ML17252B039
| ML17252B039 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 05/31/1974 |
| From: | Stephenson B Commonwealth Edison Co |
| To: | O'Leary J US Atomic Energy Commission (AEC) |
| References | |
| BBS Ltr.#391-74 | |
| Download: ML17252B039 (2) | |
Text
50-249 e
Commonwea&dison
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One First National Plaza, Chicago, Illinois
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- Address Reply to: Post Office Box 767 Chicago, Illinois 60690
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BBS Ltr.1391-74
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- Dresden Nuclear Power Station Regulatory Docket Ale U~~~l9~4 l :f
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-POcir.-' -~ Tf:ON Mr. J. F. O'Leary, Direc Directorate of Licensing
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U. s. Atomic Energy Commission Washington, D. c.
20545
SUBJECT:
LICENSE DPR-25, DRESDEN NUCLEAR POWER STATION, UNIT #3, REPORT OF ABNORMAL OCCURRENCE PER SECTION 6.6.B.l.a OF 'l1IE TECHNICAL SPECD'ICATIONS.
2/3 CORE COVERAGE INSTRUMENT DRD'T.
References:
l) Letter from W. P. Worden to Mr. J. F. O'Leary dated November 19, 1973 concerning.same subject;
- 2) Notification of Region III of AEC Regulatory Operations Telephone: Mr. F. Maura, 1345 hours0.0156 days <br />0.374 hours <br />0.00222 weeks <br />5.117725e-4 months <br /> on May 24, 1974.
Telegram: Mr. J. Keppler, 1353 hours0.0157 days <br />0.376 hours <br />0.00224 weeks <br />5.148165e-4 months <br /> on May 24, 1974.
- 3).Dwgs: P&ID M-26 S&L l2E3437
Dear Mr. O'Leary:
This letter is to.report a condition relating to the operation of the unit at about 1600 hours0.0185 days <br />0.444 hours <br />0.00265 weeks <br />6.088e-4 months <br /> on MBy 23, 1974 *.
- At this. time, the 2/3 core height water level sensor LITS 3-263-73A was found* to have-a setpoint above the Technical Specification limit of ~ 257" of water differential-pressure decreasing.
This malfunction is contrary to table 3.2.2 of the Technical Specifications which requires that the containment spray system be inter-
- locked to prevent operation if reactor level is at or below 2/3 of the core height
- PROBLEM During routine monthly surveillance of the 2/3 core* height con-tainment spray interlock level switches LITS-263-73A and B, switch "A" was found with a setpoint of 259" H20 differential pressure decreasing. The switch was immediately set to 254. S" H20 differential pressure decreasing.
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Mr. J. P. O'Leary
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INVESTIGATION
- May 31, 1974 The switch in question is a Yarway number 4418EC device.
Past surveillance history shows that the switch has been found out of specif ica-tions seven times iD the past four years.
The switch setpoint is normally observed every month, during calibration and functional surveillances.
The manufacturer (Yarway) has been consulted concerning the drift problem and bas identified five possible sources of setpoint drift. The procedure used by the Dresden Instrument *Mechanics has been analyzed by Yarway Corporation and.has been described as "acceptable".
CORRECTIVE ACTION Level switch.LITS 3-263-73A was immediately reset to comply with the Technical Specifications.
The corrective action to resolve the drift problem will be to replace the magnet, spring, and mercury switch on LITS 3-263-73A and B.
These parts were identified by the manufacturer as a source of setpoint drift. Proper installation of the above.parts will ensure that all five possible problem areas pointed out by the manufacturer are corrected.
Other similar switches do not need this repair due to their more reliable nature.
EVALUATION Level swit_ch LIT~.,3-263-73A is normally set at. 96/144ths core height. The"out of. specifi~~tion trip point _would have.bee~*.. 94/144ths.*
core height.
The function< of the' 8.ensors.is.'..to.. provide *a periniss ive to allow the.use of thE!' contaiilment spray system.
Station abnormal procedures state that the reactor vessel level be normal prior to utilizing the LPCI system in *the containinent cooling mode.
Even though the setpoint for loop "A" interlock was low, the operator would have verified the vessel level before manually initiating containment cooling. Therefore, this situation did not present a safety hazard to either the plant personnel or the general public *.
The.cumulative experience to date indicates that Yarway level sensors are normally very*reliable de~ices, the particular switch in question being an exception. The failures associated with.LI~S 3-263-73A are of a random nature. The manufacturer has approved the procedure used*
to calibrate the instruments, _and specific recommendations have been specified. The corrective action stated above will implement the recommend-ations.
BBS:WEH:do