05000254/LER-1979-034-03, While Adding Nitrogen to Suppression Chamber & After Decreasing Differential Pressure,Suppression Pool Level Noted Below Limit.Caused by Slow Response by Chamber Narrow Range Instrumentation

While Adding Nitrogen to Suppression Chamber & After Decreasing Differential Pressure,Suppression Pool Level Noted Below Limit.Caused by Slow Response by Chamber Narrow Range Instrumentation

ML19257C633
Person / Time
Site:	Quad Cities
Issue date:	01/18/1980
From:	Vahrenwald J COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19257C628	List: 05000254/LER-1979-034, Forwards Updated LER 79-034/03L-1 05000254/LER-1979-034-03, While Adding Nitrogen to Suppression Chamber & After Decreasing Differential Pressure,Suppression Pool Level Noted Below Limit.Caused by Slow Response by Chamber Narrow Range Instrumentation
References
LER-79-034-03L, LER-79-34-3L, NUDOCS 8001290518
Download: ML19257C633 (2)

LER-1979-034, While Adding Nitrogen to Suppression Chamber & After Decreasing Differential Pressure,Suppression Pool Level Noted Below Limit.Caused by Slow Response by Chamber Narrow Range Instrumentation

Event date:
Report date:
2541979034R03 - NRC Website

text

NRC FORM 366, U. S. NUCLEAR REGULATORY CCMMISSION (7 77)

LICENSEE EVENT REPORT UFOATE REPORT - PREVIOUS REPORT DATE 11-22-79 CONTROL BLOCK:

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While adding nitrogen to the suppression chamber and af ter decreasing the drywell-l g

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suppression chamber differential pressure from 1.48 psid to 1.23 psid, the suppress io[1 g

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Specification 3.7.A.I.b limit for suppression pool inventory.

Since the suppression l g

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The suppression chamber narrow range level instrumentation was slow in respondino I

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to a small change in suppression pool level, the readina of which was Cnmoounded bv I maintaining a differential pressure in the drywell and suopression chamber.

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Corrective action was to add more water to the suppression pool, bringing the level I

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7 8 9 to 68 69 80 5 NAME OF PREPARER PHONE:

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LER NUMBER:

LER/R0 79-34/03L-0 11.

LICENSEE NAME: Commonwealth Edison Company Quad-Cities Nuclear Power Sta tion Ill.

FACILITY NAME: Unit One IV.

DOCKET NUMBER: 050-254 V.

EVENT DESCRIPTION

On October 30, 1979, while adding nitrogen to the suppression chamber and after decreasing the drywell-suppression chamber differential pressure from 1.48 psid to 1.23 psid the suppression pool level was observed to be approximately 3/8 inches below the Technical Specification 3 7.A.I.b limit for suppression pool inventory.

VI.

PROBABLE CONSEQUENCES OF THE OCCURRENCE:

The safety implications of this event were minimal.

Since the suppression pool tempera ture was modera te (85 F) and because the limits for suppression pool level are conservative, the pressure suppression system was always available and would have performed as designed. All other pressure suppression and emergency cooling systems were available.

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CAUSE

The instrumentation used for measuring narrow range suppression pool level is sometimes slow in responding to small changes in pool level as in the case of this report.

The reading of the instrument is also compounded by maintaining a drywell-suppression chamber differential pressure.

A small increase in drywell pressure will cause tne water in the downcomers to be forced into the pool inventory and subsequently raise the pool level. A small decrease in drywell pressure will result in a small decrease in pool level.

These small variations inherent to the level instrumentation do not af fect the safety factors which have been established, nor in any way jeopardize safe plant operation.

The suppression, cool level is closely monitored to assure that the proper level is maintained.

In addition, it was not until a change in drywell to suppression chamber differential pressure was initiated that the control room level indicator showed slightly less than the required level.

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CORRECTIVE ACTION

The immediate corrective action taken was to add water to the suppression pool bringing the level within the Technical Specification limits.

The inability of the suppression pool level instrumentation to always promptly respond to small

))}f[{ changes in pool level has been acknowledged in the past. At present an erfort is being made to evaluate the instrument design to determine the feasibility of improving the instrument by adding a more advanced electronic package to the existing instrument configuration. }}