ML20084Q387
| ML20084Q387 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 11/19/1973 |
| From: | Stephenson B COMMONWEALTH EDISON CO. |
| To: | Oleary J US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20084Q390 | List: |
| References | |
| BBS-73-243, NUDOCS 8306130247 | |
| Download: ML20084Q387 (3) | |
Text
O Comm e lth Edisen C
Outd-Cities Generating Station
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Post Office Box 216 Cordova, Illinois 61242 Telephone 309/654-2241 0
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$f November 19, 1973 Mr. John F. O' Leary, Director Directorate of Licensing U. S. Atomic Energy Commission Washington, D. C. 20545
Reference:
Quad-Cities Nuclear Power Station, Unit One Docket No. 50-254; DPR-29 Appendix A, Sections 1.0. A.2, 3 2. A, and 6.6.B
Dear Mr. O' Le ary :
The purpose of this letter is to inform you of the details concerning an abnormal occurrence which took place on Nov-ember 9,1973, whereby the setpoint of three Primary Contain-ment Isolation System instruments drifted.
This abnormal occurrence was reported to you by telephone and telegraph on November 9, 1973 PROBLEM AND INVESTIGATION During the day shift hours on November 9,1973, with the Unit One reactor in the Hot Standby mode, routine calibra-tion of the sixteen main steam line differential pressure switches which monitor flow was conducted.
The setpoints of three of these switches were found to exceed the limiting condition for operation (Te ch Spec Table 3.2.1. ).
The three switches in question and their "found" setpoints are as follows:
DPIS No.
Setpoint Location 1-261-2G 110 PSID "B" Steam Line 1-261-2J 109 5 PSID "C" Steam Line 1-261-2M 109 5 PSID "C" Steam Line A setpoint of 109 PSID has the equivalent of 120 percent flow.
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Mr. J. F. O ' Le ary November 19, 1973 Recalibration of these switches was undertaken immediately with the following new setpoints established.
DPIS NO.
SETPOINT 1-261-20 105 5 PSID l-261-2J 105 5 PSID l-261-2M 106.5 PSID EVALUATIONS AND CORRECTIVE ACTIONS SAFETY IMPLICATIONS The failure of the above mentioned pressure switches did not effect plant safety.
With all other pressure switches operable, isolation would have occurred if high flow was experienced.
DPIS 1-261-2G is the "A" channel sensor on the "B" steam line.
Isolation would have occurred with the other three correctly set pressure switches.
DPIS 1-261-2J is located on "C" steam line and is the input for RPS channel "A" and DPIS 1-261-2M is on the same steam line but in RPS channel "B".
The two re-maining-pressure switches would have been sufficient to isolate the "C" steam line at less than 120% flow.
DETERMINATION OF CAUSE AND CORRECTIVE ACTION The exact cause of instrument drift is not known and an inves-tigation by Commonwealth Edison is continuing.
The involved
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switches are Barton model 278.
The setpoints of these and all other similar instruments were recalibrated to 107 !o psid in January 1973, thus providing at least-2 psid margin for-the instrument drift.
The reduction of the instrument setpoint
'by 2 psid from the LCO setpoint has significantly reduced the frequency of similar incidents.
Consequently we do not consider justifiable a further reduction cf the setpoint or an increase in calibration surveillance requirement.
Hence, no further j
corrective action is being considered.
EVALUATION OF CUMULATIVE EXPERIENCE FOR SAFETY IMPLICATIONS Setpoints of instruments of this type have a tendency to drift occassionally.
Through continued surveillance recalibration and the existing setpoint margin for possible drift, occurrences of this nature are expected to be minimal in severity and
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Mr. J. F. O ' Le ary November 19, 1973 e
frequency.
The only other occurrence since the setpoint change to 107 psid was reported in my letter of March 6,1973 That event also included a drift of no more than one psi on the instrument switches.
Very truly yours, COMMONWEALTH EDISON COMPANY QUAD CITIES NUCLEAR POWER STATION
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B. B. Step nson Station S erintendent BBS/lk i
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Regional Director Directorate of Regulatory Operations - Region III O
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