ML19317D776
| ML19317D776 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 03/14/1977 |
| From: | DUKE POWER CO. |
| To: | |
| Shared Package | |
| ML19317D771 | List: |
| References | |
| RO-269-77-08, RO-269-77-8, NUDOCS 7912100534 | |
| Download: ML19317D776 (2) | |
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DUKE POWER CO. N i OCONEE UNIT 1 Report No.: R0-269/77-8 Report Date: March 14, 1977 Occurrence Date: February 28, 1977 Facilitv: Oconee Unit 1, Seneca, South Carolina Identification of Occurrence: Primary-to-secondary system leakage in "lB" once-through steam generator Conditions Prior to Occurrence: Unit at 100 percent full power Description of Occurrence:
On February 28, 1977, an increase in radiation levels as registered by air ejector monitor RIA-40 indicated a possible primary-to-secondary system leak. Sampling of the steam lines and portable instrument readings con-firmed that primary-to-secondary leakage was occurring in the "lB" once-through steam generator (OTSG). A reactor shutdown was initiated at this time due to an unrelated dropped control rod incident that is described in R0-269/77-7. Within ten hours from the time that increasing readings were observed on RIA-40 reactor shutdown was completed and preparations were made to drain the Reactor Coolant System and investigate the source of the steam generator leakage.
The Reactor Coolant System was cooled and drained within 3 days following the initial high radiation indication and an internal inspection of the "lB" OTSG was initiated.
Apparent Cause of Occurrence:
Eddy current testing was performed and revealed one leaking tube, identical as tube number 13 in row 32.
The leaking tube was discovered to have a leak at the fourteenth support plate. The tube could not be visually inspected to determine the character of the leak due to the location of the leak.
Eddy current examinations of 490 other tubes revealed no additional tube leaks.
However, eddy current signal distortions were found on tube 4 of row 101, tubes 7 and 8 of row 2 and tube 14 of row 33.
Therefore, as a precautionary measure, these four tubes were plugged. Also, a section of one tube with an eddy current signal distortion, tube 25 of row 77, was removed for further inspection.
This tube was also plugged.
With regard to this and previous Oconee steam generator tube leaks, evalua-tion by Duke and the OTSG vendor, the Babcock & Wilcox Company, is continu-ing. However, there is no evidence to date to indicate that the leaks have resulted from tube wastage / thinning, chemical attack, or intergranular stress-corrosion cracking.
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e Analysis of Occurrence:
Primary-to-secondary system leakage, resulting f rom this occurrence, was approximately 0.1 gallons per minute and was detected by installed radia-tion monitoring equipment. The leakage did not exceed the operational limits of Oconee Technical Specification 3.1.6.1.
The calculated gaseous activity released to the environment via the air ejectors was 0.83 curies. This amount is considered insignificant in comparison to the station's annual release limit.
This report describes the seventh occurrence of steam generator tube leakage experienced on the three Oconee units. Defective tubes were previously reported in Reportable Occurrence Reports R0-287/76-10 RO-269/76-17 R0-270/76-15, R0-269/76-19, R0-269/77-2 and RO-287/77-2, submitted by our letters of August 5, 1976, November 15, 1976, December 20, 1976, December 22, 1976, January 31, 1977 and February 28, 1977, respectively.
In the first three occurrences and the fifth and sixth occurrences, the defective tubes edged an open tube lane (a radial row with no tubes, used for inspection purposes).
In the fourth instance, 0
the Icaking defective tube was angularly located approximately 150 counterclockwise from the locations of the other defective tubes and was not adjacent to an open tube lane.
In the seventh instance, the leaking tube was located approximately 450 clockwise from the open tube lane.
It is considered that this incident did not affect the health and safety of the public.
Corrective Action The leaking tube, tube 13 of row 32, and three other tubes with questiona-ble eddy current signals, tube 4 of row 101 and tubes 7 and 8 of row 33, were plugged at both ends utilizing explosive plugs. Tube 14 of row 33 was explosively plugged in the bottom of the tube and plugged from the top by insertion of a metal rod to increase the tube's stability. A section of tube 25 of row 77 was removed for inspection. This tube was pluppad at both ends with explosive plugs.
As stated in R0-269/77-2 submitted by my letter of January 31, 1977, the OTSG vendor, Babcock & Wilcox, is currently involved in a program to further evaluate the cause of the tube failures. This program includes a review of deposit samples, a computer evaluation of all available eddy current data, a review of visual observations from fiber-optics and videotapes, and macro-microscopic analysis of two of the defective tubes that were removed from the Oconee Unit 2 "2B" OTSG and one which was removed from the Unit 1 "1B" OTSG. Additionally, the open lane flow characteristics are being analyzed and a detailed stress / vibration analysis is being conducted on the tubes in rows 75 and 77.
A review has been made of the Oconee station operating history, the Oconee steam generator manu-facturing history and previously conducted OTSG analysis and testing results and no explanation of the phenomena has been determined to date.
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