ML20040D998
| ML20040D998 | |
| Person / Time | |
|---|---|
| Site: | McGuire, Mcguire  |
| Issue date: | 01/26/1982 |
| From: | Parker W DUKE POWER CO. |
| To: | Adensam E, Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8202020474 | |
| Download: ML20040D998 (8) | |
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1 DUKE POWEH COMPANY Powsu Dun.rnwo 422 SouTu Cuencu STREET, CHAH1DTTz. N. C ana42 waum o. eaa.uta.sa.
January 26, 1982 Vier Patsiorst TELtraosit; AntA 704
$f tame PROOvCitO*e 373-4083 a)
Mr. Harold R. Denton, Director 8
Office of Nuclear Reactor Regulation 4
U. S. Nucicar Regulatory Commission ggggWCD Washington, D. C.
20555 r
f rea 11982> 3 Attention:
Ms. E. G. Adensam, Chief a
r g
Licensing Branch No. 4 yngr ewJts u 7
,g M
l Re: McGuire Nuclear Station Docket Nos. 50-369, 50-370 g
Dear Mr. Denton:
' is Duke Power Company's justification for the acceptability of continued operation of McGuire Unit 1 through February 15, 1982 with the power history shown on page 3 of the attachment. Notice that this program l
places more restrictive limits on power operation than specified in my l
December 29, 1981 letter which provided for 6 weeks at 75% power.
The basis for this program is to assure that no tube damage beyond the technical specification limit of 40% would be expected based on very con-servative analyses. There are two conservatisms inherent in this program.
The first conservatiam is the assumption regarding tube wear. rates which is described in some detail in Attachment 1.
The second conservatism is in the 40% tube plugging limit which has considerable margin to account for eddy current inaccuracies and uncertainty in wear rates.
Additionally, based on the analysis in Attachment.1, indications of tube wear on the order of 20% should have been observed during the last eddy current examination. In fact there were no indications of tube wear which demonstrates the conservatism in the analysis.
r This information is being provided to respond in part to Mr. Robert L.
Tedesco's letter of January 7, 1982. The remainder of the information requested by Mr. Tedesco's letter will be provided by January 29, 1982.
V 'y truly yours. [
JD
- d. g
. William O. Parker, Jr.
i GAC/jfw Attachment DOKof a
PDR t
Harold R. Denton January 26,' 1982 Page 2 1
cc:
Mr. P. R. Bemis Senior Resident Inspector McGuire Nuclear Station Mr. James P. O'Reilly, Director U. S. Nuclear Regulatory Commission Region II 101 Marietta Street, Suite 3100 Atlanta, Georgia 30303 e
.,,..v.,.
McGuire Nuclear Station Program for Power Ascension at McGuire 1 Introduction The significant tube wear problem encountered in Westinghouse Model D steam generators at Ringhals 3 and Almarraz l'has caused Duke Power Company to modify our plans for power ascension at McGuire 1.
The philosophy behind this modification has been our intent to proceed cautiously so that the effects of the tube wear phenomenon, should it be found that McGuire 1 is susceptible to the damage mechanism found at the European units, is kept to a minirum.- The purpose of this document is to set forth a plan for maximizing the allowable normal operating power level for McGuire 1 consistent with the prevention of steam generator tube damage.
Technical Basis for Duke Power Company Position A significant effort is being expended to address the engineering aspects of the tube wear problem in Westinghouse Model D steam generators. This research and development program has been previously discussed with the NRC staff, and an update of this program appears in this document. However, it is possible to establish justification for continued operation and power ascension at McGuire prior to the completion of the research and development program. This justification has two major aspects - eddy current examination of the McGuire 1 steam generators, and estimation of the rate of tube wear due to the flow induced vibration occurring in the steam generators.
Eddy Current Examination Duke Power Company concludes that eddy current examination provides a reliable and conservative measure both of the threshold of wear and of the extent of tube wall penetration after wear begins to occur. This conclusion is based on the following:
1.
The eddy current testing method used by Westinghouse at Ringhals 3 has been shown to be a conservative method of detecting and estimating the extent of tube damage by the particular wear mechanism which is occurring.
Measurements made in the laboratory on the two tubes removed from Ringhals 3 of the actual through-wall penetration have been compared with the measurements of the damage made in the field with eddy current equipment.
In every case where the actual maximum through-wall penetration was greater than 10%, field eddy current measurement overestimated the extent of the damage, usually by a factor of two.
A summary of the data from defects on the two tubes removed at Ringhals 3 is shown in Table 1.
Thus it is shown that eddy current testing is a reliable and conservative measure of the extent of tube degradation by the wear mechanism present in Westinghouse Model D steam generators, once the wear progresses beyond 10% of the tube wall (a depth of.0043. inches). For the eddy current techniques used by Westinghouse, a threshold of detectability of 10% through-wall may be assumed.
2.
In addition to the eddy current technique usc by Westinghouse at Ringhals 3 which Duke Power Company has used at McGui Duke Power Company 1
i i
is sponsoring eddy current development work at the EPRI Non-Destructive Examination Center to improve both the threshold of detectability and the i
i accuracy of the through-wall measurements for the type of tube defects found at Ringhals 3.
If this program is successful, the usefulness of eddy current testing as a measure of the tube wear problem will be increased.
It should be noted that the eddy current techniques previously used at Ring-i hals 3 and McGuire 1 connot be assumed to be reliable if the amount of through-wall penetration is less than 10% - this is supported by the data in Table 1.
Accordingly, Duke Power Company will assume that as much as 10% through-wall penetration has occurred even if eddy current testing indicates no detectable degradation, unless a lower threshold of detecta-bility can be justified on the basis of our eddy current measurement technique development program.
Rate of Tube Wear i
]
There are several ways to establish a rate of tube wear as a basis for continued operation of McGuire.
1.
At the time of the tube leak which occurred at i'inghals 3, that unit had operated at power levels of 50% and above for 37t', hours. If it i
is assumed that wear _ begins at 50% and does not increase in rate for power levels above 50% (a very conservative assumption) the wear rate may be estimated as:
l 100%
.0266 % tube wall penetration
=
3760 hours0.0435 days <br />1.044 hours <br />0.00622 weeks <br />0.00143 months <br /> hour at or above 50%
On this basis, McGuire could operate for 40%
1500 hours0.0174 days <br />0.417 hours <br />0.00248 weeks <br />5.7075e-4 months <br /> at 50%
=
j
.0266 l
and not reach a level of degradation which required that a tube be plugged.
Similar calculations may be performed assuming that tube wear starts at 75%,
90%, and 95%, as summarized in Table 2.
2.
A wear rate may be established for McGuire based on the previous eddy current test results. An eddy current inspection was performed at McGuire in November, 1981, after 18 days at 50%. The results of that inspec-tion showed no detectable degradation anywhere in the preheater. Using the previously justified 10% threshold for eddy current testing, the degradation rate may be calculated to be:
10%
.02315 % tube wall penetration 432 hours0.005 days <br />0.12 hours <br />7.142857e-4 weeks <br />1.64376e-4 months <br /> hour at 50% power j
On this basis, with an assumed 30% allowable additional degradation, McGuire could operate for l
30%
00 hours0 days <br />0 hours <br />0 weeks <br />0 months <br />
=
.02315
, (
l
- _ - _.. ~ _, _-
at 50% power without reaching as much as 40% through-wall penetration, the level at which plugghig would be required. A similar calculation may be performed for the December, 1981, inspection.after six days at 75% power, conservatively assuming that no tube wall degradation occurred prior to the six days of operation at 75%.
(As previously reported to NRC, this inspection also showed no evidence of tube wall degradation).
10%
.0694% tube wall degradation
=
144 hours0.00167 days <br />0.04 hours <br />2.380952e-4 weeks <br />5.4792e-5 months <br /> at 75%
hour at 75% power In summary, it is possible to catablish a conservative measure of tube wall degradation rate based on the eddy current testing program previously used at McGuire or on the single maximum point of tube wear noted at Ringhals 3.
These calculated tube wear rates may then be used to establish eddy current inspection intervals which may be used to support power ascension at McGuire with a large amount of margin with respect to nuclear safety concerns.
Basis for Continued Operation of McGuire 1 Presented above is justification for the use of eddy current measurement as a conservative prediction of the progress of the tube wear phenomenon found in Westinghouse Model D steam generators. Also illustrated are two methods of predicting tube wear as a function of power level, one based on the single observed tube leak at Ringhals 3 and the other based on the successful eddy current examination program at McGuire 1.
These techniques may be applied to the present operation of McGuire 1 as follows. During the period from January 1, 1982, to February 15, 1982, McGuire I will be at the following power levels for the approximate times shown:
Power level Approximate number of days 50%
36 75%
6 90%
3
.t00%
1 l
Using the actual wear rates for McGuire, as determined by Method 2 above, for 50% and 75%, and the Ringhals 3 wear rate data for 90% and 100%, the total amount of wear which would be estimated for McGuire for the operating schedule above is shown in Table 3.
Power Ascension Program for McGuire Following the eddy current inspection to be performed during the outage beginning February 15, 1982, Duke Power intends to follow a program of power ascension based on calculated wear rates and periodic eddy current examinations. The details of this program will be provided to NRC well in advance of the return to power date for reciew.
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+
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Table 1 i
Tube No.
Intersection No.
Field Eddy Current Actual Lab Measurement Measurement R49-C55 1
0 5%
2 0
2%
3 100%
100%
4*
5 e
60%
-30%
6 59%
25%
7*
l 8
.0 9*
10 0
7%
11 0
0 R49-C66 1
less than 20%
0 2.
less than 20%
0 3
less than 20%
12%
4 36%
16%
5 34%-
12%
i 6
61%
49%
7 43%
16%
8 less than 20%
9%
9 less than 20%
16%
10
'less than 20%
5%
11
'less than 20%
0
- There is a flow windcw et this location, therefore there is no tube to tube support plate intersection here.
- This part of the tube was recained by the Swedish State Power i.
Board; lab results are not available.
t i.. -, _
o.
+
A Table 2 Tube Wear Rates at Ringhals 3
~ Assumptions:
(a) the leaking' tube represents the maximum through-wall penetration point on any tube - this value is 100%
(b) wear rate calculated at a particular power level assumes that no wear occurs prior to reaching that power level (c) wear rate is linear with time (d) for a wear rate calculated at a particular power level, wear is assumed not to increase in rate as power level is increased i
Power level Calculated Wear Rate
)
50%
.0266 % tube wall penetration hour at or above 50%
75%
.0459 % tube wall penetration hour at or above 75%
90%
.061 % tube wall penetration hour at or above 90%
95-100%
.073 % tube wall penetration j
hour at 95% - 100%
i l
l l -
i Table 3 McGuire estimated tube wear - January 1 --February 15, 1982 e
for 50% power period 864 hours0.01 days <br />0.24 hours <br />0.00143 weeks <br />3.28752e-4 months <br /> x.02315 20%
=
75%
144 hours0.00167 days <br />0.04 hours <br />2.380952e-4 weeks <br />5.4792e-5 months <br /> 2:.0694 10%
=
90%
72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> x.061 4.4%
=
i 100%
24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> x
'.073 1.8%
=
36.2%
the total estimated wear for McGuire for the period January l'- February 15, 1982 is 36.2% which is less than the limit given in the McGuire Technical Specifications above which tube plugging is required.
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