ML20084Q192
| ML20084Q192 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 01/25/1974 |
| From: | Stephenson B COMMONWEALTH EDISON CO. |
| To: | Oleary J US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20084Q196 | List: |
| References | |
| BBS-74-18, NUDOCS 8306130162 | |
| Download: ML20084Q192 (2) | |
Text
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C:m rJth Edison I'
Quid-Generating Station V
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January 25, 1974
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.*'f Mr. John F. O ' Leary, Dire ctor Directorate of Licensing j
Regulation United States Atomic Energy Commission Washington, D.
C.
20545
Reference:
Quad-Cities Nuclear Power Station, Unit Two Docket f50-265, DPR-30 Appendix A, Sections 1.0.A.2, 3.1.1.B, and 6.6.B
Dear Mr. O ' Le ary :
The purpoce of this letter is to inform you of the details concerning an abnormal occurrence which took place on Jan-uary 17, 1974 whereby the setpoint of one high drywell pres-sure instrument drifted.
This abnormal occurrence was re-ported to you by telephone and telegram on January 18, 1974.
PROBLEM AND INVESTIGATION With Unit Two running at a steady state load of 780 MWe, routine calibration tests were being conducted on four high drywell pressure instruments which provide a reactor scram when drywell pressure reaches the instrument setpoint of 1.95 psig.
The setpoint of one of these four instruments (2-1001-88A) was found to be 2.05 psig.
This "as found" setpoint exceeded its limiting condition for operation.(Table 3.1.1.B) of < 2.0 psig.
Recalibration of the 2-1001-88A instrument was begun immediately with a new setpoint of 190 established.
EVALUATIO:I AND CORRECTIVE ACTION SAFETY IMPLICATIONS The failure of this pressure switch did not effect plant safety.
Instrument 2-1001-88A is an "A"
channel sensor in conjunction with 2-1001-88C.
The setpoint of this latter pressure switch and of "B" channel pressure switches 2-1001-88B and 2-1001-88D were found to be within their limit ng gil(
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L) l Mr. J. F. O' Leary January 25, 1974 condition for operation.
The 88C pressure switch in combina-tion with either one of "B" channel's pressure switches would have provided a reactor scram if high drywell pressure had l
occurred.
DETERMINATI0:I 0F CAUSE AND CORRECTI'E ACTION The exact cause of instrument drift is not known.
The in-volved switch is a Static-o-ring model 12N-AA5-PP.
The set-point of this switch was calibrated at 1.95 10*1 psig on Oct-ober 17, 1973 providing a.05 9318 instrument drift margin.
Functional tests using pressure of 3 psig were also performed on November 15, 1973 and Decemoer 22, 1973 with successful test results.
The reduction of the instrument setpoint ranging from.05 to.15 psig from the LCO setpoint on these pressure switches has significantly reduced the frequency of similar occurrences.
Consequently we do not consider j ustifiable a further reduction of the setpoint or an increase in the calibration surveillance requirement.
Hence, no further corrective action is being considered.
EVALUATION OF CUMULATIVE EXPERIENCE FOR SAFETY IMPLICATIONS Setpoints of instruments of this type have a tendency to drift occasionally.
Through continued surveillance recalibration and the existing setpoint margin for possible drift, occur-rences of this nature are expected to be minimal in severity and frequency.
This is reflected in the fact that this is the first such occurrence with this type pressure switch since the setpoint reduction from 2.0 psig on January 14, 1973 Very truly yours,
COMMONWEALTH EDISON COMPANY QUAD CITIES NUCLEAR POWER STATION
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Stephe' son Station Sup rintendent BBS/lk cc:
Regional Director Director of Regulatory Operations, Region III t
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