ML20100K340
| ML20100K340 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 04/11/1985 |
| From: | Churchill B SHAW, PITTMAN, POTTS & TROWBRIDGE |
| To: | Edles G, Gotchy R, Johnson W NRC ATOMIC SAFETY & LICENSING APPEAL PANEL (ASLAP) |
| References | |
| CON-#285-517 OLA, NUDOCS 8504120451 | |
| Download: ML20100K340 (96) | |
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April 11, 1985
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(202) 822-1051 Gary J. Edles Dr. W. Reed Johnson Administative-Judge' Administrative Judge Chairman,' Atomic Safety and Atomic Safety and Licensing
~ Licensing Appeal Board Appeal Board
-U.S.. Nuclear Regulatory Commission U.S. Nuclear Regulatory Commission
. Washington, D.C..
20555 Washington, D.C.
20555 Dr. Reginald L. Gotchy Administrative Judge Atomic Safety and Licensing Appeal Board U.S.-Nuclear Regulatory Commission Washington, D.C.
20555 In-the Matter of Metropolitan Edison Company, Et.Al.
(Three Mile Island Nuclear Station, Unit No. 1)
Docket No. 50-289-OLA (Steam' Generator Repair)
Dear Administrative-Judges:
Enclosed for the. Appeal Board's information-are two docu-ments entitled " Evaluation of the'1984 Required Technical Specification Examination for the TMI-1 0TSG" (TDR-652) and
" Adequacy;of1TMI-1 OTSG_ Return to Service Safety Assessment After 1984 Technical Specification ECT Examination" (TDR-666) which I
have just been released.
The documents were submitted to the Estaff on April 11,_1985.
1
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SHAw, PITTMAN, PoTTs & TROWBRIDGE A samTNEnsMep OF pmOFtes40 mat CompOmATeONs ASLAB-Administrative Judges Page Two April 11, 1985 During the oral arguments heard on April 3 in this proceeding, a number of questions were posed by the Appeal Board to counsel.
In reviewing the transcript, it appears that it might be helpful to the Appeal Board in some instances to provide specific references to documentation pertinent to those questions:
1.
Cause of 1984 ECT indications (Tr. 29-32):
TDR-638 at 11-24; TDR-666 at 4-6; TDR-652 at 25-47; January 10, 1985 Affidavit of F. Scott Giacobbe (Answer to Motion to Reopen),
11 3-13.
See also TR-008 at 7-15, 21-28; February 24, 1984 Affidavit of F. Scott Giacobbe (Motion for Summary Disposition),
11 4-51.
2.
Long-term corrosion test program-reflected reactor conditions during layup, hot functional testing, and future operation through the first refueling cycle after restart, including stresses, temperatures, and reactor coolant chemistry (Tr. 30-32):
TR-008 at 26-27; TDR-638 at 11-19; February 24,.1984 Giacobbe Affidavit, 11 120-124; January 10, 1985 Giacobbe Affidavit (Answer to Motion to Reopen), 4 4; Testimony of Don K. Croneberger and F. Scott Giacobbe on Contention 1.D at 4-9; Testimony of Conrad E. McCracken and Paul C. S. Wu on Contention 1.A at 11-13; Hearing Transcript at 345-346 (Croneberger) ; 359-361, 366-368 (Giacobbe) ; 369-370 (Giacobbe, Croneberger).
3.
Fiberscopic examination of IGA (Tr. 32-33) :
TDR-638 at 20, 23; January 10, 1985 Giacobbe Affidavit, 1 11; February 24, 1984 Giacobbe Affidavit, 11 131-148.
4.
The hot functional testing and cooldown and the kinetic expansion occurred after the 1982 100% baseline ECT and prior to the 1984 100% ECT.
(Tr. 33-34):
TDR-638 at 6, 7, 23; TDR-652 at 25-27, 34.
5.
Threshold of ECT detectability without grain dropout is below critical crack size for tube rupture during main steamline break accident (Tr. 42-44, 47-50):
TDR-666 at 5, 7-9; TDR-652 at 47; TR-008 at 78-89.
6.
Axial stresses during hot functional testing and cooldown (Tr. 47-49):
TDR-638 at 23; TR-008 at 85, 119; February 24, 1984 Affidavit of David G. Slear (Motion for Summary Disposition), 1 4 5 (g).
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SHAw, PITTMAN. PoTTs & TROWBRIDGE A SANTNERSMiP OF PnOFtemeONAL COW 80 mat Omss ASLAB-Administrative Judges Page Three April 11, 1985 7.
Tensile, fatigue and other properties of tubes un-affected (Tr. 67-69):
TR-008, 1 b, at 10; Hearing Transcript at 346-347, 349 (Giacobbe); 527-534, 546-548, 572-575 (Slear, Giacobbe) ; 668-669 (McCracken).
Respectfully submitted, p
3ruce W. Churchill Counsel for Applicant Enclosures cc:. Service List.(attached) r n
e h
UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION Before the Atomic Safety and Licensing Appeal Board In the Matter of
)
)
METROPOLITAN EDISON COMPANY, ET AL.
)
Docket No. 50-289-OLA
~ ~ ~ ~
)
(Steam Generator Repair)
(Three Mile Island Nuclear Station,
)
Unit No. 1)
)
SERVICE LIST
- Gary J..Edles Dr. James C. Lamb, III Administrative Judge Administrative Judge Chairman, Atomic Safety and Atomic Safety and Licensing Licensing Appeal Board Board U.S. Nuclear Regulatory 313 Woodhaven Road Commission Chapel Hill, N.C.
27514 Washington, D.C.
20555
- Mary E. Wagner, Esq.
.*Dr. W. Reed Johnson Office of Executive Legal Director Administrative Judge U.S. Nuclear Regulatory Atomic. Safety and Licensing Commission Appeal-Board Washington, D.C.
20555 U.S. Nuclear Regulatory Commission Atomic Safety and Licensing Washington, D.C.
20555 Appeal Board Panel
- Dr. Reginald L. Gotchy U.S. Nuclear Regulatory Commission Administrative Judge Washington, D.C.
20555 Atomic Safety and Licensing Appeal Board U.S. Nuclear Regulatory Atomic Safety and Licensing Board Panel Commission U.S. Nuclear Regulatory Washington, D.C.
20555 Commission Washington, D.C.
20555 Administrative Judge Docketing and Service Secticn (3)
Chairman, Atomic Safety and Licensing Board Office of the Secretary U.S. Nuclear Regulatory U.S. Nuclear Regulatory Commission Commission Washington, D.C.
20555 Washington, D.C.
20555
- *Joanne Doroshow, Esq.
Dr. David L. Hetrick Louise Bradford Administrative Judge Atomic Safety and Licensing Board Three Mile Island Alert, I r.,.
315 Peffer Street College of Engineering Harrisburg, PA 17102 Dept. of Nuclear and Energy Engr.
The University of Arizona Tucson, Arizona 85721
~
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-ASLAB Scrvica List
'4 Page Two TMI-l Thomas Y. Au Assistant Counsel Commonwealth of Pennsylvania Department of Environmental Resources Bureau of Regulatory Counsel Room 505 Executive House
-P. O. Box 2357 Harrisburg, PA 17120
- Hand Delivered
- - Hand Delivered to The Christic Institute, 1324 North
' Capitol' Street,tiashington, D.C.
20002
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NTF.D CORRESPO4Q,
-'snr-OPU Nuclear Corporation NUCIM7
'UhTC' loo tnterpace Parkway Parsippany,New Jersey o7o541149 (201)263-8500
'85 ffR 12 P12:14
[E E 1j6-482 0ialNumt;er:
$dd b d N M gl April 11, 1985 ggy REW-0464 5211-85-1073 j
Office of Nuclear Reactor Regulation Attn:
J. F. Stolz, Chief Operating Reactors Branch No. 4 Division of Licensing U.S. Nuclear Regulatory Comission Washington, D. C.
20555
Dear Mr. Stolz:
TMI-l Steam Generators 1984 Eddy Current Examination In accordance with the TMI-l Technical Specification 4.19, an eddy current examination of the steam generator tubes was conducted in November and December 1984. An initial report on the results of the examination was contained in LER 84-007-00, submitted on December 17, 1984. GPU Nuclear Corporation identified in LER 84-007-00 that supplemental information would be provided as available.
GPUN has recently completed TDR-652 entitled " Evaluation of the 1984 Required Technical Specification Examination of the TNI-l OTSG", a copy of which is provided as Attachment 1.
Also provided, as Attachment 2, is TDR-666 " Adequacy of THI-l OTSG Return to Service Safety Assessment After 1984 Technical Specification ECT Examination," which sumarizes our analyses and conclusions with respect to the eddy current test results.
Sincerely, d44 44444
/pi. R. F.
son Vice r sident Technical Functions Ir/1652f GFU Nuclear Corperation is a subs:d.ary of Geretal Pubbc Uti:it.es Corporation 1
i ortATED j
g TDR NO.
652 REVISION NO.
1 BUDGET TECHNICAL DATA REPORT ACTIVifDIOp-423125 PAGE 1
OF 60 PR2 JECT:
~ ~
DEPARTMENT /SECTION Oualite Assur,nc OTSG y
rrent Program R EA DNTE I6 REVISION DATE CWENT ME:
Evaluation of the 1954; Required Jechnical Sneri fi e n t i nn Fv,-i nn t i on' f or tha TMT 1 OTCC ORIGINATOR SIGNATURE' DATE APPROVAL (S) SIGNATURE DATE G. E. Rhedrick M / M [3 M u M 1///W R. O. Barlev/s/
3/1/85
' '3/k/85 N. C. Kazanas A)C L -~
= 1, lar M. T. Torbore/s/
IL i,nenn/s/
1/1/95 O
kPPRhAL hR EXTERNAL DISTRIBUTION DATE W-um
- T i
Does this TDRinclude recommendation (s)? Oyes @No if yes.TFWR/TR #
o DISTRIBUTION ABSTRACT: Statement of Problem The results of the 1984 eddy current examination performed on B. E. Ballard the TMI-l steam generator tubing had identified 328 tubes with R. O. Barley confirmed indications of t 40% through wall penetration. These G. R. Capodanno indications were not identified in previous eddy current examin-J. J. Colitz ations performed prior to mechanical thermal and hydraulic load-B. D. Elam ing evolutions which took place in the steam generators.
I. R. Finfrock Technical Acoroach F. S. Giacobbe Knowing the locations of the 1984 confirmed indications, a re-H. J. Graham view of the 1983 and 1982 examinations have confirmed the earli-H. D. Hukill er presence for a majority of these indications. A characteriz-J. J. Janiszewski ation of the 1984 indications by defect location, sigial ampli-N. C. Kazanas tude, percent through wall and circumferential extent was per-D. Langan formed and compared to the 1982 examina, tion results. A growth R. L. Long sample study on a random selection of tubes was performed after R. Ostrowski the detection of the 1984 indications in order to determine if T. J. Patterson evidence of an active mechanism was occurring.
G. E. Rhedrick Findings T. A. Richter It was observed that the 1984 indications were located in the M. T. Torborg same affected axial and radial areas previously identified dur-R. F. Wilson ing 1982 examination. The 1984 indications were predominately shorter in circumferential extent. The review of 1984, 1983 and 1982 examination results revealed that the percent through wall DRF 029572 determination showed no change. 90% of the new indicatiens were of size at or near the threshold of GPUN standard differential technique sensitivity of detection. The results of the growth sample study showed no evidence of an active mechanism occurring during the period of observation.
Conclusion The 1984 examination identified indications that were already present in the tubes in 1982 but because of their weak signal amp li::ude were masked by background noise. The mechanical, thermal and hydraulic loads imposed on the OTSG since 1982 examination may have enhanced the eddy current detection of small indication i
by increasing the signal amplitude but without evidence of in-crease to percent through wall.
cCOVER PAGE ONLY Aooooo30 4 83
. R
TDR 652 Rev. 1 Page 2 of 60 TABLE OF CONTENTS Page
SUMMARY
3 I.
INTRODUCTION 6
II.
METHOD OF EXAMINATION 7
III.
SCOPE OF EXAMINATION 8
IV.
RESULTS OF 1984 EXAMINATIONS 10 A.
INDICATIONS REPORT 10 B.
ISI TESTS 10 C.
CHARACTERIZATION OF INDICATIONS 15 1.
RADIAL DISTRIBUTION 16 2.
AXIAL DISTRIBUTION 17 3.
SIGNAL AMPLITUDE 18 4.
PERCENT THROUGH WALL 18 5.
CIRCUMFERENTIAL EXTENT 20 0.
SUMMARY
OF INDICATION CHARACTERIZATION 21 FIGURES la-b, 2a-b, 3a-b, 4a-b, Sa-b, 6 V.
REVIEW PRE-KINETIC, POST KINETIC AND POST HOT FUNCTIONAL EXAMINATION DATA 25 VI.
GROWTH PROGRAM 44 VII.
CONCLUSION 46 VIII.
REFERENCES 47 APPENDIX A
ABSTRACTION ON THE OVAL INSPECTION DEVELOPMENT ANU PERCENT THROUGH HALL CONVERSION CURVE 49 8
1982-1984 ED0Y CURRENT STATISTICS 53 1
7 TDR 652 Rev. O Page 3 of 60
SUMMARY
During the 1984 Technical Specification required eddy current examination, performed on the once through steam generator tubing at TMI Unit 1, a number of new relevant ' indications were detected in the "A" and "B" steam generator tubes.
These new indications were not detected back in November 1982 when a full length eddy current examination was conducted on all the inservice "A"
and "B" steam generator tubes.
During both inspection periods the same eddy' current examination technique was employed.
Since the 1982 eddy current examination both steam generators had undergone mechanical loading due to kinetic expansion. tube repair and thermal / hydraulic loading due to two hot functional tests.
GPUN first determined that a new corrosion mechanism was not active.
This was determined through repeat eddy current examinations on a controlled group of tubes in 1984 after initial detection of the new indications.
This revealed that no growth or change in given eddy current signals occurred for the time period studied.
The 1984 Indications were characterized as to size, location, depth and then compared to the 1982 examination results.
GPUN concluded that the 1984 Indi-cations are a smaller additional subset of those detected in 1982 examina-tion.
The percent through wall and circumferential e< tent for 90% of the l
n,
TDR 652 Rev. O Page 4 of 60 1984 Indications are of a size that approximates the threshold of detection for the measured sensitivity curve using the GPUN qualified standard differen-tial eddy current examination process.
Detailed analysis of the new 1984 indications reveal, that by knowing the specific location of the indication the majority can be found in the 1982 eddy current tapes.
The indications that could be measured in the 1982 tapes in-cluding the in service inspection tubes reveal that:
(1)
No new indications were detected in the ISI subset (one exception explained)
(2)
The percent through wall assignments, as determined by phase angle measurement remain constant from 1982 to 1984 (3)
For indications not previously identified in 1982, the amplitude of the eddy current signal has substantially increased in the 1984 tapes which would result from some increase in the discon-tinuity volume.
Presumably the latter is a reflection of the mechanical / thermal working of the tubing.
(4)
For indications not previously identified in 1982 the increase in the amplitude of the indications in 1984 contributed to our abil-ity to detect the small indications which now revealed themselves above the surrounalng cackground noise.
The latter combined with the low amplitudes associated with the signals frcm the indica-tions pr evented earlier Jetection.
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TDR 652 Rev. O Page-5 of 60 rc Implicit'within this fact, is that the earlier undetected indications were in l
fact very small.
This is substantiated by the characterization studies for
'the.1984 indications which show them to be smaller percent through wall and circumferential' extent than the 1982 indications.
Additionally, the 1984 in-dications~are located in areas which identify closely to intergranular stress assisted corrosion cracking revealed earlier in the 1981-1982 examinations.
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TOR 652 Rev. 1 Page 6 of 60 I.
. INTRODUCTION In November of 1984, eddy current examination was performed on the THI -
Unit ~1, once through steam generator (OTSG) tubing in accordance with Technical Specification, 4.19.
The examination ultimately included
-14,615 tubes in the "A" 0TSG and approximately 6,500 tubes in the "B" OTSG.
This examination was concluded with a total count of 328 tubes with confirmed indications having tube wall degradation measuring 40 percent through wall or greater.
This is a criterion that requires engineering disposition.
There were another 319 tubes that had confirmed i
indications with a measured through wall degradation less than 40 per-cent.
Those tubes with 20-40% through wall indication are classified
" degraded" tubes and are required to be monitored for change at fute.
examinations.
In addition, those tubes which contain indications of 40%
through wall or greater but do not meet the approved plugging criteria will also be monitored.
Since the last complete eddy current examination (1982 baseline) per-formed on the OTSG in 1982, the OTSG tubes have been subjected to mechan-ical loading due to kinetic expansion repairs and thermal and hydraulic loadings due to the two hot functional tests.
The eddy current examina-tions performed subsequent to these loadings have resulted in the detec-tion of indications not seen previously.
E n
1 TOR 652 Rev. O Page 7 of 60 The analysis performed herein has the following purposes:
~
1.
To characterize and report the indications identified during the 1984 examination and compare these characteristics with indications re-ported during the 1982 baseline examination.
The purpose of this comparison is to evaluate the pattern of defect distribution and to determine if the affected treas correspond to the previously affected areas.
2.
Determine the correlation of the kinetic expansion and subsequent hot functional test to the detection of indications not detected prior to these loading events. And, evaluate the impact from a chronological perspective.
3.
Review the data from the 1984 Growth Program and evaluate the results to determine if evidence of continued tube degradation existed.
II. METHOD OF EXAMINATION The_ eddy current examinations performed in November of 1984 utilized both standard differential and absolute eddy current examination techniques.
This dual examination method was developed by GPUN to specifically detect and confirm small volume but predominately circumferentially oriented inner diameter defects.
(See Appendix A).
n
1 TOR 652 Rev. O Page 8 of 60 The dual examination method involved first examining the tubing with a high gain standard differential technique using a.540" diameter eddy current probe.
If no indications are detected the examination is com-plete.and the tube is considered acceptable.
Tubes found to have standard differential indications were examined a second time using the absolute 8xl technique which used a probe having 8 independent coils.
The absolute 8xl examination determines the circumferential extent of the defect and also determines if the indications are relevant or non-rele-vant.
A relevant indication is a flaw that has been confirmed by abso-lute 8 1 examination.
This dual examination method is the same method GPUN qualified and used for the 1982 baseline eddy current examination of the TMI-l 0TSG tubing (Ref. 1)
III. SCOPE OF EXAMINATION The initial set of tubes for the 1984 eddy current examinations was a 3%
sample selected in accordant.e with the requirements of Technical Specif1-cation 4.19.
As required by 4.19, this set included all tubes remaining in service which were classified " degraded tubes." These tubes had prev-lously reported indications of 20-40% through wall and are referred to as the ISI tubes.
Approximately 50% of the 3% sample was from the high de-fect area (outer periphery) with the remaining 50% being located randomly throughout the generators.
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7
)
TOR 652 Rev. O Page 9 of 60 The examination.of the initial sample identified some discontinuities which exceeded the 40% through wall technical specification limit. As a
. result of these discontinuities, the examination scope was increased to include 100% of the tubes in the affected area of both OTSGs.
This in-creased scope included 100% of the tubes in OTSG "A" and 100% of the tubes in the outer periphery of OTSG "B".
This outer periphery is de-fined as the area outside the outer tie rod circle and includes approxi-mately 6500 tubes.
The November 1984 examination was not continued into the center of the "B" generator because no confirmed indications >40% through wall were found in this area during the random examination.
The indications re-ported in the "B" generator.were at a significantly lower frequency than reported in the "A" generator. And their distribution declined sharply with distance from the outer perimeter and was bounded by the outer tie rod circle.
As part of the expanded scope, a selected 100 tube sample, designated the "A" Growth Program, was monitored in order to determine if there was an active mechanism initiating the 1984 eddy current indications.
This sample was also comparatively evaluated against the eddy current tapes from the 1982 examination.
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TOR 652 Rev. 1 Page 10 of 60 Examinations discussed within this report included the full length of the unexpanded region of the tubes.
Expanded portions of the tubes cannot be
-effectively examined and evaluated with the standard differential tech-nique and are therefore not included in the tubing examinations.
IV. RESULTS OF 1984 EXAMINATIONS A.
INDICATIONS REPORT As a result of expanding the scope of the examinations, 14,615 tubes in OTSG "A" and approximately 6500 tubes in OTSG "B" were examined.
Of these tubes, 298 in OTSG "A" and 30 in OTSG B were identified as having relevant. indications 40% through wall or greater.
In addi-tion, 274 tubes in OTSG "A" and 45 tubes in OTSG "B" were identified as having confirmed indications from 20-40% through wall and are classified as " degraded tubes".
These tubes and any tubes with con-firmed indications 40% through wall or greater which do not meet the approved plugging criteria will be monitored during future examina-tions as "ISI tubes".
B.
ISI TUBES The subset of ISI tubes included 28 tubes in OTSG A and 56 tubes in OTSG B which had indications of 20-40% through wall pcnctration iden-tified and recorded during previous examinations, w
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~
-3 TOR 652 Rev. O Page 11 of 60 These ISI tubes were examined as a subset and an in depth evaluation and comparison of~the 1984 data to the previous data was performed.
The purpose of this evaluation and comparison wa's to determine if the previously identified indications had " grown".
The criteria used to establish growth addressed significant changes in percent through wall determinations, changes in signal voltage or changes in arc length of the monitored indication. When performing evaluations of this type, it must be noted that changes of about 10%
through wall can be caused by a change of only 3 degrees in the phase angle measurement of the standard differential reponse signal. When addressing small voltage signals, measurement errors of this type can be expected.
For the absolute 8x1, the orientation of the coils to the defect may change the number of Coils an indication appears on by I additional coll during repeat examinations.
The evaluations must therefore factor in these limitations on repeatability.
ISI Tubes in the "A" Generator From the "A" generator 28 of the 28 ISI tubes showed no evidence of growth for any of the previously identified indications.
Two tubes, A-2-9 and A-88-128, had Indications previously identified as being <40% through wall which were subsequently reported as >407 through wall in 1984.
These indications were compared by the data n
- v =-
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TDR 652 Rev. 1 Page 12 of 60 t
analyst on_a one-to-one basis to the previous data and it was deter-mined that the change in the percent through wall determinations were caused'by variations in the repeatability of the overall eddy current process and not by the physical changes in the tube.
(See Table 1).
ISI Tubes in the "B" Generator In OTSG "B" there was no indication of " growth" for 56 of the 56 tubes. One tube B-98-5 did have an indication reported as greater than 40% through wall and required further evaluation.
The details
'for this tube are shown in Table 1.
The 1984 and previous data for this tube was re-evaluated by the data analyst to compare the eddy current signal's' shape.
The analyst de-termined the variation in the percent through wall determinations was attributed to distortion of eddy current signals caused by multiple indications and was not a result of physical changes in the tube.
Status of ISI Tubes A number of tubes previously placed in the ISI category during the 1982 baseline examination were determined to have non-relevant indi-cations as a result of the 1984 absolute 8x1 examination.
These tubes, 13 in "A" OTSG and 27 in "B" OTSG, had non-relevant indications as determined by absolute 8x1 in 1982 but were placed on
_p
l 3
TDR 652 Rev. 1 Page 13 of 60
-the ISI list for monitoring purposes in order to verify the precision of the absolute 8xl confirmation exams during future dual examination exercises. With the completion of the 1984 examination and the con-sistency of reporting the same standard differential indication as non-relevant, these tubes _were removed from the ISI list.
The number of ISI tubes has increased as 264 tubes in OTSG A and 20 tubes in OTSG B had confirmed ~ indication from 20-40% through wall in 1984 which were not previously identified.
This puts the present population of.ISI tubes between 20-40% through wall at 274 tubes in "A" and 45 tubes in "B".
9 i
^
j TDR 652 Rev. 1 Page 14 of 60 Table 1 ISI Confirmed Indications Greater Than 40% Through Wall in 1984 April Nov.
Indication 1983 Post KE Data 1984 Post HFT Data Gen Row Tube Elevation Origin
% T.W.
Volts Volts A
2-9 US+06*
ID 40%
1.7 45%
1.6 A
88 - 128 12+05 10
< 20%
0.9 31%
1.4 13-09 ID
< 20%
0.6
<20%
0.6 05-11 ID 23%
1.9 41%
2.5 B
98 - 5 US+07*
ID 37%
2.3 48%
4.0 US+01 ID
<20%
1.9
<20%
2.0 US+04 ID
< 20%
2.3 21%
3,5
- immediately below expanded area
- o-TDR 652 Rev. O Page 15 of 60 2
C.
CHARACTERIZATION OF INDICATIONS The indications detected during the 1984 examinations were character-ized by the location and extent of degradation based on the eddy cur-rent response signal. Details, listing the data in support of this secticn are included in Appendix B.
The characterization is further defined by comparing the 1984 indica-tions with those reported in 1982.
For this comparison GPUN used the 1984 data described previously and the 1982 standard differential high gain data base.
The 1982 data base included all tubes examined using the GPUN dual examination method prior to 1984.
This data base was previously used to disposition the OTSG tubes for the kinetic expansion process and subsequent tube plugging.
This data base con-tains the 1982 baseline results which are summarized in TDR 442.
(See Ref. 2).
Both the standard differential and absolute techniques are used to furnish these characterization as described below.
Standard differential response signal offers the following:
a.
Amplitude (this relates to the defects geometry and volume, and is reported as a voltage reading).
b.
Percent through wall (this relates to the response signal's phase angle and is measured in degrees).
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- w TOR 652 Rev. 1 Page 16 of 60 c.
Axial locations are reported by distance from the tube support plates that are spaced at known elevations in the generators.
Absolute 8x1 signal offers the following:
a.
Number of coils (this relates to the defect's circumferential extent).
The maximum circumferential extent is 8 coils and represents a. defect circumferential arc length that could be as l
much as 360 degrees.
NOTE:
Amplitude, phase and axial location are also recorded on the. absolute 8xl results; however, these results are used only to confirm the standard differential indica-tions.
R 1.
RADIAL DISTRIBUTION The indications detected during the 1984 examination were located in essentially the same areas of the OTSGs as those discovered in 1982.
The indications were located predominately towards the outer periphery of both OTSG A and B.
In addition to the indica-tions located in the periphery there was also a smaller number of indications present-.in the center of OTSG A.
No indications greater than or equal to 40% through wall were reported in the center of OTSG B. '(See Figures la and Ib).
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TOR 652 3
Rev. O Page 17 of 60 F
- 2. -AXIAL DISTRIBUTION The axial location of the 1984 indications can be characterized as being towards the top of the OTSGs.
For OTSG A, 79 percent of
.the indications during the 1984 examination are located in or above the 15th span with 57 percent of the indications in OTSG B located in this region.
This corresponds with 82 percent in "A"
generator and 74 percent in "B" generator for the 1982 examina-tion.
In order to compare the 1982 and 1984 axial distributions, it must.be noted tnat the majority of the indications detected dur-ing 1982.were within the upper tube sheet area and were captured by'the kinetic expansion process. As a result of the expansion process ar.d the coining of the tube wall against the tube sheet an examination of the coined area was not possible using the standard differential probe. Only the area of the tube below the expansion zone could be examined using the standard differential technique.
With-the exception of the upper tube sheet region, the overall distribution of the indications in 1984 closely resembles the 7
1982 distribution.
This distribution shows the indications are concentrated towards the uppermost regions of the OTSGs and the frequency of occurrence decreases sharply at the lower regions.
(See Figures 2a and 2b).
et e
':o1 3
TDR 652 Rev. O Page 18 of 60 3.
SIGNAL AMPLITUDE The majority of.the discontinuities detected in 1984 were small volume as indicated by the amplitude of the standard differential signal.
In OTSG A, 93 percent of the 1984 indications detected were 2 volts or less in amplitude, while in OTSG B 74 percent of the indications were in.this category.
This voltage distribution corresponds to approximately 93 percent of the 1982 indications in OTSG A and 78 percent of the indica-D tions in OTSG B as being 2 volts or less.
(See Figures 3a and 3b).
To establish a reference volume for the discontinuities in this range, a comparison can be made to the responses from the cali-bration standard. ~This standard has a 100% through wall 0.052" a
diameter drilled hole which produces a 15 volt response signal for calibration purposes.
This indicates tnat the discontinu-ities-present in the OTSGs are of a significantly smaller volume than the calibration standard.
'4 PERCENT THROUGH HALL The 1984 eddy current examination results have shown that a con-siderable number of the reported indications measured less than 40% through wall penetration.
The 1984 examination reported 572 a
n 18
)
TOR 652 Rev. O Page 19 of 60
. tubes.in "A" and 75 tubes in "B" with confirmed indications.
In the "A" generator the indications in 48% of the 572 tubes were less than 40% through wall and in the "B" generator the indica-tions in 60% of the 75' tubes were less than 40% through wall.
For the 1982 examination, the results indicated higher percent through wall degradation.
In the "A" generator, 50% of the indi-cations reported were 90% through wall penetration or greater while 3% of the reported indications were less than 40% through wall.
In the "B" generator, 16% of the indications reported were 90% through wall penetration or greater and 40% of the reported indications were less than 40% through wall.
(See figures da and 4b).
The contrast between the 1982 and 1984 examination results for
. percent through wall comparison must consider that most of the tubing within the upper tubesheet region could not be examined in 1984 This region accounted for 63% in "A" and 61% in "B" of the reported indications in the 1982 examination.
This comparison serves as an approximation only, since an improved inner diameter conversion curve was used for the November 1984 examinations (Ref. 3).
m_
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p TDR 652 Rev. O Page 20 of 60 l:
5.
CIRCUMFERENTIAL EXTENT To confirm the relevancy of the reported standard differential indication an absolute 8xl examination is performed.
The number of coils that respond to a relevant. indication provides an esti-mate of the indication's circumferential extent.
The 1984 exam-ination results showed that the confirmed indications ranged from I to 3 coils.
The circumferential extent for a one coil indica-tion is from the threshold of detection to 0.194".
A two coil indication is from 0.024" to 0.413" whereas a three coil indica-tion is from 0.219" to 0.632".
(Ref. 4).
For the "A" generator approximately 90% of the confirmed indications were I coll, ap-proximately 10% were 2 coils, and only 2 indications were 3 coils of which one was outer diameter.
For the "B" generator 79% of the confirmed indications were 1 coil, 20% were 2 coils, and only one was 3 coils.
For the 1982 examination the results showed that the confirmed indications ranged from 1 to 8 coils.
For the "A" generator 66%
of the confirmed indications were 1 coil, and for the "B" gener-ator 50% of the confirmed indications were 1 coll. A greater number of 2 coil and greater indications were confirmed by abso-lute 8xl during the 1982 examination than in the 1984 e+amina-tion.
(See figures 5a and 5b).
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- o TDR 652 Rev. O Page 21 of 60 3
D.
SUMMARY
OF INDICATION CHARACTERIZATION 1The eddy current examinations performed in 1982 and 1984, both util-ized the GPUN qualified examination program using a combination of Standard differential high gain.540" probe and absolute 8x' probe.
This dual examination method was developed to detect intergranular stress assisted cracking, predominately circumferential1y oriented and initiated on the tube's inner diameter wall.
The 1982 eddy current examinations prior to the kinetic expansion-repair were full length examinations performed on all in service tubes in both "A" and "B" generators.
The 1984 examination were also-full length however the kinetic expanded area could not be examined.
Some tubes could not be examined with the S.D.
540" probe below the center of the lower tubesheet due to ligament distortion from adja-cent explosive plugs.
The comparison of the 1982 to 1984 data showed both similarities and differences in the characterization of the indications reported.
The characterization of the axia'l and radial distribution showed the in-dications occurred in the same regions of the OTSGs in both 1982 and 1984.
The amplitudes of the indications also appears to be similar in 1982 and 1984.
The differences between the two sets of data ap-pear in the percent through walls, which are significantly lower in 1984 than in 1982 and in the circumferential extent which is also smaller in 1984 than in 1982 l
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c.
.o TDR 652 Rev. O Page 22 of 60 5
e-This characterization and comparison would suggest the 1984 indica-tions are a smaller additional subset of those detected during the 1982 examination.
To determine how the size of the new 1984 indications reflect on the given sensitivity curve established in TDR 401 and 423, the maximum
. size of the new indications detected was established and compared to the above.
It was determined that approximately 90% of the indica-tions are a maximum of one coll.
(Note:
a one coil indication if not preferentially oriented could give a two coil response).
Addi-tionally, approximately 90% of the new indications were determined to be between 20-60% through wall.
Using this data against the sensi-tivity curve shown in TDR 423, the'new indications appear to predom-Inately reveal themselves at or near the threshold of detection of the given sensitivity curves.
It was determined that approximately 10% was from a population that has 160% through wall determination.
For indications 160% through wall all were 1 or 2 coils with the exception of one indication in tube B-97-5.
The indication (76% through wall, 3 coils) was located at the upper tube sheet lower face region.
It is expected that the sensitivity for detection is suppressed during the eddy current probe passage into and out of (0.5" distance) this region. (Ref. 1).
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s.
o.
TOR 652 yi Rev. O Page 23 of 60 The two other'3 coil indications in tubes A-84-131 and A-79-1 had (20% and 52% through wall determinations respectively.
The three, 3 coil circumferential extent indications, and the >60%
1through wall indications are of dimension below those analyzed to withstand the main steam line break loadings (See Figure 6).
The following-is the breakdown of the 1982 and 1984 characterization:
1982 1984 1.
Radial Distribution Predominately in the outer Predominately in the periphery of both "A" &
outer periphery of both "B" (significantly fewer "A" & "B" (significantly in "B")
fewer in "B")
2.
Adlal Distribution Predominately in the UTS Most in UTS Region :50%.
Region 263%, and Some in 16th span 19%
16th span 214%
3'.
Amplitude-76% less than 2 volts in 75% less than 2 volts in (Voltage)
"A" and 51% less than "A" and 47% less than 2 volts in "B" 2 volts in "B" 4.
Percent' 50% greater than 90% T.W.
2% greater than 901 T.W.
Through Wall and 96% greater than 40%
and 40% greater than 40%
T.H. In "A".
16% greater T.W. In "A".
1% greater than 90% T.H. and 60%
than 90% T.W. and 27%
greater than 40% T.W. In greater than 40% T.H. In "B"
"B" b
7-
- s'.
TDR 552 Rev. 0 Page 24 of 60 1982 1984 5.
Circumferential The indications ranged The indications ranged Extent from I to 8 coils in both from 1 to 3 coils in'both "A" and "B".
For "A" "A" and "B",
For "A" 90%
more than 90% of the in-of the indications were i dications were 1 and 2 coll.
For "B" more than coils (66% - 1 coil and 90% of the indications-30% - 2 coils).
For "B" were I and 2 coils (79% -
more than 90% of the in-I coil and 20% - 2 coils).
dictations were 1, 2, 3 There was a total of 3 coils (50% -1, 34% -2 indications with 3 coils coils and 8% - 3 coils) 2 were inner diameter and I was outer diameter
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0 20 40 80 80 100 DEFECT DEPTH IN % WALL THICKNESS
TOR 652 Rev. O Page 25 of 60
-V.
REVIEW OF PRE KINETIC, POST KINETIC &-POST HOT FUNCTIONAL EXAMINATICN OATA A.
OVERVIEW GPUN performed a 100% Examination of the OTSG tubes in 1982.
This examination is referred to as the 1982 baseline.
Since performing this examination GPUN has reexamined a select number of the OTSG tubes to monitor the effects of the kinetic expansion repair (KE) and the subsequent hot functional testing (HFT).
l These examinations revealed the presence of Indications which were not previously identified during the 1982 baseline examinations.
To more fully understand the appearance of these Indications GPUN per-formed detailed evaluations of the available eddy current data to determine if the indications had been present but could not be de-tected on previous examinations or if the indications were in previ-ously unaffected areas of tubing.
Included in these evaluations were data sets of:
f 1982 In Process Examinations for Kinetic Expansion (October, 1982)
Purpose:
Determine the effects of kinetically expanding the OTSG tubes.
i
TOR 652 Rev. 1 Page 26 of 60 This data set consisted of examining 437 tubes in OTSG A and 8 after the tubes were expanded.
The data was then compared to the 1982 baseline.
1983 Post KE Examinations ( April.1983)
Purpose:
Determine the effects of the complete kinetic expansion process on the OTSG tubes.
This data set consisted of examining 477 tubes in OTSG A & B after the kinetic expansion repair was completed.
The data was then com.
pared to the 1982 basellne.
This data set includes the ISI tubes.
1984 Post HFT Examinations (November. 1984)
Purpose:
Determine the cumulative effects of the kinetic expan-slon repair and subsequent HFT on the condition of the OTSG tubes.
A data set of 375 tubes was identified from the November 1984 popula-l tion which remained in service for which GPUN had 1983 post kinetic espansion data.
This data set includes the 15! tubes.
This data was t
then compared to the 1983 post kinetic expansion and the 1982 base-line data.
TDR 652 Rev. O Page 27 of 60 Also included in the review were 45 tubes with indications identified as 140% through wall, during the 1984 examinations.
These tubes were selected from tubes included in the 1984 flaw growth program. Since no 1983 post KE data was available, the evaluation results were com-pared to the 1982 baseline.
8.
METH00 0F EVALUATION During the evaluations, the data analyst reviewed the magnetic tapes of the previous eddy current data for tubes with newly detected indt-cations.
This review was accomplished by isolating the specific area of Interest and performing a detalled review of the eddy current sig-nals.
By isolating the known area of interest, the data analyst was able to perform an intense analysis of the eddy current signals at a higher level of sensitivity than allowed by production analysis tech-niques.
This intense focus permitted the data analyst to identify
'the possible presence of low level eddy current signals which may be masked by background noise during production analysis.
Once the signal was identified and isolated, the analyst then measured and recorded the signals amplitude, which Indicates the vol-une of the discontinuity, and the phase angle, which Indicates the depth of the discontinuity.
TOR 652 Rev. O Page 28 of 60 The amplitudes and phase angles of the signals were then character-Ized to determine the relative size of the discontinuities.
The evaluations from the successive examinations were then compared to estabitsh when the signals were first detectable by eddy current.
This also characterized any changes which made the signal detectable by production eddy current techniques.
C.
RESULTS OF EVALUATIONS As a result of the evaluations performed on these data sets GPUN con.
cluded that:
1.
Knowing the exact location of a reported Indication, most of the indications could be identifled in previous examination data.
This indicated the discontinuities were previously present but not detectable due to their low amplitude.
2.
As a result of the kinetic expansion and the hot functional test-Ing the amplitude of previously unidentifled signals increased making the $lgnal response more detectable.
This was typically a 100-200% increase in amplitude which brought the signals above the threshold of detection.
This can be attributed to an in-crease in the volume of the discontinuity.
Example:
1984 data shows 1.5 volt signal in 0.5 volt noise, re-review of 1982 data shows 0.5 volt signal in 0.5 volt nolie at :ne same locitton.
+=
TOR 652 Rev. O Page 29 of 60 3.
Although the amplitude of the signals increased, the pnase angle of the signals did not show a corresponding increase for the in-dications first detected in 1984.
This would indicate that, al-though the volume of the discontinuity changed, the percent through wall penetration remained constant.
4.
The new (1984) indications which were reviewed are located at the upper elevations of the OTSGs.
This corresponds to the previous-ly affected areas of the OTSGs identified during the 1982 e< amin-ations.
D.
OETAILS OF EVALUATIONS PERFORMED The following is a brief description of the evaluations performed and the details of the data sets utilized.
The data sets are presented in chronological order to demonstrate the cumulative effects of the various OTSG activities upon the tubes since the 1982 basellne.
This Chronology is also contained in Table 2.
1982 In Process Examinations for Kinetic Expansion (October 1982)
Purpose:
Determine the effects of kinetically expanding the OTSG tubes.
l
7 TDR 652 Rev. O Page 30 of 60 In order to monitor the effects of the kinetic expansions GPUN ex-amined 437 tubes.
The tubes selected for these examinations were the first tubes to be expanded, located in rows 1-8, in both OTSGs.
This examination identified discontinuities which were not previously recorded in 15 of the 437 tubes examined (3.5%). An evaluation was performed at that time to determine why the indications were not identified previously.
This evaluation is documented in TDR 401 (Ref. 4) and TR-008 (p. 44-45) (Ref. 5) and concluded that:
1.
The indications were not initiated by the kinetic expansion pro-cess nor was there any evidence of detectable propagation of existing indications.
2.
The defects were small (threshold) type indications that had either been masked by the high background noise levels in the upper tube sheet regions or were sufficiently tight that signifi-cant metal removal was not present to permit detection. Kinetic expansion may have altered these areas to make them more detect-able.
I?
l TDR 652 Rev. O Page 31 of 60 1983 Post Kinetic Expansion Examinations (April, 1983)
Purpose:
Determine the effects of the Kinetic Expansion Repair and associated Tube Plugging Activities GPUN examined a sample of 477 tubes in OTSGs A and 8 using the dual examination method. _This sample was selected to determine if the kinetic expansion process had significantly altered the condition of the OTSG tubes.
The sample was based on the requirements of GPUN specification SP-1101-22-014 which is summarized in TR-008 Appendix A (p. 109-113).
The sample requirements are summarized below:
(a) All tubes with (40% through wall indications which remained in-service.
(ISI Tubes)
(b) All tubes adjacent to 10 selected simply plugged tubes with defects in the 15th, 10th and 1st spans.
(10 tubes each OTSG).
(c) All tubes adjacent to 10 selected simply plugged tubes. In the periphery of each OTSG.
(d) 50 tubes in high plugging density areas in each CTSG.
- e TOR 652 Rev. O Page 32 of 60 (e) All tubes adjacent to 5 plugged tubes in each OTSG with >3 volt signals in the lower part of the OTSGs.
(f) In addition to (a) through (e) above, all tubes identified as
_ leaking during the post repair drip and or bubble tests were included.
The examination of the above sample of tubes provided an evaluation of the " worst case" areas-of the OTSGs. The examination resulted in the identification of indications 1 0% through wall which were not 4
previously recorded in 35 tubes (7.5%).
In addition, 1 of the indi-cations previously identified as being <40% through wall in OTSG A appeared as 140% and required further dispositioning.
The comparison of the tube status prior to and after the kinetic expansion process is summarized in Table 3 and in TR-008, Appendix A (p. 109-113).
In its 1983 evaluation GPUN reviewed the 1982 baseline to establish the_cause of the newly detected indications.
This review concluded r
that:
1.
The majority of the Indications could be detected during detailed reviews of specific areas of the 1982 baseline data.
These re-views showed the indications had typically been present at low t
amplitudes and signal to noise ratios of 1 to 1 or less.
l i
N
~_
TOR 652 Rev. O Page 33 of 60 2.
The kinetic expansion process apparently caused the amplitude and corresponding signal to noise ratio of the indications to in-crease thereby making them more detectable.
3.
The indications were located near the top of the OTSG.
Twenty eight (28) of the 35 (80%) of 'the indications >40% through wall which had not previously been detected were located within the upper tube sheet.
This would be the area most affected by the kinetic expansion process.
4.
The phase angles of the indications reported in 1983 did not show a relevant increase in the percent through wall uhen compared to the 1982 baseline data.
GPUN also reviewed the 1982 baseline and 1983 post KE data to de-termine if the indication (ISI tube in 1982) previously identified as being<40%throughwallin1982,andthen($portedasgreaterthan 40% through wall in 1983, indicated a change in the status of the tube. A detailed review of this tube and prior associated indica-tions revealed that they were outside diameter originated and are therefore not part of this evaluation for primary side attack.
Its disposition was covered by the TMI Unit I technical specifications
-requirements and the tube was removed from service.
c.
TDR 652 Rev. 1 Page 34 of 60
~
1984 Pos' Hot Functional Testing Examinations (November, 1984)
Purpose:
Determine the cumulative effects of the kinetic expan-sion repair and subsequent hot functional testing on the condition of the OTSG tubes.
Following the hot functional testing (HFT) performed after the kin-etic expansion repairs (KE) GPUN performed the 1984 examinations of the TMI OTSGs.
These examinations provided a basis for determining
-the cumulative effects of the kinetic expansion repair and subsequent hot functional' testing of the OTSG tubes.
These examinations identi-fled indications not recorded in previous examinations.
To charac-terize the newly recorded indications and determine when they could first be detected, GPUN performed extensive reviews of the historical data for 2 data sets.
These data sets are discussed in (A) and (B) below.
(A) The first data set selected for evaluation from the November,
'1984 data set was 375 tubes for which post kinetic expansion data l
was available.
This data set included:
(1) All tubes remaining in service in OTSG A which were previous-ly examined during the 1983 post KE examination.
This con-sisted of 163 tubes with no previously recorded indications and 28 tubes previously identified as having 20-<40% through wall indications (ISI Tubes).
h
n.
TOR 652 Rev. 1 Page 35 of 60
.(2) All tubes in the outer periphery of OTSG B which remained in service following the 1983 post KE examinations.
This con-sisted of 128 tubes with no previous indications and 56 tubes previously identifie'd as having 20-<40% through wall indications (ISI Tubes).
As a result of these examinations, 14 of the 291 (5%) tubes with l
no previous indications were identified as having indications 140% through wall. Of the 84 previous ISI tubes, 3 tubes had l indications reported in 1984 which had not been previously iden-tified in 1983.
These 14 tubes with no previous indications and the:3 ISI tubes are discussed separately below.
The results of the examinations are summarized in Tables 4 and 5.
Tubes With No Previous Indications for the 14 tubes with indications 240% through wall which were not previously recorded, a complete evaluation of the historical data was performed.
The review characterized the indications and determined if they had been present'during the previous examina-tions.
This evaluation concluded that:
1.
During the review of the 1983 post KE data, 14 of the 14 in-dications were detectable but were low amplitude signals l
within the noise.
During the review of the 1982 baseline
o TDR 652 Rev. O Page 36 of 60 L
' data, 9 of the-14 Indications could be identified.
This would suggest that both the Kinetic expansion and not func-tional testing increased the detectability of the indications.
2.
The amplitude of the indications increased from the 1983 post KE examination to the 1984 post HFT examinations making them more detectable from the surrounding noise.
3.
The' indications recorded during the 1984 Post HFT examina-tions have-a small circumferential extent as shown by the 8x1 absolute probe. Of the 14 indications having >40% through wall penetrations, 13 appear as-1 coil and I appears'as a 2 coil-indication. A 360* indication would appear as an 8 coil indication.
r ISI Tubes For the three previous ISI tubes which have. indications >40%
.through wall, which were not previously identified and reported in-1983, the evaluations are as follows:
One tube A-120-106 showed an additional indication which was identified as being 95% through wall and 4.0 volts and was lo-cated at the edge of the 15th support plate.
.n
r 1
TDR 652 Rev. O Page 37 of 60 Upon a re-review of the 1983 Post Kinetic Expansion Data it was determined that the' indication was present at approximately 551 through wall and 2.1 volts but the' signal was masked by the sig-nalffrom the tube support plate.
The effects of the support
~ late signal also_ distorts the phase angle of the. eddy current p
signal making an accurate percent through wall determination im-practical.
This particular tube support is a drilled support and cannot be
" mixed out" using the multifrequency eddy current. techniques used to examine the broached supports located throughout the remainder
.of the OTSGs.
This creates a zone of reduced sensitivity (approximately.5" above and below the edges of the support plate) at the drilled suoport locations.
The 1983 signal at 2.1 volts is below the 3.3 volt threshold of detection for the drilled support plate as established in TOR 423.
This zone of reduced sensitivity applies to the edges of both the upper and lower tubesheets and the drilled hole in the 15th sup-port plate.
The drilled holes are located only in the extreme outer periphery of the 15th support plate.
The remainder of the 15th support plate and the other 14 support plates are the
" broach" design and do not have this zone of reduced sensitivity.
~
e
.o TOR 652 n
Rev. O Page 38 of 60 The other two tubes, A-3-31 and A-149-14, had indications greater than 40% through wall reported in 1984 which had not been previ-
- ously identified.
In the re-review of the 1983 data at the spec-ified location, the indications were identified and compared to the 1984 data.
This comparison showed the indications were low amplitude signals masked by noise in the 1983 data.
(See Table 5).
(B) The second data set selected for evaluation from the November 1984 data set was 46 tubes with indications first identified dur-.
ing the 1984 examinations.
This data set included:
(1) 12 tubes with indications less than 40% through wall and 34 tubes with indications greater than 40% through wall.
The
-tubes selected for this evaluation were previously included in the 1984 Growth Program.
The tubes were located in the outer periphery of the OTSG A.
The indications were characterized and compared to the 1982 baseline data.
The results of the-evaluation conclude that:
1.
Knowing the exact location of the 1984 Indications, the corres-ponding indications could be identified during a review of the 1982 baseline data for 32 (70%) of the tubes.
This would indi-cate the areas had been affected prior to the 1982 baseline exam-inations.
's
.o TDR 652 Rev. O Page 39 of 60
~2.
A comparison of the 1982 to 1984 data shows the average amplitude
. increased from 0.6 volts in 1982 to 1.5 volts in 1984.
This demonstrates the amplitude of the indications increased during Jthis time period making them more detectable.
3.
.The comparison of the 1982 to 1984 percent through wall determin-ations showed a slight downward tread of approximately 11 percent through wall (equivalent to a 3* phase angle change).
Based on this phase angle evaluation, no significant trend of through wall growth can be established.
^
TDR 652 Rev. 1 Page 40 of 60 Table 2 Chronology of Steam Generator Evolutions and Corresponding Eddy Current Examination
-Steam Generator Eddy Current' Examination Event Duration Data Sets Results > 40% T.H.
A B
Start-up.& Test 131 tubes leak 0ct-Nov 1981 July-Sept 1982 885 273 (1982 baseline)
- Kinetic Expansion Repair
Oct-Dec 1982 Oct-Nov 1982 9
6 (in process)
April-May 1983 22 14 (Post)
-Hot Functional-Aug-Oct 1983 Test May 1984-Leak Test June 1984 July 1984 0
1 Dry Lay up June-Nov 1984 Tech Spec 4.19 Nov-Dec 19o4 Nov-Jan 1984 298 30
_ ~. _ __.
TOR 652 Rev. 1 Page 41 of 60 Table 3 Results of 1983 Post Kinetic Expansion Examinations Status Prior to Kinetic Expansion (1982 Baseline)
ISI Tubes Tubes Tubes Tubes Tubes Preventivel 0TSG Examined NRI
<40% (ISI Tubes) 3,40%
Plugged A
215 200 14 0
1 B
263 212 51 0
0 TOTALS 478 412 65 0
1
-Status After Kinetic Expansion (1983 Examinations)
ISI Tubes Tubes Tubes Tubes Tubes Preventivel 0TSG Examined NRI
<40% (ISI Tubes)
>40%
Plugged A
214 163 28 (12 previous ISI) 22 (l* previous ISI) 1 (16 previous NRI)
(21 previous NRI)
B 263 193
-~~ ( 5 Previous NRI)
(14 Previous NRI) 56 (51 Previous ISI) 14 (0 previous ISI) 0
-~~
TOTALS 477 356 84 36 1
NRI - No Relevant Indications NOTES:
- In 1 tubes, indications reported as <40% through wall in 1982 were reported as >40% through wall in 1983. These indications are outside diameter initiated and are not considered relevant to the present evaluations.
- These ISI tubes were preventively plugged in accordance with engineering dispositioning based on location (axial and/or radial) of <40% thru wall indications.
-s.
TDR 652 Rev, 1 Page 42 of 60 Table 4 Results of Post Hot Functional Testing Examinations Status of Tube; Prior to H.F.T.
Tubes.
Tubes Tubes Tubes OTSG Examined.
NRI
<40% (ISI Tubes) 4 1 0%
l A.
191 163 28 0
18 184 128 56 0
Total 375 291 84 0
l
^
Status of Tubes After H.F.T.
Tubes Tubes Tubes Tubes OTSG Examined.
NRI
<40% (ISI Tubes) 140%
-A
'191-133 39 (23 previous ISI) 19 ( 5 previous ISI)
(16 previous NRI)
(14 previous NRI)
B
-184 127 56 (55 previous ISI)
_1 ( 1 previous ISI)
( 1 previous NRI)
( 0 previous NRI)
Total 375 260 95 20 NRI - No Relevant Indications i
TDR 652 Rev. 1 Page 43 of 60 Table 5 ISI Confirmed Indications Greater Then 40% Through Wall in 1984 April Nov.
Indication 1983 Post KE Data 1984 Post HFT Data Gen Row Tube Elevation Origin
% T.W.
Volts Volts 4
A 3 - 31 13+0 ID 33%*
1.1 33%
125 13+04 ID 27%**
0.8
<20%
1.3 13+05 ID 33%**
1.3 36%
3.3 13+08 ID 40%**
0.6 45%
1.5 13+15 ID 30%**
0.3 2831%
0.8 A
149 - 14 14-06 ID 86%**
0.4 76%
0.6 15-16 ID 80%**
0.5 69%
0.7 US+04 ID 20%
l.0 Not Detected A
120 - 106 12+09 ID 40%**
0.5 41%
1.4 13-08/15-08 ID 50%**
0.4 48%
0.7 15+0 ID 55%**
2.1 95%
4.0 US+02 10 20%
1.1 20%
1.2 Represents re-evaluation of 1983 data.
- Indications not previously identified during production examinations, indi-cations first identified during 1984 review of 1983 data.
l l
-z.
TDR 652 Rev. O Page 44 of 60
'VI. GROWTH PROGRAM GPUN initiated a growth program during the examinations in November 1984 to determine-if a grcwth mechanism was' active during the current (July-Nov 1984) period of extended dry layup of the THI-1 GTSGs.
This sample included a population of 100 tubes in 'A' and 50 tubes in
'B'.
The tubes for both generators were selected from high defect areas of the generators and were examined full length using the GPUN dual examination method.
OTSG'A GRONTH PROGRAM The growth program in the 'A' OTSG consisted of examining a population of
.100 tubes 3 times at approximately 2 week intervals.
Initially, these tubes were examined as part of the production eddy current program in Mid-November 1984.
The tubes were subsequently examined a second time in late November 1984 and a third time in Mid-December 1984.
Results of the 3 examinations of each tube were then compared for changes in the number-of indications and for changes in signal response voltage or percent through wall determinations.
The 100 tubes in the 'A' Growth Program included 55 tubes with confirmed indications and 45 with no relevant indications.
The comparisons of the repeat examinations were performed by evaluating the signal amplitudes and percent through wall determinations.
These evaluations revealed es-sentially no change in the voltage or percent through wall determina-tions.
These results indicate that there was no continued degradation curing the three examinations from November to December. 1984
1 TOR 652 Rev. O Page 45 of 60 OTSG B GROWTH PROGRAM
.The Growth Program in 'B' consisted of a Mid-November 1984 examination of 50 tubes which were previously examined in July 1984.
These 50 tubes were selected from the high defect area.for full length examination-in July 1984 during a limited scope examination performed when primary to secondary leakage was detected.
The July and November 1984 Eddy Current results were then compared and no previously undetected indications were found to exist in the November 1984 results.
There was no evidence of continued degradation in these tubes between July and November 1984.
GRONTH PROGRAM CONCLUSIONS The Growth Program evaluations indicate there was no significant change in the-condition of the tubes from July to November 1984 in the
'B' OTSG or-from Mid-November to Mid-December in 1984 for the 'A' OTSG.
This in-formation does not indicate any correlation between extended dry lay-up and identification of previously undetected indications.
TOR 652 Rev. 0 Page 46 of 60 VII. CONCLUSIONS Based on the characterization of the 1984 indications, a review of the 1982, 1983 and the growth program data, GPUN was able to draw the follow-ing conclusions for the 1984 examination-results.
1.
The characterization of the 1984 Indications by axial and radial lo-cations, and their correlation to the indications reported in the 1982 baseline, suggest that the 1984 Indications are an additional subset of the 1982 indications.
2.
'The re-evaluation of previous data suggests that the indications identified in 1984 were already present during the 1982 examination but were within the background noise.
The kinetic expansion repair and hot functional testing may have in-creased the amplitude of these previously existing indications and made them detectable during production examinations.
There was no trend of through wall growth associated with this amplitude increase.
3.
Based on the evaluation of the Growth Program, there is no evidence
-of continuing. tube degradation since the OTSGs were placed in dry layup in July 1984.
4
['
TDR 652 Rev. I Page 47 of 60 L
L 4.
The characterization of the 1984 indications shows that approximately 90% of the indications are 20-60 percent through wall and I coll.
These indications are at or near the threshold of detection for the p
previously established sensitivity curve.
5.
Approximately 10% of the indications are higher percent through wall
-(>60%) with a circumferential extent of 1 or 2 coils.
There is a l
total of three (3) coil circumferential extent indications. All of these indications are between the threshold for detection and the most conservative curve for critical crack size.
(Main Steam Line Break).
u:-
TOR 652 Rev. O Page 48 of 60 VIII.
REFERENCES 1.
GPUN TOR 423,.Rev. 1, R. Barley, J. Janiszewski, G. Rhedrick, M. Torborg, "Three Mile Island - Unit 1 OTSG Tubing Eddy Current Program Qualification," 3/15/84.
2.
GPUN TDR 442, Rev. O, G. Rhedrick, " Eddy Current Examination Results of Three Mile Island Unit 1 OTSG," 8/29/83.
3.
GPUN TDR 642, Rev. O, M. Torborg, G. Rhedrick, " Qualification of Conversion Curve for Inner Dianeter Discontinuities," 1/29/85.
4.
GPUN TOR 401, Rev. O, G. Rhedrick, " Report on Eddy Current Indica-tions Found Subsequent to Kinetic Expansion of TMI-I Steam Generator Tubes," April 1983.
5.
GPUN Topical Report 008, Rev. 3, T.M. Moran, " Assessment of TMI-I Plant Safety for Return to Service After Steam Generator Repair",
August 19, 1983.
u
TDR 652 Rev. O Page 49 of 60 l
APPENDIX A ABSTRACT ON THE DEVELOPMENT OF THE DUAL INSPECTION TECHNIQUE AND PERCENT THROUGH WALL CALIBRATION CURVE
TOR 652 Rev. O Page 50 of 60 Prior to the 1982 OTSG tubing inspection, GPU Nuclear had always performed its OTSG tubing examinations with the standard differential eddy current technique for detecting indications that normally originated on the outer diameter of the tube wall.
The eddy current inspection system was operated at normal gain and the. probes used for these inspections measured 0.510" diameter.
These parameters traditionally were considered acceptable for inspecting the OTSG tubing which has a nominal inner diameter of 0.557".
After 131 tubes leaked upon start-up and test in November 1981, eddy current examinations were immediately performed with the standard differential (S.D.)
.510" technique and some of the leaking indications were not. detected.
A sub-sequent examination was performed with a multi-coil absolute eddy current technique and indications were identified in the roll transition of the leak-ing. tubes.
In addition, other indications which had not been detected by the previous S.D.
510" examination were identified.
The defects discovered in the OTSG tubing were metallurgically evaluated as inner diameter initiated, very tight, and orientated around the circumference of the tubes.
It was then recognized that the 5.0.
510" technique was not sensitive enough for detect-ing all_ of the new inner diameter discontinulties.
GPU Nuclear modified and improved the sensitivity of its standard differential technique by increasing the probe's diameter to 0.540", and increasing the operating gain.
This modification improved the standard differentia 1's sensi-
.tivity for detection of predominately circumferential, I.D. Initiated indica-tions by approximately 1757. over the older technique.
The disadvantage of using the nigh gain and impr)ved fill facur is that the standard differential examination oeccmes overly sensitive to surface anomalies.
TOR 652 Rev. O Page 51 of 60 The absolute. technique used to confirm the standard differential inspection results was also modified and improved.
The development of the 8X1 Absolute probe with eight pancake shape coils placed around the probe body provided 360 degrees coverage on the circumference of the tube wall.
This design permitted a single pass of the probe in the tube during an examination as compared to multiple passes when fewer coils are used.
The eight coils also provided a fair estimate of the arc length of an indication because the response signal from each coil represents its proximity to the indication.
Using the improved S.D.
540" high gain and absolute 8xl techniques, GPU Nuclear developed a dual method eddy current inspection technique.
The ini-tial examination was performed by the S.0.
540" high gain technique.
If the examination.by S.D.
540" showed no evidence of a defect, its examination be-came the final inspection of record.
If the S.O.
540" examination reported an indication, a second examination was performed using the absolute 8xl technique.
The absolute 8xl examination de-termined if the reported indication was relevant or non-relevant.
For those indications determined to be relevant, the absolute 8xl result was used_to estimate the arc length and also confirm the origin (I.O./0.D.) and axial lo-cation of the indication.
During a standard differential eddy current examination the percent through wall penetration of a flaw is determined by measuring the response signal's phase angle and converting that measurement to the percent through wall.
A L-
~
7.-
TOR 652 Rev. O Page 52 of 60 calibration for-this conversion is established by setting up the standard dif-ferential equipment and testing a known standard.
The phase angle for the eddy current response signal is adjusted to a specified measurement which gen-erally is 40. degrees for a 100 percent through wall by.052" diameter hole standard.
This calibration is done in accordance with the ASME Section XI code.
The traditional conversion curve for phase angle measurement to inner diameter initiated percent through wall is determined by the values that are extrapolated from the 40 degree phase angle-100 percent through wall (given by the.052" diameter hole standard) to zero degree phase angle--zero percent through wall.
The estimated percent through wall that is extrapolated from the conversion curve tends to overcall the actual percent through wall of a small volume flaw.
This over calling is considered conservative eddy current evaluation
-and was instituted in the 1982 dual inspection technique.
It had always been acknowledged that-this traditional curve overcalled small
- volume inner diameter discontinuities. The presence of smaller inner diameter initiated cracks in the TMI-I OTSG's had required GPUN to develop a more ac-curate means of assigning the percent through wall penetration.
Therefore, the traditional inner diameter conversion curve was enhanced by using supple-mental data from EDM with various known depths.
This data was used to develop
-a conversion curve which more accurately represented small volume, inner di-
- ameter initiated discontinuities and this accuracy was verified through metal-Turgical correlations using-actual intergranular stress assisted crack samoles.
-2 h
r; TDR 652 Rev. O Page 53 of 60 APPENDIX B 1982, 1984 EDDY CURRENT STATISTICS n
o 4
TOR 652 Rev. O Page 54 of 60 TMI STEAM GENERATOR A AXIAL LOCATIONS OF CONFIRMED INDICATIONS 0-100% THROUGH WALL PERCENT VS SPAN 1982 VS 1984 1982-1984
. Support-
-Frequency Frequency LP-1 6
.19 1
.090 1-2 23
.717 2
.181 2-3 8
.249 8
.726
~ 4-8
.249 19 1.725 4-5 17
.53 7
.635 5 15 8 1.808 19 1.725 6-7 34 1.714 26 2.361 7-8 55 1.060 5
.458 8-9 34 1.714 12-1.1 9-10 11
.343 4
.367 10-11
'24
.748 8
.726 11-12 54 1.683 13 1.181 12-13 63 1.964 54 4.900 13-14 146 4.551 57 5.177 14-15 97 3.024 78 7.084 15-US 530 16.'521 217 19.70 US-UP 2040 63.591 571 51.861 TOTAL.
.3208 1101 Note:
(1) 1984 data includes the length of tubing below the kinetically ex-panded zone. -(Approximately US+7 and below).
(2)'1982 data includes the length of tubing from US+15 and below.
(3) Data taken frcm 1982 and -1984 data bases as of 2/15/85.
L
..s-TOR 652 Rev. O Page 55 of 60 TMI STEAM GENERATOR B AXIAL LOCATION OF CONFIRME0 INDICATIONS 0-100% THROUGH WALL PERCENT VS SPAN 1982 VS 1984 1982 1984 Support-Frequency Frequency LS 6
.468 6
3.109 1-2 3-
.234 2
1.036 2-3 4
.312 1
.518 3-4'
~20 1.561 3
1.554 4-5 9
.703 6
3.109 5 9
.703 4
2.072 6-7 24 1.874 8
4.145 7-8 12
.937 7
3.627 8-9 19 1.483 4
2.072 9-10
~20 1.561 9
4.663 11 15 1.171 2
1.036 11-12 34 2.654 12 6.218 12 34 2.654 12 6.218
.13-14 106 8.275 7
3.627 14-15 81' 6.323 7
3.627
'15-US 98 7.650-25 12.953 US 787 61.144
_78 40.414 TOTAL' 1281 193 Note: -(1) 198J data includes the length of tubing below the kinetically ex-
-par.deo zone.
(Approximately US+7 and below).
~(2) 1982 data includes the length of tubing from US+15 and below.
(3) Data taken from 1982 and 1984 data bases as of 2/15/85.
e
s g-TOR 652-Rev. O Page 56 of 60
'THI STEAM GENERATOR A VOLTAGE DISTRIBUTION FOR CONFIRMED INDICATIONS 0-100% THROUGH WALL PERCENT VS VOLTS 1982 VS 1984 1982 1984 Volts Percent-Volts Percent
-0 31.807 0
34.968 1
44.653 1
35.15 2
16.595 2
23.615 3
4.702 3
4.814 4
1.537 4
.636
~5.
.338 5
.363 6
.184 6
.091 7
.061 7
.182 8-
.092 8
.182 9
0 9
0 10
.031 10 0
Note:.(1) 1984 data includes the length of tubing below the kinetically ex-panded zone.
(Approximately US+7 and below).
-(2) 1982 data includes the. length of tubing from US+15 and below.
I (3) Data taken from 1982 and 1984 data bases as of 2/15/85.
Y-l
TOR 652 Rev. O Page 57 of 60 TMI STEAM GENERATOR 8 VOLTAGE DISTRIBUTION FOR CONFIRMED INDICATIONS 0-100% THROUGH HALL
(', !
PERCENT VS VOLTS 1982 VS 1984
-1982 1984
. Volts.
Percent Volts Percent 0
23.878 0
26.425 1
28.897 1
20.207 2
25.019 2
27.979 3
9.810.
3 11.917 4
6.844 4
5.699 5
1.901 5
3.109 6-1.597 6
1.036 7
.608 7
1.554 8
1.217 8
1.554 9
0 9
0 10
.076 10
.518 11
.152 11 0
Note:
(1).1984 data includes the length of tubing below the kinetically ex-panded zone.
(Approximately US+7 and below).
(2) 1982 data' includes the length of tubing from US+15 and below.
(3) Data taken from 1982 and 1984 data bases as of 2/15/85.
L J
s TOR 652 Rev. O Page 58 of 60 TMI STEAM GENERATOR A CONFIRMED PERCENT THROUGH WALL.
DISTRIBUTION-FOR CONFIRMED INDICATIONS 0-100% THROUGH WALL PERCENT VS PERCENT THROUGH WALL 1982 VS 1984 1982 1984
% Thru-Hall
% Thru-Wall 0-19.
.281 0-19 0
20-29' 1.434 20-29 39.055 30-39
'1.309 30-39 21.163 40-49 6.827 40-49 17.802 50-59 13.685 50-59 7.629
.60-69 9.757 60-69 5.904 70-79 7.512 70-79 2.186 80-89 8.635 80-89 1.907 90-100 50.561 90-100 3.724 Note:
(1) 1984 data includes the length of tubing below the kinetically ex-panded zone.
(Approximately US+7 and below).
(2) 1982 data includes the_ length of tubing from US+15 and below.
(3) Data taken from 1982 and 1984 data bases as of 2/15/85.
..s
. TOR 652:
Rev. 0-Page 59 of 60 THI STEAM GENERATOR 8 CONFIRMED PERCENT THROUGH WALL DISTRIBUTION FOR CONFIRMED INDICATIONS 0-100% THROUGH HALL PERCENT VS PERCENT THROUGH HALL 1982 VS 1984 1982 1984
- % Thru-Wall
-% Thru-Wall
'0-19 11.788 0-19 0
20-29 11.866 20-29 63.212
'30-39
.16.472 30-39 13.99 40-49 10.617 40-49 11.917 50-59 13.349 50-59 4.663
'60-69 8.041 60-69 3.109-70-79 6.401 70-79 2.073 89 5.699 80-89 0
90-100 15.769 90-100 1.036
- Note: L(1) 1984 data' includes the length of tubing below the kinetically ex-panded zone.
(Approximately US+7 and below).
-(2) 1982 data includes the length of tubing from US+15 and below.
(3) Data taken from 1982 and 1984 data bases aslof 2/15/85.
r
rv 4
y..: -
TOR 652 Rev. O Page 60 of 60 CIRCUMFERENTIAL EXTENT FOR CONFIRMED INDICATIONS GENERATOR A 1982 1984
-Colls Frequency Colls Frequency 0-270 (N/A) 0 321 (N/A) 1 655 66.973 1
1111 89.959 2
301 30.777 2
122 9.878 3
18 1.840 3
2 0.162 4
1 0.102 4
0 0-5 1
0.102 5
0 0
6
.0 0
6 0-0 7-1 0.102 7
0 0
'8.
1.
0.102 8
0 0
TOTAL 978--
1235 GENERATOR B 1982 1984
-Colls Frequency 1
Coils Frequency 0-361' (N/A) 0 321 (N/A) 1 147 50.000 1
102 79.069
.2 102 34.694 2
26 20.155 3-26 8.843 3
1
.775 4
7 2.381 4
0 0
'S 4
1.360 5
0 0
6 0
0 7
0 0
7 0
0 8
0 0
8 8
2.721 9
0 0
TOTAL-294 129 Note: '(1) 1984 data includes the length of tubing below the kinetically ex-panded zone. -(Approximately US+7 and below).
(2) 1982 data includes the length of tubing from US+15 and below.
-(3) Data taken from 1982 and 1984 data bases as of 2/15/85.
C.
Document NO.
ME TDR-652 TITLE Evaluat. ion of the 1984 Required Technical Specification Examination for the TMI-1 OTSG REV
SUMMARY
OF CHANGE APMt0 VAL DATE 1
The number of confirmed indicationsz40% thru Wall in "A" Once Through Steam Generator has J/pg/Of.
"/c chanced tn P98 tubps frnm P97 tilhet The tntal
- wwer' vt tuuua witn incicaticasy.Ws t er Dotn NA# 18Du has ineressed by cae Lv 3CO.
g I
Pg.12 add subtitle " Status of ISI Tubes."
gC( 3 It7[W Revised Table 1, % T.W. & Volts 1983 & 1984 Revised Table 2, quantity of tubes in "A" OTSG with indications 2 40% to 22 from 20 and to:298 i
from 297.
Revised Table 3, add column to report ISI tubes that were preventively plugged.
Revised Table 4, revised quantity of tubes examined and tubes NR I to be in agreement with revision made to Table 3.
Revised Table 5, 5 T.W. & Volts - 1983 & 1984.
8 Y
o I
2 1
I mn
TDR NO.
--~666 Am nes0N NO. _ 0 TECWNCAL DATA REPORT Activity NO. 123125 pass 1
_Op _18 PROJECT:
yd?
E8D/ Mech. Conn.
,,y, Tiil-1 OTSG REPAIRS
- oc P c' i ?_
D17 5 a IM.5ASE DATE REVtS40N DATE ---
DOCUMENT TITL8: Adequacy of TNI-l UT5G Return to dervice datety Assessment After 1984 Technical Specification ECT Examination ORIGINATt'A SIGNATURE DATR APPROVALISI SIGNATURE OATE T. A. Richter 88 M 3/&//5 B. D. Elam db ;-
f/E.Mr
._ G. R. Capodanno 8,0 - h -
3l2(/rf APPROVAL IBOR EXTElg@l, StepteUTION Daft D. K. Croneberger/f & _ L,
J.gg g3-poes this TOR instude reeemmendationW QYes ENe if yes.TPWR/7R #
e DISTR 480T10N ASSTRACT:
i R. O. Barley Statement of the Problem T. G. Broughton
- 3. R. Capodanno The safety assessment of the return to service of the J. J. Colitz D. K. Croneberger THI-1 OTSG's was made in 1983 (TR-008) and encompassed the examination, evaluation and repair of defects known l
B. D. Elam F. S. Giacobbe up to that time and the prevention of reoccurrence. The 1984 technical specification eddy current examination
[ [ [ga reported further indications in both OTSG's.
s R. F. Wilson Summary SEF 0 Wi 5f/,
The examinations done in 1984 have identified enhanced visibt11ty of pre-existing indications on the threshold of detectability as the most probable and reasonable explanation for the new indications.
It was concluded that the corrosive failure mechanism identified in 1983 is still the correct description of what the OTSG's have undergone. The precautions taken to prevent reoccurrence have been adequately observed and are effective; no new material attack has occurred.,
1 Conclusion The safety assessment as originally performed in TR-008 remains valid and the 1984 inspect on results neither call into question, nor invalidate, nor require a revision to the assessment.
u, _ PAe8 MT
- w
- 700___,
Ain nu mm nm m et qm en 3
TDR 666 Rev. 0 Page 2 of 18
1.0 INTRODUCTION
The safety assessment of the results of the TMI-1 OTSG repairs was originally done in Reference (1) and encompassed the examination, evaluation, and repair'of the defects known up to the reports' release date and the subsequent testing and examination of those repairs.
Recent examination in support of THI-1 Technical Specification requirements in 1984 has uncovered additional indications. These indications may be generally characterized as follows (Ref. 3, page 23-24):
1.
They are predominantly located within the outer periphery of both OTSG's. Some indications appear entirely across OTSG-1A; none of greater than 40% through wall penetration appear in the core region of OTSG-18.
2.
They are mostly (approximately 50%) in the upper tubesheet and (approximately 20%) in the 16th tube span area.
3.
They predominantly exhibit voltages below 2 volts.
4.
They are, in the majority, of less than 50% through wall penetration.
5.
They exhibit circumferential extent by 8 x 1 absolute ECT of predominantly 2 coils or less (90% of all indications).
This report reviews the 1983 evaluation for accuracy in light of the 1984 examination results. Discussion will center on the information contained in References 2 & 3 as it pertains to the logic and conclusions of Reference 1.
2.0 METHOD The logic of the safety evaluation done in TR-008 is set forth in Section ID and describes the points to be demonstrated and assured by the repair program to allow OTSG return to service. This logic is graphically captured in Figure 1-7 (attached) and stated in ID (1) through (5) as follows (Ref.1. Section ID, page 3):
"1.
The failure mechanism is understood well enough to define the root cause of the steam generator damage; 2.
Other components in the RCS and supporting safety systems were not visibly damaged by the failure mechanism The plant can be operated such that this fafIure mechanism is 3.
arrested and will not recur; i
4.
The Steam Generators can be repaired and operated within the design basis; 5.
The plant can be operated with some tube leakage without adversely impacting the environment."
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Rev. O Page 4 of 18 l
The issues raised by the results of the 1984 inspection principally impact points (1), (2) and (4), specifically:
(1)
Have the inspection results indicated the presence of a failure mechanism different than that set forth in TR-008?
(2)
Have the steps taken under the assurance of preventing reoccurrence been followed accurately and proven effective?
I (4)
Has the confidence in ECT detectability been compromised by the discovery of new indications in the period Sept.1982 to Jan.
1984 and has the lack of flaw growth and non-reoccurrence predicted by TR-008 been supplanted by the latest observations?
Each of these issues will be addressed in turn and the evidence to support or refute the positions set forth in TR-008 examined.
3.0 RESULTS 3.1 Issue (1): Failure Mechanism Identification The discussion of failure mechanism is contained in Section II B and C and III in TR-008 (Ref.1, Section IIB, 2g, page 11).
Succinctly put, the OTSG tubing was found to have undergone intergranular stress-assisted cracking (IGSAC) producing predominantly circumferential cracking under the influences of a reduced sulphur species and axial stresses.
In con. junction with cracking, intergranular attack (IGA) was observed.
The cracking appeared to initiate and propagate in the presence of the thiosulphate agent, oxygen, and ambient temperatures.
Since the writing of TR-008, the results of the Long Term Corrosion Test (LTCT) have become available. The test followed conditions comparable to plant operatitn and confirmed that "in the absence of the intentionally added aggressive sulphur species, normel operations would not cause corrosion of TMI-1 OTSG tubing" (Ref. 2, Pg 12). Some IGA was noted in the LTCT samples that was not detectable by ECT (P.ef. 2, page 12) most reasonably due to its superficial wall penetrations.
Additionally, the ECT indications seen in 1982 were characterized as to voltage, percentage through-wall penetration, circumferential extent and spatial distribution. The comparison of recent ECT results with those of the 1982 examinations is accomplished in detail in Reference 3 (Section IYC page 15).
Here note was made that the amplitude and distribution of the total population of indications below the kinetic expansion zone appeared similar in 1982 and 1984, and both the through-wall a
4 0838d
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4 TDR 666 Rev. O Page 5 of 18 penetration and the circumferential extent seen in 1984 were lower than those seen in 1982. For the smaller population of indications that are reported in 1984 but only seen on re-review of 1982 tapes the amolitudes have g.enerally increased while the through-wall p,enetration has not. Inis is tndicative of newly i
reported but previously existing indications formerly below the threshold of reportability.
Hot Functional Testing (HFT) provided mechanical loading necessary to cause enhanced detectability, in degrees which varied according to the severity of loading. All tubes at each elevation saw flow loads both inside and out. Lateral loads due to buffeting and cross-flow were present at varying elevations.
and heat-up and cool-down axial loads in excess of those generated by normal operations were experienced by all OTSG tubes. The axial load varies from a maximum on peripheral tubes to a minimum on core tubes; both the ISGAC defects found previously and the 1984 indications reflected this radial bias.
The kinetic expansion (KE) process produced loads significant enough to enhance detectability as well. Additionally, larger IGA areas would be more susceptible to enhancement after mechanical i
loading, and smaller areas are structurally insignificant.
Fourteen (14) tubes with no previous history of indications were identified in this 1984 ECT examination (Post - HFT) as having indications of over 405 through-wall penetration. A review of the 1983 ECT (Post - KE) tapes identified all 14 indications as marginally detectable but of low amplitude. One of the 14 indications could be seen in the review of the 1982 examination, which preceded both hot functional testing and kinetic expansion. The amplitude increase in these indications is demonstration of increased detectability with "...no trend of through-wall growth associated with this amplitude increase."
(Ref.3,page46).
These observations and appreciations support the plausibf11ty of enhanced visibility of pre-existing indications on the threshold of detectability as the most probable and reasonable explanation for the new indications. The failure mechanism identified in 1983 is still the correct description of what the OTSG's have undergone.
3.2 Issue (2): Prevention of Re-occurence The steps to be taken to prevent the reoccurrence of the 1981 IGSAC incident were outlined in Reference 1,Section IV. These involved four areas: physical removal of the source of l
contamination, chemical removal of the existing contaminant, introduction of strict administrative controls on the use of l
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1 TOR 666 Rev. 0 Page 6 of 18 other potential contaminants, and the revision of allowable RCS chemistry limits. The first two steps had been accomplished and were discussed in Reference 1.
l The administration of the last two of these steps was reviewed for the period of time between 1982 and 1984.
It was stated that 4
a 95% adherence to the imposed limits was achieved; excursions were for brief periods and the environment remained protective (Ref. 2, pg.16). It was therefore concluded that the adherence to the measures taken was adequate to prevent re-initiation of 2
j primary side corrosion.
The consideration of the ECT techniques used in 1982 to detect defects in the OTSG tubes is discussed in Reference 1,Section IX, as is the argument against recurring defects. Taking the last point first, the arguments against re-initiation are i
threefold:
"a)
Cracking will not occur unless an active reduced species of sulfur is present and cracks in SG tubing will not propagate in the present chemical environment.
b)
Suldur induced cracking requires an oxidizing potential which does not exist under normal hot operating conditions, c)
Lithium hydroxide is an effective inhibitor of the cracking mechanism."
The results of both the short term corrosion tests (Reference 1, Section IIID) related in TR-008 and the Long Term Corrosion Tests (Ref. 2, pg.11) bear out the accuracy of the original assessment.
Additional assurance of non-reoccurrence is obtained from the absence of flaw growth (Ref.1. III) or the development of i
significant leaks since the 1982 inspections. The cracking mechanism is rapid, propagating up to 1 millimeter through wall per day, and if the mechanism were still active the period of time past would have allowed the development of many severely leaking tubes. The bubble test of both OTSG's in Oct.1984 minor leakage above showed 8 tubes in the lane area exhibiting'eakage was stopped by l
the bottom of the kinetic expansion; the The leakage was via the kinetic expansion rolling the tubes.
joint and in no way inus ative of flaw growth in the tubes and as such had no safety impact. The most recent bubble test (3/11/85) showed no bubbling at all.
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TDR 666 Rev. O Page 7 of 18
)
3.3 Issue (4) - Eddy Current Testing Limits of Detectab_111ty as It Impacts OT5G Operability This leaves the question of why ECT found defects in 1984 that were not seen in 1982. Three possible classes of undetected defects were outlined in Reference 1 (IXC page 81):
"1)
Local intergranular attack (IGA) i 2)
Below the detection limits of ECT 3)
Detectable by ECT but missed through random error" These causes were deemed to present no significant hazard because local shallow surface IGA results from the manufacturing process and is only 1-2 grains deep. Its long term behavior would be assessed by the Long Term Corrosion Testing. Additionally, small cracks below eddy current detectability will not propagate by chemical means in the absence of active corrodants and are far smaller than the crack size above which mechanical loading will cause propagation (Ref.1 Section IXC page 82).
Taking the last point first, protection against randomly occurring failure to correctly read test results has been provided by Quality Assurance overview and the use of permanent magnetic tape records, allowing call-up and review of inspection results at any date. Additional protection is afforded by the GPUN practice of having a second data analyst separately review all tape records for missed or incorrectly analysed indications.
Subsequent to the release of TR-008 the observations obtained from the outcome of the Long Term Corrosion Tests and failure analysis are now seen to support the presence of local IGA which may not be visible to the standard.540 differential probe but have the p(otential to be exercised into visibility by mecha loadings Ref. 2, pg. 22).
the distribution of new indications (in tubes of higher mechanical loading) and the results of fiberscope observations in OTSG tubes in which rounded dark areas consistent with IGA in appearance were seen at locations where ECT reported indications (See Figures 3a and 3b).
The new indications can in fact be IGA that interacts with the ECT probe in a manner similar to IGSAC.
1his reflects the different geometries of IGA and IGSAC and the qualification method for ECT which employs constant width EDM slots more j
characteristic of IGSAC than IGA in as much as IGSAC impf fes significant depth of wall penetration for a given volume while l
IGA does not.
0838d
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TDR 666 Rev. O i
Page 8 of 18 Consider the difference between IGSAC and IGA:
Inter-Granular Stress-Assisted Cracking is characterized by sharp-edged, tight cracks running between metal grains and not visible optically prior to straining. It can be propagated under mechanical loading; the rate and threshold of this propagation has been determined in detail for the OTSG tubes and this knowledge was 4
used to formulate the plugging and stabilizing criteria employed to determine which tubes must be removed from service, and how they shall be removed. Since circumferentially-oriented IGSAC posed the chief threat to the OTSG tubes, the examination methods were appropriately tailored to finding and measuring it accurately. Hence, ECT calibrations were done on electro-<!ischarge machined slots in which the principal contributions to defect volumes were thrcugh-wall penetration and circumferential extent, not crack width.
Inter-Granular Attack, however, is characterized as roughly hemispherical pits penetrating as much as 50% of the tube wall, as seen in both the failure analysis (Ref. 8.Section IV, page 4 Fig.17) and the Long Term Corrosion Test; the circumferential extent of an IGA pit of this size would be approximately.035".
Two methods by which these pits of metal grains could become visible under mechanical loading were identified in Reference 2 (page 22) as:
" (1)
Crea ion of a uneven grain boundary' separation within the IGA islands as was seen in the LTCT...., or (2)
Disconnected grains dropping out and leaving pits."
It is important to note that this addresses the enhancement of visibility, and not propagation; the pit depth (to sound metal) remains the same. It has been demonstrated that IGA pits up to 835 through-wall do not significantly reduce tube burst strength (Ref. 4). Cracks originating in patches (" islands") of IGA would show no distinct orientation preference in the absence of loading and would not grow because the metal surrounding this IGA pit maintains its original ductility and would blunt the crack tip.
Additionally, in the absence of an aggressive corrodant the pit will not grow chemically. Therefore tube damage done by IGA is already accomplished and is static; it remains only to evaluate the extent of that damage.
Nonetheless, for conservatism all 1984 indications have been dispositioned as if they were defects capable of active mechanical propagation in service (cracks). When this was done it could be seen that none of the defects individually challenged the Main Steam Line Break criteria for peripheral tubes. This is depicted on Figura 1 (a thru c), where the effects of through-wall penetration uncertainty and absolute ECT probe coil overlaps are used to show each defect as a probability area 0838d 600 6TO'Ot1 dv3TO4 nd9 er:GT 68/0L r0 n
[
I TDR 666 Rev. O Page 9 of 18 rather than a point. The indications plotted in Figure 1 (a thru c) include all the worst combinations of through-wall penetration and circumferential extent for single defects (See Table 1).
These tubes have all been removed from service in 1985. Three tubes exhibited defects of large circumferential extent but lesser penetration: 3 coil signals coupled with 20-50%
through-wall penetration, with one showing 755 through wall but located within the upper tubesheet. These extreme cases are also plotted and they nonetheless did not approach the MSLB line for i
peripheral tubes. It should be noted that, minority extremes i
aside, the great majority of all 1984 ECT indications fall below or in the immediate vicinity of the limits of ECT detectability (See Figure 2).
It can be seen from Figure la-c that the maximum possible size characterization of several indications both extend above the ECT detectability curve and include areas above curve A.
Areas above curve A represent crack sizes which will propagate through-wall in service. Nonetheless, assuming the worst confluence of events (1-the indication is truly at the maximum extent of its characterization range, and 2-the defect is a crack and not an IGA pit) there is still no unanticipated hazard. Degradation in rupture (Leak Before Break)gh-wall penetration before tube this range will be by throu and OTSG 1eak detection systems and procedures will enable operators to deal with the leaking tubes safely.
Many of these defects were nonetheless used as justification for removal of a tube from service. This arose from considering these pits as behaving like cracks and therefore capable of propagative interaction. Additionally, circumferential extent was characterized solely by the maximum number of ECT probe coils signalling; no credit was taken for the overlap of coils (See Figure la thru c) whereby a defect only slightly larger than one-half of one-coil sensitivity would register as a two-coil defect. These are inherent conservatisms which should not be used to mask the actual appreciation of the comparatively benign nature of these defects.
4.0 CONCLUSION
To recapitulate, TR-008 postulated a failure mechanism, a plan to prevent reoccurrence, and an assurance of the detectability of potential flaws before they propagate to tube failure. The results of the 1984 inspectiqns (Ref. 2 and 3) indicate no alternative failure I
mechanism, general adherence to preventative guidelines, and reassurance of flaw detectability. There is nothing in the 1984 inspection results which invalidates, calls into question, or necessitates a revision to TR-008.
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TDR 666 Rev. O Page 10 of 18
5.0 REFERENCES
1)
GPUN TR-008 Rev. 3. " Assessment of TMI-1 Plant Safety in Return to Sonice After Steam Generator Repair". T.M. Moran, 9/3/83.
2)
GPUN TDR 638, " Evaluation of Eddy Current Indications Detected During TDR 1984 Tech. Spec. Inspection",
J. A. Janiszewski, 1/11/85.
3)
GPUN TDR 652, " Evaluation of the 1984 Tech. Spec. Inspection for TMI-1 OTSG" - G. Rhedrick.
4)
" Steam Generator Operating Experience Update,1982 -
1983".
5)
GPUN TDR 388, " Mechanical Integrity Analysis of THI-1 OTSG Unplugged Tubes". S. D. Leshnoff, 5/11/83.
6)
GPUN TDR 401, ' Task IV Report on Eddy Current Indications Found Subsequent to Kinetic Expansion of THI-1 Steam Generator Tubes",
G. Rhodrick, 4/8/83.
7)
GPUN TDR 423 Rev.1. "TMI Unit 1 OTSG Tubing Eddy Current Program Qualification", R. Barley, 3/15/84 8)
A. K. Agrawal, W. N. Stiege1meyer, and W. E. Berry, " Final Report I
on Failure Analysis of Inconel 600 Tubes from OTSG A and B of Three Mile Island Unit 1", Batta11e Columbus Laboratories, June 30,1982 9)
GPUN TDR 642, "Qua11fication of Conversion Curve For Inner i
Diameter Discontinuties", M. T. Torborg,1/24/85.
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TDR 666 Rev. O Page 11 of 18 TA8LE 1 Major 1984 ECT Indications 5 THRU-COIL-CALL (S)
OTSG R0hVTU8E ELEVATION WALL ($4050)
_ (8XI A85)
A 2-13 15 + 17 97 2
A 9-1 9 + 11 97 2
A 12-4 15 + 11 87 2
A 13-2 06 - 9 90 2
A 15-3 US + 0 97 1
A 16-3 15 + 6 97 1
A 57-1 03 - 13 99 1
A 57-128 15 + 43 95 1
A 63-127 US + 2 90 2
A 92-5 US + 5 99 2
A 111-113 15 - 13 93 1
A 112-117 10 + 14 99 2
A 115-110 US - 4 90 2
A 115-114 11 + 2 93 2
A 117-2 13 + 04 99 1
A 120-106 15 + 0 97 2
A 127-97 14 + 07 97 i
A 133-2 15 + 31 93 1
A 134-72 15 + 13 99 1
A 135 -1 US - 14 97 1
A 138-64 US - 03 92 2
A 139-65 US - 03 86 2
A 139-73 US + 01 97 2
A 142-1 07 - 11 93 2
A 14 2-50 U$ - 08 97 2
A 143-31 US - 03 97 1
A 147-4 15 + 27 98 2
A 147-45 US + 01 99 2
A 149-14 15 - 17 99 1
A 151-8 15 + 00 86 2
A 9-4 15 + 26 72 1
A 63-127 US - 1 76 2
A 64-126 US + 6 86 2
A 78-126 US - 4 69 2
A 96-125 US + 1 72 2
A 115-110 US + 3 90 2
8 65-1 15 + 32 72 2
8 88-5 US + 1.1 66 2
8 97-5 US + 0 76 3
A 14 7-4 15 + 22 98 2
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