05000440/LER-1992-001, :on 920227,loss of Reactor Protection Sys Occurred.Caused by Failure of EPA Logic Board.Logic Board Was Replaced Following Satisfactory Calibration & 6 H warm-up Period

:on 920227,loss of Reactor Protection Sys Occurred.Caused by Failure of EPA Logic Board.Logic Board Was Replaced Following Satisfactory Calibration & 6 H warm-up Period

ML20094M504
Person / Time
Site:	Perry
Issue date:	03/27/1992
From:	Hegrat H CENTERIOR ENERGY
To:
Shared Package
ML20094M507	List: 05000440/LER-1992-001, :on 920227,loss of Reactor Protection Sys Occurred.Caused by Failure of EPA Logic Board.Logic Board Was Replaced Following Satisfactory Calibration & 6 H warm-up Period 05000440/LER-1992-002, :on 920228,pre-modification Cable Installation Was Declared as Violation of Integrity of Control Room Envelope.Caused by Failure to Identify pre-modification Activity.Controls Will Be Implemented 05000440/LER-1992-003, :on 920228,RWCU Isolation Occurred as Result of High Differential Flow.Caused by Deficiency Associated W/Sys Vioding Phenomenon.Ts Change to Increase Differential Flow Timer Setpoint Implemented PY-CEI-NRR-1472, Forwards Licensee Event Repts 92-001,92-002, & 92-003 for Perry Nuclear Power Plant
References
LER-92-001, LER-92-1, NUDOCS 9204010058
Download: ML20094M504 (4)

LER-1992-001, on 920227,loss of Reactor Protection Sys Occurred.Caused by Failure of EPA Logic Board.Logic Board Was Replaced Following Satisfactory Calibration & 6 H warm-up Period

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv), System Actuation
4401992001R00 - NRC Website

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. e _e e.,e.~.o-o., o m On February 27, 1992 the Reactor Protection System (RPS) distribution Bus B became deenergized, resulting in a Nuclear Steam Supply Shutoff System Balance of Plant isolation, along with a Reactor Vater Cleanup isolation. The operators responded in accordance with plant procedures to restore the affected systems.

The cause of this event was failure of an Electrical Protection Assembly (EPA) logic board. Troubles 30 ting resulted in spurious trips of the EPA under load conditions, and identified unsatisfactory reading for the trip and time delays settings, The RPS Motor Generator Set was determined not to be a factor in this event.

The faulty EPA logic board was replaced and, following a successful load test, the EPAs were returned to service.

The board is being returned to the manufacturer for failure analysis.

Additionally, this event vill be reviewed with licensed and nonlicensed operators as part of routine opera sr requalification training-9204010058 920327 DR ADOCK 05000440 PDR

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I. Introduction

On February 27, 1992 at 2148 the Reactor Protection System (RPS) [JC]

distribution Bus B became deenergized, resulting in Nuclear Steam Supply Shutoff System (NSSSS) fJH] Balance of Plant (BOP) isolation, along with a Reactor Vater Cleanup (RVCU) [CE] isolation.

At the time of the event, the plant was in Operational Condition 1 at 100 percent rated thermal power. The reactor pressure vessel [RPV) was at 1026 psig and saturated conditions.

At 0053 on February 28, the required n7n-emergency four-hour notification was made to the NRC pursuant to the requirenients of 10CFR50.72(b)(2)(li). This event is being reported under the requirements of 10CFR50.73(a)(2)(iv).

II. Event Description

At 1549 on February 27, 1992, the Reactor Protection System B Motor Generator [MG) and Electrical Protection Assemblies (EPAs) were declared operable following routine maintenance and implementation of a design change. At 2132, the RPS Bus B was shifted from its alternate power supply to the normal MG supply.

At 2148, an EPA trip resulted in a loss of RPS Bus B.

The loss of supply power to RPS trip channels B and D resulted in an Inboard BOP isolation and a RVCU isolation.

The operators reacted appropriately by entering Off-Normal Instruction (ONI-C71-2) " Loss of One RPS Bus".

RFS Bus B vas transferred to the alternate power supply at 2151. The BOP and RVCU isolations were reset at 2156.

The RVCU system was restarted at 2318 and ONI-071-2 was exited at 2337.

Troubleshooting on the system continued unti) 1930 on March 2, 1992 when the EPA logic board was replaced and calibrated.

Following a successful retest, the system was declared operable at 0020 on March 4, 1992.

III. Cause Analysis The cause of this event was failure of one of two EPAs provided for RPS Bus B MG set.

Prior to the event, the EPA logic boards had been replaced as part of preventive maintenance.

Additionally, at that time, design changes were made to the MG set to facilitate calibration and testing. To determine the cause of the event, the MG set was subjected to load changes while the voltage regulator performance was monitored; no problems with the MG set operation vere identified.

A normal plant load was then applied at the output of the suspect EPA.

Vith the MG set operating properly, the EPA spuriously tripped after approximately one hour.

In an attempt to calibrate the installed EPA it was energized for fivt hours, at which time the overvoltage and undervoltage trips and the undervoltage and underfrequency time delays were determined to be out of tolerance.

Additional sputious trips of the EPA vere noted when the simulated input was at the normal supply conditions of 120 volts AC and 60 hersz. Therefore, the troubleshooting concluded that the trip was not related to the MG set and the component responsible for the loss of RPS Bus B was the EPA logic board [CBD),

Gene *-1 Electric, model number 147D8652G001.

Following replacement of the logic board, the EPAs successfully completed a four hour load test and were returned to service.

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IV. Corrective Action

As described above, the EPA logic board was replaced following satisfactory calibration and a six hour varm-up period, and no further corrective r.ctions were necessary to return the system to service. To determine the exact cause of the logic board trip, the board is being returned to the manufacturer for failure analysis. Additionally, this event vill be revieved with licensed and nonlicensed operators as part of routine operator requalification training.

V. Safety Analysis

There are two EPAs in series between each source of power (a motot generator set and an alternate power transformer [XFMRj) and the issociated RPS bus.

Each EPA senses the supply voltage, and if voltage or frequency deviates beyond ret limits, the EPA vill trip open causing a loss of power to the respective bus.

Although the faulty EPA was demonstrated to be unreliable during this event, the redundant EPA remained operable and available to protect the RPS Bus.

In this event, all systems functioned as designed upon the loss of RPS power, including the appropriate NSSSS BOP and RVCU isolations received.

Operators acted appropriately and quickly to restore the systems.

Therefore, this event is considered to have no safety significance.

Previous losses of the RPS buses were reviewed for similarity to this event; no prior events within the past two years were related to EPA failures.

Additionally, no failures had occurred with newly installed EPA logic boards.

Energy Industry Identification System Codes are identified in the text as [XX].

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