05000237/LER-1977-022-03, /03X-1 on 770605:CRD L-5 Uncoupled & Overtraveled When W/Drawn to Pos 48.Caused by Unlatched Inner Filter & Abnormally Long Uncoupling Rod.Procedure Rev & QA Coverage Improved to Prevent Future CRD Uncouplings

/03X-1 on 770605:CRD L-5 Uncoupled & Overtraveled When W/Drawn to Pos 48.Caused by Unlatched Inner Filter & Abnormally Long Uncoupling Rod.Procedure Rev & QA Coverage Improved to Prevent Future CRD Uncouplings

ML20027A285
Person / Time
Site:	Dresden
Issue date:	06/05/1978
From:	Wujciga J COMMONWEALTH EDISON CO.
To:
Shared Package
ML17173A343	List: 05000237/LER-1977-022-03, /03X-1 on 770605:CRD L-5 Uncoupled & Overtraveled When W/Drawn to Pos 48.Caused by Unlatched Inner Filter & Abnormally Long Uncoupling Rod.Procedure Rev & QA Coverage Improved to Prevent Future CRD Uncouplings
References
LER-77-022-03X, LER-77-22-3X, NUDOCS 7811090130
Download: ML20027A285 (2)

LER-1977-022, /03X-1 on 770605:CRD L-5 Uncoupled & Overtraveled When W/Drawn to Pos 48.Caused by Unlatched Inner Filter & Abnormally Long Uncoupling Rod.Procedure Rev & QA Coverage Improved to Prevent Future CRD Uncouplings

Event date:
Report date:
2371977022R03 - NRC Website

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!ol:l l During routine startup operations, CRD L-5 was found to uncouple and overtravel when I

i o 13 l l withdrawn to pos. 48.

CRD L-5 was inserted and disamed.

Rx startup operations re-l 101. l lsumed after it was determined that L-5's pos. and core location did not adversely l

i o I s l l af fect core symmetry. Following start-up an overtravel check of L-5 proved matis-l

ojel l factory, verifying that CRD L-5 was recoupled and operable.

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i>j lpreviously with this rod as ref. in R.O. #50-237/1977-15.

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, i ; o ; l An unlatched inner filter and abnormally long uncoupling rod resulted in the uncoupling t i ;i ; j of CRD L-5 during normal operating conditions.

Since the last overhaul of CRD L-5 in I

,7,g [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 77-022/03X-1 COM'!ONWEAL'ni EDISON COMPA'iY (CWE)

DRESDEN UNIT-2 (ILDRS-2)

DOCKET #050-237 During routine startup operations, control rod drive (CRD) L-5 became uncoupled and overtraveled when withdrawn to position 48.

This event occurred previously with this control rod on April 2, 1977 (Reportable Occurrence Number 50-237/1977-15).

CRD L-5 was inserted and electrically disarmed.

Reector startup operations were resumed since the position and core location of control rod L-5 did not adversely affect core

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symmetry.

At a reactor power above 20%, L-5 was recoupled and with-drawn to position 48 and checked for overtravel.

The overtravel check verified CRD L-5 to be recoupled and operable.

This was the twelfth Control Rod Drive (CRD) uncoupling event at Dresden Unit 2 during the preceeding four years.

The inspection of CRD's which had previously experienced this event indicated that improper inner filter j

installation was probably responsible for the uncoupling. If the inner

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filter becomes unlatched, full withdrawal of the control rod to position 48 could result in CRD uncoupling.

Symptoms of this event indicated that the same inner filter probler probably existed with CRD L-5.

I On November 30, 1977 CRD L-5 was disassembled and inspected per Control Rod Drive Inspection and Maintenance Procedure DMP 209. To assure a com-prehensive inspection a special operating procedure (SOP 216) was pre-pared and followed.

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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 + 0.750").

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

As part of the reassembly procedure, C.E.Co. Quality Control Personnel performed the inner filter installation and a required 20-30 pound pull test.

In Feb.,1978 the Control Rod Drive Inspection and Maintenance Procedure DMP 209 was further 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 continue to conduct the 20-30 pound pull test.

The revised procedure coupled with improved Quality Control coverage of CRD overhaul and reassembly are believed to be adequate to prevent future similar events.

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