ML20084L644

AO-50-237/1974-38:on 740805,torus Water Level Found to Be Below Specs.Caused by Mechanical Failure of Water Level Instrumentation.Sight Glasses for Verifying Torus Level Will Be Installed

ML20084L644
Person / Time
Site:	Dresden
Issue date:	08/14/1974
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20084L651	List: ML20084L644 ML20084L655
References
582-74, NUDOCS 8305230589
Download: ML20084L644 (3)

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m i',,g) c:mnwnith Edis:n One Fm s stional P!aza. Chicago. tilinois (.,

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b Address fleply to: Post Office Box 767 L'-

Chicago, IHinois 60690 ,

BBS Ltr.#582-74 Drcsden Nuclear Power Station R. R. #1

. Morris, Illinois 60450 August 14, 1974 gyy '

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Mr. James G. Keppler, Regional Director ([5 b$

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Directorate of Regulatory Operations-Region III U. S. Atomic Energy Commission ( h ,N.p pen g/

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799 Roosevelt Road \('N 6 p,i, jh Clan Ellyn, Illinois 60137 C#

Y[I'7'I SUBJECI: PEPORT OF ABNORMAL OCCURRENCE PER _SECTION 6.6.B OF THE TECHNICAL SPECIPICATIONS.

TORUS UATER LEVEL IN EXCESS OF TECHNICAL SPECIFICATION LIMITS.

References:

1) Regulatory Cuide 1.16 Rev.1 Appendix A

2) Notification of Region III of AEC Regulatory Operations Telephone: Mr. F. Maura,1615 hours0.0187 days <br />0.449 hours <br />0.00267 weeks <br />6.145075e-4 months <br /> on August 6,1974 Telegram: Mr. J. Keppler, 0820 hours0.00949 days <br />0.228 hours <br />0.00136 weeks <br />3.1201e-4 months <br /> on August 7,1974

3) Drawing Number M-25 Report Number: 50-237/1974-38 Report Date: August 14', 1974 Occurrence Date: August 5, 1974 Facility: Dresden Nuclear Power Station, Morris, Illinois I_DE?frIFICATION OF OCCURRENCE Dresden Unit 2 torus level was found to be at -6.5 inches, which is one inch below the -5.5 inch limit as _ described in the Technical Specifi-cations.

CONDITIONS PRIOR TO OCCURRENCE Unit 2 was operating at a steady load of 636 MWe. No testing or surveillance was in progress.

-DESCRIPTION OF OCCURRENCE At 1337 hours0.0155 days <br />0.371 hours <br />0.00221 weeks <br />5.087285e-4 months <br /> on August:5,1974 a " torus hi/lo level" alarn was sounded on Dreaden Unit 2. The . operator of Unit 2 read the torus level indicator in the control room and estimated the level at -2.2 inches. The h

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Mr. James G. Ke or August 14, 1974 indicator has a range of 50 inches, with the smallest division being one inch.

The alarm is. net to sound at approximately -2 inches. The characteristics of the alarm contacts are such that an exact number cannot be obtained. The shif t supervisor then requested that an instrument mechanic verify actual torus level by connecting transparent tubing to the torus level sensing lines.

The instrument mechanic failed to reference the top of the tubing to the torus

. pressure, and therefore received an erroneous level reading. The reading of

+1.6 inches was reported to the shif t engineer, and a decision was made to begin puuping down the torus. At 0255 hours0.00295 days <br />0.0708 hours <br />4.21627e-4 weeks <br />9.70275e-5 months <br /> on August 6,1974, the torus had been pumped down to a level of -4 inches, as erroneously indicated by using the transparent tubing vented to atmosphere. At approximately 1300 hours0.015 days <br />0.361 hours <br />0.00215 weeks <br />4.9465e-4 months <br /> on August 6,1974, the error was discovered by an instrument supervisor. Work was immediately initiated to properly install the transparent tubing. The task was completed at 1702 hours0.0197 days <br />0.473 hours <br />0.00281 weeks <br />6.47611e-4 months <br /> on August 6,1974 and the actual level of

-6.5 inches was observed. The shift immediately began to add water to the torus and level was again within specifications (-2 inch) at 2000 hours0.0231 days <br />0.556 hours <br />0.00331 weeks <br />7.61e-4 months <br /> on August 6, 1974.

DESICHATION OF APPARElrP CAUSE OF OCCURPINCE Operator Error The cause of this error was failure of instrument mechanic to properly measure the torus water level. All instruments functioned properly until improperly adjusted to match erroneous torus level reading.

ANALYSIS OF OCCURRENCE The level of the Unit 2 torus was below the Technical Specification by only one inch, for a period of approximately twelve hours. The torus diameter is 30 feet, and the normal level is between 1.5 and 5.5 inches below the conter line. Therefore, the loss of one inch in 14 feet 6 inches is a small percentage. Adequate water was available in storage tanks at all times and could have been added to the torus if needed. Therefore, it is concluded that the public and plant safety was in no way compromised during this abnormal occurrence.

CORRECTIVE ACTION Prior to this occurrence, a modification had been initiated and approved to install sight glasses for verifying torus level on both Dresden Unit 2 and 3. The modification will be installed as soon as the materini is roccived f rom purchasing. The procedure which outlines the action to be taken when a torus hi/lo level annunciator is sounded is approved and will be followed upon completion of the sight glass modification. In addition, l another modification has been proposed to provide another alarm circuit l independent of the present level transmitter. This would prevent a calibra-I tion error from invalidating all level and alarn indication available, t

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Mr. Jr:cos G. K er August 14, 1974 es FAILURE DATA This occurrence was not a result of equipment failure, but one of operator error and lack of. redundent instrumentation.

Sincerely,

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fh2iucw BI B./Stephenson Superintendent BES:WEH:do 1

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