05000277/LER-1985-016-02, :on 850826,full Scram & Primary Containment Isolation Sys Groups II & III Initiated Due to Reactor Low Level Signal.Caused by Failure to Ensure That Pressure Transmitter Returned to Svc from 850822 Event

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:on 850826,full Scram & Primary Containment Isolation Sys Groups II & III Initiated Due to Reactor Low Level Signal.Caused by Failure to Ensure That Pressure Transmitter Returned to Svc from 850822 Event
ML20132G817
Person / Time
Site: Peach Bottom Constellation icon.png
Issue date: 09/20/1985
From: Birely W
PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:
Shared Package
ML20132G754 List:
References
2-85-16, LER-85-016-02, LER-85-16-2, NUDOCS 8510010633
Download: ML20132G817 (3)
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LER-1985-016, on 850826,full Scram & Primary Containment Isolation Sys Groups II & III Initiated Due to Reactor Low Level Signal.Caused by Failure to Ensure That Pressure Transmitter Returned to Svc from 850822 Event
Event date:
Report date:
2771985016R02 - NRC Website
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Abstract:

2-85-16 On August 26, 1985, with Unit 2 at about 5% power, the reactor protection system initiated a full scram due to an inadvertent reactor low level signal.

Additionally, the primary containment

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isolation system initiated Group II and Group III isolations due to the same signal.

The event occ,urred wh'en a reactor pressure transmitter was being returned to service.

The scram signal and Group II and Group III isolations were reset and the affected systems were returned to service.

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..e, - u..m Description of the Event:

On August 26, 1985, at 12:14'a.m., with Unit 2 at about 5% power, a full scram was initiated by the reactor protection system (RPS) due to an inadvertent reactor low level signal.

Additionally, the Primary Containment Isolation System (PCIS) initiated Group II and Group III isolations as a result of the same signal.

RPS and PCIS responded properly.

The inadvertent signal was generated when reactor pressure transmitter PT-2-6-53B was being returned to service following replacement of the transmitter block valve.

The scram and Group II and Group III isolations were reset and.all affected systems were returned to service.

Consequences of the Event:

The reactor protection system logic and the primary containment isolation system operated properly.

This pressure transmitter provides pressure indication in the control room and has no safety function.

It should be noted that reactor pressure indicators PI-2-6-90A and 90C were both operational at the time of the event.

Therefore, there were no adverse consequences.

Ca0se of the Event:

On August 22, 1985, the block valve for reactor pressure transmitter PT-2-6-53B was determined to have excessive seat leakage as evidenced by an inadvertent scram during surveillance testing.

The block valve was replaced on August 24, 1985, and left in the closed position.

When the safety block for replacement of the. pressure transmitter instrument shutoff valve was removed, the tag on the instrument rack shutoff valve'was removed and that valve was opened.

However, the position of the instrument shutoff. valve that had been replaced was not checked, and therefore was left in the i

closed position.

This resulted in the pressure transmitter being left valved out.

The past practice of using a stamp on the L

permit to require that an instrument technician be contacted to r

return instruments to service was not followed.

The operator'who removed the safety block did not ensure that the pressure transmitter was returned to service.

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Reactor startup commenced on August 25, 1983.

During startup, the reactor operator observed that reactor pressure indicator PI-2-6-90B was not responding to increasing reactor pressure.

An instrument technician was dispatched to investigate the discrepancy.

The technician determined that the PT-2-6-53B block valve was' closed.

(PT-53B provides the input signal to PI-90B.)

Pressure immediately upstream of the block valv'e was reactor pressure'(600 psig).

Pressure downstream of the block valve, between the valve and the transmitter, was zero because this volume had been vented during the valve replacement.

The technician opened the block valve slowly to return the instrument to service.

Although the valve was opened slowly, a pressure spike occurred on the instrument rack.

PT-2-6-53B shares a sensing line with reactor level transmitters LT-2-2-3-101C and LT-2-2-3-101D.

These two level transmitters actuate the RPS and PCIS systems during a resctor low level condition.

The spike caused LT-101C and'LT-101D, which respond to pressures of the magnitude of inches of water, to generate low level signals.

Simultaneous low level signals from LT-101C and LT-101D generate a full scram and Group II and Group III isolations.

Corrective Actions

e The operator who cleared the permit was counseled on the proper return of equipment to service.

The practice of requiring that an instrument' technician be dispatched to return instruments to service af ter a safety block is cleared is being reinstituted as part of clearing a safety block.

Previous Similar Occurrences:

LERs 2-85-04 and 2-85-15 concerned an instrument rack pressure spike resulting in a full scram and Group II and Group III isolations.

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