05000270/LER-1977-017-03, /03L-0:on 771229,during Withdrawal,Control Rod 4 Group 6 Dropped Into Core Causing Power Runback to 55%. Caused by Excessive Moisture Buildup & Failure of O-ring Seals.Stator & O-ring Seals Replaced
| ML19317F307 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 01/26/1978 |
| From: | Ken Wilson DUKE POWER CO. |
| To: | NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| Shared Package | |
| ML19317F303 | List: |
| References | |
| LER-77-017-03L, LER-77-17-3L, NUDOCS 8001100673 | |
| Download: ML19317F307 (2) | |
| Event date: | |
|---|---|
| Report date: | |
| 2701977017R03 - NRC Website | |
text
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- - DUKE POWER. COMPANY OCONEE UNIT 2 Repo t No.:.RO-270/77-17.-
Report Date: January 26, 1978 Occurrence Date: December 29,.1977 Facility: Oconee Unit 2, Seneca, South Carolina
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Identification of Occurrence:
Control Rod Stator Failure Conditions Prior to Occurrence:
75 percent full power Description of' Occurrence:
At.0603 on December 29, 1977 Rod 4 Group 6 dropped.into the core causing a reactor runback to 55 percent full power.
At 0646 a power reduction of 10%/hr was commenced to reduce the quadrant tilt. Personnel determined that a short had occurred between phase AA and the neutral which prevented any rod withdrawal. 'At 2116 a unit shutdown was commenced. The stator and the 0-rings were replaced on December 31.
Apparent Cause of Occurrence:
Th'e cause of the incident was a short-in the AA phase. An 0-ring seal failure allowed excessive moisture to build up in the stator causing the
'short.
Analv_ sis of Occurrence:
The dropped rod resulted in an immdiate power runback to 55 per~ cent due to an as'ymmetric control rod configuration.' The maximum encountered quadrant tilt was'7.0% which is less than the error adjusted Technical Specification
- - of 8.05% (T.S. 3. 5.'2. 4. (c)). - The reactor instrumentation and control systems controlled' runback and shutdown functions correctly, resulting in safe reactor conditions at. all times. The reactor was shutdown to replace the stater and perform other unrelated maintenance. The health and safety of the public were not endangered by this incident.
Corrective' Action:
The control rod stator and the 0-ring seals were replaced on the failed stator.-
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