ML19317D815
| ML19317D815 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 11/15/1976 |
| From: | DUKE POWER CO. |
| To: | |
| Shared Package | |
| ML19317D809 | List: |
| References | |
| RO-269-76-17, NUDOCS 7912100551 | |
| Download: ML19317D815 (2) | |
Text
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Report No.:
A0-269/76-17 i- --
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Report Date:
November 15, 1976 Occurrence Date:
October 31, 1976 Facility: Oconee Unit 1, Seneca, South Carolina Identification of Occurrence:
Primary-to-secondary system leakage in "lA" once-through steam generator Conditions Prior to Occurrence:
Unit at 100 percent full power Desc-iption of Occurrence:
On October 30, 1976, an alarm was received on the Oconee 1 air ejector off-gas monitor, indicating a possible primary-to-secondary system leak.
Subsequent checking of this monitor and sampling of the steam line for approximately 11 hours1.273148e-4 days <br />0.00306 hours <br />1.818783e-5 weeks <br />4.1855e-6 months <br /> confirmed that primary-to-secondary leakage was occurring in the "lA" once-through steam generator (OTSG) and a reactor shutdown was initiated at this time. Within approximately seven hours, reactor shutdown was completed and preparations were made to cool and drain the Reactor Coolant System and investigate for steam generator tube damage.
The Reactor Coolant System was cooled and drained within three days following the initial radiation alarm, and an internal inspection of the "1A" OTSG was initiated.
Apparent Cause of Occurrence:
l Inspection revealed one leaking tube in the "lA" OTSG.
The tube leak location was found by gradually filling the secondary side of the steam generator with feedwater and observing tube leakage from the primary side.
The leaking tube, identified as tube #17 in row 77, was discovered to have a circumferential crack near the interface of the tube with the bottom of
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the upper tube sheet. The crack extended 150 to 1800 of the tube's circumference.
Inspection of 15 adjacent tubes revealed no other defective l
tubes. A questionable signal vas obtained, however, during an eddy current test of one of the other tubes inspected. The cause of the damage to the defective tube and the possible damage to the second tube is undetermined.
Both tubes have been plugged.
Analysis of Occurrence:
Primary-to-secondary system leakage, resulting from this occurrence, was approximately one gallon per minute (gpm) and was detected by installed radiation monitoring equipment. The leakage was within the operational limits of Oconce Technical Specification 3.1.6.1.
In this instance, a l
7 91210 0 $/
o reactor shutdown was initiated within approximately 11 hours1.273148e-4 days <br />0.00306 hours <br />1.818783e-5 weeks <br />4.1855e-6 months <br /> af ter the initia11eakage indication, following extensive sampling and monitoring of components and systems during this interval.
The calculated gaseous 1
activity released to the environment via the air ejectors was 8.0 curies.
This amount is considered insignificant in comparison to the station's i
annual release limit.
This tube defect occurred on a tube located within three inches of the radial position of a similar defective tube in Oconee Unit 3 "3B" OTSG as reported in Reportable Occurrence Report R0-287/76-10 submitted by our letter of August 5, 1976.
The tube defects, however, occurred at different tube elevations and there is no evidence to indicate that this is other than a random occurrence.
It is concluded, therefore, that this incident did not affect the health and safety of the public.
Corrective Action:
The leaking steam generator tube and the adjacent tube with possible damage were both plugged at both ends with explosive plugs.
Subsequent leak testing was performed and no additional leakage was identified.
Tnspections of 15 adjacent tubes were performed and no additional indications of tube degradation were noted.
This steam generator will be examined during the next steam generator inservice inspection and efforts will be con-centrated on the inspection of tubes within the vicinity of this tube defect to assess whether additional tube degradation in this area has occurred.
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