ML19317F473

RO 270/77-05:on 770329,during Control Rad Movements Test Rod 2 Group 1 Dropped Into Core,Causing Reactor Quadrant Tilt Limit to Exceed Tech Spec Requirements.Caysed by Failed Control Rod Drive Stator Fuse.Fuse Replaced

ML19317F473
Person / Time
Site:	Oconee
Issue date:	04/28/1977
From:	DUKE POWER CO.
To:
Shared Package
ML19317F465	List: ML19317F464 ML19317F473
References
RO-270-77-05, RO-270-77-5, NUDOCS 8001140704
Download: ML19317F473 (2)

Text

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V bUKE PLWF.R COMPANY OCONEE UNIT 2 l

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Repo.t_ No._: R0-2/0/77-5 Report Date: April 27, 1977 r

Occurrence Date: M.rch 29, 1977 .

Facili ty,i Oconce Unit 2, Seneca, South Carolina Identification of Occurrence: Reactor quadrant tilt limit exceeded C gditions Prior ___to Ocgurrence: Unit at 100 percent full power Description of Occurrence:

On March 29, 1977 while perfurming a control rod movement test with the re 'ct' r in the manual mode, rod 2 group 1 dropped into the core due to a j fa._ed control rod drive stator fuse. Reactor power was manually reduced i to 55 percent full power due to the resulting asymmetric rod indication.

! Approximately 15 minutes later, reactor power was reduced to 35 percent full power due to feedwater swings.and low reactor coolant system average temperature. During this reduction, the quadrant power tilt increased above the 9.44% limit specified by Technical Specification 3.5.2.4.c. A controlled shutdown was promptly initiated, as required by this technical specification. Approximately twenty-five minutes later, the fuse was replaced and rod 2 group 1 was realigned. The quadrant power tilt was determined to be within the limits of Technical Specification 3.5.2.4.c in an additional ten minutes and the shutdown was terminated.

Apyarent Cause f Occurrence:

This becurrence resulted from the drop of rod 2 group 1 due to the f ailure of a fuse in the "A" phase of the control rod drive stator.

! Analysis of Occurrence:

' This occurrence resulted in the core quadrant tilt exceeding the limits specified in Technical Specification 3.5.2.4.c. A reactor shutdown was promptly initiated and quadrant tilt returned to a normal value within thirty-five minutes of the incider t. The maximum tilt recorded was +10.15%.

The limits on allowable quadrant tilt, in conjunction with the limits on power Icvel, control rod group position, axial imbalance and xenon condi-tions, are -specified to prevent the maximum linear heat rate fro,o exceeding the LOCA limited values. In this incident, although the indicated tilt exceeded the maximum allowable value, a linear heat rate below the estab-lished limits was assured by the conservative values of the other power peak inducing parameters and the gradual power decrease. Also, the shutdown margin as calculated during the incident was determined to be acceptable.

The capability of the reactor protective system was not affected by this incident and therefore, it is concluded.that the health and safety of the  !

public was not affected.

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• Con r ce t t ve_ Ar t f on,:

The cont rol rod drive stator fuse was replaced and rod 2 group I was realigned. The procedure for control rod movement tests will be revised by June 1,1977 to require an inspection of the status of the fuses in the "A" and "CC" phases of control rod groups 1 through 4 prior to a rod novement test.

In addition, a program will be instituted which will require testing and, as necessary, replacement of all control rod drive stator fuses for control rod groups 1 thrvech 4 during each unit's refueling outage.

This program will be initiated beginning with the refueling outage for Oconee Unit 1, Cycle 4.

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