05000278/LER-1987-001, :on 870317,reactor Scrammed from 85% Power on High Neutron Flux Signals from Neutron Monitoring Sys.Caused by Spurious Electrical Noise Due to Malfunctioning Cabinet Cooling Fans.Cooling Fans Replaced

:on 870317,reactor Scrammed from 85% Power on High Neutron Flux Signals from Neutron Monitoring Sys.Caused by Spurious Electrical Noise Due to Malfunctioning Cabinet Cooling Fans.Cooling Fans Replaced

ML20235T913
Person / Time
Site:	Peach Bottom
Issue date:	07/17/1987
From:	Birely W, Logue R PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
LER-87-001, LER-87-1, NUDOCS 8707220304
Download: ML20235T913 (5)

LER-1987-001, on 870317,reactor Scrammed from 85% Power on High Neutron Flux Signals from Neutron Monitoring Sys.Caused by Spurious Electrical Noise Due to Malfunctioning Cabinet Cooling Fans.Cooling Fans Replaced

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv), System Actuation
2781987001R00 - NRC Website

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3-87-01, Revision 1 On March 17, 1987 at 0254 hours0.00294 days <br />0.0706 hours <br />4.199735e-4 weeks <br />9.6647e-5 months <br />, Unit 3 scrammed:-from 85% power on high neutron flux signals from the neutron monitoring system.

The unplanned activation of an engineered safety

• feature makes this event reportable.

The high flux resulted from an increase l,

in reactor coolant system pressure caused by turbine control valve fluctuations.

Investigation indicated that circuitry in the Electrohydraulic Control System (EHC) was affected by spurious electrical noise believed to have been caused by malfunctioning cabinet cooling fans.

Philadelphia Electric Company investigations have determined that operators'were inatter.tive to instrumentation indications during the hours preceding the scram.

Five fans were electrically disconnected, 4 fann were replaced, and 4 EHC cards were replaced.

To prevent recurrence, the cooling fans in all 6 EHC electronics bays will be rep 2 aced, as'part of the1 preventive maintenance program, during every other refueling outage.

The operators onEduty during this event received counseling regarding the importance of attentiveness.

The operations staff received a letter from plant management, emphasizing the need to monitor various plant parameters and respond to deviations from normal conditions.

Other than the unit shutdown transient, there were no adverse consequences of this event.

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Acronyms Used in this LER:

I APRM - Average Power Range Monitor EHC

- Electrohydraulic Control System RPS

- Reactor Protection System Unit Conditions Prior to the Event:

Unit 3 was operating at 85% power.

Description of the Event:

l On March 17, 1987 at 0254 hours0.00294 days <br />0.0706 hours <br />4.199735e-4 weeks <br />9.6647e-5 months <br />, the reactor protection system initiated a full reactor scram due to high flux signals from the neutron monitoring system.

A description of the events which led to the high flux condition follows.

The reactor coolant system experienced pressure spikes for approximately 1-1/2 hours prior to the reactor scram.

Review of main control room instrumentation for this time period indicated that small fluctuations in various plant parameters occurred.

Plant control systems automatically compensated for these small oscillations.

None of these parameters reached alarm or trip setpoints before the scram.

These pressure spikes were caused by the control valves partially cycling due to oscillations in the valve positioning signals from the EHC system.

The increase in pressure introduced positive reactivity to the core by collapsing steam voids, thereby increasing the neutron flux level.

At 0254 hours0.00294 days <br />0.0706 hours <br />4.199735e-4 weeks <br />9.6647e-5 months <br />, the flux signals measured by the neutron monitoring system spiked from 85% to 100% and caused the reactor scram.

The high flux setpoint at 85% power is 100%.

The EIIS code for the EHC system is TG; and for the incore monitoring system (APRM), the code is IG.

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Consequences of the Event:

Aside from the unit shutdown transient, this event produced no adverse consequences.

The automatic scram led to a safe and j

orderly shutdown.

All cystems functioned properly during the i

transient.

Cause

.,f the Event:

4 Investigation of the event revealed that the control valves had 1

cycled partially opened and closed due to oscillations in the valve positioning signals from the EHC system.

Further investigation indicated that the mest likely.cause of the spiking signals was the ROTRON Type ST, Series 682YS, Spartan

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fans in the EHC electronics bays.

The fans, designed to run continuously, experienced mechanical failures due to age and normal wear.

The intermittent stopping and restarting of these l

fans is believed to have induced sufficient radio frequency l

electrical noise to affect the electronic cards, resulting in spikes in the signals to the turbine control valves.

The subsequent control valve movement produced the pressure spikes discussed in the " Description of Events" section, thereby causing the reactor scram.

l Corporate and plant management initiated an additional investigation of the events leading to the scram.

This i

investigation revealed that operators were not attentive to p] ant I

parameters during the hours preceding the event.

Corrective Actions

Pour faulty Spartan fans have been replaced with IMC Boxer fans, Model WS2107SL-1000, and five have been electrically disconnected.

As a precautionary measure, the following electronic cards in the EHC system were replaced and calibrated:

Card Nos. 54 and 71, Model No. 114D6005G4,

'A' and

'b' Pressure Amplification; and Card Nos. 42 and 46, Model No. Il8D1302G3,

'A' and

'B' Steam Line Resonance Compensator.

No further pressure spikes have been observed since these corrective measures were l

implemented.

Station technical personnel are continuing with an investigation while Unit 3 remains shutdown, and another revisionto ?)'

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1 will be submitted if additional information regarding the root cause is identified.

In addressing the issue of operator attentiveness, the individual operators involved received counseling regarding the importance of attentiveness.

The operations' staff received a letter from plant management, emphasizing the need to monitor various plant parameters and respond to deviations from normal conditions.

Action Taken to Prevent Recurrence:

To prevent recurrence, the " Spartan" f ans in all 6 EllC electronics bays will be replaced during every other refueling outage.

Previous Similar Occurrences:

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I PHILADELPHIA ELECTRIC COMPANY 2301 M ARKET STREET i

P.O. BOX 8699 PHILADELPHIA A PA.19101 (215)841 4000 July 17, 1987 1

Docket No. 50-278 U.S. Nuclear Regulatory Commission ATTN:

Document Control Desk Washington, DC 20555

SUBJECT:

Licensee Event Report Peach Bottom Atomic Power Station - Unit 3

{

I This revised LER concerns a full scram of Unit 3, due to i

high flux, caused by fluctuations in the main turbine electrohydraulic control system signals.

Reference:

Docket No. 50-278 Report Number:

3-87-01 Revision Number:

01 Event Date:

March 17, 1987 Report Date:

July 17, 1987 Facility:

Peach Bottom Atomic Power Station RD 1, Box 208, Delta, PA 17314 This LER was revised to include additional information regarding the cause of the scram and the corrective actions.

The changes are indicated by a vertical bar in the margin.

This LER is being submitted pursuant to the requirements of 10 CFR 50.73(a)(2)(iv).

Ver truly you,rs, i

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~f R. H.

Logue l

Assistant to the Manager l

Nuclear Support Department l

cc:

Mr. W.

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Russell, Administrator, Region I, USNRC T.

P.

Johnson, NRC Resident Inspector 7

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