ML17252A943

Letter Reporting a 11/09/1973 Occurrence Relating to Discovery of the 2/3 Core Height Level Sensors LITS-263-73A and B to Be Out of Calibration - Dresden Unit 3

ML17252A943
Person / Time
Site:	Dresden
Issue date:	11/19/1973
From:	Worden W Commonwealth Edison Co
To:	O'Leary J US Atomic Energy Commission (AEC)
References
WPW Ltr. #862-73
Download: ML17252A943 (2)

Text

CommonwAh Edison One First Natio1"Plaza, Chicago, Illinois Address Reply to: Post Office Box 767 Chicago, Illinois 60690 Wl>W Ltr .11862- 73 Power Station 60450 Regul~tory Docket File

\~

NOV 211973 a>

Mr. J. F. O'Leary, Director REGULATORY

• 11 MAIL SECTION Directorate of Licensing DOCKET CLERK U. s. Atomic Energy Commisdon Washington, D. C. 20545

References:

l) Letter from W. P. Worden to A. Giambusso dated January 19, 1973 concerning same subject.

2) Notification of Region Ill of AEC Regulatory Operations Telephone: H. Dance 1550 hours0.0179 days <br />0.431 hours <br />0.00256 weeks <br />5.89775e-4 months <br />. on*November 9, 1973 T~legram: J. Keppler 1600 hours0.0185 days <br />0.444 hours <br />0.00265 weeks <br />6.088e-4 months <br /> on November 9, 1973

3) Dwgs: P & ID M-26(SF)

Dear Mr. O'Leary:

This letter is to report a condition relating to the operation of the unit at about 1600 hours0.0185 days <br />0.444 hours <br />0.00265 weeks <br />6.088e-4 months <br /> on November 9, I"'."\1973. At this time,. the 2/3 core height .water level sensors LITS-263-7L~ and.B were found to have setpoints above the Technical Specifica~i.on* of. !5;_257" decreasing.

This malfunction is contrary to Table 3.2.2 of the Technical Specifications which requires that the containment spray system be inter-locked to prevent operation if reactor level is at or below 2/3 of the core height.

PROBLEM During routine monthly surveillance of the ~/3 core height containment spray interlock level switches, LITS-263-73A and B, the setpoints were found to be 261" H20 dP and 262" H20 dP respectively.

The Technical Specifications require that these switches operate at

~257" H20 df. The switches were immediately set to 254. 5" H20 dP and 255.0" H20 dP. '

~

~

Mr. J. F. O'Leary November 19, 1973 INVESTIGATION The switches in question are Yarway number 4418EC devices. Past surveillance history indicates that they are normally very reliable devices which seldom drift. Switch LITS-263-738 was last calibrated on October 28, 1973 as a post maintenance check after a valve manifold was replaced. The switch setpoint was found to have drifted 9" after only 12 days. Therefore, it is concluded that an increased surveillance schedule will not guarantee consistant compliance with the Technical Specification setpoint.

Previous to this Technical Specification violation, LITS 3-263.-nA has failed four times since September, 1971 with the last failure occurring in January, 1973. Each month since January, the switch was found to be within Technical Specification limits. Switch LITS-3-263-738 has failed three times since September, 1971 with the last failure occurring -?ii August 3, 1972 when both switch A and B failed.

CORRECTIVE ACTION The switches were immediately reset to comply with Te.chnical Specification r~~}lirements. The problem now will be to determine the cause of this sp~radic change in setpoint. The following steps ,will be taken to resolve t.he problem. * * *

l. Consult the manufacturer for assistance in solving the problem.

2. Analyze the procedure used by the Instrument Mechanics who set the switches to determine if errors in technique are causing the problem.

EVALUATION Normal setpoint of these switches is 96/144ths core height.

The out of specification trip points would have been 91/144ths and 92/144ths.

For all practical purposes this is still 2/3 core height and therefore it is concluded that the safety of the plant personnel or the general public was not jeopardized as a result of this setpoint drift.

Sincerely,

~U,~-~~

W. P. Worden Superintendent WPW:do