ML20056A681
| ML20056A681 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 03/31/1990 |
| From: | Diercks D Argonne National Lab (ANL) |
| To: | Office of Nuclear Regulatory Research |
| References | |
| CON-FIN-L-10050 ANL-90-2, NUREG-CR-5524, NUREG-CR-5524-V01, NUREG-CR-5524-V1, NUDOCS 9008090018 | |
| Download: ML20056A681 (43) | |
Text
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,NU,R,EG /CR-5 5 2 4 Vol.1 TMI-2 Vessel Investigation Project (VIP) Metallurgical Program Progress Report January-September 1989 Prepared by D.11. Dicrcks Argonne National Laboratory I'repared for U.S. Nuclear Regulatory Commission p0k"U' 00h!! '$$000ftPo a
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NUREG/CR-5524 ANL-90/2 Vol.1 T MI-2 Vessel Investigation Project (VIP) Metallurgical Program Progress Report January-September 1989 hianuscript Completed: January 1990 Date Published: htarch 1990 Prepared by D. R. Dicrcks hiatcrials and Components Technology Division Argonne National laboratory 9700 South Cass Avenue Argonne. IL 60439 Prepared for Division of Engineering Omce of Nuclear Regulatory Research U.S. Nuclear Regulatory Commission Washington, DC 20555 NRC FIN L10059
TMi 2 Vessel Investigation Project (VIP) Metallurgical Program by D. R. Diercks Abstract This report summarizes the work performed by Argonne National Laboratory on the TMI 2 Vessel Investigation Project (VIP) Metallurgical Program during the nine months from the initiation of the program in January 1989 through September 1989. During the reporting period, archive material for the program was obtained from the sower head of the cancelled Midland nuclear reactor in Midland, MI, in the form of four plates. Chemical analyses and hardness measurements were performed on samples from the four plates, the as received microstructure was characterized, and a tentative determination of rolling direction was made. initial results from heat treatment experiments on the archive material indicate that those reg ons of the TMI 2 material where the maximum temperature exceeded 727*C should be readily identifiable on the basis of microstructural observations. A series of round robin mechanical tests and microstructural studies on the as received archive material was developed, and specimens and specimen blanks for tensile and stress rupture tests were distributed to the participating OECD laboratories. Two trial specimens cut from a plate of A30 plain carbon structural steel by PCI Energy Systems using metal disintegration machining (MDM) were examined metallographically.
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Contents Ex e c u tiv e S u m ma ry................................................................................................................. I 1
Introduetion............................................................................................................................3 2
ElChg!TJurKl.................................................................................................................................3 3
Acquisition and Charaeterization of Archive Materials............................................ 5 3.1 Acquisttton..................................................................................................................5 l
3.2 Chernical Analysts....................................................................................................... 5 3.3 I lartinms Mmsurements........................................................................................... 9 3.4 Microstructurni Characterization of As Received Material.......................... 9 3.5 De t e rmina t t o n of Rolli ng Direc t t o n.................................................................... 13 4
Ileat 'ncatment thperiments on Archive Material................................................... 13 4.1 Smtunary of I% posed 1% gram............................................................................ 13 4.2 Development of 1icai Treating Procedures................................................... 17 4.3 Results of I leat 'Reating Experiments............................................................... I 9 5
M echa nical Testing of Archive Ma t ertal........................................................................ 2 4 5.1 Sununary of I Yolmsed Pmgmrn............................................................................ 2 4 5.2 Mechanical Test Specimens.................................................................................. 2 4 G
Charaeterization of Ma tertal from Trial Seetions....................................................... 2 7 Referuxts........................................................................................................................................31 v
1
Figures 1.
Cutting Diagram Showing the Locations of the Four Plates of Archive Material Cut from the 14wer licad of the Midland Nuclear Reactor.................... 6 2.
Through Wall Hardness of Archive Material Sample 41 As Received and afler Additional 26 h Stress Rellef at 607'C................................................... 10 3.
Through Wall liardness of ArcF vc Material Sample 4 2 As Received and aIler Additional 26-h Stress Relief at 607'C.....................................................10 4.
Through Wall liardness of Archive Material Sample 4 3 As Received and after Additional 26 h Stress Rellef at 607'C........................................................ I 1 5.
Through Wall liardness of Archive Material Sample 4 4 As Received and after Addittonal 2 6 h Stress Relief a t 607'C........................................................ I 1 4
6.
Microstructure of As Received Archive Material in Base Metal near inner Surfam Weld Clad........................................................................................................ I 2 7.
Microstructure of As Received Archive Material near Center of Plate..............12 8.
Microstructure in Metallographic Section Parallel to Rolling Direction..........14 9.
Microstructure in Metallographic Section Nonnal to Rolling Direction........... ? 4
- 10. Generalized Representation of Isothermal lleat Treatments for Archive Matertal.....................................................................................................................................15
- 11. Generalized Representation of Transient lical Treatments with Normal I i ca tin g Ra te fo r Arc hive M a t er1a1.................................................................................. I 6
- 12. Generalized Representation of Transient lleat Treatments with Rapid 1 Icating Rate for Archive Mater 1a1............................
......................................17
- 13. Microstructure of As Received Archive Material in Base Metal near i nner Surfam Weld Clad....................................................................................................... 2 0
- 14. Microstructure of Archive Material in Base Metal after Isothermal Heat
'Ihn tment a t 700 T.................................................................................................
- 15. Microstructure of Archive Material in Base Metal after Isothermal lleat
'Thn tmea t a t 75(TC..............................................................................................................., 2 1
- 16. Microstructure of Archive Material in Base Metal after Isothermal lleat
'lhn tmen t a t 800t......................................................................................................
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- 17. Microstructure of Archive Material in Base Metal after Isothermal IIcat
'n ea tn rn t a t 900'C...........................................................................................................
- 18. Microstructure of Archive Material in Base Metal after Transient lleat Treatment at 750'C with !!cating Rate of 40*C/ min and Cooling Rate of 10'C/min..................................................................................................................................22
- 19. Microstructure of Archive Material in Base Metal after Transient IIcat Treatment at 800'C with Heating Rate of 40'C/ min and Cooling Rate of 10'C/min..................................................................................................................................23
- 20. Microstructure of Archive Material in Base Metal after nw;.slent lleat Treatment at 900*C with IIcating Hate of 40'C/ min and Cooling Rate of 10'C/min....................................................................................................................................23
- 21. Plot of NRIM Stress Rupture Data for Five lleats of A5330 Steel and Manson.1laferd Extrapolation to Iligher Tempera tures.......................................... 2 5
- 22. Design of Flat Tensile and Stress Rupture Test Specimen for Round-Robin Testing Progmm on Arrhlve Ma terial................................................................ 2 6
- 23. Design of Round Tensile and Stress Rupture Test Specimen for Round-Robin Testing Progmm on Archive Ma teda!................,,.............................................. 2 6
- 24. Sectioning Diagram for Archive Plate 4 2 Showing I,ocations from Which Metallographic and Mechanical Test Specimens Were Taken............... 28
- 25. Metallographic Section through A3G Steel Sample Cut by PCI Energy Sys t ems Using M etal Disin t egra tion Machining......................................................... 2 9
- 26. Sa me Region as in Fig. 25. In Etched Con dit10n........................................................ 2 9
- 27. Metallographic Section through Second A3G Steel Sample Cut by PCI Energy Systems Using Metal Disintegration Machining......................................... 30
- 28. Region at and Slightly Delow That Shown in Fig. 27. In Etched Condit10n....................................................................................................................................30 vil
.ar Tables 1.
Comparison of Fabrication llistories of TMI 2 and Midland Lower licads.......... 7 2.
Results of Chemical Analysis of Midland Reactor Archive Matcr1al........................ 8 i
3.
Experimental !! cat Treatment Matrix for A533 Grade B Steel Archive Material......................................................................................................................................I8 4.
Test Specimen Configurations Requested for Round Robin Testing of Midland Rea e tor Archive M at er1al................................................................................. 2 7 1
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Executive Summary This report summarizes the work performed by Argonne National Laboratory (ANL) on the TMI 2 Vessel Investigation Project (VIP) Metallurgical Program during the nine months from the initiation of the program in January 1989 through September 1989. This program is a part of the international utl-2 Vessel Investigation Project being conducted jointly by the U. S. Nuclear Regulatory Commission and the Organisation for Economic Co-operation and Development (OECD), TrA cverall project consists of three phases, namely (1) recovery of material samples from the lower head of the TMI 2 reactor, (2) examination and analysis of the lower head samples and the preparation and testing of archive material subjected to a similar thermal history, and (3) procurement, examination, and analysis of companion core material located adjacent to or near the lower head material.
The specific objectives of the ANL Metallurgical Program, which comprises a major portion of Phase 2, are to prepare metallographic and mechanical test specimen blanks from the TMI-2 lower head material, prepare similar test specimen blanks from suitable archive material subjected to the appropriate thermal processing, determine the mechanical properties of the lower vessel head and archive materials under the conditions of the core-melt accident, and assess the lower head integrity and margin to failure during the accident. The ANL work consists of three tasks: (1) Fabrication of Metallurgical and Mechanical Test Specimens from the TMI-2 Pressure Vessel Samples, (2) Archive Materials Program, and (3) Mechanical Property Characterizatlon of TMI-2 Lower Pressure Vessel licad and Archive Material.
During the reporting period, archive material was obtained from the lower head of the Midland nuclear reactor (which was never operated due to cancellation of the plant before completion) in Midland, MI, in the fonn of four plates, each approximately 0.3 x 1.2 x 0.14 m thick (12 x 48 x 5 5/8 in, thick). Chemical analyses were performed on samples from near the inner surface, center, and outer surface of each plate. 'lhese analyses verifled that the composition of the archive material is relatively unifonn through the thickness of the plates and that the material satisfles all of the specifications for A533 Grade B steel, liardness readings were taken at 10 mm (0.4 in.) intervals through the thicknesses of samples from each of the four plates to further characterize the archive material. No appreciable variation in hardness through the thickness of the plate was observed, and it was determined that the as received archive material required ne further stress relief heat treatment.
2 Through+ wall microstructural sections from each of the four plates were prepared and examined to determine the microstructure of the as received material, in all four cases, the microstructures were similar, it was determined that, for the purposes of subsequent heat treatment experiments, two distinct microstructures were present in the as received archive material, i.e., that near the inner surface weld clad and that near the center of the plate. A tentative determination was also made of the rolling direction in the plate.
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A heat treats tent program for the archive material was developed to produce a set of standard microstructures for comparison with those observed in the actual TMI 2 lower head material. Three types of thermal cycles will be studied, each designed to simulate the thermal history at some point in the TMI 2 lower head during the accident. Initial results from the heat treatment program indicate that those regions of the TMI 2 material where the maximum temperature exceeded 727'C should be readily identifiable on the basis of microstructural observations.
A series of round robin mechanical tests and microstructural studies on the as-j received archive material was developed to better characterize this material and to determine the level of variability in mechanical test data obtained by the participating OECD laboratories. The series will consist of tensile teus at room temperature and 600'C, as well as short-term stress rupture tests at 600'C. Flat and round cross section specimen designs have been developed for these tests, and specimens and specimen blanks have been distributed to the participating laboratories.
]
Two trial specimens cut from a plate of A36 plain carbon structural w:A by 1
PCI Energy Systems using metal disintegration machining (MDM) har been examined metallographically. The MDM process will be used for cu!. n mater' samples from the TMI 2 lower head. Both specimens exhibited a tb 4
'M layer of martensite immediately adjacent to the cut face and another M slightly altered base metal ~100 m thick immediately below the ma w "
k was concluded that the maximum depth of disturbed metal produced %
MM.
a process is ~200 m.
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1 Introduction i
Extensive studies have been conducted during the past Dve years to determine the extent of damage suffered by the Three Mile Island Unit 2 (TMI-2) nuclear reactor as a result of the loss of-coolant accident in March 1979. These studies have focused primarily on the end-state core connguration, and they have confirmed the occurrence of signincant core material melting and relocation to the lower plenum region of the reactor vessel. It is estimated that approximWy 20 metric tons of molten core debris fell onto the bottom head of the reace.C mui evidence of thermal damage to instrument structures in the lower pienum and around flow holes in the Dow distributor has been seen, 'Ihe objectives of the present program are to (1) determine a scenario for, and deduce the temperatures of the steel in, the lower vessel head during the accident: (2) determine the mechanical properties of the steel from the lower head under the core melt accident conditions; and (3) assess the integrity of the TMI-2 vessel and the margin to fa!!ure during the accident.
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2 Background
l This program is a part of an international TMI-2 vessel investigation project being conducted jointly by the U. S. Nuclear Regulatory Commission and the Organisation for Economic Co-operation and Development (OECD), Participants in the international project include the United States, Japan, the Federal Republic of Germany (FRG), Finland, France, Italy, Spain, Sweden, Switzerland, and the United Kingdom (U.K ). Government agencies from these countries are contributing to the cost of the project, in return for which they will share the results obtained. Several of these countries are actively participating in the research, and this participation constitutes a part of their financial contribution.
The first phase of the TMI-2 Vessel Investigation Project (VIP) is the recovery of material samples from the lower head. A contract for this work has been placed with MPR Associates, Inc., and extraction tools and procedures have been I
developed. The first samples from the TMI-2 lower head are scheduled to be shipped to Argonne National Laboratory (ANL) in about January 1990. A total of 8 to 20 prism-shaped samples, each approximately 152 to 178 mm (6 to 7 in.) long, 76 to 102 mm (3 to 4 in.) wide, and 64 to 76 'mm (2-1/2 to 3 in.) in depth, will be cut from the inner surface of the lower head. The locations from which the specimens are to be taken include (1) near the area of impact by the primaryJet of molten material on the lower head. (2) toward the radial center of the lower head underneath the maximum thickness of debris, (3) in the quadrant of the lower head where a " wall" of consolidated debris similar to a lava front has developed, (4) in a location of the lower head not contacted by the molten material (to act as a s
4 control sample), and (5) locations with one or more instrument penetrations, particularly where surface cracks have been observed visually, The second phase of the TMI-2 VIP is the examination and analysis of the lower head samples and the preparation and testing of archive material subjected to a similar thermal history. This second phase will be carried out by ANL (in the present program) and by the Idaho National Engineering Laboratory (INEL). The lower head samples recovered from TMI-2 will be documented, examined by optical metallography and other techniques to determine the maximum temperature reached, decontaminated, machined into mechanical test specimens, and tested. Because the supply oflower head material is limited, further mechanical tests will be conducted on archive material of similar chemistry and fabrication history that has been subjected to heat treatments simulating those to which various regions of the lower head was subjected during the accident. Some of these testing and evaluation activities will be carried out by other members of the NRC/OECD joint program, and all of the results obtained by the vanous j
participating laboratories will be integrated into a comprehensive final report.
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The third phase of the TMI-2 VIP, to be carried out by INEL,' is the i
procurement, examination, and analysis of companion core material located adjacent to or near the lower head material that is to be studied in Phase 2. This core material will be analyzed to determine, in conjunction with the information obtained in Phase 2, the maximum temperature attained and the nature of the attack that occurred at the lower head inner surface during the accident. The -
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temperature distribution obtained will be used to calculate a stress distribution in the lower head. Based on this information and the mechanical properties of the lower head and archive material determined in Phase 2, the margin to failure of the lower head will be assessed.
The specific objectives of the ANL portion of the project are to prepare metallographic and mechanical test specimen blanks from the TMI-2 lower head i
t materie.1, }'repare similar test specimen blanks from suitable archive material subjected to the appropriate thermal processing, determine the mechanical properties of the lower vessel head and archive materials under the conditions of the core-melt accident, and assess the lower head integrity and margin to-failure during the accident. INEL will be responsible for the microstructural characterization of the TMI-2 lower head material, the integration of all experimental and analytical data and studies po. fumed on the TMI-2 lower head material, and the issuance of a final report on th work conducted in Phase 2.
The ANL program consists of three tasks: (1) Fabrication of Metallurgical and Mechanical Test Specimens from the TMI-2 Pressure Vessel Samples, (2) Archive Materials Program, and (3) Mechanical Property Characterization of TMI-2 Lower a
5 Pressure Vessel Head and Archive Material. 'Ihe progress to date under these tasks is summarized here.
3 Acquisition and Characterization of Archive Materials 3.1 Acquisition Archive material for this program has been obtained from the lower head of the Midland nuclear reactor in Midland, MI, 'Ihis plant, the construction of which was cancelled by Consumers Power Company before it was completed, was to use a Dabcock & Wilcox pressurized water reactor (PWR) similar in design to that of TMI 2. The material was obtained under a subcontract to the Electric Power Research Institute (EPRI), which oversaw the partial disassembly of the reactor pressure vessel to obtain samples for several experimental programs before abandonment of the plant.' 'Ihe plates were cut out by Babcock & Wilcox.-
The archive material was received in the form of four plates, each approximately 0.3 x 1.2 x 0.14 m thick (12 x 48 x 5-5/8 in, thick), which were torch cut from near the bottom center of the Midland lower head, These plate samples are designated 41, 4 2, 4 3, and 4-4, respectively, Figure 1 is a cutting diagram showing the locations of the four plates.
Detailed information on the fabrication histories and chemistries of the TMI-2 and Midland lower heads was included with the archive material. The fabrication histories, which are compared in Table 1, are quite similar except that the Midland lower head was fabricated from a somewhat thicker plate and was machined down to final thickness after forging and heat treating but before weld cladding. The post-weld stress relief heat treatment was also about 26 h shorter for the Midland lower head than for the TMI-2 lower head. Although the weld clad is listed as having a nominal thickness of 4.8 mm (3/16 in.), observed thicknesses in samples cut from the plates were on the order of 6.4 to 7.9 mm (1/4 to 5/16 in.).
3.2 Chemical Analysis Three samples were cut from each of the four plates for chemical analysis.
These samples were taken from locations within approximately 13 nun (0.5 in.) of the inner surface (or about 6 mm (0.25 in.] below the clad), at the center of the plate thickness, and within about 6 mm (0.25 in.) of the outer surface. These locations were selected to check for any possible segregation of alloying elements or impurities through the thickness of the archive plate.
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Cutting Diagrat.t Showing the Locations of the Four Plates of Archive.
Material Cut from the Lower Head of the' Midland Nuclear Reactor. The pgure shows a circurnferential section through the beltline of the reactor pressure vessel looking down on the lower head.
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7 Table 1.
Comparison of Fabrication Histories of 7MI 2 and Midland Lower Heads.
i TMI 2 Reactor Midland Reactor Parameter -
Lower Head
. Lower Head Initial plate thickness 5.375 in.- (137 mm) 6.375 in. (162 mm)
Forming operation Hot-pressing Hot pressing Austenttizing temp.
871-899'C 871-899'C i
Austenttizing time-5.5 h 5.5 h Cooling method Brine quench Brine quench Tempering temp.
649 677'C 649 663*C Tempering time 5.5 h 5.5 h Cooling method Air cooling Brine quenching Finishing operation none Machined at I.D.
(minimum final and O.D. to 127 mm thickness = 127 mm (5 in.) minimum.
[5 in.1)
. thickness I.D. weld cladding ER308L ER308L Cladding thickness 3/16 in. (4.8 mm) 3/16 in. (4.8 mm)
Stress relief temp.
607'C 607'C Stress relief time 50 h
- 23.8 h The results of the chemical analyses are summarized in Table 2, along with the supplier's heat analyses for the Midlet.?. nnd 'INI-2 lower head material and the specifications for A533B steel. The three samples from each plate are designated OD (outer diameter), C (center), and ID (inner diameter). 'Ihe most important points to be noted in this table are that the chemical composition of the archive material is relatively uniform through the thickness of the plates and that the material satisfles all of the specifications for A533 Grade B steel. Although the supplier's analyses indicate that the Midland archive material is somewhat higher in sulfur than is the TMI 2 material, the independent analyses reported here show sulfur levels in the archive material to be similar to those reported by the supplier
'for the TMI-2 material. However, both analyses indicate that copper levels are higher in the archive material.
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9 3.3 Hardness Measurements Hardness readings were taken at 10 mm (0.4 in.) Intervals through the thicknesses of samples from each of the four plates to further characterize the archive material. These readings were taken on material in both the as received condition and after an additional 26 h of heat treatment at 607 C. This additional heat treatment was carried out because the Midland material was stress relieved for 23,8 h at 607 C after fabrication, whereas the TMI 2 lowe: head material was stress relieved at the same temperature for 50 h (see Table 1), liardness readings on the samples in both conditions should help determine whether the additional stress relief time affected the properties of the plate.
The results of these two sets of hardness determinations are summarized in Figs,2 5. No appreciable difference in hardness was observed,-implying that the additional 26-h heat treatment did not significantly affect mechanical properties.
Metallographic sections of the as received and stress-relieved archive material from all four plates likewise revealed no perceptible differences in the microstructures, thus providing a further indication that the additional 26 h heat treatment was of no significance.
3.4 Microstructural Characterization of As Received Material Through-wall microstructural sections from each of the four archive material pieces were prepared and examined to determine the microstructure of the as-received material, in all four cases, the microstructures were similar. Near the weld clad at the inside-diameter surface, the A533B steel was found to consist primarily of fine tempered bainite, along with regions of tempered martensite (see Fig.6). Near the center of the plate, where cooling from the initial austenttizing treatment was somewhat slower, the microstructure consisted almost entirely of tempered bainite, possibly accompanied by small regions of primary ferrite (Fig. 7).
The microstructure near the outside diameter of the plates was similar to that at the center, except that the bainite was somewhat finer and no primary ferrite was visible.
Dased on these observations, it was determined that two distinct microstructures were present in the as received archive material: that near the inner surface weld clad (Fig. 6) and that near the center of the plate (Fig. 7).
Specimens with these two initial microstructures will be used in the heat treatment experiments described in Section 4.
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Through-Wall Hardness of Archive Material Sample 4-4 As-Received and after Additional 26-h Stess RelicJat 607*C.
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k.
Figure 6.
Microstructure of As-Received Archive Malertal-(Plate 4-2) in Base.
Metal near inner Surface Weld Clad.
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1 Figure 7.
Microstructure of As-Recclued Archive Material (Plate 4-2) near Center ofPlate.
13 3.5 Determination of Rolling Direction Microstructural studies have also been carried out to identify the rolling direction of the archive plate.
his determination is of interest because of possible differences in mechanical properties parallel and normal to the rolling direction.
As a first step, metallographic samples were cut from all four archive pieces parallel to the plane of the plate and examined. 'Ihese samples should lie in the plane of the rolling direction, and it was hoped that microstructural banding or stringing out ofinclusions along the rolling direction could be observed. However, no such features were observed.
One of the samples was then austenitized for 45 min at 875*C and furnace-cooled to produce a primary ferrite plus pearlite microstructure. The purpose of this heat treatment was to produce banding of the pearlite along the rolling direction. Unfortunately, no banding could be observed. Babcock & Wilcox was then contacted to determine if the plate had been cross-rolled prior to final fabrication. After checking their files, they stated that they had no records identifying the rolling direction in the Midland lower head plate.
Identillcation of the rolling direction was finally made on the basis of metallographic sections through the thickness of plate 4-2 in several orientations.
Microstructural banding was observed in all of these sections, but the section exhibiting the most pronounced banding was identifled as lying parallel to the rolling direction. Figures 8 and 9 show the microstructures of the sections parallel and normal to the rolling direction.
4 Heat Treatment Experiments on Archive Material 4.1 Summary of Proposed Program One purpose of the archive materials program is to develop a set of standard microstructures produced under controlled heat treatment conditions.
Comparison of these standard specimens with the microstructures observed in the material from TMI-2 will permit more accurate determination of the thermal history of the TMI-2 lower head during the accident.
The A533 Grade D steel archive specimens will be subjected to three general types of heat treatments. The flrst and simplest is the isothermal treatment shown schematically in Fig.10. The sample will be brought up to the specified maximum temperature at a heating rate of 40 C/ min, held at the maximum temperature for 2 h, and then slow-cooled at l'C/ min to below 300 C before being air cooled to
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Microstructure in Metallographic Section Parallel to Rolling Dircclion (Plate 4-2).
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Microstructure in bietallographic Section Normal to Rolling Direction (Plate 4 2).
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~40 C/ min l
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N Cooling rate =
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l l
i Time Agure 10. Generalized Representation of isothermal Heat Treatments for Archive Material.
room temperature. This heat treatment simulates the thermal cycle at.the mid-wall and outer-wall locations in the lower head with no quench, In this scenario, the massive vessel and its contents slowly cooled to ambient temperature after the accident, and essentially equilibrium microstructures would be expected.
Maximum temperatures for the isothermal heat treatments will range from 500 to 1300 C in 50 C increments or, above 900'C,100 C increments, for a total of 13 heat treatments.
The second type of heat treatment to be used is the transient heat treatment -
shown in Fig. I1. The heating rate to the maximum temperature will again be
~
40'C, but specimen cool!ng will begin immediately upon reaching the maximum temperature, with no hold time. Three cooling rates,1,10, and-100'C/ min, will a
be used down to temperatures of <300 C, below which the specimens will be air-cooled to room temperature. This heat treatment again simulates the thermal-cycle at the mid-wall and outer-wall locations, but now with the added effects of a quench. Maximum temperatures will range from 750 to 900 C in 50 C increments-and from 1000 to 1300'C in 100 C increments, for a total of eight temperatures.
Because three different cooling rates will be employed for each of these eight maximum temperatures, a total of 24 temperature-cooling rate combinations will be studied. Maximum temperatures below 750*C will not be investigated in these heat treatments because they are below the cutectoid transformation temperature, and no microstructural effect of the varied cooling rates would be expected.-
a i
16 i
g T max -
5[
Three cooling E
rates
~40 C/ min Time -
Figure 11. Generalized Representation of Transient' Heat Treatments with Normal Heating Ratefor Archive Material.
)
(Lower temperatures are included in the isothermal heat treatments, because the relatively long time at temperature might produce some tempering of the bainite phase.)
The final type of heat treatment to be investigated, the transient heat treatment with rapid heating, is shown in Fig.12. This treatment is similar to that described above except that a very rapid heating rate, on the order of 100 C/sec, to the maximum temperature will be employed. This heat treatment simulates the -
rapid thermal ramp that probably occurred at the lower head inner wall when the molten core material was deposited on it. A single cooling rate of ~10*C/ min will-be used. Four. maximum temperatures, namely 1000,' 1100,1200,' and 1300*C, will be studied.
4 A test matrix outlining the series of heat treatment experiments described above is shown in Table 3. The 1200 and 1300*C heat treatments indicated in this table will be performed only if microstructural analyses of the TMI-2 lower head material actually reached temperatures this high. A total of 31 specimens.
excluding the 10 for the 1200 and 1300*C exposures, will be required to carry out the thermal treatments shown in this table for each location through the thickness of the plate. Heat-treatment specimens will be taken from two locations in the t
1 l
17
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E T max 3
Cooling rate =
{
10 C/ min 8
% ~100 C/sec Time Agure 12. Generalized Representation of 7Yansient Heat 7Yeatments with Rapid Heating Ratefor Archive Material.
archive plate, corresponding to the two distinct microstructures initially present (Figs. 6 and 7). This means that the total number of archive specimens to_be heat :
treated and examined is 62 (or 82 If the 1200 and 1300 C treatments are necessary).
4.2 Development of Heat Treating Procedures During the present reporting period, techniques and procedures have been
. developed for carrying out the experimental heat treatments. Because of the thermal inertia associated with conventional resistance heating furnaces,.it was decided to use inductive heating. A specimen size of 10 x 10 x 5 mm (0.4 x 0.4 x 1
0.2 in.) has been selected, and heating is done with a 2.5-kW, 455-kHz Lepel induction heating unit. The specimen is placed in the center of an induction coil approximately 30 mm (1.2 in.) in diameter and 17 mm (0.67 in.) long, and temperatures and ramp rates are controlled by a Barber-Colman model 570 programmable digital controller.
Because initial experiments indicated that the steel specimens oxidized excessively above about 700'C, the apparatus was modilled by placing a glass tube around the specimen inside the induction coil and by flowing argon through this -
18 Table 3.
Experimental Heat Treatment Matrixfor A533 Grade B Steel Archive.
Material.
Isothermal Transient lleating rate ('C/ min) =
40 40 40 40 100 C/sec Cooling rate ('C/ min) =
1 1
10 100 10 Maximum temo. l'Cl 500 X
550 X
600 X
650 X
700 X
750 X
X X
X 800 X
X X
X 850 X
X X
X 900 X
X X
X 1000 X
X X
X X
1100 X
X X
X X
1200a X
X X
X X
1300a X
X X
X X
Number of specimens =
13 8
8 8
4 aThe 1200 and 1300*C heat treatments will be carried out only if the metallographic studies indicate that these temperatures were attained in the TMI 2 lower head material during the accident, tube. This protective argon atmosphere greatly reduced surface oxidation of the specimens.
Experiments were also conducted to check the temperature distribution on the surface and through the thickness of the specimen during induction heating.
Four chromel alumel thermocouples were spot-welded to the outside surfaces of the specimen, with two thermocouples on each of the larger faces. Two additional thermocouples were inserted in small holes drilled in the specimen. However, heat transfer to the two internal thennocouples was unsatisfactory because of poor contact with the specimen, and the temperature readouts from these two thermocouples were not reliable. A modified test specimen was therefore made up of two half thickness specimens tack welded together,.with a thermocouple first spot welded to the internal surface of one of the two pieces, in this way good contact with the internal surface was obtained. Experiments with this specimen l
19 design indicated tempcratmc variations of15'C across the specimen at temperatures up to 1100'C, and temperature control was generally within 12*C, 4,3 Results of Heat Treating Experiments A limited number of controlled heat treatments have been carried out on the archive material to date. Specifically, isothermal treatments at 700,750,800,and 900 C and transient heat treatments (10'C/ min cooling rate) at 750,800,and 900'C have been completed. In all cases, the starting microstructure was that immediately below the weld clad, and the heat treatment specimens were from plate 4 2, Figure 13 shows the microstructure of the plate 4 2 archive material in the as received condition. Although this microstructure is somewhat different from that seen previously in Fig. 6 the general features are similar. The major constituent is tempered bainite, and the prior austenite grain boundaries are visible. Small Islands of tempered martensite may also be present as the darker acicular regions, but no primary ferrite is evident.
The isothermal heat treatment at 700*C produced virtually no change in the microstructure (Fig.14). This is to be expected, because this temperature lies below the critical At temperature of 727'C at which bainite begins to transform to austenite during heating. (The transformation temperatures quoted here are for a pure Fe 0.22% C binary alloy; the presence of other alloying elements in this steel may shift these temperatures by a few degrees.)
However, when the same material is heated to 750'C, which lies above the transfonnation temperature, significant microstructural changes occur (Fig.15).
The microstructure now consists of a fine dispersion of unresolved pearlite (and perhaps bainite) islands in a matrix of ferrite. Further heating to 800'C (Fig.16) and 900'C (Fig.17) results in further coarsening of the microstructure, a consequence of the increased degree of austenitization and greater opportunity for grain growth at these higher temperatures.
Qualitatively similar effects are observed in the specimens subjected to the transient heat treatments at 750, 800, and 900'C (Figs.18 20). The microstructures are now somewhat liner because of the shorter time at the maximum temperature, and the darker transformed regions are probably now primarily bainite rather than pearlite because of the faster cooling rate from the austenite region. The faster cooling rate also results in the formation of less primary ferrite.
20
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ct.~ 4. y c4
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m a2i' dr.t: Ik an;niu Figure 13. Microstructure of As-Received Archive Material (Plate 4 2) in Base Metal near Inner Surface Weld Clad.
ya -
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7
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i Figure 14. Microstructure of Archive Material (Plate 4 2) in Base Metal qfter Isothermal Heat Treatment at 700*C.
4
21 F
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o
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aW.44&TM Figure 15. hiicrostructure of Archive hiaterial (Plate 4-2) in Base Metal qfter isolltermal Heat Treatment at 750*C.
k k
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V Figure 16. bilcrostructure of Archive biaterial (Plate 4 2) in Base bietal qfter Isothermal Heat Treatment at 800*C.
L _ _ _ _ _ _ _ _ _ _
22 1
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l
23 ll.
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4
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Rgure 19. Microstructure of Archive Material (Plate 4 2) in Base Metal qfter TYansient Heat Treatment at 800*C with Healing Rate of 40*C/ min and Cooling Rate of 10*C/ min,
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m -.
mm-a
24 The results from these preliminary heat treatments indicate that those regions of the TMI 2 material for which the maximum temperature exceeded 727'C should be readily identifiable on the basis of microstructural observations Results from additional experiments at other temperatures and other temperature histories will indicate what additional information can be deduced on the basis of microstructural observations.
5 Mechanical Testing of Archive Material 5,1 Summary of Proposed Program A series of round robin mechanical tests and microstructural studies on the as-received archive material was developed to better characterize this material and to determine the level of variability in mechanical test data obtained by the participating laboratories The OECD partner laboratories participating in this test program are in Belgium, France, the FRG, Italy, and Spain. Finland and the U.K.
will participate in the metallographic studies, but will not conduct any mechanical tests.
A total of six tensile tests are to be conducted in the round robin program, with three duplicate tests at room temperature and three duplicates at 600*C, The strain rate is to be 4 x 10 4 per second. In addition, three stress rupture tests are to be conducted at 600*C. The suggested stress levels for these tests are 215,155, and 110 MPa v'h'ch should result in stress rupture lives on the order of 1,10, and 100 h, respectively. These stress levels were obtained on the basis of a Manson llaferd extrapolation from stress rupture dah on A533B steel obtained by the Japanese National Research Institute for Metals (NRIM) at 450 to 550*C (Fig.
21).2 Decause one purpose of these tests is to generate a stress-rupture curve at-600 C, the laboratories have been given the option of employing slightly lower stress levels to obtain somewhat longer lives. A more extensive stress-rupture testing program, consisting of approximately eight to ten tests, will be conducted by ANL to generate a stress rupture curve for the archive material from <1 h to
~500 h to failure.
5,2 Mechanical Test Specimens The round-robin tensile and stress rupture tests described above will be conducted on flat and/or round cross-section specimens, depending on the preference of the individual laboratory. The design adopted for the flat cross-section specimen is shown in Fig. 22, and that for the round cross-section specimen is shown in Fig. 23. These designs were chosen to satisfy ASTM Standards E8 and E139, as well as applicable standards of the Deutsches Institut 1
1
25 8
10 i
i i
i i
l
~
,s UQN,,N 2
N N
E
'[' 10 h s
10, m
N N
w 100 h 1000 h 10' 450 500 550 600 650 700 Test Temperature ( C)
Agurc 21. Plot of NRIM Stress Rupture Datafor Rue Heats of A533B Steel (solid lines) (Ref. 2] and Manson-Hqferd Extrapolation to Higher Temperatures (shaded lines).-
for Normung (DIN). The test specimen configurations requested by the various.
participants in the testing program are summarized in Table 4.
The flat specimens were prepared by ANL and distributed.to the requesting laboratories. The holes in each end (for gripping the specimens during testing)
~
were om!!v.d so that the various laboratories might drill holes with diameters appropclate for their testing equipment. In the case of the round specimens (Fig.
23). grips and extensometry vary so greatly from one laboratory to the next that it was not possible to. agree on a standard design. Figure 23'therefore indicates the suggested configuration for the specimen gage section; details of the grips and the possible presence of extensometer shoulders are left to the individual laboratories.
Specimen blanks rather than machined specimens, have been sent for the round~
specimens. Specimens for metallographic studies, consisting of two pieces each
~25 mm (1. in.) on a side and 145 mm (5.7 in.) long (the archive plate thickness),
were also sent to each of the participants listed in Table 4.
l 1
26 DIA = 6.3 to 6.
- 12.0**- 15.0++
24.0 *
,I+0.1,-0.
-+
4.0010.08 +
y
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8
(/
\\/
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~
~
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/"
^
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R = 7.0 78.0 i 1.0 3.0 +
4-Figure 22.
Design of Flat Tensile and Stress Rupture Test Specimen for Round-Robin Testing Program on Archive Material. All dimensions are in mm.
- - 24 min.-->
+
+
r U
w 4.00 0.08 8.0 min. I ',[~.'-
+
+
L R = 4 min -
Figure 23.
Design of Round Tensile and Stress-Rupture Test Specimen for Round Robin Testing Program on Archive Material. All dtmensions are in mm.
27.
Table 4.
Test Specimen Cottflgurations Requested for Round Robin Testing qf Midland Reactor Archive Material.
Tensile Stress Rupture Participant Specimens Specimens Belgium Flat Flat i
France Round & Dat Round & Dat l
IPG Round & Dat Round & Dat j
Italy Flat Flat Spain Round Round Finland (metallography only)
U.K.~
(metallography only)
Figure 24 is a sectioning diagram that shows the locations on archive plate 4-2 from which the various metallographic and mechanical test specimens have been taken.
6 Characterization of Material from Trial Sections As stated in Section 2, the first phase of the TMI-2 Vessel Investigation Project is the recovery of material samples from the lower head. MPR Associates, Inc., of Washington, DC. has the lead responsibility for this part of the program,'
and, in turn, has subcontracted PCI Energy Systems of Lake Bluff, IL, to develop the -
necessary extraction tools and cutting procedures. A series of trial cuts has been carried out by PCI Energy Systems on a plate of A36 plain carbon structural steel, using the metal disintegration machining (MDM) procedure that they.have developed. Two wedge shaped samplesicach approximately 160 mm (6-3/8 in.)
long, 73 mm (2 7/8 in.) wide, and 67 mm (2-5/8 in.) high, were cut out and sent -
to ANL for microstructural examinatfor to determine the extent of damage at the cut faces caused by the MDM technique, These samples are approximately the l
same size as those to be cut from the TMI 2 lower head.
Metallographic sections were cut perpendicular to the long axis of these two specimens to reveal the microstructure near the cut faces. The results for the Drst sample are shown in Figs,25 and 26, for the unetched and etched conditions,
28 C
90
?
[
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D I L E
f andles
\\
h 12.5
~
3IHill 32 g
g g3 p
- 12.5 5 s(
,%/
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=
15 ->
U Identification of Sections' A and B: Flat tenslie and creep specimens for round-robin tests (center of plate).
C: Metallographic specimens for round robin tests (through thickness),
D: Round tensile and creep specimens for round-robin tests (center of plate).
E and F: Metallographic specimens for ANL heat treatment experiments (center and near I.D,).
G,H, and I: Preliminary metallographic specimens for characterization of as recolved plate.
Figure 24.
Sectioning Diagram for Archive Plate 4 2, Showing Locations from Which Metallographic and Mechanical Test Specimens Were Taken.
All Dimensions are in cm.
I respectively. The corresponding micrographs for the'second section are shown in Figs. 27 and 28. The cutting process produces irregular shallow scallops along the cut face, one of which is seen in cross section in Figs. 25 and 26. After etching, both samples show a thin, somewhat discontinuous layer of martensite (dark region) immediately adjacent to the cut face. This indicates that the temperature in this layer, which is on the order of 100 m thick, exceeded 727"C during the cutting process. Immediately below the martensite layer. the banded pearlite plus ferrite microstructure shows some evidence of alteration, due to high temperature exposure, for an additional depth of approximately 100 m. At depths greater than
~200 m below the cut face, the microstructure is undisturbed It was concluded from these observations that the maximum depth of disturbed metal produced by-the MDM process is ~200 pm.
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Figure 25. Metallographic Section through A36 Steel Sample Cut by PCI Energy Systems Using Metal Disintegration Machining (unctched).
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Agure 27. Metallograpitic Section titrough Second A36 Steel Sarnple Cut by ICI Energy Systerns Using Metal Disintegration Machining (unctched).
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31 References i
l 1.
R. L. Moore and E. L. Tolman, Estimated 7MI-2 Vessel Thermal Response Based on the Lower Plenum Debris Cortflguration. EGG M 01288, Idaho National Engineering Laboratory (July 1988).
2, Data Sheets on the Elevated Temperature Properties of 1.3 Mn D.5 Mo 0.5 Nt Stect Plates for Dollers and Other Pressure Vessels (SBV 2), NRIM Creep Data Sheet No.18D, National Research Institute for Metals Tokyo (1987),
1.'
t
32 Distribution for NUREO/CR-5224 VOL. I (ANIr90/21 Internal:
D. R. Diercks (25)
TIS File (3)
ANL Libraries (2)
ANL Patent File ANL Contract File Prternal:
Manager, Chicago Operations OITice, DOE Materials and Components Technology Divbion Review Committee:
P. Alexander, Lord Corporation. Eric, PA M. S. Dresselhaus, Massachusetts Institute of Technology, Cambridge, PA S. Green, Electric Power Research Institute, Palo Alto, CA R. A. Greenkorn, Purdue University, West Lafayette, IN L. J. lardine, lawrence Livermore National Laboratory, Livermore, CA C. Y. Li, Cornell University, Ithaca, NY R. E. Scholl, Counter Quake Corporation, Redwood City, CA P. G Shewmon, Ohio State University Columbus, Oil R. E. Smith, EPRI NDE Center, Charlotte, NC D. W. Akers, Idaho National Engineering Laboratory, EG&G Idaho, Inc., Idaho Falls, ID Dr. Danaschtk, Gesellschaft for Reaktorsicherheit Zentralstelle Forschungsbetreuung, K61n 1, Federal Repub!!c of Germany E. Beckjord, Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, Washington, DC G. A. Berna. Idaho National Engineering Laboratory, EG&G Idaho, Inc., Idaho Falls, ID J. Dros, TECNATOM S.A., Components Integrity Group, Madrid, Spain S. Chakraborty, Swiss Federal Nuclear Safety inspectorate, W0erentingen, Switzerland N. Cole, MPR Associates, Washington, DC F, Corst, ENEA/ VEL MEP, Rome, Italy J. Cortez, U.S. Nuclear Regulatory Commission, Washington, DC F. Costanzi, U.S. Nuclear Regulatory Commission, Washington, DC P. DeJonghe, Study Centre for Nuclear Energy. SCK/CEN, Bruxelles, Belgium J. Duco, Department d' Analyse de Snrett, CEN/FAR, Cedex France J. M. Figueras, Consejo de Seguridad Nuclear, Subdireccion de Analysis y Evaluacion. Madrid, Spain D. W. Golden, Idaho National Engineering Laboratory, EG&G Idaho, Inc., Idaho Falls, ID W. Gomolluski, IPSN/OSSN, CEN/FAR. Cedex, France J. A. Iludson, D388 Ilanvell laboratory, UKAEA, Oxfordshire, United Kingdom S. Kawasakt Department of Fuel Safety Research, Japan Atomic Energy Research Institute, Ibaraki ken, Japan
33 J
S. Kinnersly. Technical Area, Severe Accident Analysis, UKAEA, Dorset. United Kingdom R. Landry, U.S. Nuclear Regulatory Cornmission, Washington, DC S. Levin, TMI 2. GPU Nuclear, Middletown, PA Mr. C. Martechtolo, ENEA/ DISP, Division of Mechanical Analysts & Technology, Rome, Italy M. Mayfleid. Omce of Nuclear Regulatory Research, Materials Engineering Branch, j
U.S. Nuclear Regulatory Commission, Washington, DC R. K. McCardell, Idaho National Engineering laboratory, EO&O idaho, Inc., Idaho Falls, ID N. R. Mcdonald, Nuclear Safety Dinston, OECD, Agence pour l*$nergie Nucleaire, Paris, France R. O. Meyer, U.S. Nuclear Regulatory Commission, Washington, DC P. Milella, ENEA/ DISP, Didslon of Mechanical Analysis & Technology Rome, Italy S. Miyazono, Japan Atomic Energy Research Institute, Reactor Safety Research Center, Ibarakt ken, Japan R. C. Monroy, Planning Department, Nuclear R&D Projects. UNIDAD Electrica, S.A.,
Madrid, Spain
- 11. Njo, Swiss Federal Nuclear Safety Inspectorate, W0erenlingen, Switzerland C. Ottoson, Finnish Centre for Radiation and Nuclear Safety, llelsinki, Finland W. F. Pasedag, U.S. Department of Energy, Omce of LWR Safety and Technology, Washington, DC R. Pelli, Technical Research Centre of Finland, Espoo, Finland G. Petrangelt. ENEA/ DISP, Sector for Development and Research, Rome, Italy K. Pettersson, Department of Structural Integrity, Swedish Nuclear Power inspectorate, Stockholm, Sweden G. Saponaro ENEA DISP, Regulatory Research Commitment Rome, Italy
- 11. Schulz, Gesellschaft for Reaktorsicherheit Zentralstelle Forschungsbetreuung, Koln 1, Federal Republic of Germany C. Z, Serpan. Omce of Nuclear Regulatory Research, Materials Engineering Branch, U.S. Nuclear Regulatory Commission, Washington, DC L. C. Shao Division of Engineering RES, U.S. Nuclear Regulatory Commission, Washington, DC D. Sheron. U.S. Nuclear Regulatory Commission, Washington, DC M. Shiba, Japan Atomic Energy Research Institute, Ibaraki ken, Japan K. Shibata, Japan Atomic Energy Research Institute, Mechanical Strength and Structures Laboratory, Ibaraki ken, Japan 31911 P. Soulat, Service de Recherches Metallurgiques Appliquees CEN Saclay, Cedex, France K. D. Stadie. OECD, Agence pour l'$nergie Nucleatre, Paris, France D. Sturm, Staatliche Materialprofungsanstalt. Universitat Stuttgart, Stuttgart, Federal Republic of Germany W Vandermeulen, Study Centre for Nuclear Energy. SCK/CEN, Bruxelles, Belgium P. Veron, Equipos Nucleares S.A., Maliano, Cantabria, Spain T. J. Walker, U.S. Nuclear Regulatory Commission, Washington, DC F. Weehuizen, Swiss Federal Nuclear Safety Inspectorate, W0erenlingen, Switzerland
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BIBLIOGRAPHIC DATA SHEE1 NUREC/CR-522\\ Yol. I an,,,,,,,.,,,,..,,,,,,
ANL-90/2
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t uiti anu weniti Dil-2 Vessel Investigation Project (VIP)
Metallurgical Progrnto.
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.rF Progress Report. January-September 1989 March 1990 4 f 6N oR oRaN' EUVBlk L10050 i, Avinons, e not o, niivu D. R. Diercks Technicalt Progress
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This report summarizes the work performed by Argonne National Laboratory on the TMI-2 Vessel Investigation Project (VIP) Metallurgical Program during the nine months f rom the initiation of the program in January 1989 through September 1989. During the reporting period, archive material for the program was obtained from the lower head of the cancelled Midland nuclear reactor in Midland. MI. in the form of four plates.
Chemical analyses and hardness measurements were performed on samples from the four platen the as-received microstructure was characterized, and a tentative determination of rolling direction was made.
Initial results from heat treatment experiments on the archive material indicate that those regions of the THI-2 mater 3a1 where the maximum temperature exceeded 727'C should be readily identifiable on the basis of micro-structural observations. A series of round-robin mechanical tests and microstructural studies on the as-received archive material was developed, and specimens and specimen blanks for tensile and stress-rupture tests were distributed to the participating OECD laboratories. Two trial specimens cut from a plate of A36 plain-carbon structural steel by PCI Energy Systems using metal disintegration machining (MDM) were examined metallographically, u u v won us ut sc on ow s,... -.
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NUCLE AR REGULATORY COMMISSION i
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i June 27, 1990 t
ERRATA SHEET l
Report Number:
!WREG/CR-5224, Vol. 1 ANL-90/2 i
Report
Title:
TMI-2 Vessel Investigation Project (VIP)
Metallurgical Program, Progress Report, January - September 1989 s
Prepared by:
Argonne National Laboratory i
Argonne, II. 14 39 Date Published:
March 1990 Instructions:
Please make the following correction to the NUREG report identification number.
Delete:
NUREG/CR-5224, Vol. 1 Replace With:
NUREG/CR-5524 Vol. 1 L
Division of Freedom ofInformation and Publications Services Omce of Administration
UNITED STATES spec t eovat etiss aan y
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c WASHINGTON, D.C. 20556 e
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