ML20084K431

AO 50-237/1974-36:on 741023,control Rod Drive P-12 54-47 Became Uncoupled.Cause Undetermined.Control Rod Will Be Removed During Nest Refueling Outage

ML20084K431
Person / Time
Site:	Dresden
Issue date:	10/31/1974
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
787-74, NUDOCS 8305190401
Download: ML20084K431 (2)

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. @" One First National P'a:a. Chicago. Ilknois Address Reply to: Post Office Box 767 Chicago, Illinois 60690

. BBS Ltr.#787-74 Dresden Nuclear Power Station R. R. #1 Morris, Illinois 60450 October 31, 1974 Mr. James G. Keppler, Regional Director Directorate of Regulatory Operations-Region III U. S. Atomic Energy Cocmission 799 Roosevelt Road Glen Ellyn, Illinois 60137 e

SUBJECT:

REPORT OF APl!OFF1sL OCCURRENCE PER SECTION 6.6.B 0F THE TECHNICAL SPECIFICATIC::5.

ECOUPLING OF CO:7I'ROL ROD DRIVE P-12 IN UNIT 2.

References:

1) Regulatory Guide 1.16 Rev.1 Appendix A

2) Notification of Region III of AEC Regulatory Operations Telephone: Mr. P. Johnson, 0845 hours0.00978 days <br />0.235 hours <br />0.0014 weeks <br />3.215225e-4 months <br /> on October 24, 1974 Telegram: Mr. J. Keppler, 0930 hours0.0108 days <br />0.258 hours <br />0.00154 weeks <br />3.53865e-4 months <br /> on October 24, 1974 -

3) Drawing Number: M-34 N / s,. x Report Number: 50-237/1974-36 '[] \

Lj' Report Date: October 29, 1974 ln9 m , 197 % .,

Occurrence Date: October 23, 1974 Qurr

. Facility: Dresden Nuclear Power Station, Morris, Illinois '

S: '7 IDENTIFICATION OF OCCURRENCE -

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At about 1700 hours0.0197 days <br />0.472 hours <br />0.00281 weeks <br />6.4685e-4 months <br /> on October 23, 1974, CRD P-12 (54 47), was being with-drawn from position "00" to "48" following a scram test. The CRD went into an overtravel condition. The overtravel indication is indicative of an uncoupled CRD.

CONDITIONS PRIOR TO OCCLTRENCE Prior to the occurrence, the reactor was holding at a steady state of 283 M4e and 1150 M4t for scram testing.

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e30519o4o1 741031 pMud PDR ADOCK 05000237 S PDR 11381;

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y Mr. Jam n G. Keppler Ohobar 31, 1974 DESCRIPTION OF OCCURREIE While CRD P-12 (54-47) was being withdrawn from position "00" to "48" following a scram test, a " rod overtravel" alarm annunciated and both the four rod and full core displays for the rod went blank.

The initial action taken was to in: mediately insert the CRD t'o "00" and remove it from service.

DESIGNATION OF APPARE."P CAUSE OF OCCURRENCE (Component Failure)

At this time, the failure mechanism is not known, therefore, a followup letter will be issued subsequent to overhaul.

ANALYSIS OF OCCURREICE This drive uncoupling did not endanger public health or safety because the control blade was capable at all times of being inserted into the reactor core.

CORRECTIVE ACTIONS y A The corrective action taken was to incart the rod to position "00", electri-cally disarm it, and remoya it from service. This action was completed on October 23, 1974. In addition, the three rods symmetrical with respect to P-12 were inserted to position "00" in order to enhance computer monitoring capabilities.

The control rod drive will be removed during the forth'Oming refueling outage.

At that time, a thorough inspection will be made to determine the mode of .-

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failure and a followup letter sutnitted to your office.

FAILURE DATA Control rod Drive P-12 (54-47)

Prior failures of this type were expla'ined as having occurred because of dislocated inner filters. This CRD, as were the previous failed CRD's, was modified and overhauled in the Spring 1972 refueling outage. Six drives have experienced this type of failure in the past. Inspections have shown

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that dislocated inner filters were at fault.

Sincerely,

( f hdf B. D' Stephencon Superintendent BBS:IJD:do L