05000280/LER-1984-001, :on 840106,reactor Trip Occurred W/Unit at 100% Power.Caused by Over Temp delta-t Signal.Feedwater to Steam Generator a Isolated & Source Range Channels Manually Reinstated

:on 840106,reactor Trip Occurred W/Unit at 100% Power.Caused by Over Temp delta-t Signal.Feedwater to Steam Generator a Isolated & Source Range Channels Manually Reinstated

ML20116D674
Person / Time
Site:	Surry
Issue date:	04/11/1985
From:	Saunders R VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:
References
84-005A, 84-5A, LER-84-001, LER-84-1, NUDOCS 8504290512
Download: ML20116D674 (4)

LER-1984-001, on 840106,reactor Trip Occurred W/Unit at 100% Power.Caused by Over Temp delta-t Signal.Feedwater to Steam Generator a Isolated & Source Range Channels Manually Reinstated

Event date:
Report date:
2801984001R00 - NRC Website

text

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POW 28-06-01 seRC Fw.moe U.S. NUCLEAA REautATORY COsaseetsOss APPROVED OMS feo.3130-0104 LICENSEE EVENT REPORT (LER)

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, ii.i On January 6, a reactor trip occurred as a result of an Over Temperature Delta-T (0 PAT) signal.

Plant parameters did not indicate a valid OTAT condition.

At the time of the event, instrument technicians were performing a Periodic Test which required the ch II OTAT bistables to be in the trip mode, and maintenance was being performed on the plant Gaitronics (P. A. ) sys tem.

The Gaitronics system is powered from the Unit I Vital Bus I.

When the Gaitronics was re-energized, an apparent power surge occurred in the Gaitronics system.

The power surge is believed to have induced a voltage transient in Vital Bus I which resulted in tripping the relays for OTAT reactor trip ch I.

Since ch II was in trip at the time in order to support performance of P.T. 2.1, the 2/3 matrix was completed and as a result, a reactor trip occurred.

An analysis has been completed to evaluate the ef fects of the Gaitronics system on the vital instrument bus.

Maintenance procedures have been developed and hardware modifications are being evaluated.

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Description of the Event On January 6,1984 at 1324 hours0.0153 days <br />0.368 hours <br />0.00219 weeks <br />5.03782e-4 months <br />, with the unit at 100% power, a reactor trip occurred as a result of an Over Temperature Delta-T (OTAT) signal. Plant parameters did not indicate a valid OTAT condition at the time of the event.

At the time of the trip, instrument technicians were performing a Periodic Test (P.T. 2.1-0 TAT Tech ch II) which required the ch II OTAT bistables to be in the trip mode and maintenance was being performed on the plant Gaitronics (P. A.)

system.

Immediately following the reactor trip, operators noted all control and protection systems to function properly except for the isolation of the ' A' main feedwater line and the automatic reinstatement of the source range channels.

The 'A' feed regulation valve, FCV-FW-1478 (EIIS No. FCV), would not fully close and the under compensation of the intermediate range channel NI-36 (EIIS No. J1) prevented the source range from automatically reinstating.

Operators followed appropriate plant procedures and quickly stabilized the plant following the trip.

e 2.

Safety Consequences and Implications

The isolation of the feed reg. valves following a reactor trip in coincilence with low Tave or a Safety Injection minimizes excessive primary plant cooldown in the event of a steam line break. Source range channels,when reinstated, prevent any uncontrolled power increases during a reactor startup.

The main feed pumps would have tripped in the event of a Safety Injection Signal and would have provided the required feedwater isolation. Also, the source range channels were manually reinstated prior to resetting the reactor trip breakers.

In addition, all other safety related systems remained operable during the event and plant parameters remained within the bounds of the accident analysis. Therefore, this event did not constitute an unreviewed safety question nor affect the health and safety of the public.

3.

Cause

The cause of the reactor trip was due to an OTAT signal. At the time of the reactor trip, maintenance was being performed on the Gaitronics system, which is powered f rom Unit I Vital Bus I.

When the Gaitronics was re-energized, an apparent power surge occurred in the Gaitronics system. The power surge is believed to have induced a voltage transient in Vital Bus I which resulted in tripping the relays for OTAT reactor trip ch I.

Since ch II was in trip at the time in order to support the performance of P.T. 2.1, a 2/3 matrix was completed and as a result, a reactor trip occurred. In addition, the power surge in the Gaitronics tripped its feeder breaker on Vital Bus 1.

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PAGE (3) 5'R=t' vi*a SURRY POWE'R STATI ON, UNIT 1 0 l5 l0 l0 l0 l 2l8 l 0 g4 oj o lt olt ol 3 OF ol3 TEXT M more spece e reevned, esse eWoone/ hAC fome J66Nsl(171 tue 'A' feed reg. valve was due to a 1/2" nut discovered in The ma~'

the valve zu..nr, which had lodged between the valve plug and cage preventing complete closure.

The nut was not a part of the valve internals and its origin is not known. The failure of the automatia reinstatement of the Source Range Channels was due to the underco npensation of the intermediate range channel NI-36.

4.

Immediate corrective Action

Operators performed all appropriate Emergency Procedures and Function Restoration Procedures to ensure the plant was returned to a stable condition. This included isolating the feedwater to the "A" steam generator by closing isolation valve MOV-W-154A, and manually reinstating the source range channels.

Also, the STA performed the status tree reviews to ensure specific plant parameters were noted and the appropriate procedures were used to maintain those parameters within safe bounds.

5.

Additional Corrective Actions

The ' A' main feed regulation valve was disassembled and a 1/2" nut was observed and removed. Although no damage was noted, the valve cage, plug and stem were replaced with new parts from spares.

6.

Action Taken to Prevent Recurrence An analysis has been completed to evaluate the ef fects of the Gaitronics system on the vital instrument bus. Maintenance procedures have been developed and hardware modifications are being evaluated.

7.

Qn?.ric Implications None.

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49 April 11, 1985 vincrNia powen Surry Power Station P. O. Box 315 Surry, Virginia 23883 Serial No:

84-005A Docket No:

50-280 License No: DPR-37 U.S. Nuclear Regulatory Camission Document Caltrol Desk 016 Phillips Building Washington, D.C.

20555 Gentelmen:

Pursuant to Surry Power Station Technical Specifications, Virginia Power hereby subnits the following Licensee Event Report for Surry Unit 1.

REPORT NUfEER 84-001-01

'Ihis report has been reviewed by the Staticn Nuclear Safety and Operating Cmmittee and will be reviewed by Safety Evaluaticn and Control.

Very truly yours, R. F. Saunders Station Manager Enclosure cc: Dr. J. Nelson Grace Regicnal Administrator Suite 2900 101 Marietta St.reet, IM Atlanta, Georgia 30323 f6LL ll: