ML20085J827

Ao:On 740611,two Reactor High Pressure Scram Switches Found W/Setpoints Above Tech Spec Limit.Caused by Instrument Drift.Program in Progress to Precondition All Barksdale & Meletron Bourdon tube-type Switches

ML20085J827
Person / Time
Site:	Dresden
Issue date:	06/19/1974
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20085J829	List: ML20085J827 ML20085J832
References
441-74, NUDOCS 8310190114
Download: ML20085J827 (2)

Text

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~,,' Address hdy to: Post Oitce Box 767 Chicago I;hnois 60630 BBS Ltr.#441-74 Dresden Nuclear Power Station r is Illinois \

6045 [

June 19,1974 -

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4p*k.,g Mr. J. F. O' Leary, Director *A .

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Directorate of Licensing 50-2,49 / C)*~i. c'" x >'

U. S. Atomic Energy Commission A_ f-Washington, D. C. 20545

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SUBJECT:

_LICSUSE DPR-25, DRESDEN NUCLEAR POWER STATION, UNIT #3. REPORT

_OF ABNOR!'AL CCCURRENCE PER SECTION 6.6.B.1.a OF THE TECHNICAL SPECIFIGTIONS.

REACTOR HIGH PRESSURE.

References:

1) Notification of Region III of AEC Regulatory Operations Telephone: Mr. F. Maura, 1300 hours0.015 days <br />0.361 hours <br />0.00215 weeks <br />4.9465e-4 months <br /> on 6/12/74 Telegram: Mr. J. Keppler,1358 hours0.0157 days <br />0.377 hours <br />0.00225 weeks <br />5.16719e-4 months <br /> on 6/12/74

2) Dwgs: P & ID M-26 S & L 12E2464 l

n--c Mr. O' Leary:

This letter is to report a condition relating to the cperation of the unit at about 1000 hours0.0116 days <br />0.278 hours <br />0.00165 weeks <br />3.805e-4 months <br /> on June 11, 1974. At this ttme, tuo of the reactor high pressure scram switches were found with setpointst of 1064 psi and 1066 psi. This malfunction is contrary to Table 3.1.1 which requires y a setpoint of ,$_ 1060 psig.

PROBLEM At the time of the occurrence, Unit 3 was operating at a steady load of 460 ige. During reutine monthly surveillance of reactor high pressure switches PS3-263-55 A,B,C and D, switches A and C were found with setpoints of 1064 psi t and 1066 psi t respectively. These setpoints are above the Technical Specification limit .5,1060 psi. The switches were insnediately reset to 1048 psi and 1044 psi. The normal function of these switches is to provide a reactor scram if pressure reaches a value of 1060 psi.

INVESTICATION This violation of setpoint limit is-attributed to instrument drift. The switches are Heletron Model 372 pressure sensors with bourdon tube operators. The switches are very similar to the Barksdale Model 132T-AISS which has an inherent drift tendency. The vendor recocznend d My %5 8310190114 740619 PDR ADOCK 05000249 S PDR g h COPY SENf RiMION _ Zll _ h

f Mr. J. F. O'Lenry Jrne 19, 1974 1

fix for the Barksdale switch is to return it to the factory for pre-cycling.

All manufacturing and service for Meletron switches is now performed by the t j Barksdale Company. Therefore, the Meletron switches will be sent to Barksdale, Inc. for pre-conditioning.

l CORRECTIVE ACTION i

A program is presently in progress to pre-condition all Barksdale and Heletron bourdon tube type switches. The reactor high pressure switches will be pre-conditioned as soon as practicable. At this time, Unit 2 has 8 pre-cycled switches installed and Unit 3 has 4 pre-cycled switches installed.

j Eight more switches are now at the factory for pre-cycling.

l EVALUATION The switches in question are two of four which are connected in a "one out of two twice" logic configuration. This would have provided a scram at 1064 psi, which is only slightly above the 1060 psi Technical l Specification value. It is therefore concluded that the safety of the plant

{ personnel or the general public was not jeopardized as a result of this occurrence.

The cumulative experience with th::: switches.dae= not indicata that wuaw fanguem.s.llL .ilva vi it ..ld L. ?! a..y Lali,.

The cumulative experience of pressure switch drif t is inconclusive at this time because of lack of history, however, the vendor indicates that 3

lack of pre-cycling is the cause of the persistent drift problem at Dresden j

Station.

Sincerely, ,-

t /#

1 fB. B. r? W" Stephenson Superintendent BBS:WEH: do i

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