05000237/LER-1977-014-03, /03X-1 on 770402:during Normal Startup Oper,Crd H-8 Was Found to Uncouple & Overtravel When Withdrawn to Pos 48.Caused by an Unlatched Inner Filter & Abnormally Long Uncoupling Rod

/03X-1 on 770402:during Normal Startup Oper,Crd H-8 Was Found to Uncouple & Overtravel When Withdrawn to Pos 48.Caused by an Unlatched Inner Filter & Abnormally Long Uncoupling Rod

ML20027A317
Person / Time
Site:	Dresden
Issue date:	10/27/1978
From:	Wujciga J COMMONWEALTH EDISON CO.
To:
Shared Package
ML17173A352	List: 05000237/LER-1977-014, Forwards LER 77-014/03X-1 05000237/LER-1977-014-03, /03X-1 on 770402:during Normal Startup Oper,Crd H-8 Was Found to Uncouple & Overtravel When Withdrawn to Pos 48.Caused by an Unlatched Inner Filter & Abnormally Long Uncoupling Rod
References
LER-77-014-03X, LER-77-14-3X, NUDOCS 7811140163
Download: ML20027A317 (2)

LER-1977-014, /03X-1 on 770402:during Normal Startup Oper,Crd H-8 Was Found to Uncouple & Overtravel When Withdrawn to Pos 48.Caused by an Unlatched Inner Filter & Abnormally Long Uncoupling Rod

Event date:
Report date:
2371977014R03 - NRC Website

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

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60 68 OOCK ET NUMBER 68 63 EVENT DATE 74 75 REPORT DATE 80 EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h 10 l:] l During routine startup operations. CRD H-8 was found to uncouple and overtravel when l l O l 31 l withdrawn to pos. 48.

All CRD's were inserted to pos. "00" and verified.

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l C t. l l then withdrawn to pos. 48 and checked for overtravel four separate times.

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J3 25 36 37 40 48 42 43 44 47 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h i i 10 l l An unlatched inner filter and abnormally long uncoupline rod result.ed in the un-l gl.aij l coupling of CRD H-8 during normal startup.

Since the last overhaul of CRD R-R -h I

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i,2; 1 Jan. 1975, a pull test on the inner filter has been incorporated in the overhaul &

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4 ATTACHMENT TO LICENSEE EVENT REPORT 77-014/03X-1 1

COMMONWEALTH EDISON COMPANY (CWE)

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DRESDEN UNIT-2 (ILDRS-2) noCxrT co30-237 During routine start-up operations, control rod drive (CRD) H-8 was found to uncouple and overtravel when withdrawn to position 48.

All CRD's were subsequently inserted to position 00 and verified to be fully inserted by computer. CRD H-8 was then withdrawn to position 48 and checked for overtravel four separate times.

Each overtravel check proved satisfactory, and the drive was determined to be operable and recoupled. lformal start-up operations were resumed.

Control rod drive / blade uncoupling events have occurred several times in the past.

Symptom and performance evaluations indicated that a loosened inner filter in the CRD may have potentially 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 ppring 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 event were minimal.

As a precautionary measure, an operating order was issued to ensure that a coupling check was performed whenever drive H-8 was withdrawn to position

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48.

On October 20, 1977, CRD H-8,was disassembled and inspected per Control Rod Drive Inspection and Itaintenance Procedure DMP 209. -To assure a comprehen-sive inspection a special operation procedure (SOP 216) was prepared and followed.

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 + 0.500").

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

CRD H-8 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 the revised procedure have not experienced uncoupling. The revised procedure coupled with improved Quality Control Coverage of CRD overhaul and reassembly are believed adequate to prevent future similar events.

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