electrical Load). All components in the RCS were designed to withstand the effects of cyclic loads due to reactor system temperature and pressure changes. For this event, rod control was in automatic and all rods inserted upon initiation of a RT. The AFWS actuated and provided required FW flow to the SGs. RCS pressure remained below the set point for pressurizer PORV or code safety valve operation and above the set point for automatic safety injection actuation. Following the RT, the plant was stabilized in hot standby.