05000237/LER-1978-015-03, /03X-1 on 770402:CRD L-5 Uncoupled & Overtraveled When W/Drawn to Pos 48.Caused by Unlatched Inner Filter & Abnormally Long Uncoupling Rod.Procedure Rev & QA Coverage Improved to Prevent Future CRD Uncouplings

/03X-1 on 770402:CRD L-5 Uncoupled & Overtraveled When W/Drawn to Pos 48.Caused by Unlatched Inner Filter & Abnormally Long Uncoupling Rod.Procedure Rev & QA Coverage Improved to Prevent Future CRD Uncouplings

ML20027A284
Person / Time
Site:	Dresden
Issue date:	04/02/1978
From:	Wujciga J COMMONWEALTH EDISON CO.
To:
Shared Package
ML17173A338	List: 05000237/LER-1978-015-03, /03X-1 on 770402:CRD L-5 Uncoupled & Overtraveled When W/Drawn to Pos 48.Caused by Unlatched Inner Filter & Abnormally Long Uncoupling Rod.Procedure Rev & QA Coverage Improved to Prevent Future CRD Uncouplings ML17173A336
References
LER-78-015-03X, LER-78-15-3X, NUDOCS 7811090119
Download: ML20027A284 (2)

LER-1978-015, /03X-1 on 770402:CRD L-5 Uncoupled & Overtraveled When W/Drawn to Pos 48.Caused by Unlatched Inner Filter & Abnormally Long Uncoupling Rod.Procedure Rev & QA Coverage Improved to Prevent Future CRD Uncouplings

Event date:
Report date:
2371978015R03 - NRC Website

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LICENSEE EVENT REPORT UPDATE REPORT:

PREVIOUS REPORT DATE 4/29/77 CCNTROL CLOCK: l l

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!al2l lDuring routine startup operations, CRD L-5 uncoupled and overtraveled when withdrawn l

l0l2l lto pos. 48.

L-5 immediately inserted and disarmed.

Startup operations resumed after l 1o la l l determination that L-5's pos. and core location did not adversely affect core symmetrvj fifif] [ Following startup overtravel check of L-5 proved i atisfactory, verifying it was re-I t o le 1 l coupled and operable.

Because uncoupling occurred only when drive was fully with-l Q l (i Idrawn, safety implications were minimal.

CRD uncouplings have occurred previously.

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i i o l l Unlatched inner filter and abnormally long uncoupling rod resulted in unecupling of f

iilil lCRD L-5 during startup.

Since earlier overhaul of CRD L-5 on Jan. 1975. a ou11 tese I

.i,,.] lon inner filter has been incorporated in overhaul & assembly procedure. Revised l

lil3j l procedure and improved OA coverage is believed adequate to prevent future CRD un-l

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ATTACH:IENT TO LICEN5EE EVENT REPORT 77-015/03X-1 COFCIO% MLTH EDISON COMPANY (CWE)

DRESDEN UNIT-2 (ILDRS-2)

DOCKET # 050-237 l'

During routine start-up operations, control rod drive (CRD) L-5 was found to uncouple and overtravel when withdrawn to position 48.

L-5 was immediately inserted and electrically disarmed.

Reactor start-up operations were resumed after it had been determined that the position and core location of the L-5 control rod did not adversely affect core symmetry. At a reactor power level of approximately 30%,_L-5 was withdrawn to position 48 and checked for overtravel.

The~ overtravel check proved satisfactory, verifying that CRD L-5,was recoupled and operable.

Control rod drive / blade uncoupling incidents had occurred several times in the past.

Symptom and performance evaluations indicated that a loosened CRD inner filter could have caused the blade and drive to uncouple at the fully withdrawn position. Loosening of the filter could have resulted from a combination of improper installation and latching spring fatique.

It was also determined that a loosened filter could not exert sufficient pressure to uncouple the blade except when the drive was fully withdrawn to position 48; upon insertion, the blade and drive automatically recoupled. Because the potential for uncoupling the blade existed only when tHe drive was fully withdrawn, the safety implications of this

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event were minimal.

e As a precautions.ry measure, an operating order was? ss6ed to ensure that I

a coupling che :k was performed whenever drive-t-5 was withdrawn to position 48.

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On November 30,1977 CRD L-5 was disassembled and, inspected per Control Rod Drive Inspection and Maintenance Procedure DMP'209. To assure a' comprehensive inspection a special operating procedure (SOP 216) was prepared and followed.

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Upon inspection it was found that the inner filter was unlatched. 'In

addition the distance between the CRD flange and the end of the fully seated uncoupling rod was abnormally long (173.406 + 0.750").

The abnormal 1ength coupled with an unlatched inner filter resulted in the uncoupling of the CRD.

C CRD L-5 had been overhauled in January,1975.

Since May, 1975 a 20 to 30 pound pull test on the inner filter has been incorporated in the overhaul and reassembly procedure.

Control Rod Drives overhauled and reassembled under this revised procedure have nct experienced uncoupling.

The revised procedure coupled with improved Quality Control coverage of CRD overhaul andreassemblyarebelievedtobeadequatetopreventfuturesimilare{enes.

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