05000443/LER-1990-015
| ML20055G742 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 07/20/1990 |
| From: | Belanger R, Feigenbaum T PUBLIC SERVICE CO. OF NEW HAMPSHIRE |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| LER-90-015, LER-90-15, NYN-90141, NUDOCS 9007240126 | |
| Download: ML20055G742 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| 4432090015R00 - NRC Website | |
text
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. j New H$mpshwe Ted C.. ._. . - . :: !
J Senior Vice President and -
L Chief Operating Officer l NYN-90141 July 20, 1990 j i
l United States Nuclear Regulatory Commission l Washington, DC 20555- i Attention: Document Control Desk l
References:
Facility Operating License No. NPF-86 Docket No. 50-443 ,
Subject:
Licensee Event Report (LER) No. 90-015-00: Turbine Trip With Reactor Trip Due to Ground Fault Relay Actuation Gentlemen:
Enclosed please find Licensee Event Report (LER) No. 90-015-00 for Seabrook Station. This submittal documents an event which was identified on June 20, 1990, and is being reported pursuant to 10CFR50.73(a)(2)(iv).
Should you require further information regarding this matter, please
-contact Mr. Richard R. Belanger at (603) 474-9521, extension 4048.
l Very truly yours, ,
I
[M Ted C. Feigen aum
. Enclosures NRC Forms 366, 366A
-! cci Mr. Thomas T. Martin !
Regional Administrator United States Nuclear Regulatory Commission .t Region I 475 Allendale Road t King of Prussia, PA '19406 Mr. Noel badley ,
NRC Senior Resident Inspector ;
P.O. Box 1149 Sea 5 rook, NH 03874 INPO '
Records Center 1100 Circle 75 Parkway )
Atlanta, GA 30339 i
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New Hampshire Yankee Division of Public Service Company of New Hampshire I P.O. Box 300
- Seabrook, NH 03874
- Telephone (603) 474 9521 fj
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DI: t,i .. . .. twerto svevissioN e4 m P ~~lNO 0 l9 2;O 9;O intxcim,,. ,= . a.. .. .,Pa,. .,.. -. w.n....,Hei On June 20, 1990, at 4:39 p.m., while in MODE 1 at 302 reactor power and increasing, a turbine-generator trip with reactor trip occurred. The trip was initiated by the actuation of a main generator ground fault relay designed to protect the last 52 of generator windings from a ground fault.
An Emergency Feedwater (E W) actuation also occurred due to low-low steam generator narrow range level. Steam generator 'A' EW isolated due to high EW flow one minuto into the event.
The turbine-generator tripped due to the ground fault relay actuating. All the applicable trips and interlocks associated with a turbine generator, reactor trip and feedwater isolation functioned as designed. Parameters associated.with the reactor were reviewed by the on-shift reactor. engineer and determined to be normal. The EW isolation occurred when the turbine driven pump came up to full speed. thus creating a situation where both EW pumps were supplying feedwater simultaneously.
The root cause of this event is undetermined thus far. The relay is currently being monitored and causes are still being investigated.
Corrective actions include revising the EW isolation setpoint as well as reviewing and updating emergency operating procedures.
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" """En*7Ene*" 7 179 O O : 39 p.m. EDT, a turbine-generator trip with reactor trip occurred while plant load was being increased from 302 reactor power. j The turbine trip was initiated by a main generator ground fault relay actuation. 4 Descriotion of Event Prior to the event Work Request 90W003354 was initiated to periodically monitor ground fault relay 64 (1002) 70-1. This relay, which to an ,
r additional protection function not required by the generator manufacturer, protects the last 52 of the generator windings using a neutral transformer secondary circuit. The relay monitors the third harmonic of the generator output frequency through a bandpass filter arrangement. A ground fault will .
upset the third harmonic and de-energize the relay, causing the actuation of ,
the generator primary protection breaker lockout relay. In order for the ground fault relay to perform its monitor $ng function, there must be sufficient current through the neutral transformer secondary circuit.
Sufficient current for the relay to i. elf-activate its monitoring function occurs at approximately 302 power. Ground fault relay 64 (1002) TG-1 was being monitored because of a vendor recommendation to substantiate the validity of previously calculated settings.
When the trip occurred, reactor power was at approximately 302 and was being ?
increased, using the load limiter to maintain e rate of less than 52 per hour. The initiating event was recorded as, " Generator Neutral Volts High'.
This caused a main generator breaker lockout, initiating the turbine-generator trip with reactor trip. An Emergency Feedwater (EW) [BA) actuation occurred as designed due to low-low steam generator narrow range level.
The Unit Shift Supervisor (USS), entered Emergency Operating Procedures E-0 :'
and ES 0.1, ' Reactor Trip or Safety Injection' and ' Reactor Trip Response' l-responding to the reactor trip / turbine trip without a safety injection.
Approximately one minute into the event, steam generator 'A' E W isolated due l to high EW flow on both trains. Once the other three steam generators {
reached levels greater than 252, the steam turbine driven E W pump was '
shutdown. This was done to minimite cooldown of the Reactor Coolant System (RCS) (AB) due to steam flow going to the EW turbine. The electric EW pump and startup feed pump continued to feed the steam generators.
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Safety Consecuences The turbine-generator tripped due to the ground fau'lt relay actuating. All the applicable trips and interlocks associated with a turbine-generator trip, reactor trip and feedwater isolation functioned as designed.
E W actuation occurred as designed due to low-low steam generator narrow l range level. The isolation of EW to steam generator A' due to high flow occurred when the turbine driven pump came up to full speed, creating a situation where both E W pumps were supplying feedwater simultaneously. The setpoint for EW isolation on high flow was 425 GPM.
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UCENSEE EVENT REPORT (LERI TEXT CONTINUATION ** aovio owe no sew-eio.
winsi+:me l ..csiv, . . m con:: ...c". m j ti . .u . i., ... m Scabrook Station o ]s j o j o lo l4 l 413 9 10 0l1l 5 0l0 0l3 or 0l3 vir, ,, . l, =c , mu mm All operator actions were determined to be appropriate to ensure the safety l of the plant. Parameters associated with the reactor were reviewed by the l- on-shift reactor engineer and determined to be normal. At no time during this transient was there any impact on the health and safety of plant employees or the public.
Root Cause The root cause of this event has not been conclusively determined. We are investigating the operation of the relay due to lower than expected values for the third harmonic. A potential cause of the event could be a low third harmonic value when the relay first self-activates at approximately 302 -
power. We are continuing to review the operation of the relay, once the I
root cause is determined, a supplemental report will be submitted. This is expected to be submitted by September 20, 1990. '
Corrective Actions After the trip and the plant was placed in HOT STANDBY in accordance with operating procedure OS1000.11, ' Post Trip to HOT STANDBY', an event evaluation, root cause analysis, and Human Performance Enhancement System (HPES) analysis were initiated and completed before restart of the reactor.
A Temporary Hodification (THOD) has been implemented and is currer ly monitoring the relay and bypassing the trip function. This relay protection is not required by the generator manufacturer. Voltage and current data collected thus far has shown the relay to be operating properly, and that the setpoint was correct based on the information available at that time.
Further monitoring of the relay has shown that the relay trips when first activated at approximately 302 power. The relay then resets at a high power level. The basis for the setpoint is under investigation.
l A Minor Modification (MMOD) was implemented to revise the setpoint for automatic isolation of a faulted steam generator from 425 to $25 GPM. This HMOD included rescaling the EFU transmitters and associated indicators and recorders.
In addition Operations Departmc.A Personnel are reviewing and updating emergency operating procedures to include further guidelines associated with RCS cooid en. This is expected to be completed by October 1, 1990.
Plant Conditions At the time of this event, the plant was in MODE 1. Power Operation, at 30!
power, with an RCS temperature of $61 degrees Fahrenheit and pressure of 2235 psig.
This is'the first event of this type at Seabrook Station, u e.ca= =.. .u s cao i +.e. sw is N , _ . _ _ -