05000443/LER-1991-001, :on 910212,turbine-generator Trip W/Reactor Trip Occurred.Caused by Inadequate Procedure.Plant Placed in Hot Standby.Human Performance Evaluation Sys & Root Cause Analysis Initiated

:on 910212,turbine-generator Trip W/Reactor Trip Occurred.Caused by Inadequate Procedure.Plant Placed in Hot Standby.Human Performance Evaluation Sys & Root Cause Analysis Initiated

ML20070K845
Person / Time
Site:	Seabrook
Issue date:	03/13/1991
From:	Feigenbaum T, Legendre A PUBLIC SERVICE CO. OF NEW HAMPSHIRE
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-001, LER-91-1, NYN-91041, NUDOCS 9103190173
Download: ML20070K845 (5)

LER-1991-001, on 910212,turbine-generator Trip W/Reactor Trip Occurred.Caused by Inadequate Procedure.Plant Placed in Hot Standby.Human Performance Evaluation Sys & Root Cause Analysis Initiated

Event date:
Report date:
4431991001R00 - NRC Website

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h hd C. Feigenbaum-Pre ="'ent and -

Chlef Executive Officer NYN 91041 March 13,1991

- Document Ccattol-Desk United 1.ates Nuclear Regula' tory Commission

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.. Washington,lD.C. 20555 i

References:

Facility, Operating License No, NPF 86, Docket No. 50 443

Subject:

Licensee Event Report (LBR) No. 91 001 00: Reactor Trip Due to Loss of Electrohydraulle Control System Pressure Ocutlemeni Enclosed ' picuo find Licensee Event Report (LER) No 9100100 for Scabrook

- Station.-- This submittal: documents an event which occurred on February 12,1991' and is

- being reported pursuant to 10CFR50,73(a)(2)(lv),:

Should you' require further information regarding this matter,'please contact Mr, Allen L, Legendre,' Lead EngineereCompliance,- at (603) 474 9521, extension 2373.

Very truly yours, k

Ted C Fe genbaum TCP:WJT/act

- Enclosures:o ~NRC Forms :366, 366A s

i 9103190173 910313 PDR - ADOCK 05000443 i

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New Hampshire Yankee Division of Public Service Company of.Now Hampshiro

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' P.O. Box 300

• Seabrook, NH 03874 o Telephone (603) 474 9521

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United States Nuclear Regulatory Commission March 13,19914

!- Attention:- ~ Document Control Desk -

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Mr. Thomas T. Martin -

. Regional Administrator s

- United: States Nuclear Regulatory Commission Region I 475 Allendale Road'.

King _of-Prussia,-PAL 19406.

Mr. Gordon E; Edison _Sr. Project Manager' j

Project Directorate I 3 i

Division of Reactor. Projects -

.U.S. Nuclear Regulatory Commission -

Washin'gton, DC; 20555_

Mr ' Noel: Dudley NRC. Senior.Realdent Inspector

- P.O. Box 1149

- Seabrook,' NH 03874

lNPO i Records Center -

- 1100 Circle 75 Parkway -

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. u.u.,v, ~,......, n ei On February 12,1991, at 8:22 a.m. EST, a turbine generator trip with a reactor trip occurred while the plant was at 100% power. The trip was initiated by a loss of Electrohydraulic Control (EHC) system pressure. A Main Feedwater Isolation and an Emergency Feedwater Actuation also occurred subsequent to the trip.

Prior to the evens, 480 volt AC unit substation ED US 14 was cross connected to unit substation ED US 21 in preparation for various electrical maintenance tasks on the primary breaker, secondary breaker and transformer for ED US 14.

Approximately twenty five minutes following the cross connection, the secondary breaker for ED US 21 tripped due to the energization of two large cyclic loads, the turbine building crane and the guardhouse megatherm tank heaters. Consequently, power wa.s lost to both EHC pumps causing a loss of EHC system pressure that resulted in a turbine-generator trip with a reactor trip as designed.

The root cause has been determined to be an inadequate procedure. A contributing cause was inadequate training. To prevent recurrence, operating procedures, maintenance Repetitive Task Sheets and planning and scheduling procedures will be revised to provide additional controls to ensure that the overall connected load is fctmally evaluated and controlled prior to cross connecting unit substations. The lessons learned from this event will be discussed with all operating crews.

Additionally, a Training Development Recommendation (TDR) will be written to address failure mode and consequence thought processes during abnormal system alignments.

This is the first event of this type at Scabrook Station.

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"Olf OlOl1 OlO Ol2 0F 0l3 Seabrook Station 016101010 l 41413 9 11 TIKI f# sure Amses s steasd. par eestett MC Arm JEE4,1lih On February 12,1991 at 8:22 a.m., EST, a turuine generator trip with a reactor trip occurred while the plant was at 100% power. The turbine trip was initiated by.i loss of Electrohydruulic Control (EHC) [TG) system pressure.

Descriotion of Even.1 Prior to the event, 480 volt AC unit substation ED US 14 was cross connected to unit substation ED US 21 in preparation for various electrical maintenance tasks on the primary breaker, secondary breaker and transformer for ED US 14. A total load of 975 amps was verified locally immediately following the cross connection. The cross connection was performed in accordance with section 6.8 of procedure ON1046.08, 'Non Vital 480V Operation".

Approximately twenty five minutes following the cross connection, the secondary breaker for ED-US 21 tripped due to the energization of two large cyclic loads, the turbine building crane and the guardhouse megatherm tank heaters. Consequently, power was lost to both EHC pumps causing a loss of EHC system pressure that resulted in a turbine generator trip with a reactor trip.

Following the turbine trip and reactor trip a Main Feedwater Isolation [JE] occurred. Pressure pulses were created by the rapid closure of the turbine control valves. These pressure pulses were transmitted through the steam flow transmitters' water filled lines and sensed by the high pressure side of the steam generator narrow range level transmitter. This resulted in the steam generator high high level signal. Actual steam generator levels did not approach the high high level setpoint at any time. Additionally, an Emergency Feedwater Actuation [JE] occurred as designed, due to the loss of feedwater to a steam generator.

Safety Consecuences There were no adverse safety consequences as a result of this event. All the applicable trips and interlocks associated with the reactor trip functioned as designed.

All operator actions were determined to be appropriate to ensure the safety' of the plant. At no time during this event was there any impact on the health and safety of plant employees or the public.

Root cause The root cause has been determined to be an inadequate procedure. The procedure only required a verification of current loads, it did not require the evaluation and control of other loads which may automatically energize. A contributing cause was inadequate training. A failure mode and consequence thought process during an abnormal system alignment was not properly applied.

Corrective Actions

After the trip, the plant was placed in HOT STANDDY in accordance with operating procedure OS1001.11 " Post Trip to llot Standby". An event evaluation and post trip review were immediately initiated. A Human Performance Evaluation System (HPES) analysis as well as a root cause analysis were also initiated.

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- anwauniin Operating procedures, maintenance Repetitive Task Sheets and planning and scheduling procedures will be revised to provide additional controls to ensure that the overall connected load is formally evaluated and controlled prior to cross connecting unit substations.

procedure revisions are expected to be completed by May 15, 1991. The lessons learned from this event will be discussed with all operating crews.

Additionally, a Training Development Recommendation (TDR) will be written by April 15,1991 to address failure mode and consequence thought process during abnormal system alignments. This training will be given to operations and technical staff personnel.

Plant Conditions

At the time of this event, the plant was in Mode 1 Power Operation at 100%, with an RCS temperature of 587 degrees Fahrenheit and pressure of 2,235 psig.

This is the first event of this type at Seabrook Station.

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