ML20027A320

LER#77-029/03X-1 on 770802:during 1/2 Core Scram Test,Crds F-5 & H-7 Uncoupled When W/Drawn to Position 48.Caused by Unlatched Inner Filter & Abnormally Long Coupling Rod a Pull Test Has Been Incorporated Into Overhaul Procedure

ML20027A320
Person / Time
Site:	Dresden
Issue date:	10/27/1978
From:	COMMONWEALTH EDISON CO.
To:
Shared Package
ML17173A358	List: ML17173A357 ML20027A320
References
LER-77-029-03X, LER-77-29-3X, NUDOCS 7811140213
Download: ML20027A320 (2)

Text

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LICENSEE EVENT REPORT UPDATE REPORT:

PREVIOUS REPORT DATE 9/1/77 CONTROL BLOCK: l i

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l 8 60 61 DOCK ET Nuv9ER 68 69 EVENT OATE 74 75 REPcp DATE EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h lal2l lDuring one-half core scram testing, CRD's F-5 & H-7 uncoupled when withdrawn to po- l 10l3IIsition 48. Event has little safety significance since uncoupling occurred only at l I o l a I l pos. 48 and CRD's retain capability to scram as before uncoupling. Event occurred l lo}3) lpreviously with CRD F-5 as ref in R.O. 50-237/1976-68. CRD's F-5 & H-7 were recoupledi l o le I l according to procedure and recaupling verified by observing no overtravel indication i Q i

!when each CRD was twice withdrawn to position 48. I o is l l -

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i i i c l l An unlatched inner filter and abnormally long uncoupling rod resulted in the un- l g ,ij l coupling of CRD F-5 and H-7. Drives had been overhauled in Jan. 1975. A pull test I

,;,jjon inner filter has now been incorporated in the overhaul and reassembly procedure. l

,;3, l Revised procedure and improved QA coverage believed adequate to prevent future CRD l

, ;_;;uncouplings. l

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ATTACHMENT TO LICENSEE EVENT REPORT 77-029/03X-1 COMMONWEALTH EDISON COMPANY (CWE)

DRESDEN UNIT-2 (ILDRS-2)

DOCKET #050-237 During routine one-half core scram testing, control rod drives (CRD's)

F-5 & H-7 uncoupled and overtraveled when withdrawn to position 48 following testing. This event has little safety significance since uncoupled CRD's still retain the same capability to scram as before uncoupling and uncoupling only occurs at position 48. This event had occurred previously

( with CRD F-5 on December 12, 1976 (Reportable Occurrence #50-237/1976-68).

CRD's F-5 & H-7 were recoupled according to procedure and recoupling verified by observing no overtravel indication when each CRD was twice withdrawn to position 48.

On October 6, 1977 and September 30, 1977 CRDs F-5 and H-7 were 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.

t Upon inspection it was found that in both cases the inner filter was un-latched. In addition the distance between the CRD flange and the end of the fully seated uncoupling rod on both rods was abnormally long (173.406

+ 0.562). The abnormal length coupled with an unlatched inner filter resulted in the uncoupling of the CRD's during normal operating conditions.

' As part of the reassembly procedure, C.E.Co. Quality Control persennel '

performed the inner filter installation and the required 20-30 pound pull test. In Feb., 1978 the Control Rod Drive Inspection and maintenance procedure DMP 209 was changed to permit maintenance personnel .

to install the inner filter. This change occurred due~to existing Management-Union work agreements. However, Quality Control personnel will verify proper installation of the inner filter and continue to conduct the 20-30 pound pull test. The revised procedure coupled with improved Quality Control coverage of CRD overhaul and reassembly are be-lieved to be adequate to prevent future CRD uncouplings.

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