05000237/LER-1977-014, Forwards LER 77-014/03X-1

Forwards LER 77-014/03X-1

ML17173A351
Person / Time
Site:	Dresden
Issue date:	10/27/1978
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
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/03X-1 on 770402:during Normal Startup Oper,Crd H-8 Was Found to Uncouple & Overtravel When Withdrawn to Pos 48.Caused by an Unlatched Inner Filter & Abnormally Long Uncoupling Rod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
NUDOCS 7811140160
Download: ML17173A351 (3)

LER-1977-014, Forwards LER 77-014/03X-1

Event date:
Report date:
2371977014R00 - NRC Website

text

Commonwe'9 Edison Dresden Nuclear Power Station R.R. #1 Morris, Illinois 60450 Telephone 815/942-2920 BBS Ltr. #78-1437 James G. Keppler, Regional Director October 27, 1978 Directorate of Regulatory Operations - Region III U.S. Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, IL 60137 Reportable Occurrence "Update' Report 77-014/03X-1, Docket 11050-237 is hereby submitted to your office to update the cause description and final corrective actions taken to prevent recurrence.

This event was reported to your office under Dresden Nuclear Power Station Technical Specification 6.6.B.2.(b), conditions leading to operation in a degraded mode permitted by a limiting condition for operation or plant shutdown required by a limiting condition for operation.

BBS/deb Enclosure cc:

Director of Inspection & Enforcement 9

ep nson Station Superintendent Dresden Nuclear Power Station Director of Management Information & Program Control File/NRC

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[QJ:3J I During routine startup operations, CRD H-8 was found to uncouple and overtravel when withdrawn to pos. 48.

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

CRD H-8 then withdrawn to pos. 48 and checked for overtravel four separate times.

Each check!

proved satisfactory and the drive was determined to be operable and recoupled.

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startup operations resumed.

CRD blade uncouplings had occurred several times in the ITI?J past.

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CAUSE DESCRIPTION AND CORRECTIVE ACTIONS 43 44 47*

An unlatched inner filter and abnormally long uncoupling rod resulled in the un-coupling of CRD H-8 during normal startup.

Since the last overhaul of CRD,H-8 *in I

Jan. 1975, a pull test on the inner filter has been incorporated *in the overhaul &

OJ)) I assembly procedure.

The revised procedure and improved QA coverage believed adequate I

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e ATTACHMENT TO LICENSEE EVENT REPORT 77-014/03X-l COMHONWEALTH EDISON COMPANY (CWE)

DRESDEN UNIT-2 (ILDRS-2)

DOCKET 1!050-237 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.

Normal 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 ~pring 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

48.

On October 20, 1977, CRD H-8.was disassembled and inspected per Control Rod Drive Inspection and Maintenance Procedure DMP 209.

To ass.ure 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.

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