ML20084S647

AO 50-265/75-40:on 751016,while Performing Routine Surveillance,Three High Drywell Pressure Scram Switches Found to Exceed Tech Spec Limit.Apparently Caused by Instrument Drift.Pressure Switches Recalibr & Tested

ML20084S647
Person / Time
Site:	Quad Cities
Issue date:	10/24/1975
From:	Flasch M, Hooverson O COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20084S650	List: ML20084S647 ML20084S656
References
AO-50-265-75-40, NUDOCS 8306170146
Download: ML20084S647 (4)

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October 24, 1975 Director of Office of. Muclear Reactor Regulation .

U.S. Nuclear Regulatory Commission Washington, D. C. 20555 Refe rence: Quad-Ci ties Nuclear Power-Station

. Docket No. 50-265, OPR-30, Uni t 2 Appendix A, Sections 1.0. A.2, 3.1. A, Table 3.1.1.c, 6.6.1.B.a Enclosed please find Abnormal Occurrence Report No. A0 50-265/75-40 for quad-Cities Nuclear Power Station. This occurrence was previously reported to Region lil, Of fice of Inspection and Enforcement by telephone on Octo-ber 16, 1975 and to you and Region 111, Office of Inspection and Enforce-

. ment by telecopy on October 16, 1975 This report is submi tted to you in accordance with the requi rements of Techni cal Spect fication 6.6.B. I .a.

Very truly yours, COMMONWEALTH EDISON COMPANY QUAO-CITIES NUCLEAR POWER STATION

//fh J4' N. J. Kalivianakis ,

Station Superintendent NJK/MPF/lk ,

cc: Region lil, Of fice of inspection and Enforcement G. A. Abrell 190 l v t.

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o o REPORT NUMBER: A0 60-265/75-40 REPORT DATE: October 24, 1975 .

OCCURRENCE DATE: October 16, 1975 FACILITY: quad-Cities Nuclear Power Station Cordova, Illinois 61242 IDENTI FICATION OF OCCURRENCE: .

High drywell pressure switches PS-2-1001-88 A, B, and D out of calibration.

CONDITIONS RPRIOR TO OCCURRENCE:

Unit Two was shutdown for a core maintenance outage with the mode switch in RE FUEL.

DESCRIPTION OF OCCURRENCE:

While performing routine surveillance on October- 16, 1975 at approximately 1:00 p.m., three of the four high drywell pressure scram switches were '

. found to exceed the Technical Specification setpoint limit of ;c 2.0 psig.

The as-found setpoints were as follows:

FS 2-1001-88A 2 35 psig PS 2-1001-88B 2.15 psig PS 2-1001-880 2.20 psig DESIGNATION OF APPARENT CAUSE OF OCCURRENCE:

Equipment Fai lure The apparent cause of this occurrence is designated as Instrument drift.

The switch involved is a static-o-ring, Model 12N-AAS-PP. The setpoints were calibrated at 1.95 1 0.05 psig on September 9,1975 for PS 2-1001-88A and B and.on September 10,1975 for PS 2-1001-88D.

ANALYSl$ OF OCCURRENCE: -

l Pressure switches PS-2-1001-88 A through D are part of the Reactor Protection System one-out-of-two-twice logic. They provide a scram signal during a loss of coolant accident to minimize the energy which must be accomodated by the- 1 emergency core cooling systems and to prevent the reactor from going critical following the accident.

Since PS-2-1001-88A and C' are in Channel "A" and 'PS-2-1001-88 B ,and D are .

E in Channel "B" the. scram'would have occurred at a.drywell pressure of_2.15 j- psig rather that the' desired 2.00 psig. The effect .of this _ elevated trip f

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' #[0 50-265/75-40 .

Octob:;r 24, 1975 point on the functions described above is minimal because there are several other scram signals that would actuate prior to the drywell high pressure signal and thus accomplish the desi red scram. The health and safety of the pabile were not affected by this occurrence.

CORRECTIVE ACTION:

The corrective action involved an immediate recalibration and functional test of the affected pressure switches. This recalibration resulted in the following acceptable setpoints:

2-1001-88A 1.93 psig 2-1001-888 1.90 psig *

'2-1001-88D 1.90 o'sig FAILURE DATA:

Instrument setpo*nt dri f ts of the drywell high pressure sensors have occurred in the past. Through continued surveillance recalibration and the existing setpoint margin for possible drif t, occurrences of this nature are expected

. to be mininal in severi ty and frequency.

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