ML19317D856
| ML19317D856 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 05/20/1977 |
| From: | DUKE POWER CO. |
| To: | |
| Shared Package | |
| ML19317D851 | List: |
| References | |
| RO-269-77-16, NUDOCS 7912100579 | |
| Download: ML19317D856 (4) | |
Text
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DUKE POWER COMPANY OCONEE UNIT 1 Report No.: R0-269/77-16 Report Date: May 20, 1977 Occurrence Date: May 7, 1977 Facility: 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 Mcy 7, 1977, an increase in radiation levels as registered by air ejector monitor RIA-40 indicated a possible primary-to-secondary system leak occurring in the "lB" once-through steam generator (OTSG). A reactor shutdown was initiated within six hours, and operating procedures for control of secondary contamination were commenced. Within an addi-tional 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> from the time that increasing readings were observed on RIA-40, the reactor was in hot shutdown 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 and an internal inspec-tion of the "1B" OTSG was initiated within 4 days of the high radiation indication. One leaking tube and one tube with a questionable eddy current indication were plugged.
In addition, one tube previously plugged was removed along with its stabilizing rod. The Nuclear Regula-tory Commission was informed of these actions prior to plugging and stabilizing the tubes.
Apparent Cause of Occurrence:
Eddy current testing was performed and revealed one leaking tube, identi-fied as tube number 15 in row 77.
The leaking tube was discovered to have a circumferential crack approximately one fourth inch below the upper tube sheet.
Eddy current examinations of 507 other tubes revealed no additional tube leaks. However, an eddy current signal distortion was found on tube 5 of row 17.
Therefore, as a precautionary measure, this tube was plugged. Also, one tube, tube 18 of row 75, previously plugged in December, 1976 was removed along with its stabilizing rod to examine the integrity of the tube and rod. This tube was also plugged.
With regard to this and previous Oconee steam generator tube leaks, evaluation by Duke and the OTSG vendor, the Babcock & Wilcox Company, is continuing. 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. Studies indicate, however, that leaks occurring in,the tube lanes are caused by propagation of a local defect by high cycle fatigue due to vibration.
7912100 9 7
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e Analysis of Occurrence:
Primary-to-secondary system leakage, resulting from this occurrence, was calculated to be approximately 16 gallons per minute after the reactor shutdown. This was detected by installed radiation monitoring equipment.
The leakage exceeded the operational limits of Oconee Technical Specifica-tion 3.1.6.1.
A reactor shutdown was initiated within six hours of the initial radiation indication and immediately upon indication of a rapid increase of the radiation monitor.
The calculated gaseous activity released to the environment via the air ejectors was 160 curies.
This ainount is considered insignificant in comparison to the station's annual release limit.
This report describes the eighth occurrence of steam generator tube leakage experienced on the three Oconee units.
In the first three occurrences and the fifth, sixth and eighth occurrences, the defective tubes edged an open tube lane (a radial row with no tubes, used for inspection purposes).
In the fourth instance, the leaking defective tube was angularly located approximately 1500 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.
Table 1 provides a summary of the major OTSG tube experience at Oconee.
lt is considered that this incident did not affect the health and safety of the public.
Corrective Action:
The leaking tube, tube 15 of row 77, and one other tube with questionable eddy current signals, tube 5 of row 17 were explosively plugged at both ends. Tube 18 of row 75 was removed along with its stabilizing rod for inspection. This tube was plugged 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 l
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, one which was removed from the Unit 1 "lB" OTSG, and one tube removed along with its stabilizing rod from the Unit 1 "1B" OTSG. Additionally, the open lane flow charac-teristics 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.
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TABLE 1
SUMMARY
OF MAJOR OTSG TUBE EXPERIENCE AT OCONEE LANE
- TUBES EXAMINED GENERATOR ROW TUBE ELEVATION DATE TUBE LEAKER CONDITION ACTION RO#
(excludes leakers) 1-A 77 17 Tubesheet 11/76 Yes Yes Crack Plugged R0-269/76-17 15 1-A 77 18 Tubesheet 11/76 Yes No Distorted Eddy Plugged Current Signal 1-B 114 109 14th Plate 12/76 No Yes No Visual Nailed R0-269/76-19 139 Inspection 1-B 113 115 14th Plate 12/76 No No Distorted Eddy Plugged Current Signal r
1-B 113 110 14th Plate 12/76 No No Similar to Nalled 114/109 1-B 75 18 Tubesheet 12/76 Yes No 3000 Crack Nailed 1-B 75 12 Tubesheet 1/77 Yes Yes 3500 Crack Nailed R0-269/77-2 140 1-B 81 128 Tubesheet 1/77 No No Eddy Current Nailed Ind ica tion 1-B 32 13 14th Plate 2/77 No Yes Eddy Current Nailed R0-269/77-8 3%
Indication 1-B 33 14 14th Plate 2/77 No No Eddy Current Nailed Indication 1-B 77 25 14th Plate 2/77 Yes No Eddy Current Removed Indication 1-B 2
7 13th Plate 2/77 No No Eddy Current Plugged Indication 1-B 2
8 13th Plate 2/77 No No Eddy Current Plugged Indication 1-B 101 40 4th Plate 2/77 No No Eddy Current Plugged Indication
TABLE 1
SUMMARY
OF MAJOR OTSG TUBE EXPERIENCE AT OCONEE (Cont'd)
LANE
- TUBES EXAMINEh GENERATOR ROW TUBE ELEVATION DATE TUBE LEAKER CONDITION ACTION RO#
(excludes lenkers) 1-B 77 25 Tubesheet 3/77 Yes Yes Weld Crack Replug-R0-269/77-11 100 ged 1-B 77 3,5,8, 3/77 Yes No Distorted Plugged 22,29 Eddy Current Signal 1-B 77 15 Tubesheet 5/77 Yes Yes Crack Plugged R0-269/77-16 507 1-B 77 18 5/77 Yes No Removed s
1-B 17 5
5/77 No No Distorted Plugged Eddy Current Signal 2-B 77 23 Tubesheet 12/76 Yes Yes 2700 Crack, Removed R0-270/76-15 133 IIole 2-B 77 27 15th Plate 12/76 Yes No Wear Appearance Removed 2-B 124 42 12th Plate 12/76 No No Eddy Current Pitagged Indication, 40-60%
2-B 118 52 12th Plate 12/76 No No Similar to Left 124/42, 15%
)
3-B 77 11 15th Plate 7/76 Yes Yes No Visual Plugged R0-287/76-10 9
Inspection 3-B 77 19 15th Plate 2/77 Yes Yes Eddy Current Nailed R0-287/77-2 14't 450 Crack 3-B 77 12,13,14,15 2/77 Yes No Eddy Current Nailed 16,17,18,20, 21 3-B 75 2
2/77 Yes No Eddy Current Nalled