ML17252A976

Letter Reporting a 05/15/1973 Occurrence Relating to the Isolation Condenser High Condensate Flow Switch DPIS-3-1349-B Was Found to Actuate at a Differential Pressure of 32.7 Inches of Water - Dresden Unit 3

ML17252A976
Person / Time
Site:	Dresden
Issue date:	05/25/1973
From:	Worden W Commonwealth Edison Co
To:	Giambusso A US Atomic Energy Commission (AEC)
References
WPW Ltr. #407-73
Download: ML17252A976 (2)

Text

• Dresden Nuclear Power Station

-~* R. #1 Morris, Illinois 60450 WPW Ltr. #407-73 May 25, 1973 Mr. A. Giambusso 50-249 Deputy Director for.Reactor Projects Directorate of Licensing U. S. Atomic Energy Commission Washington, D.C. 20545

SUBJECT:

LICENSE DPR-25, DRESDEN NUCLEAR POWER STATION, UNIT #3, S~TION 6.6.B.2 OF THE TECHNICAL SPECIFICATIONS.

Dear Mr. Giambusso:

This is to report a condition relating to the operation of the unit, in which, during routine calibration of the isolation condenser high conden-sate flow switch DPIS-3-1349~B the setpoint was found to exceed the value specified in Table 3. 2 .1 of the Technical Specifications.

PROBLEM AND INVESTIGATION On May 15, 1973, during a* routine calibration, the isolation conden-ser high condensate flow switch DPIS-3-1349-B was found to actuate at a differ-ential pressure of 32.7 inches of water. The Technical Specification limit as set forth in Table 3.2.l for the high condensate flow switches is c:::. 32 inches of water. The high condensate flow switches have a range of 0 to 60 inches of water and an accuracy specification of +/- 4% of full scale.

CORRECTIVE ACTION This switch last exhibited excessive drift on September 22, 19~.

At that time the setpoint was lowered from30 +/- 1 inches of water to 2B.5 +/- l inches of water to increase the range* to prevent the switch from drifting above the Technical Specification limit. On February 7, 1973~ a locking de-Vice was installed to also help prevent the drifting situation. Since the switch is still drifting beyond allowable limits, further action* is warranted.

The station procedures will be changed to require calibration ad,justment to_

27.5 + 1 inches of water for both switches in the condensate return line.

This action will furth~r increase the range to prevent the switch from drifting above limits. Also, calibration of the switches will be performed monthly rather than once every three months as listed in Table 4.2.l of the Technical Specifications.* These corrective actions will remain in effect while an iil-vestigation is conducted to determine the cause of the problem. The investi-gation will take approximately six months. This corrective action only applies to unit 3 since unit 2 switches have not exhibited this problem.

Two sensors (DPIS~3-1349 A & B) on the isolation condenser return line are provided to detect the failure of the isolation condenser line and actuate.

isolation action. The sensors are arranged .in a 1 out of 2 logic to meet the single failure criteria'Q. 0 The trip:setting and valve closure time are such as to.prevent uncovering the core or exceeding site limits. Thene are no implications or effect on the safety or public health because the redun-dant switch (DPIS-3-1349-A) would have actuated within the Technical Speci-fication limit. This switch actuated at 29.4 inches of water during the routine calibration.

Since the locking devices have been installed on si.Milar switches on units 2 & 3, this has been the first failure. Therefore, it is believed to be an isolated occurrence. These changes should prevent future recurrence of dri~ beyond Technical Specification limits in the subject switch.

W. P.*. Worden

. Sil!>E!rihtendent

, -S' Dre.Sci en Station

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