ML20084U093

Ro:On 720718,during Routine Calibr,Switch PS-3-263-55A Found to Have Drifted Beyond Limits of Instrument Accuracy. Cause Unknown.Valve History Shows Tendency for Setpoint to Drift Upward During Summer & Reverse in Winter

ML20084U093
Person / Time
Site:	Dresden
Issue date:	08/01/1972
From:	Worden W COMMONWEALTH EDISON CO.
To:	Bloch E US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084U094	List: ML20084U093 ML20084U098
References
NUDOCS 8306270049
Download: ML20084U093 (2)

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1 y Commonwealth Edison Company ONE FIRST NATOONAL PLAZA

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POST OFFICE SOX 767

• CHICACO, ILLINOl$ 40690 Dresden Nuc1 car Power Statioa ,

R. R. #1 qg Morris, Illinois 60450 *y y,y August 1, 1972 ..

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Mr. Edward J. Bloch, Acting Director i M Division of Reactor Licensing of),xI/

N'd D' U. S. Atomic Energy Commission '[,% "2

Washington, D.C. 20545 ~

Subject:

License DPR-25, Dresden Nuclear Power Station

_ Unit #3, Section 6.6.B.2 of the Technical Specifications

Dear Mr. Bloch:

This is to report a condition relating to the operation of the station in which, during the calibration, a reactor pressure scram switch was found to have drifted beyond the limits of instrument accuracy, resulting in a setpoint beyond that allowed in section 3.1 of the Technical Specifications.

_ PROBLEM AND INVESTICATION During routine calibration on July 18, 1972, switch PS-3-263-55A was found set at a value corresponding to 1075 psig, compared to the limit of 1060 psig increasing. The switch was immediately recalibrated. The switch, a meletron model 372-65549A-292, is a bourdon tube type, with 316 type stainless steel. The range is 28-1400 psig and accuracy is i 17..

A review of the calibration history of this switch and others like 4

it, shows an apparent tendency for the setpoint to drif t upward during the summer and downward during the winter.

CORRECTIVE ACTION The cause of the setpoint drift has not, as yet been determined. A spare switch will be purchased and installed so that one of the drifting switches Y Of p p p fuJ 8306270049 720801 PDR ADOCK 05000249 S

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'Mr. Edward J. Bloch August 1, 1972 I

can be removed and returned to the manufacturer for analysis. Meanwhile the calibration frequency of these. switches has been increased to monthly during the summer month 1, when drift is in the non-conservative direction.

Sincerely, u) .P. Ob -

W. P. Worden Superintendent JPW:sds i ,

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Mr. Edward J. Bloch, Acting Director Division of Reactor Licensing U. S. Atomic Energy Concission Washington, D. C. 20545 SUBJECI: LICENSE DPR-19 AND DPR-25, DRESDEN NUCLEAR POWER STATION UNITS #2 AND #3 SECTION 3.10F THE TECHNICAL SPECIFICATIONS. r

Dear Mr. Bloch:

m This is to report a condition relating to the operation of Units 2 and 3, in which on July 15, 1972, six of the eight " electrohydraulic control (EHC) oil low pressure scram switches" were found to have drif ted beyond the setpoints established it. the Technical Specifications.

PROBLEM During the routine calibration (every three months - Tech. Spec.

Table 4.1.2) the subject EHC switches were found to trip at setpoints ranging f rom 260 psig to 885 psig, compared to the limit of 900 psig decreasing.

This incident involved two of four switches on Unit #2 and all four switches on Unit #3. The switches were icnediately recalibrated and an investigation was begun to determine the cause of the drif t.

Switches: Barksdale Model TC-9622-3, dual control, weatherproof housing, diaphragm type, 7000 psig proof pressure, designed for hydraulic oil, water or air, 250-3000 psig range, 17. accuracy.

INVESTIGATION Inspections of the switch internals revealed that one switch had slight internal leakage, while the others displayed no apparent abnormalities.

The internal leakage had no effect on the setpoint. A review of the calibra-tion history of the switches showed a tendency to drift. The calibration procedure was reviewed and found to be satisfactory. The switches are cali-brated for a trip setpoint of 910 + 5 psig decreasing. A d9

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Mr. Edward J. Bloch

() () July 27, 1972 CORRECTIVE ACTION Because the reason for this large setpoint change is unexplained and because of the past tendency of these switches to drif t slightly, thev will be calibrated next conth rather than just functionally checked as required by the Technical Specifications. The one leaking switch will be replaced with a switch which has a setpoint range of 250-1500 psig. This certified switch, ordered from the Barksdale Co., is model TC-9622-2. The new switch will be cicsely observed for drif t and accuracy, and if it proves to have a better applicability to the system, all of the remaining i

switches will be replaced with 250 1500 psig setpoint range devices.

Sincerely, I c \ 3 hi,-s. -

W. P. Worden

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