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Irradiation of structural materials in contact with lead bismuth eutectic in the high flux reactor
Journal of Nuclear Materials 415 (2011) 311–315
Contents lists available at ScienceDirect
Journal of Nuclear Materials journal homepage: www.elsevier.com/locate/jnucmat
Irradiation of structural materials in contact with lead bismuth eutectic in the high flux reactor A.J. Magielsen ⇑, M. Jong, T. Bakker, N.V. Luzginova, R.K. Mutnuru, D.J. Ketema, A.V. Fedorov Nuclear Research and Consultancy Group, Westerduinweg 3, Postbus 25, 1755 ZG Petten, The Netherlands
a r t i c l e
i n f o
Article history: Available online 28 April 2011
a b s t r a c t In the framework of the materials domain DEMETRA in the European Transmutation research and development project EUROTRANS, irradiation experiment IBIS has been performed in the High Flux Reactor in Petten. The objective was to investigate the synergystic effects of irradiation and lead bismuth eutectic exposure on the mechanical properties of structural materials and welds. In this experiment ferritic martensitic 9 Cr steel, austenitic 316L stainless steel and their welds have been irradiated for 250 Full Power Days up to a dose level of 2 dpa. Irradiation temperatures have been kept constant at 300 °C and 500 °C. During the post-irradiation test phase, tensile tests performed on the specimens irradiated at 300 °C have shown that the irradiation hardening of ferritic martensitic 9 Cr steel at 1.3 dpa is 254 MPa, which is in line with the irradiation hardening obtained for ferritic martensitic Eurofer97 steel investigated in the fusion program. This result indicates that no LBE interaction at this irradiation temperature is present. A visual inspection is performed on the specimens irradiated in contact with LBE at 500 °C and have shown blackening on the surface of the specimens and remains of LBE that makes a special cleaning procedure necessary before post-irradiation mechanical testing. Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction In the framework of the materials domain DEMETRA in the European Transmutation research and development project EUROTRANS, an irradiation program was launched to characterize materials irradiated in contact with lead bismuth eutectic (LBE), the coolant and spallation target in an Accelerator Driven System (ADS) [1]. The irradiation experiment of the lead bismuth structural materials system (IBIS) has been performed in the High Flux Reactor (HFR) in Petten with the objective to investigate the synergystic effects of irradiation and LBE exposure on the mechanical properties of ferritic martensitic 9 Cr steel (T91), austenitic 316L stainless steel and their welds. Corrosion and liquid meal embrittlement of 316L and T91 exposed to LBE has been reported to be controlled by the degree of surface wetting with LBE, which depends on the exposure temperature [2–4]. Effects of neutron and ion irradiation on the mechanical properties of ferritic martensitic steels are well studied in the past [5–8]. On the other hand, only in few studies impact on the mechanical properties of both, LBE exposure and irradiation are investigated [9,10]. The IBIS experiment was designed to be complementary to the irradiation experiment TWIN ASTIR in the BR2 with respect to irradiation temperature [9]. The goal of post-irradiation examination of the materials irradiated in IBIS is to perform measurements on the total embrittle⇑ Corresponding author. Tel.: +31 224564695. E-mail address: [email protected] (A.J. Magielsen). 0022-3115/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jnucmat.2011.04.035
ment, reduction of the upper shelf toughness and irradiation hardening of the materials. Corrosion related issues are scheduled for studying with Scanning Electron Microscopy. The materials irradiated in IBIS were placed in two containers with LBE and were irradiated at two temperatures, 300 and 500 °C. The entire irradiation campaign lasted for nine cycles (about 250 Full Power Days, FPD’s) resulting in a damage level of up to 2 dpa. At the moment the tensile specimens irradiated in IBIS at 300 °C are measured and analyzed. The results are presented in this work. 2. Experimental The IBIS experiment consists of two identical containers placed on top of each other (see Fig. 1). The top capsule is irradiated at 500 °C and the bottom capsule is irradiated at 300 °C. Every capsule contains different types of specimens positioned at three levels: miniature tensile specimens, three point bend fracture toughness specimens (KLST type); and corrosion specimens for microscopy: unstressed strips, bent strips and coated specimens (FeCrAlY). As shown in Fig. 1, the tensile specimens are located at the middle level. The dimensions of the capsule and miniature tensile specimens used in this study are given in Figs. 2 and 3, respectively. Chemical compositions of the T91 and the 316L steels (the selected materials for the IBIS experiments) are given in Table 1 [11]. The thermal treatment of T91 material included normalization
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A.J. Magielsen et al. / Journal of Nuclear Materials 415 (2011) 311–315
Fig. 1. Two capsules of the IBIS experiment with specimens. The top capsule is irradiated at 500 °C and the bottom capsule is irradiated at 300 °C. The specimens in each capsule are located at three levels, with the tensile specimens in the middle.
Fig. 3. Dimensions of the tensile specimens used in IBIS.
Table 1 Chemical composition of ferritic martensitic 9 Cr steel (T91) and austenitic stainless steel 316L used in IBIS experiment (in wt.%).
Fig. 2. Axial and radial cross-sections of the IBIS container with dimensions.
at 1050 °C and tempering at 770 °C. The welds are TIG welds supplied by CMI Belgium. The highest temperature used during the heat treatment after T91/T91 and T91/316L welding was 750 °C for 1 h [11]. The LBE is delivered by Hetzel Metalle GmbH with the nominal composition 55.2 wt.% Bi and 44.8 wt.% Pb. The impurities present in the LBE are given in Table 2. The IBIS containers have been filled with LBE with 10 6 wt.% oxygen at SCK-CEN [9]. Before the filling the LBE was preconditioned by two steps. First, the lead oxides are separated in a segregation tank under Argon atmosphere. Then the tank is emptied through the bottom valve into a second tank where the surface of the liquid metal is swept with Ar + 5% H2 flow for several days. In this way, the oxide content was minimized in order to prevent corrosion.
Element
T91
AISI 316L
Fe C Mn P Si Ni Cr Mo N S V Cu Nb
Balance 0.1 0.4 0.02 0.23 0.1 9 0.9 0.044 – 0.21 0.06 0.06
Balance 0.019 1.81 0.003 0.67 10 16.7 2.05 0.029 0.0035 – – –
After solidification of the LBE segregation of a bismuth rich phase causes the LBE to develop stress on the container wall as function of time [12]. The risk of rupture was mitigated by designing the IBIS containers based on the conservative calculations that showed that using a 4 mm thick container wall the stress on the wall will be kept well below the admissible stress of AISI 316 at ambient temperature.
A.J. Magielsen et al. / Journal of Nuclear Materials 415 (2011) 311–315 Table 2 Chemical eutectic.
composition
of
lead
313
bismuth
Element Bi (%) Pb (%) Cu (lg/g) Ag (lg/g) Sn (lg/g) Tl (lg/g) Na (lg/g) Ca (lg/g) Cr (lg/g) Fe (lg/g) Ni (lg/g) Mo (lg/g) Cd (lg/g) Th (lg/g)
54.3 45.7 3.6 13 4.2 2.3 <50 <250 <10 <100 <5 <1 <1 <0.5
The entire irradiation campaign that lasted for nine cycles (about 250 Full Power Days – FPD’s) was carried out in two core positions of the High Flux Reactor (HFR) at Petten. The specimens were subjected to fluences varying between 9.54 1024 m 2 and 16.7 1024 m 2 depending on the vertical distances of these specimens from the centre line of the specimen holder. The obtained damage levels for the tensile specimens also depend on the axial position and for in the low temperature capsule range between 1.25 and 1.8 dpa and in the high temperature capsule range between 2.1 and 2.7 dpa. The temperatures were measured during irradiation at three vertical levels in each capsule (six levels in total) with 12 thermocouples. At every level two thermocouples were used, one in the central tube (Ø 6 mm) and the other in direct contact with the outside container tube (Ø 28 mm), see Fig. 2. The average temperatures measured during irradiation varied between 290 and 319 °C for the 300 °C temperature section and between 478 and 489 °C for the 500 °C temperature section. Temperature control was achieved by the design of the gas gap between the containers and the specimen holder and by movement of the experiment in its core position. Due to high radio toxicology of 210Po formed during the irradiation of LBE, restrictions and special licensing procedures have been applied during the design and commissioning phase of the experiment. The total 210Po activity of the LBE just after nine irradiation cycles (250 FPD) calculated using the FISPACT code was found to be 0.95 TBq. The activity of 210Po at the time of its planned arrival into the Hot Cell Laboratory (approximately 208 days after the end of irradiation) has been estimated to be around 0.34 TBq. A dedicated set up has been developed for the retrieval of the specimens from the container. For purposes of neutron metrology, three activation monitor sets were prepared; two of them were located above the specimen holder and the third one was placed at the bottom of the holder. The data obtained from the monitor sets was used to evaluate the actual fluences and dose levels achieved during the irradiation. The tensile machine Deben Mtest5000S, normally used for mechanical testing in SEM was adapted for testing in the hot cell line in order to handle radioactive specimens. The testing machine is equipped with a tensile fixture to perform tensile test using miniaturized specimens. The tensile specimens, with a testing area of 1.77 mm2, are fabricated according to Fig. 3. Special gripping mechanism was designed to avoid sample slipping. The tests are performed in air at 25 °C with an initial strain rate of 5 10 4 mm s 1 and maximum load 5 kN. Beside the irradiated containers one identical container including the specimens was fabricated to test the influence of LBE on the specimens without irradiation. This capsule, further referred as
Fig. 4. Specimen assemblies after retrieval from the container from left to right: LBE-0 dpa reference specimen (exposed to LBE at 300 °C), irradiated at 300 °C, and irradiated at 500 °C.
LBE-0 dpa, has experienced the same temperature cycle as the low temperature irradiated capsule: 250 days at 300 °C.
3. Results and discussion During the specimen retrieval of the LBE-0 dpa container and of the low temperature IBIS container all LBE is drained. The specimens were pressed out and visual inspection of the specimens showed no wetting and only a minimum interaction can be observed from the color of the specimens. However on the specimen assembly from the 500 °C container a blackening of the specimens and the LBE remains are visible. These specimens are soldered together with LBE and a procedure will be developed to separate the specimens. The specimen assemblies from the LBE-0 dpa and the irradiated containers are shown in Fig. 4. Tensile tests have been performed on the reference specimens (no LBE, no irradiation), the 0 dpa specimens and the ones irradiated in IBIS at 300 °C. The specimen of the 500 °C capsule will be tested after cleaning and separation procedure. All tests have been performed at room temperature. The results are summarized in Table 3 and in Figs. 5–8. The results on the dissimilar (316L/T91) welds will be evaluated at a later stage within the GETMAT program [13]. It should be noted that in determination of the total elongation an error is inevitable due to the small dimensions of the miniature specimens used in this experiment in comparison to the full sized tensile specimens. The samples are measured in the hot cell using a periscope photographing of the samples. This measurement technique on such small samples introduces an extra error. Also the amount of measured specimens is rather limited. Considering this, the total elongation of all tests must be evaluated with 1–3% of error. The Ultimate Tensile Strength (UTS) and Yield Strength (YS) measured on the T91 are demonstrated in Fig. 5. The reference specimens and the specimens from the LBE-0 dpa container show similar results for the UTS and YS. The Total Elongation (TE) of the LBE-0 dpa specimens, as demonstrated in Fig. 8, show a reduc-
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A.J. Magielsen et al. / Journal of Nuclear Materials 415 (2011) 311–315
Table 3 List of samples used in this study containing the sample code, material, irradiation conditions and tensile test results. Sample code
Material
Dose (dpa)
Capsule
UTS (MPa)
YS (MPa)
TE (%)
M299 M296 M297 L970 L971 M254 M252 M253 L934 L935 M275 M272 M273 L954 L955
T91 T91 T91 T91 T91 T91 weld T91 weld T91 weld T91 weld T91 weld 316L 316L 316L 316L 316L
0 0 0 1.25–1.8 1.25–1.8 0 0 0 1.25–1.8 1.25–1.8 0 0 0 1.25–1.8 1.25–1.8
Reference LBE-0 dpa LBE-0 dpa 300 °C irr 300 °C irr Reference LBE-0 dpa LBE-0 dpa 300 °C irr 300 °C irr Reference LBE-0 dpa LBE-0 dpa 300 °C irr 300 °C irr
656 667 648 848 802 739 712 743 957 832 576 558 554 709 705
548 553 542 809 794 630 618 644 922 818 336 327 336 581 585
23.3 18.9 21.1 15.2 16.3 17.5 18.1 20.0 15.3 14.1 76.0 72.4 71.5 44.1 41.9
Fig. 7. Ultimate Tensile Strength (UTS) and Yield Strength (YS) measured on 316L specimens.
Fig. 8. Total elongation measured on the T91, T91/T91 welds and 316L specimens. Fig. 5. Ultimate Tensile Strength (UTS) and Yield Strength (YS) measured on T91 specimens.
Fig. 6. Ultimate Tensile Strength (UTS) and Yield Strength (YS) measured on T91/ T91 welds.
tion of approximately 2–3% compared to the reference specimen. This reduction is small and is considered to be in the range of the error due to the size of the specimen and the measuring method. Also the number of specimens is to low to perform a proper statistical analysis. The 300 °C irradiated specimens, on the other hand, show a significant change in UTS and YS. The measured increase in UTS is 146–192 MPa, and in YS is 246–261 MPa. The TE
of the irradiated specimens show a significant reduction: from 23.3% to 15.2–16.3%. Similar to the base material, in the case of T91/T91 welds no significant difference between the reference and LBE-0 dpa is observed for the UTS, YS and TE. The measured YS values are, however, 83 MPa higher than those measured on the base T91 material. This might be caused by a different heat treatment used after welding, resulting in the harder weld compared to the base material. The two tested 300 °C irradiated specimens show a significant hardening: increase in UTS is 93–218 MPa and in YS is 188–292 MPa. A considerable spread in the measured values can be ascribed to different locations of the specimens within the weld. The root pass of a weld have been only partly tempered compared to the weld cap. Not fully tempered martensitic material is known to show a very high irradiation hardening [3]. The UTS measured on the reference 316L specimen is 576 MPa, which is approximately 20 MPa higher than the UTS measured in the LBE-0 dpa specimen. The YS of the reference specimen and the LBE-0 dpa specimens are in the same range, approximately 330 MPa. The total elongation of the reference specimen is slightly higher than that of the LBE-0 dpa specimen. For the 300 °C irradiated specimens the UTS and the YS show an increase due to irradiation hardening. The increase in UTS is 129–133 MPa, and in YS is 245–249 MPa. The TE of the irradiated specimens showed reduction from 76% to 41.9%–44.1%. From the tensile test performed on the reference and LBE-0 dpa specimens no effect of LBE on tensile properties is observed for all three materials. The irradiation hardening measured on the specimens irradiated at 300 °C in contact with LBE is of the same order
A.J. Magielsen et al. / Journal of Nuclear Materials 415 (2011) 311–315
315
diated materials are reported. No effect of LBE on the tensile properties of the specimen has been observed. The measured increase in YS (250 MPa) and UTS (150 MPa) is ascribed entirely to irradiation hardening. A significant spread in the tensile results measured for the T91/T91 weld specimens are explained by different specimen location in the weld (root pass or weld cap). A visual inspection is performed on the specimens irradiated in contact with LBE at 500 °C has shown blackening of the surface of the specimens and remains of LBE that makes a special cleaning procedure necessary before post-irradiation mechanical testing. The 500 °C specimens will be separated and tested later in the GETMAT program, there the emphasis of the post-irradiation testing will made on the microscopic investigation by optical and SEM. Acknowledgements
Fig. 9. Comparison of irradiation hardening measured on T91 and 316L specimens irradiated at 300 °C in IBIS experiment with the results obtained on Eurofer97 steel [14] (tested at ambient temperature).
This work has been performed in the framework of the materials domain DEMETRA in the European Transmutation research and development project EUROTRANS, funded by the European Commission and the Dutch ministry of Economic Affairs. References
as pure irradiation hardening. This is demonstrated in Fig. 9, where irradiation hardening of the T91 and T91/T91 welds from this work is compared to the irradiation hardening of Eurofer97 tempered martensitic 9 Cr steel [14,15]. The austenitic SS316 specimens irradiated in IBIS experiment show similar irradiation hardening as the T91 specimens. No extra hardening which could be attributed to exposure to LBE is observed. 4. Conclusions In the IBIS experiment structural materials and weld have been irradiated in direct contact with LBE at 300 °C up to a dose level of 1.3 dpa, and 500 °C up to a dose level of 2–2.3 dpa. The materials under study were FM T91 steel, T91/T91 weld, T91/316L weld, and 316L. The tensile measurements performed on the 300 °C irra-
[1] C. Fazio et al., Development and assessment of structural materials and heavy liquid metal technologies for transmutation systems (DEMETRA): highlights on major results, Presented at the DEMETRA International Workshop, March 2–4, Berlin, J. Nucl. Mater., in press. [2] B. Schmidt et al., J. Nucl. Mater. 296 (2001) 249–255. [3] B. Long et al., J. Nucl. Mater. 377 (2008) 219–224. [4] Z. Hamouche-Hadjem et al., J. Nucl. Mater. 376 (2008) 317–321. [5] R.L. Klueh, A.T. Nelson, J. Nucl. Mater. 371 (2007) 37–52. [6] B. van der Schaaf et al., J. Nucl. Mater. 386 (388) (2009) 236–240. [7] Y. Dai et al., J. Nucl. Mater. 318 (2003) 192–199. [8] P. Hosemann et al., J. Nucl. Mater. 389 (2009) 239–247. [9] J. Van den Bosch et al., J. Nucl. Mater. 377 (2008) 206–212. [10] Y. Dai et al., J. Nucl. Mater. 377 (2008) 225–231. [11] J. Van den Bosch, A. Almazouzi, J. Nucl. Mater. 385 (2009) 504–509. [12] P. Agostini et al., J. Nucl. Mater. 335 (2004) 275–279. [13] C. Fazio et al., J. Nucl. Mater. 392 (2009) 316–323. [14] J. Rensman, Report on 300 °C and 60 °C irradiated RAFM steels, Final Report of the EFDA Tasks TW2-TTMS-001a-D6 and TW2-TTMS-001a-D12, August, Petten, 2005. [15] J. Rensman et al., J. Nucl. Mater. 329 (333) (2004) 1113–1116.
Contents lists available at ScienceDirect
Journal of Nuclear Materials journal homepage: www.elsevier.com/locate/jnucmat
Irradiation of structural materials in contact with lead bismuth eutectic in the high flux reactor A.J. Magielsen ⇑, M. Jong, T. Bakker, N.V. Luzginova, R.K. Mutnuru, D.J. Ketema, A.V. Fedorov Nuclear Research and Consultancy Group, Westerduinweg 3, Postbus 25, 1755 ZG Petten, The Netherlands
a r t i c l e
i n f o
Article history: Available online 28 April 2011
a b s t r a c t In the framework of the materials domain DEMETRA in the European Transmutation research and development project EUROTRANS, irradiation experiment IBIS has been performed in the High Flux Reactor in Petten. The objective was to investigate the synergystic effects of irradiation and lead bismuth eutectic exposure on the mechanical properties of structural materials and welds. In this experiment ferritic martensitic 9 Cr steel, austenitic 316L stainless steel and their welds have been irradiated for 250 Full Power Days up to a dose level of 2 dpa. Irradiation temperatures have been kept constant at 300 °C and 500 °C. During the post-irradiation test phase, tensile tests performed on the specimens irradiated at 300 °C have shown that the irradiation hardening of ferritic martensitic 9 Cr steel at 1.3 dpa is 254 MPa, which is in line with the irradiation hardening obtained for ferritic martensitic Eurofer97 steel investigated in the fusion program. This result indicates that no LBE interaction at this irradiation temperature is present. A visual inspection is performed on the specimens irradiated in contact with LBE at 500 °C and have shown blackening on the surface of the specimens and remains of LBE that makes a special cleaning procedure necessary before post-irradiation mechanical testing. Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction In the framework of the materials domain DEMETRA in the European Transmutation research and development project EUROTRANS, an irradiation program was launched to characterize materials irradiated in contact with lead bismuth eutectic (LBE), the coolant and spallation target in an Accelerator Driven System (ADS) [1]. The irradiation experiment of the lead bismuth structural materials system (IBIS) has been performed in the High Flux Reactor (HFR) in Petten with the objective to investigate the synergystic effects of irradiation and LBE exposure on the mechanical properties of ferritic martensitic 9 Cr steel (T91), austenitic 316L stainless steel and their welds. Corrosion and liquid meal embrittlement of 316L and T91 exposed to LBE has been reported to be controlled by the degree of surface wetting with LBE, which depends on the exposure temperature [2–4]. Effects of neutron and ion irradiation on the mechanical properties of ferritic martensitic steels are well studied in the past [5–8]. On the other hand, only in few studies impact on the mechanical properties of both, LBE exposure and irradiation are investigated [9,10]. The IBIS experiment was designed to be complementary to the irradiation experiment TWIN ASTIR in the BR2 with respect to irradiation temperature [9]. The goal of post-irradiation examination of the materials irradiated in IBIS is to perform measurements on the total embrittle⇑ Corresponding author. Tel.: +31 224564695. E-mail address: [email protected] (A.J. Magielsen). 0022-3115/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jnucmat.2011.04.035
ment, reduction of the upper shelf toughness and irradiation hardening of the materials. Corrosion related issues are scheduled for studying with Scanning Electron Microscopy. The materials irradiated in IBIS were placed in two containers with LBE and were irradiated at two temperatures, 300 and 500 °C. The entire irradiation campaign lasted for nine cycles (about 250 Full Power Days, FPD’s) resulting in a damage level of up to 2 dpa. At the moment the tensile specimens irradiated in IBIS at 300 °C are measured and analyzed. The results are presented in this work. 2. Experimental The IBIS experiment consists of two identical containers placed on top of each other (see Fig. 1). The top capsule is irradiated at 500 °C and the bottom capsule is irradiated at 300 °C. Every capsule contains different types of specimens positioned at three levels: miniature tensile specimens, three point bend fracture toughness specimens (KLST type); and corrosion specimens for microscopy: unstressed strips, bent strips and coated specimens (FeCrAlY). As shown in Fig. 1, the tensile specimens are located at the middle level. The dimensions of the capsule and miniature tensile specimens used in this study are given in Figs. 2 and 3, respectively. Chemical compositions of the T91 and the 316L steels (the selected materials for the IBIS experiments) are given in Table 1 [11]. The thermal treatment of T91 material included normalization
312
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Fig. 1. Two capsules of the IBIS experiment with specimens. The top capsule is irradiated at 500 °C and the bottom capsule is irradiated at 300 °C. The specimens in each capsule are located at three levels, with the tensile specimens in the middle.
Fig. 3. Dimensions of the tensile specimens used in IBIS.
Table 1 Chemical composition of ferritic martensitic 9 Cr steel (T91) and austenitic stainless steel 316L used in IBIS experiment (in wt.%).
Fig. 2. Axial and radial cross-sections of the IBIS container with dimensions.
at 1050 °C and tempering at 770 °C. The welds are TIG welds supplied by CMI Belgium. The highest temperature used during the heat treatment after T91/T91 and T91/316L welding was 750 °C for 1 h [11]. The LBE is delivered by Hetzel Metalle GmbH with the nominal composition 55.2 wt.% Bi and 44.8 wt.% Pb. The impurities present in the LBE are given in Table 2. The IBIS containers have been filled with LBE with 10 6 wt.% oxygen at SCK-CEN [9]. Before the filling the LBE was preconditioned by two steps. First, the lead oxides are separated in a segregation tank under Argon atmosphere. Then the tank is emptied through the bottom valve into a second tank where the surface of the liquid metal is swept with Ar + 5% H2 flow for several days. In this way, the oxide content was minimized in order to prevent corrosion.
Element
T91
AISI 316L
Fe C Mn P Si Ni Cr Mo N S V Cu Nb
Balance 0.1 0.4 0.02 0.23 0.1 9 0.9 0.044 – 0.21 0.06 0.06
Balance 0.019 1.81 0.003 0.67 10 16.7 2.05 0.029 0.0035 – – –
After solidification of the LBE segregation of a bismuth rich phase causes the LBE to develop stress on the container wall as function of time [12]. The risk of rupture was mitigated by designing the IBIS containers based on the conservative calculations that showed that using a 4 mm thick container wall the stress on the wall will be kept well below the admissible stress of AISI 316 at ambient temperature.
A.J. Magielsen et al. / Journal of Nuclear Materials 415 (2011) 311–315 Table 2 Chemical eutectic.
composition
of
lead
313
bismuth
Element Bi (%) Pb (%) Cu (lg/g) Ag (lg/g) Sn (lg/g) Tl (lg/g) Na (lg/g) Ca (lg/g) Cr (lg/g) Fe (lg/g) Ni (lg/g) Mo (lg/g) Cd (lg/g) Th (lg/g)
54.3 45.7 3.6 13 4.2 2.3 <50 <250 <10 <100 <5 <1 <1 <0.5
The entire irradiation campaign that lasted for nine cycles (about 250 Full Power Days – FPD’s) was carried out in two core positions of the High Flux Reactor (HFR) at Petten. The specimens were subjected to fluences varying between 9.54 1024 m 2 and 16.7 1024 m 2 depending on the vertical distances of these specimens from the centre line of the specimen holder. The obtained damage levels for the tensile specimens also depend on the axial position and for in the low temperature capsule range between 1.25 and 1.8 dpa and in the high temperature capsule range between 2.1 and 2.7 dpa. The temperatures were measured during irradiation at three vertical levels in each capsule (six levels in total) with 12 thermocouples. At every level two thermocouples were used, one in the central tube (Ø 6 mm) and the other in direct contact with the outside container tube (Ø 28 mm), see Fig. 2. The average temperatures measured during irradiation varied between 290 and 319 °C for the 300 °C temperature section and between 478 and 489 °C for the 500 °C temperature section. Temperature control was achieved by the design of the gas gap between the containers and the specimen holder and by movement of the experiment in its core position. Due to high radio toxicology of 210Po formed during the irradiation of LBE, restrictions and special licensing procedures have been applied during the design and commissioning phase of the experiment. The total 210Po activity of the LBE just after nine irradiation cycles (250 FPD) calculated using the FISPACT code was found to be 0.95 TBq. The activity of 210Po at the time of its planned arrival into the Hot Cell Laboratory (approximately 208 days after the end of irradiation) has been estimated to be around 0.34 TBq. A dedicated set up has been developed for the retrieval of the specimens from the container. For purposes of neutron metrology, three activation monitor sets were prepared; two of them were located above the specimen holder and the third one was placed at the bottom of the holder. The data obtained from the monitor sets was used to evaluate the actual fluences and dose levels achieved during the irradiation. The tensile machine Deben Mtest5000S, normally used for mechanical testing in SEM was adapted for testing in the hot cell line in order to handle radioactive specimens. The testing machine is equipped with a tensile fixture to perform tensile test using miniaturized specimens. The tensile specimens, with a testing area of 1.77 mm2, are fabricated according to Fig. 3. Special gripping mechanism was designed to avoid sample slipping. The tests are performed in air at 25 °C with an initial strain rate of 5 10 4 mm s 1 and maximum load 5 kN. Beside the irradiated containers one identical container including the specimens was fabricated to test the influence of LBE on the specimens without irradiation. This capsule, further referred as
Fig. 4. Specimen assemblies after retrieval from the container from left to right: LBE-0 dpa reference specimen (exposed to LBE at 300 °C), irradiated at 300 °C, and irradiated at 500 °C.
LBE-0 dpa, has experienced the same temperature cycle as the low temperature irradiated capsule: 250 days at 300 °C.
3. Results and discussion During the specimen retrieval of the LBE-0 dpa container and of the low temperature IBIS container all LBE is drained. The specimens were pressed out and visual inspection of the specimens showed no wetting and only a minimum interaction can be observed from the color of the specimens. However on the specimen assembly from the 500 °C container a blackening of the specimens and the LBE remains are visible. These specimens are soldered together with LBE and a procedure will be developed to separate the specimens. The specimen assemblies from the LBE-0 dpa and the irradiated containers are shown in Fig. 4. Tensile tests have been performed on the reference specimens (no LBE, no irradiation), the 0 dpa specimens and the ones irradiated in IBIS at 300 °C. The specimen of the 500 °C capsule will be tested after cleaning and separation procedure. All tests have been performed at room temperature. The results are summarized in Table 3 and in Figs. 5–8. The results on the dissimilar (316L/T91) welds will be evaluated at a later stage within the GETMAT program [13]. It should be noted that in determination of the total elongation an error is inevitable due to the small dimensions of the miniature specimens used in this experiment in comparison to the full sized tensile specimens. The samples are measured in the hot cell using a periscope photographing of the samples. This measurement technique on such small samples introduces an extra error. Also the amount of measured specimens is rather limited. Considering this, the total elongation of all tests must be evaluated with 1–3% of error. The Ultimate Tensile Strength (UTS) and Yield Strength (YS) measured on the T91 are demonstrated in Fig. 5. The reference specimens and the specimens from the LBE-0 dpa container show similar results for the UTS and YS. The Total Elongation (TE) of the LBE-0 dpa specimens, as demonstrated in Fig. 8, show a reduc-
314
A.J. Magielsen et al. / Journal of Nuclear Materials 415 (2011) 311–315
Table 3 List of samples used in this study containing the sample code, material, irradiation conditions and tensile test results. Sample code
Material
Dose (dpa)
Capsule
UTS (MPa)
YS (MPa)
TE (%)
M299 M296 M297 L970 L971 M254 M252 M253 L934 L935 M275 M272 M273 L954 L955
T91 T91 T91 T91 T91 T91 weld T91 weld T91 weld T91 weld T91 weld 316L 316L 316L 316L 316L
0 0 0 1.25–1.8 1.25–1.8 0 0 0 1.25–1.8 1.25–1.8 0 0 0 1.25–1.8 1.25–1.8
Reference LBE-0 dpa LBE-0 dpa 300 °C irr 300 °C irr Reference LBE-0 dpa LBE-0 dpa 300 °C irr 300 °C irr Reference LBE-0 dpa LBE-0 dpa 300 °C irr 300 °C irr
656 667 648 848 802 739 712 743 957 832 576 558 554 709 705
548 553 542 809 794 630 618 644 922 818 336 327 336 581 585
23.3 18.9 21.1 15.2 16.3 17.5 18.1 20.0 15.3 14.1 76.0 72.4 71.5 44.1 41.9
Fig. 7. Ultimate Tensile Strength (UTS) and Yield Strength (YS) measured on 316L specimens.
Fig. 8. Total elongation measured on the T91, T91/T91 welds and 316L specimens. Fig. 5. Ultimate Tensile Strength (UTS) and Yield Strength (YS) measured on T91 specimens.
Fig. 6. Ultimate Tensile Strength (UTS) and Yield Strength (YS) measured on T91/ T91 welds.
tion of approximately 2–3% compared to the reference specimen. This reduction is small and is considered to be in the range of the error due to the size of the specimen and the measuring method. Also the number of specimens is to low to perform a proper statistical analysis. The 300 °C irradiated specimens, on the other hand, show a significant change in UTS and YS. The measured increase in UTS is 146–192 MPa, and in YS is 246–261 MPa. The TE
of the irradiated specimens show a significant reduction: from 23.3% to 15.2–16.3%. Similar to the base material, in the case of T91/T91 welds no significant difference between the reference and LBE-0 dpa is observed for the UTS, YS and TE. The measured YS values are, however, 83 MPa higher than those measured on the base T91 material. This might be caused by a different heat treatment used after welding, resulting in the harder weld compared to the base material. The two tested 300 °C irradiated specimens show a significant hardening: increase in UTS is 93–218 MPa and in YS is 188–292 MPa. A considerable spread in the measured values can be ascribed to different locations of the specimens within the weld. The root pass of a weld have been only partly tempered compared to the weld cap. Not fully tempered martensitic material is known to show a very high irradiation hardening [3]. The UTS measured on the reference 316L specimen is 576 MPa, which is approximately 20 MPa higher than the UTS measured in the LBE-0 dpa specimen. The YS of the reference specimen and the LBE-0 dpa specimens are in the same range, approximately 330 MPa. The total elongation of the reference specimen is slightly higher than that of the LBE-0 dpa specimen. For the 300 °C irradiated specimens the UTS and the YS show an increase due to irradiation hardening. The increase in UTS is 129–133 MPa, and in YS is 245–249 MPa. The TE of the irradiated specimens showed reduction from 76% to 41.9%–44.1%. From the tensile test performed on the reference and LBE-0 dpa specimens no effect of LBE on tensile properties is observed for all three materials. The irradiation hardening measured on the specimens irradiated at 300 °C in contact with LBE is of the same order
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diated materials are reported. No effect of LBE on the tensile properties of the specimen has been observed. The measured increase in YS (250 MPa) and UTS (150 MPa) is ascribed entirely to irradiation hardening. A significant spread in the tensile results measured for the T91/T91 weld specimens are explained by different specimen location in the weld (root pass or weld cap). A visual inspection is performed on the specimens irradiated in contact with LBE at 500 °C has shown blackening of the surface of the specimens and remains of LBE that makes a special cleaning procedure necessary before post-irradiation mechanical testing. The 500 °C specimens will be separated and tested later in the GETMAT program, there the emphasis of the post-irradiation testing will made on the microscopic investigation by optical and SEM. Acknowledgements
Fig. 9. Comparison of irradiation hardening measured on T91 and 316L specimens irradiated at 300 °C in IBIS experiment with the results obtained on Eurofer97 steel [14] (tested at ambient temperature).
This work has been performed in the framework of the materials domain DEMETRA in the European Transmutation research and development project EUROTRANS, funded by the European Commission and the Dutch ministry of Economic Affairs. References
as pure irradiation hardening. This is demonstrated in Fig. 9, where irradiation hardening of the T91 and T91/T91 welds from this work is compared to the irradiation hardening of Eurofer97 tempered martensitic 9 Cr steel [14,15]. The austenitic SS316 specimens irradiated in IBIS experiment show similar irradiation hardening as the T91 specimens. No extra hardening which could be attributed to exposure to LBE is observed. 4. Conclusions In the IBIS experiment structural materials and weld have been irradiated in direct contact with LBE at 300 °C up to a dose level of 1.3 dpa, and 500 °C up to a dose level of 2–2.3 dpa. The materials under study were FM T91 steel, T91/T91 weld, T91/316L weld, and 316L. The tensile measurements performed on the 300 °C irra-
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