ML19326B474

LER 77-022/01T:on 771123,loss of Required Overlap Between Operating Control Rod Groups Occurred.Caused by Group 7 Not Reaching in-limit When Motion Was Stopped.Operator Adjusted Group 5 Manually

ML19326B474
Person / Time
Site:	Arkansas Nuclear
Issue date:	12/07/1977
From:	Kinsey V ARKANSAS POWER & LIGHT CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19326B470	List: ML19326B469 ML19326B474
References
LER-77-022-01T, LER-77-22-1T, NUDOCS 8004150815
Download: ML19326B474 (4)

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l-Reportable Occurrence Report No. 50-313/77-22

2. Report Date: 12/7/77 3. Occurrence Date: 11/23/77 4 Facility: Arkansas Nuclear One-Unit 1 Russellville, AR 72801

5. Identification of Occurrence:

Loss of required overlap between operating control rods groups.

6. Conditions Prior to Occurrence:

Steady-S, tate Power Reactor Power MWth i

Hot Standby Net Output MWe Cold Shutdown Percent of Full Power 22  %

Refueling Shutdown Load Changes During Routine Power Operation Routine Startup Operation Routine Shutdown Operation Other (specify)

7. Descriptien of Occurrence:

At approximately 2040 hours0.0236 days <br />0.567 hours <br />0.00337 weeks <br />7.7622e-4 months <br /> on 11/23/77 during a test of the turbine throttle valves, the turbine-tripped. During insertion of the Group 6 control rods to prevent auto trip of the reactor, the 25.t S% overlap was not m intained as required by Technical Specification 3.S.2.S. .

o q Reportable Occurrence Report Nc- 50-313/77-22

8. Designation of Apparent Cause of Occurrence:

Design Procedure i

Manufacture Unusual Service Condition Including Environmental

Installation / -

Construction Component Failure.

(See Failure Data)

Operat'ro Other (specify)(See Item 9)

9. Analysis of Occurrence:

A detailed investigation of all corponents whose failure could have caused the sequencing malfunction revealed no component failures. It appears that Group 7 had not reached its in-limit when its motion was stopped by Group 6 being at 75%.-

n ere is no core safety. significance associated with the minimum overlap requirement, rather the concern is for an overlap greater than 30%. His 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.

10. Corrective Action:

'the operator adjusted Group 5 manually since Group 5 will not normally move unless Group 7 is at its in-limit.

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I 11. Failure Data: . .

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Similar events reimmi.ed in RORs 50-313/75-10 and 50-313/76-01.

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