ML19317F364
| ML19317F364 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 02/24/1975 |
| From: | DUKE POWER CO. |
| To: | |
| Shared Package | |
| ML19317F361 | List: |
| References | |
| NUDOCS 8001140619 | |
| Download: ML19317F364 (2) | |
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DUKE POWER COMPANY' OCONEE UNIT-3 Report No.: 'AO-287/75-3 Report Date: February 24, 1975
- 0ccurrence Date
- February 9, 1975 Facility:- Oconee Unit 3, Seneca, South Carolina Identification of Occurrence: Failure to provide proper overlap between control rod groups-Conditions Prior to' Occurrence: Unit at approximately 60 percent full power
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Description of Occurrenc'e:-
On February 9, 1975 Oconee Unit 3 was being maintained at approximately 60 percent full power.
The Integrated Control. System (ICS) initiated a run-back from 58 to 55 percent power at 2134. At 2140 it was observed that control rod ' groups 6 and :7-did not have the required 2515 percent overlap specified in Technical Specification 3.5.2.5.b.
The control room operator took manual. control of, and repositioned, the control rod groups.
' Designation of Apparent Cause of Occurrence:
The position indication switch which provides absolute position indication (API) for rod 5 in group 6 had failed prior to this occurrence. The control operator was aware of the status and implication of operating with an inoperable API. The. API provides-input to the_ plant computer for use in computing the
-rod group average position.
The rod group average position is displayed on the video and' vertical' control board displays. The faulty API for rod 5,'
group 6 provided a'zero indication to be averaged with the remainder of the
, group 6' rods, thus the group ~6 average position indicated lower than the
, actual position ~.
During the~ recovery from the runback, the control' room operator failed to-
-monitor the individual rod positions of the group 6 and 7 rods as they.were withdrawing in order to maintain-an overlap of 25 i S. percent.
- Instead, he monitored the computer, video'and the. group average on the. control
-board which were both in error.due to the inoperable API switch on rod 5 Lof. group;6.
DAnalysis of Occurrence:
The control' rod groups 6.'and 7 are'specified to have overlap limits of 2511 5 percent. A smaller. overlap will result in excessive control rod
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socion due.to the small reactivity effects of the control rods at the beginning and.end of travel.
A' greater overlap.will result in'a-higher than desired reactivity insertion rate.. In this ~ instance, the overlap of 16 perc4nt c exceeded the: limits'of:25 i.5 percent by.4 percent. This was in the' safe, 8001140 N p
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conservative direction because 'this limited the' maximum reactivity insertion rate when' moving both groups of rods. No reactor core protection limits were approached.
It is concluded that the health and safety of'the public
- was not affected.
Corrective Act' ion:
Operations' personnel have been informed of the potential sequence problems
.which can' exist during operation with an inoperable PI switch.
This problem will also be included,in the training program to ensure that operators are informed of control rod. sequence problems.
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