ML20084J577
| ML20084J577 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 12/01/1972 |
| From: | Stephenson B COMMONWEALTH EDISON CO. |
| To: | Anthony Giambusso US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20084J579 | List: |
| References | |
| BBS-72-9, NUDOCS 8305180251 | |
| Download: ML20084J577 (3) | |
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Comm<h Edison d
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Outd CitmuclearPowirS> tion W
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Post Office Box 216 p',.
Cordova,liknois G1242 Tolophone 309/654-2241 BBS-72-9 4
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.J December 1, 1972 5
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,S Mr. A. Giambusso
' N,,t" Deputy Director for Reactor Projects Directorate of Licensing U.S. Atomic Energy Commission Washington, D.
C.
20545
Reference:
Quad-Cities Nuclear Power Station Unit 2, License DPR-30 Appendix A Sections 1.0.A.2, 31, 3.2.A, and 6.6.B.3
Dear Mr. Giambusso:
The purpose of this letter is to inform you of the details concerning the drif t in trip level settings of two reactor protection system instruments and two primary containment isolation system instruments.
This abnormal occurrence was reported to you by telegram on November 21, 1972.
On November 18, 1972, routine quarterly calibration was performed on the Unit 2 condenser vacuum and main steam line pressure switches in accordance with Technical Specification surveillance requirements.
Condenser Low Vacuum pressure switches P_S 2-503A and PS 2-503D were found to have drif ted to trip set tings of 22 3" Hg -end-2Brk" Hg respectively.
The specified trip level setting in section 3.1 of the Technical Specifications is 2 23 0" Hg.
These switches are Barksdale Model DIT-H185S and have an accuracy of i 0 3"Hg.
The setpoints of the two switches were adj usted and lef t at 23 0"Hg.
g The trip level settings on Main Steam Line Low Pressure switches PS 2-261-30A and PS 2-261-300 were found to have drifted to 838 psig and 844 psig respectively.
The setpoint of these switches is 856 psig which includes a 6 psi head correction to the setting of > 850 psig required by the Technical Specifications.
These switches are Barksdale Model B2T-A12SS and have an accuracy of i 8 psig.
8305180251 721201
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Mr. A. Giambusso December 1,1972 The drift of these instruments is not considered to be of major safety significance.
The low vacuum scram is a backup to the turbine stop valve antici-patory scram.
It also limits the severity of a loss of vacuum incident where the turbine would trip at 20" and bypass valves would eventually close at 7" Hg vacuum.
A review of the "as found" setpoints of instrument channels B and C indicates that the reactor would have scrammed at 22.95" Hg vacuum.
Even if a scram did not occur until vacuum reached 22.3" Hg, this would still be well before any reactor transient begins due to a subsequent turbine trip.
The function of the 850 psig isclation is to protect against a rapid reactor depressurization and cooldown.
The difference between a setpoint of 838 psig and 856 psig is equivalent to about 2-1/2 degrees F.
In telephone conversations with Region III Compliance on November 21, 1972, we were informed that all instrument setpoints listed in the Technical Speci-fications should be considered as absolute regardless of any previous understandings and that no instrument drift beyond these valves is allowed whatsoever.
We anticipate reporting numerous instrument drift occurrences to your office in the next few months as our corrective action program outlined below is being implemented.
This is due to the fact that all of our instruments are set to actuate at the exact valve given by the Technical Specifications.
CORRECTIVE ACTION The following corrective action program is planned:
1.
The trip settings of all instruments governed by the Technical Specifications are being reviewed by the Station Technical Staff.
The goal of this review is to recommend new set points to-the Station Review Board which would allow the instruments to drift within their specified accuracy, but not exceed the absolute Technical Specification value.
Consideration will also be given to known drift problems based on experience at Quad-Cities and Dresden.
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Mr. A. Giambusso December 1,1972 2.
The Station Review Board will review the
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g recommended setpoints and authorize changes j
in accordance with the Station Administrative d
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Procedures.
All instruments will be calibrated I
with the new setpoints by February 1,1973 3.
The frequency of calibration will then be increased on those instruments which continue
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to drift beyond the absolute value in the Technical Specifications.
11.
As of November 21, 1972 all occurrences of L
instrument drift beyond the absolute value
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in the Technical Specifications are being
[N reported immediately in accordance with 1
Section 6.6. A and B of the Specifications, j
5 Instrumentation surveillance conducted during
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November,1972 will be reviewed and all instruments which drifted beyond the absolute value in the Technical Specifications will be reported to you by letter.
An additional review of past "as found" setpoints will be used to eva'ulate drift tendencies.
__q Very truly yours, COMMONWEALTH EDISON COMPANY b
Quad-Cities Nuclear Power Station
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tep[bnson Superintendent BBS/zm I!
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