ML19329A701
| ML19329A701 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 04/19/1977 |
| From: | DUKE POWER CO. |
| To: | |
| Shared Package | |
| ML19329A695 | List: |
| References | |
| RO-287-77-06, RO-287-77-6, NUDOCS 8001090683 | |
| Download: ML19329A701 (2) | |
Text
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DUKE POWER COMPANY
,m OCONEE UNIT 3 (y.
-V Report No.: R0-287/77-6 Report Date: April 19, 1977 Occurrence Date: April 5, 1977 Facility:
Oconee Unit 3, Seneca, South Carolina Identification of Occurrence: Rod overlap in excess of Technical Specification limit Cot,ditions Prior to Occurrence: Unit at 100 percent full power Description of Occurrence:
Oconee Technical Specification 3.5.2.5 specifies an overlap of 25 1 5% between two adjacent operating control rod groups. On April 5, 1977, control rod over-lap for control rod groups 6 and 7 was being maintained closed to the minimum allowable overlap to improve axial imbalance conditions. The alarm setpoint for control rod overlap is set at 22% in order to provide a warning to the operator. The operator had acknowledged the alarm and was aware of the rod overlap which existed. The power level was then reduced from 100% full power to 94 percent full power due to system requirements.
Approximately three hours after the power reduction, the operator noted that the computer point for the control rod overlap of control rod groups 6 and 7 was indicating an overlap of 19.7%.
The operator acted promptly to adjust the overlap to within the allowable rod overlap condition.
Apparent Cause of Occurrence:
This occurrence resulted from a procedural inadequacy in the respect that it did not address operation near the limiting values of Technical Specification 3.5.2.5.
Analvsis of Occurrence:
This incident resulted in a condition of approxi=ately 0.3 percent control rod overlap existing until the control rods were re-positioned and the required overlap was re-established.
This reduction in control rod overlap did not affect the safe operation of the reactor and no core protection limits were approached.
A proposed change to Technical Specification 3.5.2.5.b was submitted on November 1, 1976. The change will allow a two hour period for restoration
-of control' rod group overlap in the event the prescribed limit of 25% 1 5%
between two sequential groups'is exceeded. Provided that the required shut-down margin limits are maintained, this is considered a reasonably conserva-tive time period in which to initiate appropriate corrective action.
It is concluded that this occurrence did not af fect the health and safety of the public.
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.n Corrective Action:
The reactor operator promptly took action and adjusted the rod overlap tc within the allowable control rod overlap limits. Operating procedures will be revised to provide for additional precautions to be taken when it
-is necessary to operate at values of rod overlap nearer to the Technical Specification limits than normal. These provisions will include appro-priate warnings and requirements for resetting alarm points to values which will assure operator awareness of marginal rod overlap conditions.
These revisions will be implemented by May 15, 1977.
The approval of the proposed change to Technical Specification 3.5.2.5.b as stated in the above analysis and the implementation of the procedure revisions should eliminate recurrence of this incident.
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