05000499/LER-1991-001, :on 910109,feedwater Isolation Valve Closed During Investigation of Low Nitrogen & Hydraulic Pressure Alarms.Caused by Personnel Error & Inadequate Procedure. Licensed & non-licensed Operators Trained

:on 910109,feedwater Isolation Valve Closed During Investigation of Low Nitrogen & Hydraulic Pressure Alarms.Caused by Personnel Error & Inadequate Procedure. Licensed & non-licensed Operators Trained

ML20067C234
Person / Time
Site:	South Texas
Issue date:	02/08/1991
From:	Ayala C, Harrison A HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-001, LER-91-1, ST-HL-AE-3683, NUDOCS 9102110269
Download: ML20067C234 (7)

LER-1991-001, on 910109,feedwater Isolation Valve Closed During Investigation of Low Nitrogen & Hydraulic Pressure Alarms.Caused by Personnel Error & Inadequate Procedure. Licensed & non-licensed Operators Trained

Event date:
Report date:
4991991001R00 - NRC Website

text

e The Light company P.O. Ilm 1700 llouston. 'lixas 77001 (713) "'.'8 9211 llouston 1.lghting k Power February 8, 1991 ST llL-AE 3683 File No.:

C26 10CFR50.73 U. S. Nuclear Regulatory Commission Attention:

Document Control Desk Washington, DC 20555 South Texas Project Electric Generating Station Unit 2 Docket No. STN 50 499 Licensee Event Report 91 901 Regarding a Manual Reactor Trip Due to Full Closure of a

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Feedwnter Isolation Valve Durine Operationni Problem Investienticn l

l Pursuant to 10CFR50.73, llouston Lighting & Power Company (IIL6P) submits the attached Licensee Event Report (LER 91 001) regard.fng a manual reactor trip due to full closure of a feedwater isolation valve during operational problem investigation. This event had no adverse impact on the health and safety of the public,

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If you should have any questions on this matter, please contact l

Hr. C. A. Ayala at (512) 972 8628 or myself at (512) 972 7298.

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A-. llarrison Manager Nuclear Licensing l

RAP /ags Attachment: LER 91-001 (South Texas, Unit 2) l l

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9102110269 910209 J

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ST itL AE 3683 llouston' Lighting & Power Company File No.: C26 South Tess Project Electric Generating Station Page 2 cc:

Regional Administrator, Region IV Rufus S. Scott

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Nuclear Regulatory Commission Associate General Counsel 611 Ryan Plaza Drive, Suite 1000 llouston Lighting 6 Power Company l

t Arlington, TX 76011 P. O. Box 61867 llouston, TX 77208 George Dick, Project Manager U.S. Nuclear Regulatory Commission INPO Washington, DC 20555 Records Center 1100 Circle 75 Parkway I

J. 1. Tapia Atlanta, CA 30339 3064 Senior Resident Inspector c/o U. S. Nuclear Regulatory Dr. Joseph M. llendrio commission 50 Be11 port Lane i

P. O. Box 910 Bellisrt, NY 11713 Bay City, TX 77414 D. K. Lacker J. R. Newman, Esquire Bureau of Radiation Control Newman & iloltzinger, P.C.

Texas-Department of llealth 1615 L Street, N.W.

1100 West 49th Street Washington, DC 20036 Austin, TX 78756 3189 D. E. Ward /T M. Puckett Central Power and Light Company T. O. Box 2121 i

Corpus Christi, TX 78403 l

t J. C. Lanier/M. B. Lee City of Austin Electric Utility Department P.O. Box 1088 Austin, TX 78767 R. J. Costello/M. T. liardt City Public Service Board 1

P. 0, Box 1771 San Antonio, TX 78296 s

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On January 9,1991, Unit 2 was in Mode 1 at 100% power, At 2207 hours0.0255 days <br />0.613 hours <br />0.00365 weeks <br />8.397635e-4 months <br />, Feedwater Isolation Valve (IVIV) 2C closed during the -investiEation of low nitrogen and low hydraulic pressure alarms for FW1V 20.

The resultant loss of feedwater flow-caused a decrease in Steam Generator (50) level and the reactor was manually tripped. The cause of the manual reactor trip was a failed closed feedwater isolation valve.

The feedwater isolation valve closed when an operator incorrectly removed a power supply fuse to the trip solenoid.

The fuse was removed when trying to determine tb

'co of power loss to the IVlv hydraulic skid.

This was caused by failurt oordinate operational problem investigation and the use of information

..out providing necessary verification; annunciator responso procedures did..ot provide direction portaining to a loss of power; and lack of formal training on the investigation of power supplies.

Corrective actions include:

training of

- licensed and non licensed operators; revision of annuneintor response procedures; as well as other recurrence measures.

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On January 9,1991, Unit 2 was in tiode 1 at 100% power.

At 2207 hours0.0255 days <br />0.613 hours <br />0.00365 weeks <br />8.397635e-4 months <br />, Feedwater Isolation Valve (IVIV) 20 closed due to interruption of power to one of two safety grede solenoid dump valves during operational troubleshooting.

Steam Cenerator ($0) 2C Icvel started to decrease and the reactor was manually tripped since an automatic reactor trip was imminent due to low steam generator water level.

The turbine tripped, Auxiliary Teedwater (AIV) flow initiated on low. low steam generator level and Feedwater Isolation occurred on low Reactor Coolant System average temperature. All systems responded as expected except the-IVIV bypass valve to SC 20 opened to approximately 30%

following the Feedwater Isolation signal. At 2243 hours0.026 days <br />0.623 hours <br />0.00371 weeks <br />8.534615e-4 months <br />, the plent was stabillted in tiode 3.

The NRC was notified at 0008 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> on January 10, 1991.

'At 2145 hours0.0248 days <br />0.596 hours <br />0.00355 weeks <br />8.161725e-4 months <br />, on January 9, 1991, the low hydraulic and low nitrogen pressure alarms for IVIV 2C annunciated. A non licensed operator was dia. patched by the control room to investigate the condition locally.

The non licensed operator reported that the INIV 20 pneumatic and electric hydraulic pumps vero not operating.

The feedwater isolation valve is held open against nitrogen pressure by hydraulic pressure maintained by the pneumatic and electric hydraulic pumps.

The low nitrogen and hydraulic pressure conditions for INIV 2C indicated movement of the IVIV and impending closure although the amount of time involved before full closure of the.IVIV was not known.

Operations personnel were sensitized to a history of problems with the feedwater isolation valves which have resulted in sudden closure and subsequent plant trips and therefore took immediate actions to locate the cause of the failure. The operators believed that immediate actions were necessary to prevent a plant trip.

The Unit Supervisor joined the non. licensed operator at the FWIV 20 hydraulic skid unit and determined that a solenoid valve in the air supply line for the IVIV 20 pneumatic-and hydraulic pumps was not operating due to a loss of electrical power to the hydraulic skid. The Unit Supetvisor advised the control room to check power supplies for the hydraulic skid unit. The shift supervisor directed operators in the control room, one of which was a Reactor Operator (RO) trainee, to assist in determining the applicable power supplies.

Several sources of information were needed and used, such as diagrams and operating procedures, to establish a list of potential power supplies. The RO trainee identified the power supply to the hydraulic pumps and incorrectly identified the Class 1E power supply to one of the two safety grade solenoid dump valves for INIV 20 as possible power supplies to check.

The list was given to a second non licensed operator.

At approximately 2200 hours0.0255 days <br />0.611 hours <br />0.00364 weeks <br />8.371e-4 months <br />, the shift supervisor directed the second non licensed operator to check the various power supplies identified on the list including breakers, fuses, and A1/LER027U2.L01 gne so.w nee

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DESCRIPTION OF EVENT

(cont'd) continuity. The shif t supervisor did not recognize that the list had not been verified by one of the licensed operators. At approximately 2206 hours0.0255 days <br />0.613 hours <br />0.00365 weeks <br />8.39383e-4 months <br />, the i

Unit Supervisor locally directed a non licensed operator to check the fuse on the hydraulic skid unit. The fuse was checked with no problem found.

In the process of replacing the fuse the circuit was completed.

Subsequently, the hydraulic pumps started and the low pressure alarms cleared in the control room.

Communications were established between the Control Room and the Unit Supervisor to report the results of the pumps starting and alarms clearing.

At 2207 hours0.0255 days <br />0.613 hours <br />0.00365 weeks <br />8.397635e-4 months <br />, the control room was unsuccessful in attempting to contact the second non licensed operator by radlo who was in the process of checking power supplies in the switchgear room.

At approximately 2207 hours0.0255 days <br />0.613 hours <br />0.00365 weeks <br />8.397635e-4 months <br />, the i

non licensed operator pulled the fuse to the class lE power supply, which deenergized one of the two safety grade solenoid dump valves.

IVIV 20 began closing and a manual reactor trip was initiated as feedwater flow to SG 20 approached tero.

Other than the IVIV bypass valve failure to fully closo, there were no other unexpected post trip transients.

CAUSE OF EVENT

The direct cause of the manual reactor trip was a failed closed feedwater isolation valve.

The causes of the failed. closed feedwater isolation valvo are:

1.

The shift supervisor failed to coordinate the operational problem investigation of the skid unit and used a Reactor Operator trainee without providing rho necersary verification.

Such verification could have corrected the list of power supplies to be checked.

2.

The annunciator response procedures for the low pressure alarms were less than adequate in that they did not provido direction partaining to a loss of power.

3.

'1here is no formal training given to licensed or non licensed operators on problem investigation of power supplies.

4. -The power supply label on the hydraulic skid unit was not correct.

Had the correct power supply been indicated there would have been no need to perform reviews to identify which power supply was involved.

The TVIV Bypass Valve failed to close due to the positioner being out of calibration. The valve positioner was re calibrated.

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An unplanned reactor trip is reportabic pursuant to 10CFR50.73(A)(2)(iv). The plant was stabilized in Mode 3 following this event. This event did not result in any adverse safety or radiological concerns nor did it threaten the safety of the public at any time, i

CORRECTIVE ACTIONS

The followin6 corrective actions are bein6 taken as result of this event:

1.

It was determined that loss of power to the hydraulic skid was the result of the fuse block on the hydraulic skid losing continuity because the screws holding the block and lugs were loose.

The screws were tightened.

The remaining fuse blocks on the Unit 2 skids were checked with no problems found.

The fuse blocks in the Unit I skids will be checked prior to startup from the current refueling outage.

2.

Night Orders have been issued to Operations personnel following this event j

on the importance of attention to detail and performing proper reviews.

3.

The power supply label on the hydraulic unit was corrected and the remaining units were verified to be correct.

4.

The appropriate annunciator response procedures will be revised to incorporate direction pertaining to a loss of power.

This action will be completed by March 1, 1991.

5.

Additional training on the limitations of a trainee will be included in initial licensed operator training.

This will ensure that trainees do not participate in critical operational activities without the approprit.te supervisory oversight. This action will be completed by April 12, 1991.

6.

This event will be covered during licensed operator requalification.

Training will emphasize the importance of coordinatinB and sequencing problem investi ations, independent verification during identification of 6

components and plant operations policy regarding the use of trainees.

This action will be completed by May 25, 1991.

7.

Operational problem investigation of power supplies will be incorporated into the licensed and non licensed operator training programs. Revision to the lesson plans and appropriate training will be completed by November 15, 1991.-

HiAp has previously identified the need to separate the power supply for the pneumatic and electric hydraulic pumps. The design has been developed and is scheduled to be implemented during the current refueling outage for Unit 1 and the next refueling outage for Unit 2.

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ADDITIONAL INFORMATION

There have been two previous events, IIR 90 006 and IIR 90 023 for Unit 1, concerning a reactor trip due to inadvertent closure of a feedwater isolation valve.

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