05000237/LER-1977-015, Forwards LER 77-015/03X-1

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Forwards LER 77-015/03X-1
ML17173A336
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
ML17173A338 List:
References
NUDOCS 7811090116
Download: ML17173A336 (3)
v • d • e


LER-1977-015, Forwards LER 77-015/03X-1
Event date:
Report date:
2371977015R00 - NRC Website
v • d • e

text

CommonweA Edison Dresden NuclearWwer Station R.R. #1 Morris, Illinois 60450 Telephone 815/942-2920 BBS Ltr. #78-1447 James G. Keppler, Regional Din:~ctor

  • October 27, 1978
  • Directorate of Regulatory Operations - Region III.*

U.S. Nuclear Regulatory Commission 79-9 __ Roosevelt Road Glen Ellyn, IL : 60137.

Reportable Occurrence "Update" Rep~rt 77.,-.015/03X-l, Docket i/050-237 i.s hereby submitted ~o your office to update the cause description and final corr~ctive actions taken to. prevent recurrence.. Th:Ls event was reported* to your office under Dresden Nuclear Power. Stat;ion Techni.cal Specification 6.6.B.2.(b), ~onditions leading to operat~on ~n a.*

degraded mode permitted by a limiting condition for operation or plant shutdown required by a limiting c.ondition for operatiOn.

  • ens on Superintendent Presden Nuci~ar Power*Station.

BBS/deo*

Enclosure cc:. Director. of Insp~ction' *& Enforcement

    • Director* of Management Informad.on &

File/NRC Program Control

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.REGULATORY DOCI\\ET FILE COPY 1

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P~OUS REPORT DATE 4/29/77 CONTROL BLOCK:

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!During routine startup operations, CRD*L-5 uncoupled and overtraveled when withdrawn

@ill. I to pos. 48.

L-5 immediately inserted and disarmed; Startup operations resumed after [QITI_jdeterminai::ion that L-S's pos. and core location did not adversely affect core symmetry~

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!Unlatched inner filter and abnormally long uncoupling rod resulted in unc0upling of QJJJ I CRD L-5 during startup; Since earlier overhaul" of CRD L-5 on-Jan. 1975. *a i:mll.:test*

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DTIJ I on inner filter has been inco!'.'porated in overhaul & assembly procedure.

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i ATTACHMENT TO LICENSEE EVENT REPORT 77-0l5/03X-l

  • COMHONWEALTH EDISON COMPANY (CWE)

DRESDEN UNIT-2 (ILDRS-2)

DOCKET ii 050.:...237 During routine start.:...up operations, control rod drive (CRD) t-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 t~ position 48 and checked for overtravel.

The overtravel :

check proved s~tisfactory,' verifying that CRD. L-5 was recoup led and operaole.

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 comoination of improper.installation and latching spring fatique.

It was aiso determined that a. loosened filter could not exert. sufficient

  • pres*sure.to uncouple: the olade except when* the drive was fully withdrawn to position 48; upon insertion, the f>lade and drive automatically..

recoup led, Because the potential for uncoupling the blade existed. only*

  • wfi.en tiie drive -t.ras. fully withdrawn, the.saf~ty irp.plications of this event were minimal.

As a precautionary measure, an operating order was. issue.cl to ~nsure that.*

  • a coupling check was* performed. whenever drive L-5.was withdrawn to
  • position* 48
  • On Novemf>er 30, 1977.CRD L-5 was disassemoled and inspected: p~~ Control Rod Drive Inspection and Maintenance Procedure DMP 209,
  • To assure. a.

comprehensive inspection a special operating procedure (SOP 216) was

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Upon inspection it was found that the inner filter was unlatched. *:"tri"' *-*.' ~',;! addition the* distance between the CRD flange and the end of the fully.

  • seated uncoupling rod was af>normally long (173.406 + 0.750").* The abnormai length coupled with an unlatched inne.r filter resulted.in the uncoupling of the CRD.

CRD L-5 had oeen overha.uled 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 not experienced uncoupling.

The revised procedure coupled with improved Quality Control coverage of CRD overhaul and reassembly are believed to be adequate to prevent. future* similar ev*ents. ... ;_... :.* (~',_ '** ~.'

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