ML20027A358

LER#76-068/03X-1 on 761212:during 50% Core Scram Testing CRD F-5 Uncoupled & Overtraveled When Withdrawn to Position #48.Unlatched Inner Filter & Abnormally Long Uncoupling Rod Resulted in Uncoupling CRD F-5 During Testing

ML20027A358
Person / Time
Site:	Dresden
Issue date:	10/27/1978
From:	Wujciga J COMMONWEALTH EDISON CO.
To:
Shared Package
ML17173A373	List: ML17173A372 ML20027A358
References
LER-76-068-03X, LER-76-68-3X, NUDOCS 7811210304
Download: ML20027A358 (2)

Text

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F 6 75 RE*CRT CATE EVENT DESCRIPTION AND PRO 9ABLE CONSEQUENCES h lo l2l l During 50% cora scram testing, CRD F-5 uncoupled and overtraveled when withdrawn to l t o 13 I 16os. 48. Insertion to pos. 44 and subsecuent withdrawal to pos. 48 showed drive Io I4 i irecoupled. Second scram and withdrawal to pos. 48 uncoupled drive. CRD F-5 then l

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lofs! inserted to "0" and disarmed. Three symmetrical drives also inserted. Safety sig- l l o is 1 I nificance minimal since uncoupling occurred only at pos. 48. CRD uncoupling has l

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36 3/ 40 el 42 44 47 CAUSE DESCRIPTION AND CORRECTIVE ACTICNS 27 l i ; a l l Unlatched inner filter and abnormally long uncoupling rod resulted in uncoupling CRD l

g. l[ F-5 during testing. Drive had been overhauled in Jan. 1975. A pull test on inner i

,,,,,j filter has now been incorporated in the overhaul and reassembly procedure. Revised  ;

g,;3; l procedure and improved QA coverage believed adequate to prevent future similar events.;

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ATTACIDIE'IT TO LICENSEE EVENT REPORT 76-068/03X-1 COMMONWEAL'IH EDISON COMPANY (CWE)

DRESDEN UNIT-2 (ILDRS-2L

. DOCKET #050-237 Follow 1ng 50% core scram testing, CRD F-5 was found to uncouple and overtravel when withdrawn to position 48 An insertion'to position 44 and subsequent withdrawal to position 48 showed the drive to be recoupled.

A second scram and withdrawal to position 48 again uncoupled the drive.

CRD F-5 was then inserted to position 00 and disarmed. The three symmetrical

( drives in the remaining quadrants were also fully inserted.

On 12/30/76, an on-site review determined that a loosened inner filter caused the blade and drive to uncouple at position 48. It was also de-termined that the 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. Since the possibility of uncoupling the blade existed only when the drive was withdrawn to position 48, CRD F-5 was then declared operable. As a pre-cautionary measure, an Operating Order was issued to ensure that a coupling

~_ check was performed whenever drive F-5 was withdrawn to position 48. Also,-

if a subsequent uncoupling occurred, immediate action was to be taken to ensure that the drive's status complied with Tech Spec section 3.3.B.1.

As mentioned above, symptom and performance evaluations indicated that a loosened inner filter had caused the blade and drive to uncouple at the fully withdrawn position. Loosening of the filter could have resulted f, rom

( improper installation and latching spring fatique.

On October 6, 1977 CRD F-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.

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 + 0.375 in.) The abnormal length, coupled with an unlatched inner filter, resulted in the uncoupling of the CRD. ,

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CRD F-5 had been last 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 re-assembled 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 CRD uncoupling.

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