05000266/LER-1979-017, Discusses 791105 & 20 Meetings W/Nrc Re Info & Data on Steam Generator Tube Problems,Presented in LER 79-017/01T-0 on 791116.Certificate of Svc
| ML19260C562 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 12/21/1979 |
| From: | Burstein S WISCONSIN ELECTRIC POWER CO. |
| To: | Harold Denton, Schwencer A Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19260C561 | List: |
| References | |
| NUDOCS 8001070529 | |
| Download: ML19260C562 (8) | |
| Event date: | |
|---|---|
| Report date: | |
| 2661979017R00 - NRC Website | |
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Wisconsin Electnc m coww 231 W. MICHIGAN, P.O. BOX 2046, MILWAUKEE, WI $3201 December 21, 1979 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U. S. HUCLEAR REGULATORY COMMISSION Washington, D. C.
20555 Attention:
Mr. A. Schwencer, Chief Operating Reactors Branch 1 Gentlemen:
DOCKET NO. 50-266 STEAM GENERATORS POINT BEACH NUCLEAR PLANT, UNIT 1 On November 5 and November 20, 1979, meetings were held in Bethesda with representatives of the NRC Staff to present information and dats related to recent Unit 1 steam generator tube problems.
This information was confirmed by our letter to the NRC of November 23, 1979.
Our Licensee Event Report (LER) No. 79-017/OlT-C, dated November 16, 1979, provided information in regard to eddy current examination results obtained during the most recent Unit 1 refueling in October.
A listing of plugged tubes, defect size and defect location for each steam generator was included in the LER.
Among other things, this LER indicated there were two tubes in "A" steam generator and two tubes in "B" steam generator with defects at the top of the tubesheet and one tube in the "B" steam generator with a defect one-half inch above the tubesheet.
This letter is in response to your Mr. Trammell's request for further information in respect to these five tubes.
LER No. 79-017/0lT-0 provided details of the steam generator eddy current October 1979' inspection program, the results of the inspection and the location of plugged tubes and stated that three tubes had been physically removed for metallurgical analysis.
The results of the metallurgical analyses on these three tubes were discussed with your Staff on Movember 20 and documented in our November 23 letter.
Your attention is called to the observations and conclusions on page 3 of that letter where it is stated:
1696 223
_1_
8001070 Q2]
Mr. Harold R. Denton December 21, 19'9 "4.
Based on samples removed from the Unit 1 steam gerierator and from other plants in previous years, these defects are concluded to be intergrenular cerrosion attack of the Inconel 600 tube material in the narrow crevice area caused by residue of caustic materials remaining from phosphate chemical treatment and possibly from earlier condenser tube leakage.
"5.
Thi corrosion is confined to the crevice crea.
No evidence of this intergranular attack was found in areas of tube above the tubesheet."
Our conclusion in respect to the absence of IGA above the tubesheet is based on examinations of samples of tubes removed, ha stated on pages E3-3 and E3-4 and Viewgraphs 5, 16 and 23 of to our November 23 letter.
This conclusion is supported further by the burst tests summarized in item 7, rune 4 and detailed on pages E3-3 through E3-6, where on page E3-6, the following statement was made:
- 2.
The difference in burst strength between the specimens from deep in the crevice and that which spans the tubesheet indicates essentially no degradation in burst strength in the region of the tubesheet from a virgin tube burst strength.
This coincides with the result of the metallurgical examination which concluded that there was no intergranular attack above this tubesheet."
During our meetings, we advised you of the limitations of available eddy current techniques to detect IGA.
On page 5 of our November 23 letter, we stated the following:
"9.
Present eddy current testing has demonstrated its capability to detect cracks from a range of 20% through wall to full-wall penetration.
This technique, however, is not an effective means of detecting intergranular corrosion in the absence of cracks.
Because a diametrically unrestrained tube, such as in the space above the tubesheet and outside tube support plates, expands under internal pressure, intergranular corrosion in such areas would be revealed as cracks.
In the tightly constrained areas within the tubesheet, tube expansion under internal pressure is effectively precluded.
While this makes eddy current indication of intergranular attack incapable, the totally contained tube cannot expand under internal pressure to cause significant cracking or rupture during normal or accident conditions."
i696 224
Mr. Harold R.
Denton December 21, 1979 Confirmation of the eddy current method of crack detection was made by metallographic examination as detailed on page E3-3 and Viewgraph 5 of Enclosure 3 to our letter of November 23.
However, no correlation could be found between eddy current test results and presence of IGA.
On this basis, we made no attempt to relate the eddy current inspection results contained in LER 79-017/OlT-0 with the presence or absence of IGA.
It is our opinion, and that of our consultants, that traditional eddy current inspection techniques make such a correlation unsupportable.
You may recall that Westinghouse Electric Corporation stated at our November 20 meeting that they would be seeking to make future improvements in eddy current testing methods in order to demonstrate ability to detect IGA by this technique.
The five tubes which had eddy current indication at or above the tubesheet during the october 1979 inspection are identified as follows:
Oteam Tube Eddy Current Generator Row Column Indication A
22 46 55% defect at top of tubesheet A
30 57 80% defect at top of tubesheet B
28 38 45% defect at top c,
of tubesheet B
30 44 83% defect at top of tubesheet B
32 42 61% defect 1/2" above tubesheet In October 1979, these five tubes, and all others, were inspected utilizing multi-frequency eddy current techniques.
As a result of the defects indicated, these tubes were, of course, plugged, as reported in LER 79-017/OlT-0.
As we stated above, we made no attempt to relate these defects to IGA.
We had included them in the " crevice corrosion" column of viewgraph 1, in our November 23 letter based upon preliminary information regarding the number of tubes containing defects and, as we have since determined, this was in error.
These five tubes are in the same area of the tube bundle where many similar indications at or slightly above the tubesheet were observed in the early years of Unit 1 operation.
These multiple indications were first-reported to you in our letter dated April 7, 1975, in this docket.
Al'1 of the defec*.s were attributed to thinning or cracking.
Since our November 20 meeting, 1696 225
Mr'. Harold R.
Denton December 21, 1979 we have reviewed the single frequency eddy current test results since 1975 for these tubes and compared the signals of these past inspections to the same frequency signal obtained during the multi-frequency inspection in October.
This comparison shows that the signals have not changed through three or four annual inspections since 1975.
The use of the multi-freauency technique in the October 1979 inspection, however, allowed discrimination of the eddy current tube defect sicnal from tubesheet interference euch that identification of defects was made in these five tubes.
Based on these reviews, we believe that the defects which have apparently remained essentially unchanged since at least 1975 resulted from earlier thinning or cracking rather than to the IGA currently being experienced in the tubesheet crevice area.
The inclusion of these tubes in the " crevice corrosion" column of Viewgraph 1, attached to our November 23 letter, is now, in the light of thic comparison, incorrect.
In addition to this correction, we note that an outage in May 1978 to plug one tube in steam generator A was omitted from Viewgraph 1.
We enclose for your information a revised table which reflects these corrections.
It should be noted that, while the two tubes in steam generator A and three tubes in steam generator B are indicated as being plugged due to cracking or thinning in October 1979, the defects apparently occurred in 1975 or earlier based upon review of the previous inspection results.
We believe that the accuracy within which eddy current indications can be axially located is approximately plus or minus one-half inch.
This estimated accuracy is based on the size of the eddy current probe, the location of the two coils which are 1/8" apart on the probe, the precision of the axial measurement of the location of the probe in reference to the tube end and entrance and exit effects.
1 In response to a further question from Mr. Trammell, the metallographic examination indicated no IGA present within-3/4" of the top of the tubosheet as reported in pages E3-2, 3 and 4 and Vieworaphs 5, 10 and 16 of Enclosure 3 to our letter of November 23, 1979.
You are also aware that Unit I was shut down on December 11, following detection of steam generator tube leakage of about 250-260 gallons per day, in accordance with Section IV, item 3 of the Commission's Confirmatory order of November 30.
We are making a separate report in respect to this event, but the occasion of this shutdown also permitted us to make a more sensitive eddy current examination of the areas of concern.
Although not required by our Technical Specifications or the Confirmatory order of December 1, examination of about 1900 tubes in both A and D steam generators revealed no eddy current indications at or above the tubesheet.
i696 226
Mr. Earold R. Denton December 21, 1979 In summary, we would reiterate that all physical examination and observations indicate intergranular attack is confined to the tubesheet crevice area.
This is based on examination of tubes removed from steam generators.
Present eddy current techniques are capable of detecting tube cracks but cannot be relied upon to indicate IGA.
Any eddy current indication at or near the top of the tubesheet can, if sufficiently unscrambled from tubesheet interference, indicate a crack, but does not indicate IGA.
We believe our conclusions, and those in the NRC Safety Evaluation Report dated November 30, are not affected by these unrelated concerns regarding eddy current indications in these five tubes.
Please advise us if you have any further questions.
Very truly yours, m
W Sol Burstein Executive Vice President Enclosure Blind Copy to Messrs. C. S. McNeer R. H. Gorske/A. W. Finke C. W. Fay D. K. Porter G. A. Reed Gerald Charnoff 1696 227
12/18/79 N
UNIT 1 STEAM GENERATOR TUBE PLUGGING HISTORY Tubes Plugged Date of Thinning or Crevice Cumulative Outage Elapsed Time Denting Cracking Corrosion Other Total Percent (Years)
A B
A B
A B
A B
A B
A B
1(1) 1
<0.1 0
12/21/70 0
14 4(2) 102 95 3.1 2.9 9/30/72 1.8 87 91 103 96 3.2 2.9 1
1 4/6/74 3.3 162 194 5.0 6.0 59 98 2/26/75 4.2 168 198 5.2 6.1 11/16/75 4.9 6
4 168 198 5.2 6.1 10/1/76 5.8 168 199 5.2 6.1 1
6/24/77 6.5 179 201 5.5 6.2 1
2 10/4/77 6.9 10 2/1/78 7.1 1(3) 180 201 5.5 6.2 181 201 5.5 6.2 1
5/26/78 7.4 188 205 5.7 6.3 6
4 9/20/78 7.7 1
196 206 6.0 6.3 8
1 3/1/79 8.2 248 251 7.6 7.7 52 45 8/5/79 8.6 8/29/79 8.8 2
2(4) 252 251 7.7 7.7 10/5/79 8.9 2
3(6) 68 61 7
4(5) 329 319 10.1 9.8 Notes: (1) Plugged during manufacture.
(2) Fourteen tubes in A were plugged due to gouging during machining for clad repair.
Three tubes in B were removed for analysis and one was plugged by mistake.
(3) Plugged tube was in periphery.
- - CN (4) An audit of tubesheet photographs indicated two tubes which were plugged but previously NO not included in inspection reports.
CN (5) Seven tubes in A included three with defects less than the plugging limit, two tubes which had no indications but which were pulled for analysis, and two tubes plugged by mistake.
Four tubes in B included three tubes with indications less than the plugging limit and one g
p) tube plugged by mistake.
ao (6) Two tubes in A and three tubes in B were plugged due to defects identified at or above the tubesheet using multi-frequency eddy current techniques.
These defects are attributed to thinning or cracking in prior years, based upon comparison with single frequency eddy current results from previous inspections.
UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION In the Matter of
)
)
WISCONSIN ELECTRIC POWER COMPANY
)
Docket No. 50-266
)
(Point Beach Nuclear Plant,
)
(Modification of License)
Unit 1)
)
CERTIFICATE OF SERVICE I hereby certify that copies of " Licensee's Response to Request by Wisconsin's Environmental Decade, Inc. For Hearing on Confirmatory Order," dated December 27, 1979, were served upon those persons on the attached service list, by deposit in the United States mail, postage prepaid, or by hand delivery, on this 27th day of December, 1979.
e o
I I
b L.
Jo n H. O'Neill,Jrf[
J Dated:
December 27, 1979 1696 229
UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION the Matter of
)
)
.SCONSIN ELECTRIC POWER COMPANY
)
Docket No. 50-266
)
(Point Beach Nuclear Plant,
)
(Modification of Unit 1)
)
License)
SERVICE LIST Mr. Darrell G.
Eisenhut Kathleen M.
Falk, Esquire Office of Nuclear Reactor Regulation Wisconsin's Environmental U.
S. Nuclear Regulatory Commission Decade, Inc.
Washington, D.
C.
20555 114 East Mifflin Street Madison, Wisconsin 53703 Mr. Samuel J.
Chilk Secretary Docketing and Service Section U.
S. Nuclear Regulatory Commission Office of the Secretary Washington, D.
C.
20555 U.
S.
Nuclear Regulatory Commission Marian E. Moe, Esquire Washington, D.
C.
20555 Office of General Co:Insel U.
S.
Nuclear Regulatory Commission Washington, D.
C.
20555 Edwin J.
Reis, Esquire Office of Executive Legal Director U.
S. Nuclear Regulatory Commission Washington, D.
C.
20555 Mr. Lewis T. Mittness, Executive Secretary Public Service Commission of Wisconsin Hill Farms State Office Building 4802 Sheboygan Avenue Madison, Wisconsin 53702 C.
F.
- Riederer, P. E.
Public Service Commission of Wisconsin Hill Farms State Office Building 4802 Sheboygan Avenue Madison, Wisconsin 53702 1696 230