ML19309D995

RO 50-313/78-12:on 780424,Group 7 Control Rods Dropped Into Core Due to Gate Drive Circuit Failure.Caused by Component Failure.Group 6 Inserted to Obtain Required overlap.780425 Telecopy Encl

ML19309D995
Person / Time
Site:	Arkansas Nuclear
Issue date:	05/05/1978
From:	Shively C ARKANSAS POWER & LIGHT CO.
To:
Shared Package
ML19309D993	List: ML19309D992 ML19309D995 ML19309D996
References
NUDOCS 8004110777
Download: ML19309D995 (4)

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l-Reportable Occurrence Report No.

50-313/78-12 2.

Report Date:

May 5, 1978 3.

Occurrence Date: April 24, 1978 4

Facility:

Arkansas Nuclear One-Unit 1 Russellville, Arkansas 72801 5.

Mentification of Occurrence:

Loss of required overlap between operating control rods groups.

6.

Conditions prior to Occurrence:

Steady-State Power X

Reactor Power MWth Hot Standby Net Output MWe Cold Shutdown Percent of Full Power 75 t,

y Refueling Shutdown Load Changes During Routine f

Power Operation Routine Startup Operation Routine Shutdown operation Other (specify) 7.

Description of Occurrence:

At approximately 2045 hours0.0237 days <br />0.568 hours <br />0.00338 weeks <br />7.781225e-4 months <br /> on 4/24/78, Group 7 control rods dropped into the core due to a failure of a gate drive circuit.

Due to this failure, the 25 + 5% overlap was not maintained as required by Technical Specification 3.5.2.5.2.

J 977 8004110

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Reportable Occurrence Report No. 50-313/78-12 8.

Designation of Apparent Cause of Occurrence:

Design Procedure Manufacture Unusual Service Condition Including Environmental Installation /

Construction Component Failure r

(See Failure Data)

Operator Other (specify) i

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9.

Analysis of Occurrence:

A detailed investigation was performed but the cause of the failure is not known.

There is no core safety significance associated with the minimum overlap requirement, rather the concern is for an overlap greater than 30%. This reduction in overlap did not create an unsafe condition, and no core protection limits were approached.

This incident did not endanger the health and safety of the public.

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Reportable Occurrence Report No.

50-313/78-12 l

10. Corrective Action:

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._The corrective action taken was to insert Group 6 to obtain the required overlap.

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11.

Failure Data:i

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Similar events reported include Reportable Occurrences 50-313/75-10, i

50-313/76-01 and 50-313/77-22.

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