ML20113D949
| ML20113D949 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 01/18/1985 |
| From: | Churchill B SHAW, PITTMAN, POTTS & TROWBRIDGE |
| To: | Edles G, Gotchy R, Johnson W Atomic Safety and Licensing Board Panel |
| References | |
| CON-#185-194 OLA, NUDOCS 8501230269 | |
| Download: ML20113D949 (52) | |
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(202) 822-1051 Gary J. Edles Dr. W. Reed Johnson Administrative 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
Dear Administrative Judges:
-_ e have noticed that, because of reproduction difficulties, W
some portions of_one of the documents' submitted with-" Licensee's Answer _to TMIA's Motion to Reopen.the Record," dated January 14,
.1985,'are illegible.. Accordingly I am enclosing legible copies of Document No..TDR-638 which was attached to the affidavit of F.' Scott Giacobbe.
Respectfully submitted,.
d N ce Churchi 1 Enclosure' cc:
Service List attached' DR h 05 h
]SD3 8
PDR e.
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.1 UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION l
Before the Atomic Safety and Licensing Appeal Board In the Matter of
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4.
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METROPOLITAN EDISON COMPANY, ET AL.
)
Docket No. 50-289-OLA
)
(Steam Generator Repair)
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4 (Three Mile Island Nuclear Station,
)
Unit No. 1)
)
SERVICE LIST 4
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 4
Mary E. Wagner, Esq.
Dr. W.-Reed Johnson Office of Executive Legal Directo!
Administrative Judge U.S. Nuclear Regulatory.
Atomic Safety and Licensing Commission i
Appeal Board Washington, D.C.
20555 U.S. Nuclear Regulatory Commission Atomic Safety and Licensing Washington, D.C.
20555 Appeal' Board Panel
-U.S. Nuclear Regulatory Dr.-Reginald L. GotchY Commission Administrative Judge Washington, D.C.
20555 Atomic Safety and Licensing
~
Appeal Board Atomic Safety and Licensing U.S. Nuclear Regulatory Board Panel Commission.
.U.S. Nuclear Regulatory
. Washington, D.C.
'20555
. Commission Washington, D.C..
20555 Administrative Judge Docketing' and Service Section - (3)!
Chairman,; Atomic Safety and Office of the Secretary Licensing Board 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 Three Mile Island Alert, I..c.
. Atomic: Safety and Licensing Board 315 Peffer Street College of Engineering Harrisburg, PA 17102 Dept. of Nuclear and' Energy Engr.
The University of Arizona Tucson, Arizona 85721
l ASLAB Servica-List
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Pcg3 Two TMI-l l
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~ Thomas Y. Au j
. Assistant Counsel Commonwealth of Pennsylvania Department of Environmental Bureau of Regulatory Counsel J
Resources i
Room 505 Executive House i
P. O. Box 2357 l
Harrisburg, PA 17120 I
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GPU Nuclear Corporation g
gf t oo lnterpace Parkway Parsippany, New Jersey 07054-1149 (201)263-6500 TELO( 136-482 Wrtters Direct Dial Number:
January 14,1985 5211-85-2010 RFW-0382 Mr. John F. Stolz, Chief Operating Reactors Branch No. 4 Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D. C.
20555
Dear Mr. Stolz:
Three Mile Island Nuclear Station Unit 1 (TMI-1)
Operating License No. DPR-50 Docket No. 50-289 Steam Generator Eddy Current Test Result Evaluation In accordance with the Technical Specifications fcr TMI-1, an eddy current exavination of the steam generator tubes was conducted in November and Decembtr 1984. An initial report on the results of the examination was cor,tained in LER-84-007, submitted on December 17, 1984.
We h-Ave just completed a Technical Data Report (TDR No. 638) entitled "Evaluat ion of Eddy Current Indications Detected During the 1984 Tech. Spec.
Inspection." This TOR supplements the information contained in LER-84-007.
We are continuing our evaluation of the results of the examination and we will provide you any additional information that becomes availaL'le.
Sincer ly, TR
..F. Wi son Director Technical Functions Ir/0537e cc:
R. Conte H. Silver Dr. T. Murley C. McCracken GPU Nuclear Ccrecration is a subsidiary of General Pubhc Utihties Corporation
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TDH NO.~
638 REVIS40N NO.
O SUOGET TECHNICAL DATA REPORT ACTrvlTY NO. 123125 PAgg 1
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En inserina & Design DEPARTAIENT/SECTION a-4=1= b r7/5'* Hue. Am l.
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'INI-l OTSG,* REPAIRS RELEASE DAfg 1/11/85 RgVegaon gays E 6 TITLE: Evaluation of Eddy Current Indications Detected Durine the 1984 Tech. Spee. Inspection
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DISTRI$hTION DATE R. F. Wilson h N b --
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OISTRIBUTION ASSTRACT:
In order to identify the cause of the eddy current R. O. Barley indications detected during the IMI-l OTSG tube examination G. R. Capodanno beginning in November 1984. Materials Engineering / Failure Analysis perfor,ed an in-depth review of the eddy current J. J. Colitz resulta and plant operst.ing/che:istry history since the OTSG's were first filled af ter -he kinctic expansion repairs.
D. K. Croneberger Tv possibic causes for tha eddy current indications B. D. Elam were evslust:d: corrosion althar continuing or newly M. J. Graham initisted, an.d enhanct i addy current. detectability of N. C. Kazanas existins intergeanular attack (IGA). During unit layup.
CP'JN layup specifications were followed. Some out of spec-R. J. McCoey ificut. ion periods did occur;. however, they were promptly T. A. Richter corrected and were not of sufficient magnitude to have caused corrosion.
Additional corrosion-preventive conditions were G. R. Taylor also maintained during layup.
R. F. Wilson During hot operations, system chemistry conditions were T. G. Broughton maintained within specifications that industry experience and TMI-1 tube testing have shown are non-corrosive.
W. Bloomfield The.:ost likely reason for having eddy current indica-tions at this time was enhanced detectability of pre-existing areas of IGA. As a resu.lt of thermally induced _ strains and hydraulit forces during hot functional testing, grains could fall out or grain boundaries could separate for a short distance within pre-existing IGA, resulting in greater local disturbance and a correspondingly larger eddy current signet.
Additional plant data from leak rate observations and the fiberscope examination of a sa=ple of tubes also support the r.echanical damage scenario.
No leaks have been identi-fied in the tubs free span since 1983.
In the region of 1984 eddy current indications, patch-like indications sug&es-tive of IGA were seen by the fiberscope examination.
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o TDR 638 Rev. 00 o
Page 2 of 48 Table of Contents Page Introduction
Background
Evaluation of Eddy Current Results Post-Baseline Growth Studies In-Process Testing ISI Indications June 1984 Testing 100 Tube Sample November 1984 1984 Technical Specification Required Testing
' Spatial Distribution-Characterization of Indications
- Degraded Tubes Chemistry Specifications
- Corrosion Experience with Inconel 600 Corrosion Test Results Long Term Corrosion Test Short Tern Test Results Bulk vs. Surface Effects Tril-1 Chemistry Guidelines Hot Operations l
Layup l
Chemistry and Operating History Review Data Base Results of Operationa1/ Chemistry Review Chloride and Sulfate 0xygen Other Operational Considerations t
_. _ _ _.... _ _. ~.
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TDR 638 Rev. 0 Page 3 of 48 Page In-Plant Observations Leak Testing Fiberscope Inspection of Selected Tubes Discussion General Detectability of Indications by Eddy Current Conclusions References Appendix l
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TDR 638 Rev. 0 Page 4 of 48 Introduction In accordance with the requirements of Technical Specification 4.19, eddy current testing of the OTSG tubing at THI-1 was begun in November 1984.
Initial testing with the 0.540" high gain standard differential probe method revealed previously unreported indications in the unexpanded portions of the OTSG tubes between the tube sheets.
Two possible causes for the eddy current indications were identified and evaluated; first, whether corrosion of the OTSG tubes caused either new defects or growth of existing defects and second, whether straining of existing defects caused them-to become more detectable by eddy current. Since the original 100% baseline inspection of the OTSG tubes in 1982, the tubes have been subjected to mechanical loading during the kinetic expansion and thermal and hydraulic loads during the two hot functional tests.
In order to attempt to determine the cause of these indications, the Materials Engineering / Failure Analysis group reviewed 1) the historical eddy current data and 2) plant operational and chemistry data since the OTSG's were ff11ed after the kinetic expansion repair of the tubes.
Based on the results of this review, the cause of the indications is discussed. Data supporting the conclusion are also included.
'l 9
0 0
TDR 638 Rev. 0 Page 5 of 48
Background
As defined by Technical Specification 4.19, GPUN conducted eddy current examinations of both steam generators at TMI Unit 1.
Performance of this examination ultimately resulted in 100% of the tubes in A-0TSG and all tubes in the outer 16 tube periphery of the B-0TSG being examined.
The B-0TSG had only a ifmited number of indications with an indicated through-wall extent greater than 40%. Due to the limited number of B-0TSG indications, statistically-based analysis is not feasible. All these indications, however, are located near the outer periphery of the B-0TSG.
The following ganeralization., about the EC indications can be drawn from the A-0TSG results:
1.
They are primarily located in the upper tube sheet and 16th tube span area.
2.
They are concentrated in the outer periphery, but some indications occur across the entire OTSG.
3.
Most indications are less than 50% through wall.
4.
They generally exhibit voltages in the 0.5-2 v. range.
5.
By 8 x 1 absolute eddy current, the number of coffs tends to be 2 or less, indicating a small circumferential extent.
4
TDR 630 Rev. O j
l Page 6 of 48 Evaluation of Eddy Current Results Note: This section uses the eddy current data base as of Jan. 3, 1985.
GPUN conducted a qualified. full-length, eddy current examination program on all tubes from both generators during July to November 1982.
The purpose of this program was to screen out all relevant indications and establish.a 6" qualified length in the kinetically expanded zone immediately above the new transition zone which was essentially indication free.
It was further established that, although we were using
-a process that was approximately 175% more sensitive than previously used at TMI in performing eddy current examinations, small defects below the threshold of detection could exist. Reference 1 identifies the maximum size of these small defects which could possibly go undetected.
. Prior to the expansion, a 100-tube sample of tubes in each generator was eddy current tested periodically to check for indication l
changes. These tests were performed on seven occasions over a 7 month period. No growth was observed.
Post-Baseline Growth Studies l-In-Process Testing During and following the kinetic expansien repair, a total of 437 tubes were inspected in both the A and B generators (Ref 2, 3).
A total of 15 tubes (3.5%) with indications were found that had not been detected by our ECT inspection program prior to the repair.
l An evaluation was performed on why these indications were not l
identified previously (Ref. 3).
It was concluded that:
i 1)
.The recent indications were not initiated by the kinetic expansion process nor was there any evidence of ductile propagation of existing indications.
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l 2)
The defects were small (threshold) type indications that had
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been either masked by the high background noise levels in the L
. upper tube regions or were sufficiently tight that sufficient L
metal removal was not present to permit detection. Kinetic p
expansion may have altered these areas of IGA to make them L
more detectable.
Confirmation on the small size of the indications was estabitshed
by the visual examination using fiber-optics. Some of the indications appeared to be small pits.
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TDR 638 Rev. 0 Page 7 of 48 Additional confirmation was obtained that kinetic expansion would not cause ductile tearing by using test mock-ups and metallurgical examination (Ref. 2). Small intergranular stress assisted (IGSAC) cracks were examined using eddy current techniques before and after kinetic expansions. Expansion caused the cracks to become non-detectable by.540" S.D. techniques. However, the cracks remained visible to the 8 X 1 absolute technique with essentially no change in signal. These specimen tubes were subsequently removed from the test block and metallurgical examination did not reveal ductile tearing or generation of new indications.
ISI Indications During OTSG repairs, a subset of tubes (28 in A-0TSG, 56 in B-0TSG) was identified as having eddy current indications that did not require plugging. That is, the indications were less than 40%
through wall, not in the lane / lane wedge area, and below the 15th.
tube support plate. This group of tubes (designated as "ISI" tubes by GPUN) was fully characterized and listed for eddy current inspection in the future as a distinct subset.
The "ISI" tubes were re-examined in April /itay 1983. No growth of the existing indications was detected.
As part of the eddy current campaign which started in October 1984, all 84 of the "ISI" tubes have been retested. No growth in the ISI subset was detected.
(Growth is identified as a substantial increase in the through wall percentage, combined with an increase in voltage and circumferential extent.)
June 1984 Testing During June 1S84, 67 tubes in B-0TSG and 3 tubes in A-0TSG were eddy current tested. This set of tubes was retested in November 1984 - no new indications were detected for the two l
retests performed.
I 100 Tube Sample November 1984 Since discovery of the additional indications in McVember 1984, a second 100 tube ~ sample with indications has been re-examined at approximate two week intervals. As of December 18, 1984, no growth and no new indications have been detected for the two retests performed.
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i TDR 638 Rev. 0 Page 8 of 48 1984 Technical Specificaticr. Required Testing In November 1984, eddy current testing required by THI-1 Technical Specification 4.19 was conducted as specified. 3% of the tubes in each generator were initially exemined. This examination included tubes randomly' selected across the entire generator plus a concentrated examination in the periphery of each generator. The more extensive examination in the periphery was performed because this was the region of highest previous (1981) damage.
As a result of.this initial examination, OTSG A was classified as category "C-3" per technical specification and OTSG D was classified as category"C-2". Subsequently the entire A-0TSG was inspected while the B-0T4G inspection was complete after the entire 16-tube periphery, approximately 6500 tubes, had been examined.
The number of indications is much higher in As0TSG than B-0TSG.
In A-0TSG, 2.0% of the tubes (299 out of approximately 14589) have indfcations greater than 40% through wall whfie in B-0TSG, 0.5% (33 out of approximately 6576) have such indicatio,ns.
Spatial Distribution The indications with greater than 40% through wall extent are concentrated toward the outer periphery and top of A-0TSG.
In the outer periphery, the percentage of tubes with greater than 40%
through wall indications is higher than the 2.0% average, whfie inside the outer support rods the percentage of indications is below 1%.
71% of the indications are located above the 15th tube support plate (TSP).
Characterization of Indications To understand the nature of the defects better, we characterized the indications reported back in the 1981-1982 time frame and compared them to the indications discovered today.
The axial and radial locations of indications in A-0TSG are i
essentially the same in 1984 as in 1982, if one does not consider
-the 1982 indications in the kinetically expanded region in the 1984 evaluation.
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TDR 638 Rev. 0 Page 9 of 48 Table 1 characterizes the 1982 and 1984 eddy current signals.
The 1984 eddy current indications exhibit a similar type of signal response as the previous test program. Detafis of the differences in responses are noted belcw:
1)
Reported voltages are essentially the same. This indicates that the 1984 indications present a similar volume for the eddy current probe to detect as the 1982 IGSAC.
2)
Both through wall penetration and number of coils is significantly lower in 1984. Thus, the 1984 indications extend a shorter distance both into and around the OTSG tube.
Statistical analysis of the eddy current data reveals that 90% of the observed indications fall between 10% and 50% through wall penetration, and between.020" and.190" long.
Degraded Tubes Per GPUN procedure, tubes with indicaticns reported between 20 and 40% through wall were not required to be plugged if the tubes were nct in the lane or lane wedge and the indication was below the 15th tube support plate. At the completion of the 1982 kinetic expansion repairs, a total of 15 A-0TSG tubes and 51 B-0TSG tubes were classified as " degraded" and were included in the ISI group.
As of January 4, 1985, 347 additional A-0TSG tubes and 98 additional B-0TSG tubes are classed as degraded.
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TDR 638 Rev. 0 Page 10 of 48 Table 1 Comparison of 1982 and 1984 Eddy Current Data a)
Reported Voltage - % of indications reported A-0TSG B-0TSG Voltage 1982 1984 1982 1984 4' 1 34 40 24 27 1
44 35 30 21 2
16 20 25 29 3
4 4
10 12 5'3 2
1 11 11 b)
Reported through wall penetration - % of indications A-0TSG B-0TSG
% T.lf.
1982 1984 1982 1984 4 20 41 41 12 20-40 3
61 28 75 40-60 21 25 24 18 60-80 17 10 15 5
> 80 59 4
21 2
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Number of coils on 8 x 1 examination - % of calls A-0TSG B-0TSG Coils 1932 1984 1982 1984 1-20 90 18 80 2
26 1G 24 20 3
16 41 15
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>3 38 41 43
4.1 'liOTE
1982 data includes inspection of original tube roll transition a.rea.
The 1984 data.does not inc1Lde inspection from the top of tube sheet
~to the bottom of the kinetically expanded region.
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TDR 638 Rev. O Chemistry Specifications Corrosion Experience with Inconel 600 Three types of primary-side initiated attack have been identified in'Inconel 600.
In recirculating steam generators using mill-annealed tubes that have not been stress-relieved after U-bending, stress corrosion cracking (SCC) has initiated from the primary side in the highly stressed bend areas. Also in mill-annealed tubes in recirculatin'g steam generators, SCC has been found to initiate from the primary side at highly stressed transition areas in the lower tubesheet. Laboratory studies have shown that the stress relieved Inconel tubing used in OTSG's i
is significantly more resistant to SCC than the mill annealed type.
i The other primary side attack of Inconel 600 that has occurred in steam generators is the intergranular stress assisted cracking (IGSAC) caused by reduced sulfur species on sensitized 0TSG tubing. This is the mechanism which caused the THI-1 OTSG 1eakage in 1981. This mechanism requires sensitized tubing, low temperatures,. oxygen, and significant
- levels of reduced sulfur species, t
Corrosion Test Results As part of the overall program to evaluate the most recent eddy current testing results, we have reviewed the results of corrosion tests performed as part.of the original failure analysis and OTSG L
requalification programs. These data provided a partial basis upon which we could evaluate the layup and test conditions to which the steam generators had been subjected.
Long Term Corrosion Test (LTCT)
The primary purpose of the long term corrosion tests was to verify that the proposed operating chemistry specifications are satisfactory to prevent corrosive _ attack of the OTSG tubes. To this end, chemistry conditions for the testing were established.at the maximum allowable values consistent with the upgraded Tiil-1 operating specification (Ref. 4). The LTCT was conducted using actual TMI-1 tubing. Temperatures, tube loads and heatup and cooldownrateswererepresentativeofactualplantoperating conditions.
In addition, as the LTCT was actually performes, specific factors which parallel actual plant layup conditions were experienced. The tubes were held in a cold, aerated condition for several days'after the completion of each operating cycle.
-Aeration was done after_cooldown. Before heatups, or while waiting for other autoclaves in the test program to be ready for operation, the test loops were operated in a cold, deaerated, circulating mode. Because eddy current examinations were done after each test cycle, the tubes had to be removed from the autoclaves and drained. 'Thus, drained aerated layup conditions were also included.
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TDR 638 Rev. 0 Page 12 of 48 Table 2 summarizes LTCT operational times in each mode. All loops. spent significant time under drained, cold deaerated, and aerated conditions.
- Review of the chemistry history of the LTCT's revealed that the conditions were comparable to the plant's experience. The LTCT specification (Ref 5) for sulfate and chlorides was 0.100 ppm +
l
.050 ppm. Actual analysis results (Ref. 6, 7, 8) revealed that the concentrations of these species were maintained at or slightly above the.150 ppm upper ifmit. The actual values measured in these tests bound any of the contaminant " spikes" reported in the Chemistry and Operational History Review.
C-ring tube samples from archive tubing (tubing never installed in the THI-1 OTSG's, which was included as a control sample) showed no evidence of cracking, pitting or general corrosion.
1.
Some intergranular attack (IGA) was noted on 4 C-rings made from a single Ti1I-1 OTSG tube; this ICA was evaluated to be pre-existing damage associated with the 1981 IGSAC incident. Of a total of 38 C-rings evaluated, 31 had no visible defects, 3 showed very shallow cracks when strained severely, and 4 had IGA as described above.
Five full tube samples were metallographically examined after the LTCT.
In addition to previously reported defects, four samples exhibited scattered, shallow cracking or ICA which was not detectable by eddy current testing. This IGA was consistent in size and shape with IGA that had been seen during the failure analysis (Ref. 9). Therefore, the observed IGA on these four tubes was judged to have been present at the start of the LTCT.
One tube sample had severe IGSAC and IGA which had progressed during the term of the LTCT and had been detected by eddy current.
The tube sample which showed flaw growth during the LTCT was exposed in the test loop in which the sulfur species was thiosulfate, at a concentration of 0.100 ppm + 0.050 ppu (as during the LTCT was exposed to intentionally added, g flaw growth sulfate). -Therefore, the only tube sample exhibitin reduced corrosive sulfur species.
4 The four C-ring samples showing IGA and the full tube sample showing flaw growth were removed from the same OTSG tube. This,
' tube was recorded as having multiple eddy current indications when' inspected in the OTSG. The IGA seen in the post-test examination is.ther o re consistent with an original tube' sample which had multiple defects and, presumably, associated IGA.
- Results of metallographic examination of the LTCT samples (Ref. 8) confirmed that in the absence of intentionally added aggressive -sul. fur species,. normal operations would not cause-corrosion-of TilI-1 OTSG tubing.
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TDR 638 Rev. 0 Page 13 of 48 Short Term Test Results Several sets of tests were previously run on Inconel 600 tubing to establish corrosion resistance under various conditions representative of TMI-1 service. Those results which apply to the period of this review are summarized below:
1)
Screening work on actual Till-1 removed tubes and archive tubes (Ref. 10) identified that at oxidizing potentials, 1 ppm of thiosulfate was required to cause IGSAC.
Sulfate levels as high as 10 ppm did not cause IGSAC.
2)
Simulation of hot functional testing and cooldown (Ref.
- 11) utilizing thiosulfate contamination and actual operating temperatures and times revealed that 1 ppm of thiosulfate caused IGSAC.
These short term tests thus confirmed that in the absence of thiosulfate contamination, no short term attack of OTSG tubes is expected.
Bulk vs. Surface Effects
.The above corrosion tests were performed using actual TMI-1 OTSG tubing._ The surface film condition was therefore representative of that in the plant. Chemistry control in both corrosion testing and actual operation is done by the measurement and control of species of interest in the bulk fluid.
Since both surface conditions and chemistry control were identical between the laboratory tests and plant operations, the results of the corrosion tests can be directly applied to the plant environment, and, l
conversely, plant bulk chemistry data can be used to evaluate the propensity for corrosion, j-TMI-1 Chemistry Guidelines
)
Hot Operations i
Af ter sulfur was identified as the causative agent of the 1981 IGSAC, hot operational guidelines (Ref. 4) were reviewed to ensure that adequate corrosion protection was maintained.- As a result of this review, two changes were made to provide increased margins against corrosive attack.
l First, a requirement was added that' primary system sulfate be.
l-maintained below 0.100 ppm. Sulfate at this level does not cause
. corrosive attack of Inconel 600 in primary coolant, and maintaining sulfate below this level provided assurance that intermediate sulfur species could not exist at harmful concentrations.
e Second,-the lower ifmit on lithium concentration was increased L
to 1.0 ppm, ter take advantages of lithium's inhibiting effect on-sulfur-induced IGSAC in Inconel 600 (Ref. 12).
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TDR 638 Rev. 0 Page 14 of 48 The net result of these changes is to ensure that total sulfur species concentrations are a factor of 10 below the level at which corrosive attack might occur. At the same time, the minimum Lf/S ratio will be 30 (or Li/504 of 10), which is a factor of 3 over the recomended. (Ref.12) ratio of 10 for inhibition of IGSAC initiation.
Layup For cold layup conditions, guidelines have been established to maintain as many protective conditions as feasible. The individual protective conditions that are feasible for the THI-1 RCS are:
1)
Elevated pH - during layup, pH has been elevated, using ammonta, to at least 7.2.
The normal pH without amonia is 5.6 - 6.5.
2)
Control of contaminants - The primary water contaminants or concern are cntoriaes and sulfates. Chlorides have
~
traditionally been limited to less than 0.100 ppm during operation; we have maintained this level as a general guideline during layup. The sulfate level of less than 0.100 ppm used during hot operation also applies to layup.
3)
Control of oxygen level - When the system is filled and able to be pressurized, the oxygen level is to be maintained below 0.1 ppm. For cases where the primary system is open and oxygen cannot be excluded, air saturated conditions are specified as this is more protective than some intermediate oxygen level.
4)
Control of OTSG 1evel - One of the contributing factors to tne suus ludAc incident was the existence of a water line on the primary side of the OTSG tubes.. For layup of i
the OTSG's, wherever possible, no static waterifne shall be allowed to exist in the OTSG tubes.
Either the water l
1evel should be above the upper tubesheet or the OTSG primary side should be fully drained.
5)
Inventory Turnover - Periodic replenishing of the OTSC contents will assure that local butidup of contaminants j
I will not occur. Layup guidelines have included j
provisions for periodically turning over the water
. inventory on the OTSG primary side to meet this objective.
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TDR 638 Rev. 0 Page 15 of 48 TABLE 2 Summary of Operations for Long Term Corrosion Tests Operating Days Cold Circulating Drained Loop Hot Deaerated Aerated Layup (Note 1) Comments 1
348 52 28 132 2
308 69 27 157 Thiosulfate loop 3
241 42 23 58 4
242 40 22 61
~
Notes 1.
Does not include drained layup between completion of operational cycles and start of metallographic examination.
0 6
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TDR 638 Rev. 0 Page 16 of 48 Chemistry and Operating History Review Data Base The chemistry and operating history data were obtained from two sources. First, the on-site Plant Analysis group reviewed operational records to identify plant conditions during this time period (Ref. 13).
Then, we retrieved the primary plant chemistry parameters of interest from the GPUN computerized chemistry data base.
The major plant activities that occurred between May 1983 and October 1984 are listed in Table 3.
tlithin each of these periods, we identified different plant conditions of RCS level, tem)erature, pressure, circulation, and pH. Then, we reviewed the c1emistry data for each time period.
Chemistry data selected to be of interest with respect to corrosion
.were pH, oxygen, lithium, sulfate and chloride. As an additional check on the effectiveness of chemistry controls, we calculated the lithium to sulfur ratio for each operating period.
In cases where simultaneous analyses for 11thium and sulfate exist, we calculated the Lf/S ratio for each data point.
The data from the operational and chemistry investigations are plotted as a function of time in Appendix A.
Results of Operational / Chemistry Review During both hot shutdown and cold layup conditions, Tiil-1 has maintained conditions within chemistry guidelines for about 955 of the time. For short time periods, some deviations have occurred which are discussed in the balance of this section.
Chloride and Sulfate There have been short time periods where chlorides and/or sulfates have exceeded specified ifmits.
In all instances r
chemistry data reflect that corrective actions were appropriately and promptly taken to return the concentrations of these species to
_ specified levels. - Collectively, these out-of-specification periods can best be described as normal chemistry " spikes".
s 0
f TDR 638 Rev. 0 Page 17 of 48 j
0xygen In preparation for both the September 1983 and !!ay 1984 hot functional tests, it was necessary for the RCS to be taken from a layup to an operating mode. During this transition, oxygen levels were higher than desired for optimum protection, but other factors made it very unlikely that corrosion occurred. First, chloride and sulfate concentrations were controlled to acceptably low levels.
Second, the lithium level was maintained such that the minimum
-lithium to sulfur ratio was 66; the recommended minimum value for protection against IGSAC is 10 (Ref. 12). Chemistry control during these periods is summarized in Table 4.
Other Operational Considerations During the Integrated Leak Rate Test (ILRT) in April 1984, the primary side water level was maintained at about the 12th tube support plate for 8 days. This condition was both preceded and followed by drained layup with elevated pH, aerated water. Both sulfate and chloride levels remained within specification. Therefore, no OTSG tube corrosion was expected.
In August 1983 and May 1984 oxygenated water was injected into deoxygenated RCS during HPI testing. Most of these tests were conducted prior to the high temperature portion of the hot functional tests, and the oxygen introduced would have been consumed by hydrazine and/or
. hydrogen added_for that purpose. One test was conducted on itay 26, 1984, at the end of HFT and may be postulated to have injected 5000-6000 gallons of oxygen-saturated water.
During this time period, however, the Ifthium to sulfur ratio was greater than 30 which was more than adequate to inhibit corrosion during this test.
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TDR 638 Rev. 0 Page 18 of 48 TABLE 3 Major Plant Evolutions, 5/83 to 10/24 Event Duration Fill & Bubble Test June 1983 Peroxide Clean July 1983 Hot Functional Test Aug - Oct 1983 Circulating Wet Layup Oct - Nov 1983 DH-V1 Repair Nov 1983 Circulating Wet Layup Nov 1983 - Jan 1984 RC-P1B Repair Feb - April 1984 Integrated Leak Rate Test April 1984 Hot Functional Test itay 1984 Non-Circulating Wet Layup May - June 1984 Tube Plug Rerolling and June - Oct 1984 Bubble Testing-1 4
9 e
p
.e TDR 638 Rsv. 0 Page 19 of 48 TABLE 4 Chemistry Summary Before Hot Functional Testing
- Oxygen, Li, 50,
C1 Li/S 4
Period Days ppm ppe ppm ppm Ratio 8/83 29 0.3
.82-1.96
.047.079
.05.156 66-123 5/84 19
.075-2.2 1.06-2.17
.02.047
.05.110 127-240
)
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TDR 638 Rev. 0 Page 20 of 48 In-Plant Observations I
Leak Testing I
Since completion of the kinetic expansion repairs, several leak e
tests have been performed to measure primary-to-secondary leakrates and identify individual leaking tubes. These tests are summarized in Table 5.
j No pattern of tube leakage can be seen. After the cooldown tests included in hot functional testing some increase in leakage was seen.
Further investigation showed that this leakage was the result of leaks through a small number of tubes. These leaks were located in the expanded region within the upper tube sheet and were repaired by mechanically rolling a portion of the expanded area.
Of greatest significance is that since 1983 no tube which is in service has had a leak in an unexpanded portion of'The tube. All leaks have either been due to bypass leaks in the expanded area or leaking plugs.
Fiberscope Inspection of Selected Tubes A fiberscope inspection was performed (Ref. 14) of six A-0T5G tubes which exhibited typical eddy current indications. During the inspection features were observed on 4 out of 6 tubes at the same elevation as the eddy current indications.
The visual features were "patchlike" rounded areas having an outer ring which was darker than the general tube surface and slightly reflective components in the interior. The patches were between 0.020 and 0.060" in diameter.
The patches appeared similar to surface deposits seen during the initial tube failure analysis. These earlier deposits were found to be associated with partial through wall intergranular attack.
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'TDR 638 Rev. 0
.Page 21 of.48 Leak Tests in OTSG's Since 5/01/83 Honth/ Year Test Type Reason For Test Results Repairs Hay 1983-Drip' Test of Kinetic 2 Leaking Tubes, Plugs In. stalled / Rerolled Expansion 8 Leaking Rolled Plug 10 Leaking Explosive Plugs June 1983 Bubble / Drip Final Test of Small Nunber of Slightly Repaired welded plug Kinetic Expansion Leaking Tubes and Plugs in A OTSG - 1 Leaking welded plug Sept 1983 Kr-85 Tracer Establish Baseline Baseline Leak Rate None Required Leak Rate 1 gph May 1984 Kr-85 Iracer Measure Baseline 5 light Increase in' None Required Leak Rate Loak Rate June 1984 Bubble / Drip Identify Leaking 4-5 Leaking. Tubes in Plug 3 tubes Tube (s)
B-0T!A w/weided plugs 6 Rolled Plugs Missing Reroll all W plugs Replugged tubes.
Oct. 1984 Bubble / Drip Test Rolled Small Number of Leaking Roll 8 Tubes Repairs Tubes, one welded plug Reweld Plug foote:
No 1cals seen' in. final October 1984 Bubble Test, after tube rolling.
2
I TDR 638 Rev. O Page 22 of 48
- ~
Discussion General Removal of sodium thiosulfate from the TMI-1 site and tighter operational chemistry controls implemented since 1981 have made it highly unlikely that the conditions to cause sulfur-induced IGSAC could be The steam generator layup guidelines are specifica17y designed recreated.
to protect the steam generators from additional corrosion and are more stringent than.B&W's generic recommendations, particularly in the areas of 4
contaminant control and the use of elevated pH during cold layup.
Industry experfence on B&W PWR's also does not reveal any other primary-side initiated attack mechanisms on Inconel OTSG tubing.
TMI-1 compliance with operating and layup specifications has been Transient out-of-specification conditions, which were excellent.
identified during plant operation, have been infrequent and ccrrected Plant conditions have always been promptly by the plant operators.
bounded by those which were evaluated during corrosion testing and found to be satisfactory.
The only period of possible vulnerability to corrosion would have existed during the time when the OTSG's were drained for the kinetic expansion repair. During thfs period sulfur would have remained in the oxide film on the tube surfaces as peroxide cleaning had not yet been-During this time, however, eddy current testing done on the performed.
100 tube surveillance sample did not reveal any growth of existing fndications or any new indications. Thus, whfie the oxide ffim may have l
contained sulfur during this time, there is no evidence that corrosion continued.
Previously detected IGA, both in the failure analysis -(Ref. 9) and long term corrosion test (Ref. 8), has roughly been in the form ofA pit of hemispherical-pits penetrating approximately 50% through wall.
this shape and penetration would appear as a circle on the surface of diameter of approximately 0.035".
Areas of this circumferential extent would not be predicted to be detectable by the.540 S.D. eddy current technique (Ref. 2).
Under mechanical loadings induced by kinetic expansion.or cooldown, these areas could become more detectable by eddy current through several mechanisms:'
creation of a linear grain boundary separation within the IGA 1) islands as was seen in the LTCT (Ref. 8), or 2) disconnected grains dropping out and leaving pits.
f s
TDR 638 Rev. 0 Page 23 of 48 Two additional pieces of data from Ref.16 Tend support to the mechanical scenario. First, peripheral tubes consistently see higher loads than core tubes. Therefore, in the periphery, the highest stresses would also act on this IGA. Second, the A-0TSG cooled down nore quickly than the B unit. The peak load during the most rapid cooldown (Ref. 16) was 200 lb, or higher (12%), in the A-0TSG than in B-0TSG. Figure 1 is a representation of how the A-0TSG would have had significantly more tubes carrying loads high enough to cause IGA to become more detectable.
A previous. study (Ref.15) on crack opening displacement of archive tubes with apprcximately.5" long through-wall cracks found that loads between 1500 and 2000 lbs. would induce permanent displacements in the vicinity of the cracks. Loads less than this would induce only elastic displacements with a load of 1000 lbs. producing an elastic displacement of approximate!y.002".
Although tubes with cracks of this size are no
. longer in-service with the steam generators, this study does point out that one can expect local straining in the vicinity of smaller defects, but that it would be of proportionately lesser magnitude.
a During the 1983 HFT, the most rapid cooldown was calculated to have iriduced Joads in the tubing of between 1600 and 1700 lbs. (Ref.16).
It is such loads acting on the regions of IGA which we be11 eve leads to
' grain dropping or grain boundary separation.
Visual' observations made during the fiberscope examination of selected 0TSG tubes support the cause of the present eddy current indications being mechanical dama At locations where eddy current indications existed,ge to existing IGA.we frequently saw rounded, darkened areas of a size consistent with IGA detected in the original failure analysis.
Detectabi11ty of Indications by Eddy Current 1 tube integrity-(f.e.-tube rupture) primary defects of concern for OTSG It should be noted that the
[
are circumferential cracks. The.
l-production of 0.540" standard differentia 1' eddy-current technique is optimized and qualified for this type of defect. However, it can also be used for detecting different defect geonetries as discussed below.
The-1984 tube ID indications as detected by eddy current and as seen during the fiberscope inspection had significantly different characteristics than the IGSAC responsible for the 1981. tube leakage.
N The 1981 IGSAC consisted.of tight, circumferential cracks that penetrated A
completely through the wall. The 1984 observed IGA is more rounded and g
l
-does'not completely penetrate the tube wall.
l The different geometry will have a direct effect on'detectability.
. The current.540" S.D. ' eddy current technique wcs aptimized for the IGSAC
~ geometry; therefore, a different geccetry wib have a different detectability. The balance of this sectiv cf.hfG report will discuss changes in, sensitivity due to changes a h ai, :fon geometry.
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TDR 638 Rev. 0 Page 24 of 48 Figure 2 (Figure 2 from Reference 2) shows the measured sensitivity of the.540" S.D. technique in the range of short circumferentially oriented defects. The shaded region in Fig. 2 identifies the area in which 901; of the 1984 indications fall.
It can be seen that the eddy current calls span the 0.3 volt detectability limit. Thus only slight
- changes'in indication geometry could cause a particular indication to become detectable.
In Figure 3a and 3b, we have taken the eddy current data and visual observations from the fiberscope inspection (shown in Table 6) and indicated where the indications would be in relationship to the calibration curves. The tubes for fibresecpe inspection were chosen to be representative of the types of indications being found in 1984.
All of the below-UTS indications (Figure 3b) are close to the 0.3 y detectability limits; the within-UTS indications (Figure 3a) do not fall into the detectable range. Therefore, it is reasonable that before mechanical loading these indications may not have been detectable.
Mechanical loading, as discussed in the previous section, can alter IGA geometry.
-Because the calibration was done on a length vs. through-wall basis
- using Edit notches of a constatt axial width of about 0.004", IGA geometry
. could produce a different signal. Patch-type indications of the ::ame length would have a-larger axial extent, and therefore a larger volume, and could be expected to give a higher voltage signal. The S.D. response would-also be enhanced by increased axial extent, even at constant defect i-volume, since the. differential coils are wound in the circumferential
- direction and are core sensitive to the axial extent of defects.
The large increase in the number of degraded tubes in A-0TSG and
- B-0TSG is also consistent with the scenario of pre-existing IGA becoming more detectable.
IGA islands of 20-40% through wall extent would be expected to have a length of about.015.030 inches; this is below the 300 mV sensitivity for free-span detection (Figure 2). The additional disturbances of mechanical, thermal, and hydraulic loading could easily disturb these islands enough to now make them more detectable.
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'IDR 638 kw. O Page 25 of 48 i
Table 6 - Camparison of Preliminary Eddy Current Data and Fiberscope Results 4
EC Results
.540 S.D.
8X1 Row Tube Elevation
% T.W.
Volts-Volts Colla Visual Observations 89 124 US+5.4 98 1.6 1.6 2
US+4 Rounded indications possible ICA US+5.8 Axial aligrusent of 3 rounded indications 76 119 US+2.4 97 2.1 0.8 2
US+5.5 Small dark spot when scanning w/90* head 66 129 15+27. 6 70 2.8 1.3 2
15t24.5 Rounded indications possible ICA 61 123 15+21. 8 67 2.3 1.1 2
15+26 Small dark spot - no detail visible 15+24.7 45 1.7 0.5 1
57 128 US-2.6 92 1.3 0.3 1-2 US-1.5 Axially oriented rounded indications' 60 126 15-14.2/15-6.5
'37/42 1/1.0 NDD Small single rounded indication
- a
TDR 638 Rev.'O P se 26 of 48 "S
_ _.i l'
Peripheral Tube Location & Load E
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i TDR Rev. 0 Figure 2 - 1984 Eddy Current Date Page 27 of 48 Compared to Detectaability Limits l
187" N
N N
N N
N
\\ ., N
\\
\\
N'N
- 1 v. Detectability
\\\\
Within UTS
, 's'x x
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Ns x
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below UTS h s'sY' 020"
\\
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20 40 60 80 100
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\\
i Lie Within This Area r
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TD2 538 Rev. O Figura 33 - t!ithin - Tubesheet Page 28 of 48 Fiberscope Indications Compared to Detectability Limit,_ _.....
N3tch Length 187 l
Non-Detectable Detectable 1 Volt Detectability y
Limit Within UTS
.100
.060
m 4
A
- - " - - " ' - ~ ~ ~ - ' ' - - - - - - - - - " - - ~ ~ ~ ~ ~ ~ - - - ~ ~ ~ - - -
.020 l
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% Through Wall Tube Identification f~.
A A-89-124 B
A-76-119
- 1 p
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TDR 638 R:v. O Page 29 of 48 Figure 3b - Below - Tubesheet Fiberscope Indications Compared to Detectability Limit Netch Length
--- - - - - - - - - - - - - - ~ < '
- 187 Ton-6etectable Detectable 0.3 Volt Detectability Limit Below UTS
- - - - - - - - - - - - ~ ~ ~ - - - - - - - - - - - - -
.100
.060 ----------------a r - - - - - - -- W -- - - - - - v - - -
l 9
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.94
~
d--------#C----------
.020 1
0 20 60 60 80
% Through Wall Tube Identification C
A-66-129 D
A-61-123 E
A-57-128 F
A-60-126
.e, a -. us,,, n an a,. u t e,a ' t t
.3
TDR 638 Rev. 0 Page 30 of 48 Conclusions 1.
The TMI-1 layup guidelines are adequate to prevent any identified mechanisms for primary side initiated corrosion of Inconel 600 OTSG tubes.
2.
The TilI-1 layup guidelines have been adhered to since completion of the kinetic expansion repair. Minor deviations have been corrected promptly.
.3.
Yulnerability to corrosion may have existed during the period when the OTSG's were drained for repair prior to peroxide cleaning. However, eddy current data and the absence of OTSG leakage during this time period do not show evidence of corrosion of 0TSG tubes.
4.
Results of both GPUN-sponsored and industry corrosion test programs confirm that corrosion would not be expected during TMI-1 operations since llay 1983.
5.
Results of eddy current tests since 1982 do not indicate any trends of indication growth of pre-existing indications.
6.
Leak rate testing and 0TSG bubble cesting do not indicate any increases in leakage or new leaks in the tube free span.
7.
The eddy current data and visual observations are consistent with a nechanism where previously existing areas of intergranular attack are made more detectable by mechanical loading during kinetic expansion and thermal and hydraulic loading during cooldown from HFT.
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TDR 638 Rev. 0 Page 31 of 48 References 1.-
R. Barley, J. A. Janiszwski, G. E. Rhedrick and M. Torborg, "Three Mile Island - Unit 1 OTSG Tubing Eddy Current Pro Qualification," GPUN Technical Data Report 423, Rev.1, gram January 1984.
2.
G. E. Rhedrick, " Task IV Report on Eddy Cur ent Indications Found Subsequent to Kinetic Expansion of TMI-1 Steam Generator Tubes," GPUN Technical Data Report 401, Rev. O, April 1983.
3.
T. M. Moran, " Assessment of TMI-1 Plant Safety for Return to Service After Steam Generator Repair," GPUN Topical Report 008 Rev. 3. August 19, 1983.
'4.
" Primary Water Chemistry," GPUN Specification SP-1101-28-001, Rev.-3, July 11, 1984.
5.
"Long Term Corrosion Testing," GPUN Specification SP-1101-22-008, Rev. 2, Oct. 29,1983.
6.
"Long Term Co'rrosion Test Program of Nuclear Steam Generator Tubing Samples from Three Mile Island Unit 1 - First Interim Report," Westinghouse Electric Corp. Report No.
0914c/0127c/010684:5, October 1983.
7.
"Long Term Corrosion Test Program of Nuclear Steam Generator Tubing Samples from Three Mile Island Unit 1 - Second Interim Report," Westinghouse Electric Corp., May 1984.
8.
"Long Term Corrosion Test Program of Nuclear Steam Generator Tubing Samples from Three 1111e Island Unit 1 - Final Report,"
Westinghouse Electric Corp., unpublished draft.
9.
A. K. Aarawal, W. fl. Stiegelmeyer, and W. E. Berry, " Final Report on Failure Analysis of Inconel 600 Tubes From OTSG A anu B of Three Mile Island Unit 1," Batteile Columbus Laboratories, June 30, 1982.
10.
J. V. Monter and G. J. Theus, "TMI-1 OTSG Corrosion. Test Program - Final Report," Babcock & Wilcox Report No.
R.DD:83:5433-01-01:01, itay 9,1983.
11.
J. C.- Griess and J. H. DeVan, " Behavior of Inconel 600 in Sulfur-Contaminated Boric Acid Solutions," Oak Ridge National Laboratory Report ORNL/TM-8544, March 1983.
rt
Task 638 Rev. 0 Page 32 of 48 12.
R. Bandy and K. Kelly, " Investigation of the Sulfur and Lithium to Sulfur Ratio Threshold in Stress Corrosion Cracking of Sensitized Alloy 600 in Borated Thiosulfate Solution,"
USNRC NUREG/CR-3834, July 1984.
13.
J. R. Kasper, "TMI-1 Primary Plant Status from 5/01/83 to 11/27/84," GPUN IOM PA-TMI-84-47, Nov. 27, 1984.
14.
J. A. Janiszewski, " Observations During Fiberscope Inspection of A-0TSG Tubes, Dec. 19, 1984," GPUN IOM MT1-1550, December 28, 1984.
15.
J. A. Janiszewski, " Leakage and Crack Opening Displacement of OTSG Tubes," GPUN Technical Data Report 480, Rev. 1.
16.
G. L. Lehmann, T. M. Moran, J. R. Sipp and D. G. Slear, "TMI-1 OTSG Hot Testing Results and Evaluation," GPUN Technical Data Report 488, Rev. O, October 25, 1983.
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TDR 638 Rev. 0 i
Page 33 of 48 APPENDIX A l
TMI-1 CHEMISTRY DATA MAY 1, 1983 to OCT08ER 26, 1984 Contents Table A1
- Chemistry Guidelines Applied to TMI-1 5/1/83 to 10/26/84 Figure Al Al Chemistry Data for TMI-1 5/1/83 to 10/26/84 1
4 9
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TDR 638 Rev. 0 Page 34 of 48 Table Al CHEMISTRY GUIDELIllES APPLIED TO THI-1 5/1/83 to 10/26/84 Operating Wet Drained Hot Shutdown Peroxide Mode Layup Layup (Hot Functional Testing)
Cleaning OTSG. Primary Level Full Drained Full Full fiaximum Chloride, ppm 0.1 0.1 0.1 0.2 Maximum Sulfate, ppm 0.1 0.1 0.1 Note 2 Maximum Oxygen, ppm 0.1 N/A 0.1 Note 2 pH greater than 7.2 4.6-8.5 4.6-8.5 8.0-8.5 Li, ppm 1.0-2.0 1.0-2.0 1.0-2.0 1.8-2.5 Minimum Li/S ratio 10 10 10 N/A Notes:
1.
Limits are for bulk RCS - no water in OTSG's at this time.
2.
Sulfate and oxygen were monitored but no limit was applied.
S
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DR 638 Rev. O g
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