ML20085J951

Ao:On 740427,after Rejection of Water Commenced,Torus Level Indication Increased.Operator Tapped on Impulse Lines of Transmitter & Indication Returned to Actual Level. Transmitter Calibr

ML20085J951
Person / Time
Site:	Dresden
Issue date:	05/06/1974
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20085J954	List: ML20085J951 ML20085J957 ML20085J960
References
326-74, NUDOCS 8310190235
Download: ML20085J951 (3)

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C:mmMalth Edison -

/ One First(_,'enat Plaza. Chicago. Ilhnois

. ((/)j Address Redly to:. Post Othee Box 767 s/ Chicago, libnois 60690 BBS Ler 9326-74 Dresden Nuclear Power Station

i. . R. R. #1 1 Morris, Illinois May 6, 1974 6045

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Mr. J. F. O' Leary, Director ch Directorate of Licensing So49 2 eg.N/* o' U. S. Atomic Energy Commission j,

, Washington, D. C. 20545 'g_

SUBJECT:

LICENSE DPR-25, DRESDEN NUCLEAR POWER STATION, UNIT #3, REPORT OF ABNOR1%L OCCURRENCE PER SECTION 6.6.B.1.s OF THE TECHNICAL SPECIFICATIOUS TORUS LOW LEVEL RESULTING FROM FALSE LEVEL INDICATION AND RESULTAh'T OPERATOR ACTION

References:

1) Notification of Region III of AEC Regulatory Operations Telephone: Mr. H. Dance,1105 hours0.0128 days <br />0.307 hours <br />0.00183 weeks <br />4.204525e-4 months <br /> on April 29, 1974 Telegram: Mr. J. G. Keppler,1330 hours0.0154 days <br />0.369 hours <br />0.0022 weeks <br />5.06065e-4 months <br /> on April 29, 1974

2) P&ID M-356

Dear Mr. O'imar,

v' This letter is to report a condition relating to the operation of the unit at about 2200 hours0.0255 days <br />0.611 hours <br />0.00364 weeks <br />8.371e-4 months <br /> on April 27, 1974. At this time, it was noted that the torus level indication had increased after rejection of water had commenced. The rejection of water had been initiated subsequent to receiving a high torus level alarm and indication.

This malfunction is contragy to section 3.7.A.1, which requires a minimum water volume of 112,000 ft in the torus.

PROBLEM 1

The unit was in the refuel mode with a water temperature of 80 0F when the high level alarm annunciated. This alarm initiates at -2". Shift personnel lined up the system to reject water to Unit 2/3 Radwaste and started the transfer. Af ter pumping approximately 4900 gallons to radwaste, it was noted that the level indication had increased to +1\". The level transmitter (2-1626) was found to be indicating incorrectly when the operator -

visually observed the torus level to be noticeably low. Visual observation was possible since the torus access hatches were open to the reactor building.

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Mr. J. F. O' Leary May 6, 1974 1

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The operator tapped the low point impulse line several times and the indication returned to actual level, which was -7". The shift immediately started refilling the torus to bring the status into cumpliance with the '

Technical Specifications.

An Instrument Mechanic was called in to calibrate the transmitter I to assure it was reading correctly. Calibration revealed proper indication and clear taps. The torus was filled to -3.5" by 0350 hours0.00405 days <br />0.0972 hours <br />5.787037e-4 weeks <br />1.33175e-4 months <br /> on the 28th.

At this point, the torus level was within compliance (Technical Specification range is -l%" to -Si") .

The level transmitter provides torus level indication on panel 903-3. It also annunciates a Hi/ Low level alarm on panel 903-3.

INVESTIGATION Prior to calibration, the impulse lines were checked to be clear.

The tapping by the operator had apparently vibrated the transmitter sufficiently to clear whatever had caused the false indication. The upper and lower taps were checked to be clear of obstructions by the Instrument Mechanic. Cali-bration of the indicator (transmitter) verified proper functioning at the time of calibration. The transmitter, manufactured by Barton.Co., had been calibrated two days prior to the occurrence. It was found to be indicating a

approximately h" low at this earlier calibration. The Lmpulse taps were checked clear at this time also.

J Investigation of the occurrence revealed that there was no physical reason for the initial high level alarm other than a transmitter problem.

Subsequent observation of an increasing level indication during rejection of water and correct indication after tapping the transmitter also indicate poor transmitter operation.

CORRECTIVE ACTION As mentioned, the transmitter was calibrated and the impulse legs were checked clear. There is presently no scheduled surveillance on the transmitter and procedures require operations to respond to the level indi-cation with no checks on level indication accuracy.

In the future, via a procedure revision and a modification, the operator will respond to a level alarm and/or improper level indication by visually checking level with a sight glass which he can readily valve in service at the transmitter. Operating's response will be based on both the remote and actual level indication. If there is a discrepancy between the two sets of data, an Instrument Mechanic will be immediately called in to correct the problem.

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Mr. J. F. O'L 3- May 6, 1974 The sight glass modification will be installed on both Unit 3 and Unit 2. The valving to be used for this modification is presently installed as part of the existing level sensing system. In addition to installation of the sight glass, tags will be placed on the valves indicating they are normally closed and should be opened only to check torus level under special circumstances.

A six month surveillance program requiring calibration of the transmitter will also be instituted. The surveillance will be started as of May 15, 1974.

EVALUATIONS i

Proper operation of the level transmitter had been verified two days prior to the occurrence. As indicated in the Technical Specifications Bases Section 3.7.A. "The pressure suppression chamber water volume must absorb the associated decay and structural sensible heat released during primary system blowdown from 1000 psig". The 10mits specified for torus level and temperature are based on the volume of reactor coolant to be condensed during a blowdown. The reactor mode switch was in refuel at the i

time of the occurrence with moderator temperature at 800F and the reactor cavity was flooded. Therefore, the ability to maintain core flooded and cool under accident conditions was not affected by this occurrence.

The action initiated by shift personnel and the Instrument Mechanic w'sas opptuptiaLu fut Line given conditions.

Since the same type of transmitter failure could occur during power operation, the corrective action indicated is mandatory. Lack of proper icvel indication would be intolerable under this condition. The installation of the sight glass and the procedure revision should eliminate any possibility of a similar occurrence.

There is no previous history of failure of this system. During startup tests on Unit 2, the level sensing system was revised to a closed type sensing transmitter to avoid evaporation of the reference leg.

This occurrence poses no reason for ILuiting future operation of Unit 2 or 3.

! Sincerely. -

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B. B Stephenson Superintendent i

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