ML17321A909
| ML17321A909 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 10/10/1985 |
| From: | Alexich M INDIANA MICHIGAN POWER CO. (FORMERLY INDIANA & MICHIG |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| AEP:NRC:0936A, AEP:NRC:936A, NUDOCS 8510160021 | |
| Download: ML17321A909 (30) | |
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ACCESSION NBR:8510160021 DOC ~ DATE: 85/10/10 NOTARIZED:
NO DOCKET FACIL:50 316 Donald C ~
Cook Nuclear Power Plantr Unit 2r Indiana L
05000316 AUTH'AMiE AUTHOR AFFILIATION ALEXICHgM ~ PE Indiana<<
8 Michigan-Electr'ic Co, RECIP,NAME'i RECIPIENT AFFILIATION DE NTONeH ~ R ~
Office, of Nuclear Reactor Regulationi Director
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SUBJECT!: Informs of program 8 course of action taken re steam generator sor k during recent forced outages,Final:rept being prepared to detail tube indication datartubesheet indicat-ion mapping 8 comparison of data-from previous
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~I CI INDIANA8 MICHIGAN ELECTRIC COMPANY P.O. BOX 16631 COLUMBUS, OHIO 43216 October 10, 1985 AEP:NRC:0936A Donald C.
Cook Nuclear Plant Unit No.
2 Docket No."50-316 License No. DPR-74 STEAM GENERATOR TUBE PLUGGING INTERIM=-STATUS REPORT=
Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555
Dear Hr. Denton:
Pursuant to the request of your staff, this letter is to inform you of the program and the course of action taken by Indiana
& Michigan Electric Company (IMECo) in regard to the Donald C.
Cook Plant Unit 2 steam generator (SG).work conducted during, recent"forced outages.
Unit 2 was removed from service on July 15, 1985 with a primary-to-secondary leak of 0;22 gpm.
-Visual inspection under a static head showed one leaking tube (R16-C56) in SG 23.
Helium leak detection revealed no other leakage.
- Ojestinghouse
'Electric Corporation was brought in to perform eddy current (EC) testing of the leaking tube.
Their tests revealed a defect about 1-inch below the top of the tubesheet.
Additional EC testing of a block of 24 tubes around R16-C56 revealed. tube R15-C55 to have a pluggable indication.
Reanalysis of the 1984 data for R16-C56 confirmed that no reportable indications were present in 1984; but R15-C55 had an indication of 20$
that was not identified.
In view of the fact that previous inspections had not disclosed widespread tube degradation problems in the tubesheet
- region, and with only 90 days of fuel left in Cycle 5, a decision was made to plug the two tubes and return to servioe.
The unit was restarted on August 2.
During the start-up, increases in activity at radiation monitors on air egectors and blowdown samples indicated slight additional leakage in SG 23.
The unit was again removed from service.
Visual inspeotion under a static head revealed 2 leaking tubes (R7-C28 and R14<<C70).
Since we believed that the cause. of the problem was associated"with crevice leakage, helium testing was not performed.
EC testing was begun on an initial J
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Mr. Harold R. Denton AEP:NRC 0936A sample of about 460 tubes and subsequently expanded to approximately 1500 tubes in the sludge pile region of the tubesheet, which is an area where industry experience and our own previous examinations had indicated potential problems.
Attachment 1 provides a summary of the inspection results for SG 23 for this period.
During this inspection a primary and secondary EC data review was conducted to ensure accuracy.
Westinghouse conducted the primary data review and Conam Inspection, an-independent contractor, conducted the secondary review.
As a result of that review, 35 tubes were plugged 20 due to defects as defined by the Technical Specifications, and 15 due to our administrative plugging criteria.
Many of the tubes plugged had no previous indication of degradation.
This gave us a
- concern, because our previous history of monitoring SGs which included pulling tubes for examination and industry. experience with similar problems indicated that this type of degradation may have been caused by intragranular attack (IGA).
Westinghouse, our NSSS supplier and consultant, reoommended that we perform a boric acid soak to provide a 45-55 ppm boron concentration at 30 percent power followed by on-line"boric acid addition to provide a 5-10 ppm boron concentration.
Addition of boric acid was intended to neutralize the alkaline environment responsible for the IGA and thus possibly slow down or stop the IGA.
The unit was restarted, but on August 23, during the hold at 30 percent power for the boric acid soak, steam generator leakage was observed.
The unit was removed from service when the leak rate reached 0.20 gpm.
All four SGs were opened and visually inspected under a static head.
Two leaking tubes were identified, one each in SG 22 and SG 24.
Since it was judged that we could not operate the unit.,with continual SG leakage
- problems, a decision was made to perform an extensive EC inspection of SG tubes.
This was later expanded to include 100$ of the tubes in SGs 21, 22, and 24, and to inspect the balance of the tubes in SG 23; Attachment 2 provides a
summary of the inspection results.
Discussions were held to determine a course of action in case the rate of SG tube degradation should increase and involve either derating the unit or continually shutting down because of SG leakage problems.
Several solutions, including sleeving the tubes in areas of serious degradation, were considered.
It was noted that during the course of this complete EC inspection, defects and distorted indications at hot leg support plate intersections were found.
Since the condition of the'ubes at support, plate intersections could impact any future decision to sleeve the tubesheet
- region, we elected to remove tube samples to assess the condition of the"tubes at the support plates.
Five tubes wer e removed three including the first-to-third support plate intersections and,two including the first-to-fifth support plate intersections.'n-situ sludge samples
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Mr. Harold R. Denton AEP: NRC: 0936A and crevice scrapings were also collected at the location of the removed tubes, and fiberoptic examination of the crevice and top of tubesheet was performed.
Preliminary results of sample analyses and metallographic examinations are expected in four to six weeks from
>lestinghouse.
Final results of hot leg EC indications found during the three forced outages are given in Attachment 3.
A total of 147 tubes were plugged.
The plugging criteria implemented for this EC inspection included not only the
>405 through-wall Technical Specification plugging limit for defective tubes but additional conservatism of an administrative plugging limit for tubes with indications at the top of the tubesheet and in the crevice region.
Of the total examined, 93 tubes were plugged to comply with Technical Specification requirements.
The others were plugged for conservatism to prevent further deterioration of tubes at the top of the tubesheet and in the crevice region, since these could impact future decisions regarding remedial actions of the, type discussed above.
During the upcoming Unit 2 start-up, boric acid (1000-2000 ppm boron) crevice flushing will be conducted in each steam generator.
This will be followed by boric acid soaks and continued on-line boric acid addition during power operation.
A final report is in preparation which will detail individual EC tube-indication data, tubesheet indication mapping, and comparison of data from the previous inspection.
This report will provide the basis for our discussion with your staff at the meeting which has been requested for mid or late November.
At that meeting we will be prepared to discuss our investigations, findings, and proposed actions as well as to address any of your concerns.
This document has been prepared following Corporate procedures which incorporate a reasonable set of controls to insure its accuracy and completeness prior to signature by the undersigned.
Very truly yours, MPA/ad M.. Ale chP Vice President~at~'
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Mr. Harold R. Denton 4'EP:NRC:0936A ce: John E. Dolan M. G. Smith, Jr. - Bridgman R.
C. Callen G. Bruchmann G. Charnoff NRC"Resident Inspeotor - Bridgman
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ATTACHMENT 1 TO AEP:NRC:0936A
SUMMARY
OF INSPECTION OF TUBES IN STEAM GENERATOR NO.
23 DURING OUTAGE BEGINNING AUGUST 2, 1985 DONALD C.
COOK NUCLEAR PLANT UNIT NO.
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Attachment 1
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SUMMARY
OF INDICATIONS - Steam Generator No.
23 (Hot Leg)
(August 2-23, 1985)
Tubes to test:
1468 full length; 37 part length, U-bend Punched:
1505 Analyzed:
1505 (20'
'0-29 30-"39
>40 S
R DI TOTAL SUPPORT PLATES CREVICE REGION 18 10 33 TUBESHEET +*
MISCELLANEOUS 20 10 41
- covers an area from the top of the tubesheet to not more than 6 inches above the top of the tubesheet.
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ATTACHMENT 2 TO AEP:NRC:0936A
SUMMARY
OF INSPECTION OF TUBES IN ALL STEAM GENERATORS DURING OUTAGE BEGINNING AUGUST 24, 1985 DONALD C.
COOK NUCLEAR PLANT UNIT NO.
2
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e Attachment 2
SUMMARY
OF INDICATIONS - Steam Generator No.
21 Hot Leg Tubes to Test:
3282 full length Punched:
3282 Analyzed:
3282
<20 20-29 30-39
> 40 S
R DI TOTAL SUPPORT PLATES 7
66 97 CREVICE REGION 3
TUBESHEET +*
MISCELLANEOUS 10 14 19 12 11
69 122
- covers an area from the top of the tubesheet to not more than 6 inches above the top of the tubesheet.
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Attachment 2
t AEP:NRC:0936A
SUMMARY
OF INDICATIONS Steam Generator No.
22 Hot Leg Tubes to Test:
3250 full length Punched:
3250 Analyzed:
3250 (20 20-29 30-39
> 40 S
R DI TOTAL SUPPORT PLATES 25 49 CREVICE REGION 10 14 TUBESHEET +*
15 MISCELLANEOUS 15 12.'
8
'0 27 84
- covers an area from the top of the tubesheet to not more than 6 inches above the top of the tubesheet.
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Attachment 2
SUMMARY
OF INDICATIONS - Steam Generator No.
23 Hot Leg Tubes to Test:
2012 full length Punched:
2012 Analyzed:
2012 420 20-29 30-39 P40 S
R DI TOTAL SUPPORT PLATES 17 24 CREVICE REGION TUBESHEET +*
MISCELLANEOUS TOTAL 21 42
- covers an area from the top of the tubesheet to not more than 6 inches above the top of the tubesheet.
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Attachment 2
SUMMARY
OF INDICATIONS Steam Generator No.
24 Hot Leg Tubes to Test:
3265 full length Punched:
3265 Analyzed:
3265 4 20
'20-29 30-39
>40 S
R DI TOTAL SUPPORT PLATES 9, '2 5 ', "'6 34 66 CREVICE REGION TUBESHEET +*
I 10 12 17 16 42 MISCELLANEOUS 10 10 21 25 28 17 35 39 145
- covers an area from the top of the tubesheet to not more than 6 inches above the top of the tubesheet.
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ATTACHMENT 3 TO AEP:NRC:0936A FINAL RESULTS OF EDDY CURRENT TEST INDICATIONS FOUND DURING THREE UNSCHEDULED OUTAGES AND TOTAL TUBES PLUGGED TO DATE DONALD C.
COOK NUCLEAR PLANT UNIT NO.
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Attachment 3
0 Indication
<20 20-29 30-39
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~SR DI**
Total Support Plates Crevice Region 26 32 20 16 47 13 10 N/A 142 236 75 Tubesheet Surface 13 14 30 0
m
,7 73 Miscellaneous 26 21 0
N/A 52 Total 66 63 42 93 13 159 436 Note:
Plugging criteria are defined by the boundary line above (142 tubes); in addition, 1 tube with a cold leg defect at a peripheral tube support plate and 4 non-defective tubes (removed for analysis) were plugged.
Plugging criteria are based on Technical Specification limits and plant administrative requirements.
Administrative criteria for degraded tubes are as follows:
Tube crevice
- region, any indication reported (included (20%,
SQRs and DIs.
Tubesheet
- Surface, 30-39%, all SQRs and DIs.
- SQR (Squirrel Indication) considered to be a special class of distorted indication confined to the tubesheet region.
These indications have historically proven to compromise tube wall integrity and have thus been classified as defects and have normally been plugged even though the signal is unquantifiable.
- DI (Distorted Indication) is used in lieu of a percent
(%)
through-wall value on a signal that the analyst believes to be an indication but is too distorted to quantify.
DIs at support plate intersections were not deemed pluggable because of a weak signal" (low voltage) as compared to those previously found at the top of tubesheet and within the crevice.
In addition, when reviewing the other frequencies, they did not provide the expected correlation to further
,define the DIs at the support plates to be as significant as those found in the tubesheet regions.
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Attachment 3
Total tubes plugged to date on Cook 2 are as follows:
40 Row 1 fretting at Tube Lane Blocking Devices 16 Row 1 ECT indications 320 Row 1 preventative plugging 4 Defects at anti-vibration bar intersections 94 Defects at tubesheet
- surface, hot leg 21 Indications at tubesheet
- surface, hot leg (administrative plugging) 3 Defects at tubesheet
- surface, cold leg 39 Defects in crevice region, hot leg 41 - Indications in crevice region, hot leg (administrative
~ plugging) 4 Defects at 1st support plate intersections, cold leg 16 - Defects at support plate intersections, hot leg 6 Non-defective tubes removed for tube analysis 8 - Miscellaneous (Preservice, mistakes, etc.)
612 Total j
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