ML20086R080

AO-S2-75-02:on 750110,channel 1 of Steam Generator C Level Instrumentation Indication Drifted Beyond Allowable Limits. Caused by Packing Leak at Isolation Valve.Replacement of Packing Will Be Performed as Necessary to Minimize Leakage

ML20086R080
Person / Time
Site:	Surry
Issue date:	01/24/1975
From:	Stallings C VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	Moseley N NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20086R082	List: ML20086R080 ML20086R096
References
AO-S2-75-02, AO-S2-75-2, NUDOCS 8402280681
Download: ML20086R080 (5)

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'$1' ;y Mr. Norman C. Moseley, Director Serial No.'410 Directorate of Regulatory Operations P06M/JTB:clw United States Nuclear Regulatory Commission Region II - Suite 818 Docket No. 50-281 230 Peachtree Street, Northwest License No. DPR-37 Atlanta, Georgia 30303

Dear Mr. Moseley:

Pursuant to Surry Power Station Technical Specification 6.6.B.1, the Virginia Electric and Power Company hereby submits forty (40) copics of Abnormal Occurrence Report No, j o.-S2-75 -02.

The substance of this report has been reviewed by the Station Nuclear Safety and Operating Committee and will be placed on the agenda for the next meeting of the System Nuclear Safety and Operating Committee.

Very truly yours,

. . (WNGOl C. M. Stallings Vice President-Power Supply and Producticn Operations Enclosures 40 copics of A0-S2-75-02 cc: Mr. K. R. Coller i

l 8402280631 750124 PDR ADOCK 05000281 sef f 1 l

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j 1044 00PY SENT REGION _

,s v ABNORMAL OCCURRENCE REPORT REPORT NO. A0-S2-75-02 STEAM GENERATOR LEVEL INDICATION JANUARY 20, 1975 DOCKET NO. 50-281 LICENSE NO. DPR-37 SURRY POWER STATION VIRGINIA ELECTRIC AND POWER COMPANY l

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I. INTRODUCTION In accordance with Technical Specification 6.6.B.1 for Surry Power Station, Operating License Number DPR-37, this report describes an ab-normal occurrence which was discovered on January 10, 1975. The Directorate of Regulatory Operations, Region II, was notified on January 10, 1975.

The occurrence reported herein is classified as an abnormal occurrence pursuant to Technical Specification 1.0.1.2 which states, "An abnormal occurrence is defined as: Any unit condition that results in violation of a limiting condition for operation as established in these Technical Specif ic a tions . "

The occurrence described herein resulted in a reduction of the minimum degree of redundancy for "C" steam generator 'evel reactor trips.

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SUMMARY

OF OCCURRENCE On January 10, 1975 with Unit No. 2 operating at approximately 800 MWe, channel I of "C" steam generator level instrumentation indication drif ted beyond allowable limits thereby rendering the channel inoperable.

Investigation revealed that a packing leak at the isolation valve to the level transmitter condensate pot had resulted in an erroneoue steam generator water level indication.

A similar occurrence happened severmi days later. On January 15, 1975 with Unit No. 2 operating at approximately 580 MWe, steam generator level transmitter LT-2-484, indicated 67 per cent, 23 per cent above the two remaining narrow range level transmitters. Investigation revealed a steam leak at the condensate pot' isolation valve between the bonnet and valve body. Indicated level held steady for close to two (2) hours,

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then fell to within a few per cent of the redundant channels.

III. ANALYSIS OF OCCURRENCE The steam generator level instrumentation is designeo to indicate 100 per cent at a minimum dif ferential pressure w'aen the reference leg level equals steam generator water level. Reference leg level is main-tained constant through use of a condensate pot. As steam generator water level drops, dif ferential pressure at the transmitter increases.

Conversely, as water level increases, differential pressure decreases.

A packing leak in an isolation valve to the condensate pot lowered the level in the reference leg, decreased the diff erential pressure sensed by the transmitter, and simulated an increase in the steam generator water level.

IV. CORRECTIVE ACTION TO PREVENT RECURRENCE The initial corrective action was to place the bistable switches in the trip mode. This re-instated the minimum degree of redundancy.

Packing leaks normally develop with time, and therefore adjustment or replacement of packing will be performed as necessary to minimize leakage.

l V. ANALYSIS AND EVALUATION OF SAFETY IMPLICATIONS OF THE OCCURRENCE 1

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Redundant steam generator water level signals are required to initiate

! a reactor trip. The minimum degree of redunJancy was not available for the short period of time when chanr.el I drif ted out of allowable limits.

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VI. CONCLUSIONS _

f The licensee concludes that:

1. Steam generator level transmitter LT-2-494 indication exceeded the limiting safety system setting.

2. Several days later, steam generator level transmitter LT-2-484 indication exceeded the limiting safety system settir.g.

3. The occurrences described herein resulted from a condensate pot isolation valve packing leak.

4. The occurrences described herein did not affect the safe operation of the station.

5. The occurrences described herein did not adversely affect the health or safety of the general public.

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