05000265/LER-1978-030-03, /03L-0:on 780831,main Steam Line Radiation Monitor 2-1705-2D Failed Downscale.Caused by Instrument Drift & Elevated Chassis Ambient Operating Temp

/03L-0:on 780831,main Steam Line Radiation Monitor 2-1705-2D Failed Downscale.Caused by Instrument Drift & Elevated Chassis Ambient Operating Temp

ML20027A148
Person / Time
Site:	Quad Cities
Issue date:	09/26/1978
From:	COMMONWEALTH EDISON CO.
To:
Shared Package
ML20027A147	List: 05000265/LER-1978-030, Forwards LER 78-030/03L-0 05000265/LER-1978-030-03, /03L-0:on 780831,main Steam Line Radiation Monitor 2-1705-2D Failed Downscale.Caused by Instrument Drift & Elevated Chassis Ambient Operating Temp
References
LER-78-030-03L-01, LER-78-30-3L-1, NUDOCS 7810170202
Download: ML20027A148 (3)

LER-1978-030, /03L-0:on 780831,main Steam Line Radiation Monitor 2-1705-2D Failed Downscale.Caused by Instrument Drift & Elevated Chassis Ambient Operating Temp

Event date:
Report date:
2651978030R03 - NRC Website

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O 2 l On August 31, 1978 the Main Steam Line Radiation Monitor, 2-1705-2D, failed in a l

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o 3 l downschle condition. The other Main Steam Line Radiation Monitor in RPS channel l

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LER NUMBER: LER/R0 78-30/03L-0 11.

LICENSEE NAME:

Commonwealth Edison Company quad-Cities Nuclear Power Station Ill.

FACILITY NAME: Unit Two IV.

DOCKET NUMBER: 050-265 V.

EVENT DESCRIPTI0'N!

On August 31, 1978 at 2:00 a.m., the Main Steam Line Radiation Monitor 2-1705-2D failed in the downscale position. Un i t lix) was in the RUN mode operating at 780 MWe and 2465 MWt.

At 2:10 a.m.

the "B" Reactor Protection System (RPS), channel was placed in the tripped condition in accordance with procedure QOA 900-3-B-2, until repairs could be made under work request number 4005-78.

VI.

PROBABLE CONSEQUENCES OF THE OCCURRENCE:

The other main steamline radiation monitor in RPS channel "B" (2-1705-2B) and both radiation monitors in channel _"A" were operable during this occurrence and would have performed their intended func-tion if needed. The effected "B" RPS channel was placed in the tripped condition.

If a h?gh radiation condition had occurred, the "A" RPS channel radiation monitors would have tripped, causing a Group i Primary Contianment Isolation and reactor scram. No adverse safety implications were presented by this event.

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CAUSE

The cause of this occurrence is attributed to canponent failure. The downscale condition was due to Instrument drif t.

The radiation monitor was recalibrated and bench tested. During bench testing, it operated properly and no other malfunctions were found.

The downscale drif t of this Instrument was enhanced by higher than normal ambient temperatures in the control room where the chassis of radiation monitor 2-1705-2D is located. The high control room temperatures are of a temporary nature and are a result of work being done on the service building ventilation system, which is a major fire protection modification (M-4-1/2-76-11).

The 2-1705 zC rad!=tter, monitor was manufactured by the General Electric Company and is model number 194x629G7

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CORRECTIVE ACTION

The immediate corrective action was to place the RPS in the safe condition by tripping the "B" channel. The radiation monitor was then recalibrated and bench tested. The radiation monitor was reinstalled and procedure QlS 31-1, Main Steam Line Radiation -

Log Rad Monitor Chassis - S.T. 31A was performed. Under this pro-cedure the radiation monitor was calibrated and functionally tested satisfactorily.

• Fans have been placed in the control room panels to assure that a desirable ambient temperature is maintained until the new ventilation system is fully operable.

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