ML20062C445
| ML20062C445 | |
| Person / Time | |
|---|---|
| Site: | McGuire  |
| Issue date: | 08/03/1982 |
| From: | Tucker H DUKE POWER CO. |
| To: | Adensam E, Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8208050254 | |
| Download: ML20062C445 (9) | |
Text
.
DUKE POWER COMPANY
^ " * ****'
GENERAL OFFICES s7."d!
422 SOUTH CHURCH STREET CHARLOTfE. N. C. 28242 August 3, 1982 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C. 20555 Attention:
Ms. Elinor G. Adensam, Chief Licensing Branch No. 4 Re: McGuire Nuclear Station Unit 1 Docket No. 50-369 Model D Steam Generator Operation Report on Operating Period April - June, 1982
Dear Mr. Denton:
Attachments 1 and 2 summarize the results of the most recent eddy current inspec-tion of the steam generators in McGuire Unit 1.
This incpection was completed in early July following 720 hours0.00833 days <br />0.2 hours <br />0.00119 weeks <br />2.7396e-4 months <br /> of operation at 75 percent power. An evaluation of these inspection results was performed which bounded the tube wear rate for operation at 75 percent power. On the basis of this evaluation the following operating plan is proposed for McGuire Unit 1 until the next planned shutdown, tentatively scheduled for November or until implementation of the steam generator modifications.
It is proposed to operate McGuire during this period at a power level no greater than 75 percent. The operating time above 50 percent power will be restricted to 30 days during this period of operation. Further operation at 75 percent is justified for the following reasons:
1.
The results from eddy current examination have established a tube wear rate at 75 percent power. This wear rate, when applied to the largest existing defect, allows for an additional 30 days operation at 75 percent power (see Attachments 3 and 4).
Note that this wear rate was found on only one single tube; all other affected tubes showed wear rates significantly smaller (by a factor of four or more) than this single tube.
2.
Previous operation at McGuire Unit 1, which includes about 1000 hours0.0116 days <br />0.278 hours <br />0.00165 weeks <br />3.805e-4 months <br /> at 75 percent power and higher, has caused wear indications to appear on 29 tubes. Only four of these tubes exhibit wear hC[)L penetration greater than 12 percent through wall (approximately 5 mils).
The smaller defects have very low wear rates at 75 percent power, approximately 2 milc/30 days or less. A single large defect, presently measured to be 20 percent through wall, exhibits a larger O
R 1
Mr. Harold R. Denton, Director August 3, 1982 Page 2 wear rate and is the reason for restricting operation at 75 percent power to 30 days. There are no indications of wear in steam generator B and only two tubes showing evidence of wear in steam generator D.
It should be emphasized that almost all of the wear indications are much too small to size accurately using eddy current techniques, and the size of these defects has been conservatively overestimated due to that uncertainty.
3.
At the end of the next operating period (approximately November 1, 1982) the following inspection results are anticipated--one tube with a defect close to the plugging limit (this tube will then be plugged or removed for examination), and growth of between 0 percent and 5 percent on all other affected tubes. These tubes will be well below the plugging limit after the proposed operating period.
4.
There are 688 steam generator tubes in the first three rows of the preheater in the McGuire Unit 1 steam generators. Wear indications have been found on 29 of these tubes or about 4 percent.
Significant wear (through wall penetration greater than 20 percent) has not been found on any tubes.
It is apparent that limited operation at 75 percent power does not have a widespread effect on the steam generators and that the wear occurring at this power level does not represent a significant effect on steam generator integrity.
During the July inspection, several sophisticated eddy current techniques were used, including absolute and pancake coil techniques. For the four larger defects (greater than 12 percent) the pancake coil readings were lower than those obtained by absolute and differential methods. Measurement of circumferential extent of defects, even the largest one, showed that defects extended 90 or less around the tube.
Based on data from tubes removed from European units (Ringhals 3 and Almaraz 1), these defects with limited circum-ferential extents are very small; therefore, it is concluded that the measure-ments given in the attached summary are conservative.
Because total tube wear close to the plugging limit is expected on a single tube only, and because there is considerable margin between the plugging limit and the required minimum tube wall per Regulatory Guide 1.121, there is no impact on nuclear safety from the proposed operating plan. It is expected that additional operating time at 75 percent power will give us greater con-fidence in the calculated wear rates and, having eliminated the single tube which appears to wear at a higher rate than is typical of the remainder of the affected tubes, operation beyond the next inspection could be at 75 percent power.
Please advise if there are any questions regarding this matter.
l Mr. Harold R. Denton, Director August 3, 1982 Page 3 Very truly yours,
<db f /w H. B. Tucker, Vice President Nuclear Production REH/php Attachments cc:
Mr. P. R. Bemis Senior Resident Inspector McGuire Nuclear Station Mr. James P. O'Reilly, Regional Administrator U. S. Nuclear Regulatory Commission Region II 101 Marietta Street, Suite 3100 Atlanta, Georgia 30303 I
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STEMI GENERKr0R EDDY CURRENT 3 - 32 7 - 82 6Vol
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. Volume in >Q0._.4 CIRC. AW1 in x10 49 57 14 0
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Calculation of Projected Wear The results of the eddy current inspection provided an upper bound for the wear rate for the steam generator tubes in McGuire. This wear rate, which applies to only one tube (tube 49-40 in steam generator C) is 2 x 10-3 in3 30 days at 75%
-3 3
The conservative upper bound for this defect volume is 3 x 10 in. An additional 30daysat75gercentpowerwouldthereforeincreasethevolume 3
of this defect to 5 x 10~
in, which represents a through wall penetration of 40 percent.(see Attachment 4).
This single tube is therefore likely to be a pluggable indication at the next inspection.
A defect penetration of 65 percent, which represents the minimum required wall thickness per Regulatory Guide 1.121, corresponds to a volume of 9 x 10-3 in3 (see Attachment 4).
At the present wear rate, there is a large margin on allowable operating time at 75 percent power (about a factor of 3).
For all other steam generator tubes, wear rates at 75 percent power are much lower than that calculated above. Typical bounding values are 0.5 x 10-3 in3 per 30 days of operation at 75 percent power. This corresponds to additional through wall penetration of 2 mils or about 5 percent (see Attachment 4).
Actual wear rates range down to O percent.
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