ML20070E531

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Forwards Justification for Addl 30-day Operation of Steam Generators at 75% Power,Based on Encl Results of Recent Eddy Current Tests.Mod Scheduled for mid-Jan 1983. Concurrence Requested
ML20070E531
Person / Time
Site: McGuire Duke Energy icon.png
Issue date: 12/15/1982
From: Tucker H
DUKE POWER CO.
To: Adensam E, Harold Denton
Office of Nuclear Reactor Regulation
References
NUDOCS 8212170290
Download: ML20070E531 (11)
v • d • e


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DUKE POWER GOMPANY P.O. Box 33180 CHARLOTTE, N.C. 28242 II AL II. TUCKER TELEPHONE ver e perssorwr (704) 373-4531 anxa. ram risope.rtums Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C. 20555 Attention: Ms. E. G. Adensam, Chief Licensing Branch No. 4 Re: McGuire Nuclear Station Docket No. 50-369

Dear Mr. Denton:

The purpose of this letter is to provide a summary of the results of the eddy current testing (ECT) performed on the Unit 1 steam generators and to outline the proposed operating plans for the unit.

Duke Power Company has evaluated operation for an additional 30 days at 75 percent power using information from previous ECT. Attachment 1 is the evaluation performed to justify this operation. Attachment 2 provides information from recent ECT examinations. Although we have evaluated operation at 75 percent power for 30 days and are requesting your concurrence for this period of time, it is our intent to operate above 50 percent power only during periods of time when additional power would normally be purchased external to the Duke Power system at a cost higher than oil generation.

This situation, if it occurred at all, would be expected to occur only under very severe weather conditic7s and would likely be short term. The 00f reason for this limitation is not due to any safety concerns, but is due j

to economic, availability and long term plant performance concerns. p'.

The NRC Staff evaluation of the proposal will of necessity have to consider b,fiLAM the full 30 days at 75 percent power, but it is important that the Staff understand Duke's intention to limit operation above 50 percent power as c . C W' s T*gD described above.

g, Q:th@Y Currently, an outage is scheduled for mid-January 1983 to install the steam bO [

generator modification. This schedule is predicated on completion of all Westinghouse analyses, manufacture and delivery of hardware and approval ygg T of the Design Review Panel report by the NRC within this time frame. Since Q there remain many uncertainties, this schedule is subject to change. Duke f/. k ogi n wM.

Power Company would continue to operate McGuire Unit 1 at 50 percent power l

(as qualified above) until the modification is ready for installation but would shut down no later than April 1, 1983 for the next ECT.

l I

l If there are any questions regarding this proposal, we would be pleased to discuss them with you.

8212170290 821215 PDR ADOCK 05000369 p PDR 1 _ -

Mr. Harold R. Denton, Director December 15, 1982 Page 2 Very truly yours, uVSxfI Hal B. Tucker i CAC/php cc: 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

ATTACHMENT 1 MCGUIRE NUCLEAR STATION Justification For Additional Operation at 75% Power Introduction Since the problem of premature tube wear in Westinghouse Model D steam generators was discovered in 1981, Duke Power Company has operated McGuire Unit I at restricted power levels and has performed steam generator inspections at frequent intervals. This manner of operation, which is consistent with the guidance contained in Regulatory Guide 1.83 and 1.121, was a cautious attempt to establish the extent that the McGuire 1 steam generators were affected and the wear rate as a function of power level. The most recent inspection of McGuire, performed after the second of two 30 day periods of operation at 75% power, has provided the data which permits accurate determination of the tube wear rate and the effects of additional operating time at 75% power.

Results of Previous Inspections In July,1982, the four steam generators at McGuire 1 were inspected following

a period of operation which included 30 days at 75% power. At that time, only one steam generator tube showed significant wear (tube 49-40 in steam i

generator C) and a wear rate prediction was made based on that single tube.

The calculated wear rate at that time bounded that of all other worn tubes and could therefore be used as an estimate of the additional wear which would l occur during another 30 day period of operation at 75% power. In our report to NRC, it was noted that this single tube would wear to the plugging limit (40% through wall by Technical Specifications) and that no other tubes would show total wear as large as 40%. On the basis that the total number of i affected tubes was small, and that signficiant wear appeared on only one tube,

we recommended and NRC accepted additional operation including another 30 day

( period at 75% power.

Results of Most Recent Inspection In November, 1982, McGuire I was again shut down for steam generator inspection. This inspection was performed and evaluated in the same manner as l the July, 1982, inspection in order to ensure that the most accurate measure l of additional steam generator tube wear could be made. The results of this inspection are reported in detail in Attachment 2. As expected, steam generator tube wear continued to progress due to operation at 75% power.

l Significant wear indications (through wall depths greater than 12% or 5 mils) l appeared on 21 tubes, including tube 49-40 in steam generator C. As predicted l following the July, 1982 inspection, this tube had worn to a through wall depth just below the 40% plugging limit. This tube has been taken out of service by plugging. Five other tubes of this group were also plugged, though the measured defect depth was much less than 40%; this is discussed further in the section below on preventive plugging. The total number of tubes 1

I

. s _ _ _

4 s

r b .

showing any indication of wear is 67, including 41 which showed no indication of wear at the July, 1982 inspection. Thi r. amber of worn tubes represents 12% of the total tubes in rows 47, 48, and 49 and 0.3% of the total number of tubes in the four steam generators.

Calculation of Tube Wear Rate Duringeachofthepreviousoperatingperiods,moakoperationhasoccurredat 50% power and below. Based on operation at the Almaraz 1 ur.it in Spain, '

operation at 50% power (equivalent to 52% at McGuire, due to higherifeedwater flow) for 3000 hours0.0347 days <br />0.833 hours <br />0.00496 weeks <br />0.00114 months <br /> produces no measurable wear. It should be noted that Almaraz 1 operated at full power for several months prior to the discovery of the tube wear problem and contains many tubes with wear penetration higher than the largest wear seen at McGuire'1. Accordingly,"it is concluded that operation at 50% and below does not cont.ribute to the wear seen at McGuire 1.

Operation during each previous period at McGuire has included approximately 30 days 75% power. Though the total number of affected tubes remains small, sufficient data has been gathered to support the following conclusions:

1. When tubes are unworn, or when wear volunes are very small (on the order of 10~4 cubic inches or less), wear rat'es are very small.

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2. Once tube wear progresses to the point that the. total metal removed is N10 4 cubic inches (this corresponds to approximately 12% through wall),

then the wear rate increases. An examination of the data from the July, 1982, inspection showed nine tubes with wear indications of N10~4 cubic .

inches. These nine tubes now have wear indications between 2.6 x 10 3 and 3.4 x 10~3 cubic inches. Accordingly, an upper bound for tube wear may be established as 3.4 x 10 3 cubic inches per 30 day period at 75%

power. The tube with the highest wear tube 49-40 in stearJ generator C, ^ ,

' had a wear volume of 2x 10 3 cubic inches in ' July, 1982. The measured ,

volume based on the most recent inspection is[5.2 x 103 cubic inches.

It can therefore be concluded thit a wear rate of 3.4 x 10 3 cubic inches per 30 day operating period is consistent with the data from all worn tubes and applies as long as the total wear t mains below the plugging-limit of 40% through wall' .

Wear Projection for Additional 75% Power Operation If the wear rate determined above susedtoprojecttheconsequencesofan i

I additional 30 day period of or' u .on at 75%, the following conclusions may be stated: ,

1. Two additional tube. ilt . guire plugging based on the plugging limit of

, 40% through wall. Tr:2se two (Lbes will have indications less than 50%.

l 2. Twenty-three tubes which currently have wear indication of *104 cubic

' inches will have indications of 73.5 x 10 3 cubic inches. This wear volume corresponds to a thrc, ugh wall depth of less than 25%.

2 4

_ , _,.m..--._-r,-~- _-__e_. -

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preventive Plugging Once the wear rate was calculated based on the previous operating period, it was decided tha'. five tubes should be preventively plugged due to the progression o' tube wear. All of these tubes showed wear volumes of E3.4 x 10_3 cubic inche: or 23-25% through wall. It was noted that these tubes would grow beyono the plugging limit (to approximately 56% through wall) during a subsequent 30 day operatieg period at 75% power. The wear rates for these five tubes were equal to or less than the wear rate discussed above.

Long Te p Consequence of Additional Tube Wear Because the tube wear rate at 75% power is not zero, further operation at 75%

i . power will cause some additional tube wear. Ilowever, the magnitude of tube

!? wear and the total number of tubes affected remains small. From previous operation, an estimate of the wear rate at 75% has been established and this calculated wear rate is not expected to change in the next operating period.

An assessment of the short term consequences of an additional 30 days operation at 75% power shows that these consequences are acceptable.

The modification that Westinghouse has proposed is designed to be effective for units like Ringhals 3 and Almaraz 1 which have more severe initial wear than McGuire will have following the next operating period. It is concluded that the condition of the steam generator tubes in McGuire will not adversely affect the ability of the modification to eliminate the tube wear problem.

Duke Power Company has also considered whether the worn areas will cause the possibility of accelerated corrosion and premature tube failure. The chemical environment in the preheater area, being that of feedwater rather than steam generater bulk water, is more favorable from a corrosion standpoint. The i

temperature at the outer wall of the tubes is less than cold leg temperature and therefore much less than the temperature at which corrosive attack has

, adversely affected steam generator tubes. Finally, in the first few rows of i the preheater, flow velocities will remain high after the modification, pre-l cluding sludge deposition. We conclude that the worn condition of the tubes will have no significiant effect on the ability of the tubes to resist corrosion.

l Over the 40 year life of the steam generator, a number of corrosion mechanisms can be expected to be active in the tube bundle, causing a gradual deterioration

( in the condition of the tubes. The chemistry program at McGuire is expected i to reduce the rate of this deterioration to acceptable levels. The tubes in

( the front row of the preheater, while signiciantly affected by wear early in I

life, are expected to be much less affected by corrosion later. Accordingly, the wear created by this early operation is not expected to affect the 40 year lifetime of the worn tubes.

!\

Conclusion i An additional operating period of 30 days at 75% power is justified for j McGuire 1 on the basis that the wear rate for tubes at this power level has I

been established and that the consequences of this operation have been evaluated and found to be acceptable.

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Page 1 of 6 McGuire Nuclear Station Results of Steam Generator ECT 3-82 7-82 11-82 b #

Row Column Supp. % TV Volume  % TW Volume  % TW Volume Remarks Steam Generator 'A'

  • ' *C d d d d 46 50 14 O O O O 47 56 14 * * *
  • 4 IE-5 47 58 14 *
  • f-
  • 6 2E-5 47 59 14 * * *
  • 6 2E-5 47 60 14 * * * * <2 <5E-6 16 * * *
  • 4 IE-5 47 61 14 0 0 4 IE-5 6 2E-5 16 * * *
  • 6 2E-5 47 77 16 * * *
  • 4 1E-5 48 38 16 * * *
  • 6 2E-5 48 39 14 * * *
  • 0 0 48 40 16 * * *
  • 4 IE-5 48 41 16 * * *
  • 4 IE-5 48 53 17 * * *
  • 0 0 8 4E-5 48 55 16 * - - -

6 2E-5 48 56 12 * * *

  • 6 2E-5 48 57 11 * * *
  • 0 0 12 * * *
  • 4 IE-5 48 58 12 * * *
  • 4 IE-5 Plugged 11-14-82 14 5 1.6E-5 9 6E-5 23 3E-3 16 6 2E-5 4 IE-5 6 2E-5 17 * - - -

10 8E-5 48 59 16 * * *

  • 0 0

1 Page 2 of 6 3-82 7-82 11-82 Column b Row Supp.  % TW' Volume  % TW* Volume  % TW Volume Remarks Steam Generator 'A' 48 60 11 * * *

  • 0 0 12 * * *
  • 4 IE-5 17 * * *
  • 2 6E-6 4P. 61 11 * * *
  • 0 0 12 * * *
  • 0 0 14 * * *
  • 12 1.6E-4 17 * * *

, 19 * * *

  • 4 IE-4 48 62 16 0 0 6 2E-5 8 4E-5 49 37 16 * - a a 2 SE-6 49 38 16 * * *
  • e e 6 2E-5 49 41 16 * * *
  • 0 0 8 4E-5 49 43 15 * * *
  • 4 IE-5 17 * * *
  • 8 4E-5 49 45 16 * * *

.49 51 19 * * *

  • 0 0 49 53 12 * * *

16 * * *

  • 10 8E-5 49 52 - * * * * - -

Plugged 7/4/82

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Page 3 of 6 3-82 7-82 11-82 b b Row Column Supp. % TW Volume  % TW Volume  % TW" Volume Remarks Steam Generator 'A' 49 54 14 * * *

  • 2 SE-6 49 55 12 * * *
  • 4 IE-5 10 8E-5 19 * * *
  • 6 2E-5 49 57 12 * * *
  • 4 IE-5 14 *
  • 0 0 10 8E-5 17 * * *
  • 6 2E-5 49 58 11 * * *
  • 0 0 12 1.6E-4 16 *
  • 6 2E-5 49 59 12 * * *
  • 0 0 16 6E-4 20 * * * *
  • 4 IE-5 Plugged 11-14-82 12 * * *
  • 0 0 12 2E-4 20 * * *
  • 0 0 l

l 1

i Page 4 of 6 I 3-82 7-82 11-82 Row Column Supp. % TV" Volume  % TW Volume  % TW Volume Remarks Steam Generator 'A' 49 61 11 * * *

  • 4 IE-5 Plugged 11-14-82 12 *
  • '- v
  • 17 10 8E-5 19  ? * *
  • 0 0 49 62 10 * * * * <2 <5E-6 11 * * * * <2 <5E-6

. 12 * * *

  • 12 1.6E-4 20 * * *
  • 6 2E-5 49 63 12 * * *

6 2E-5 20 * * *

  • 4 1E-5 49 64 16 * * *
  • 0 0 20 * * *
  • 0 0 49 65 16 * * *
  • 0 0 49 74 16 * * *
  • 14 3E-4 49 76 16 * * *
  • 6 2E-5 49 77 16 f- * *
  • 4 IE-5
4 Page 5 of 6 i

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3-82 7-82 11-82 Column Supp. b Row  % TW* Volume % TW" Volume  % TW' Volume Renarks Steam Generator 'B' 49 52 14 * * *

  • 0 0 16 * * *
  • 3 7E-6 17 * * * * <3 <7E-6 19 * * *
  • 10 8E-5 49 56 17 * * *
  • 5 1.6E-5 19 * * *
  • 0 0 _.

49 57 17 * * *

  • 0 0 19 * * *

. Steam Generator 'C' 49 39 16 *

  • 4 IE-4 49 46 14 * * *
  • 5 1.6E-5 49 47 13 * * *
  • 0 0 49 73 14 * * *
  • 7 3E-5 49 76 16 * * *
  • 5 1.6E-5

Page 6 of 6 .

4 3-82 7-82 11-82 b

Row Column Supp.  % TW' Volume  % TW" Volume  % TW" Volume Remarks Steam Generator 'D' 49 74 16 *

  • 9 6E-5 21 2.6E-3 17 * * *
  • 8 4E-5 19 1.5E-3 17 * * *
  • 12 1.6E-4 49 78 17 * * ^
  • 7 3E-5 49 79 17 * * *
  • 5 1.6E-5 49 80 17 * * *
  • 7 3E-5 49 81 17 * * * '*- 12 1.6E-4
  • TW = Through Wall b

All volumes are in cubic inches C

No defect detected d

Defect detected but too small to size

" Signal noise prevented defect prediction

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