Fusion Engineering and Design

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1 Fusion Engineering and Design 84 (2009) Contents lists available at ScienceDirect Fusion Engineering and Design journal homepage: Progress in compatibility experiments on lithium lead with candidate structural materials for fusion in China Qunying Huang a,b,, Sheng Gao a,b, Zhiqiang Zhu a,b, Maolian Zhang a,b, Yong Song a,b, Chunjing Li a,b, Yaping Chen a,b, Xinzhen Ling a,b, Xingui Zhou c a Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, Anhui , China b School of Nuclear Science and Technology, University of Science and Technology of China, Hefei, Anhui , China c College of Aerospace & Materials Engineering, National University of Defence Technology, Changsha, Hunan , China article info abstract Article history: Available online 29 January 2009 Keywords: Lithium lead Structural materials CLAM steel Compatibility Liquid LiPb eutectic is one of the promising candidate tritium breeder materials for fusion reactors. This paper presents the progress in compatibility experiments with liquid LiPb achieved up to now in China for some candidate structural materials. The results showed that CLAM steel had good compatibility with flowing LiPb at 480 C with the velocity of 0.08 m/s after 5000 h in DRAGON-I loop. On the other hand, after exposed in static LiPb at 700 C for 500 h in a SiC crucible, the W and Mo specimens suffered much more weight loss compared with Nb specimen, and a thin reaction product layer was visible on the surface of all the three refractory metals. Preliminary analysis on SiC f /SiC composite specimens indicated that there was no penetration of LiPb and no reaction products on the surface with CVD SiC coating, which showed SiCf/SiC composite were stable and compatible with static LiPb under 700 C after 500 h exposure Elsevier B.V. All rights reserved. 1. Introduction The liquid metal blankets exhibit many merits which make them attractive candidates for both near-term and long-term fusion applications. The advantages include: [1] immunity to radiation damage; [2] potential for tritium self-sufficiency without a beryllium neutron multiplier; [3] tritium extraction outside blanket; [4] low pressure for a safety operation. The liquid metals can serve either as a breeder or as a breeder and a coolant at the same time. So the liquid metal blankets design, especially the LiPb breeder blanket design, became one of the most promising designs for future fusion power reactors and was under wide research in the world. However, one of concerns with the liquid metal blanket is its compatibility with candidate structural materials, especially under elevated temperature improving the power conversion efficiency. The RAFMs are considered as one of the promising candidate structural materials for DEMO and the first fusion power plant. In China, a series of fusion-driven system designs were performed by the FDS team of ASIPP (Institute of Plasma Physics, Chinese Academy of Sciences), such as FDS-I, FDS-II and FDS-III, etc. [1 4]. The candidate structural material for these blanket designs is CLAM Corresponding author. Tel.: ; fax: address: qyhuang@ipp.ac.cn (Q. Huang). (China low activation martensitic) steel [5 9], one of the RAFMs (reduced activation ferritic/martensitic steels) under development. And the SiC f /SiC composites have the potential to be applied in high performance reactors because of their good properties at elevated temperature and superior safety characteristics [10]. The refractory metals are candidate materials for the auxiliary system for their low solubility in liquid LiPb under high temperature. And these materials compatibility with LiPb needs to be investigated in details. In order to study the compatibility between fusion materials and liquid LiPb at different temperatures, a few facilities are designed and fabricated in ASIPP, such as the thermal convection loop DRAGON-I which is the first LiPb loop built in China in 2005 and running at 480 C, and the static isothermal capsule DRAGON- ST which is built in 2008 and is being under operation at 700 C. So far, experiments on compatibility for different materials have been carried out in these facilities. The specimens of CLAM steel are exposed to the flowing LiPb with velocity of 0.08 m/s at 480 C in thermal convection loop DRAGON-I for more than 5000 h. Moreover, refractory metals and three-dimensional (3D) SiC f /SiC composites are exposed to the static liquid LiPb in 700 C isothermal capsule DRAGON-ST for more than 500 h as the first step to investigate their corrosion behavior with static LiPb. Analyses by weight measurement, scanning electron microscopy (SEM) observation and energy dispersive X- ray (EDX) test for the specimens were carried out to evaluate the compatibility of the above materials with liquid LiPb /$ see front matter 2008 Elsevier B.V. All rights reserved. doi: /j.fusengdes

2 Q. Huang et al. / Fusion Engineering and Design 84 (2009) Table 1 Chemical compositions of CLAM steel (wt.%). Elements wt.% Cr 8.91 C 0.12 W 1.44 Mn 0.49 V 0.20 Ta 0.15 N S Fe Bal. 2. Experiments 2.1. Materials The investigated specimen materials are CLAM steel, three kinds of pure refractory metals i.e. W (purity 99.96%), Mo (purity 99.95%) and Nb (purity 99.9%) and 3D SiC f /SiC composites with the SiC coating made by CVD (chemical vapor deposition) method. The chemical compositions of CLAM are listed in Table 1. After machining, the specimens (except for the material SiC f /SiC composites) are mechanically polished with grinding papers (up to 1500 grades). Finally, they are all cleaned in acetone and dried before doing the compatibility experiment Experimental The specimens of CLAM steel are tested in the thermal convection loop DRAGON-I at 480 C. Their dimensions are 15 mm in length and 10 mm in diameter. Some details and related results are introduced in Refs. [11 13]. The specimens of other materials were tested in a SiC crucible with an inner diameter of 72 mm (8 mm in thickness) and a height of 70 mm and inert with liquid LiPb, and enclosed in an outer 316L steel container which is filled with pure argon gas with a purity of %. Heating of the container is performed with electric heating elements settled at the surface of the container. The temperature is measured by thermocouples placed in the center of the container and controlled by a single loop controller. 3. Results Post-test weight loss of specimens were tested after immersions in acetic acid hydrogen peroxide alcohol mixture (1:1:1) until the specimen weight remained constant. The cross-section micrographs showed the morphology of the interface between liquid LiPb and solid materials, and the chemical composition of the corrosion layer was determined by SEM associated with EDX analysis. In addition, some specimens were not washed with water or the chemical mixture in order to avoid destroying the specimen surfaces. Fig. 1. Metal loss of CLAM specimen in flowing LiPb versus exposure time. interface between the liquid LiPb and matrix, and a relatively high roughness of the interfaces was observed. The specimen surface showed little changes in the concentration profiles of Cr, Fe, W, Ta and V after 500 and 1000 h exposure [11 13]. The EDX analysis (shown in Fig. 3) indicated that the concentration profiles of specimen surface exhibited changes of its main compositions of Cr and Fe contents after 5000 h exposure. The corrosion mechanism could be assumed that a depletion layer of Fe, Cr for a few microns formed first at the specimen surface and then detached with its complete dissolution into the liquid metal [14] Refractory metals Three kinds of refractory metals i.e. W, Mo and Nb were tested in the capsule experiments. They are very stable in the eutectic LiPb at 600 C according to Ref. [15]. But when the test temperature was up to 700 C as done in this experiment, the weight loss of the W and Mo specimens reached 3.5 and 5.7 wt.% of their original weight after 500 h exposure, respectively. This was caused by a strong isothermal mass transfer to the crucible wall. Moreover, from the SEM observation (see Fig. 4a and b) and EDX line scan analysis (see Fig. 5a and b), a chemical reaction zone caused by initiation of an intergranular corrosion was observed. Unlike W and Mo, the Nb specimen showed slight weight gain. However, there was also a thin chemical reaction products zone arising on its surface morphology (shown in Fig. 4c) and the composition change as well (shown in Fig. 5c). Another con CLAM steel Fig. 1 shows the metal loss for specimens of CLAM steel versus exposure time. It is clear that the specimen was not attacked obviously at the first hundreds of hours due to the oxide layer at its surface forming during the heat treatment and its machining process [11]. In liquid metals, the wetting of the solid metal can be strongly decreased by the presence of the superficial oxide layer covering the solid material. That could be explained by the incubation period effect at the first 500 h. After the incubation period the corrosion rate increased linearly with the increase of exposure time. From the SEM observation (shown in Fig. 2), it can be seen that the corrosive attack occurred uniformly at the surface of the Fig. 2. Cross-section of CLAM specimen after 5000 h exposure (before cleaned).

3 244 Q. Huang et al. / Fusion Engineering and Design 84 (2009) The specimens exposed to liquid LiPb at 700 C for 500 h were examined by SEM without removing the LiPb adhering to the surface. The surface morphology of the SiC f /SiC composites with SiC coating after exposure is shown in Fig. 6, it is that there is no penetration and no formation of reaction products. The EDX analysis exhibits no liquid penetration into the composite and the liquid LiPb is only adherent to the surface. Therefore, no corrosion damage is observed for the SiC f /SiC composites exposed to LiPb at 700 Cfor 500 h. Further investigations are required for a complete evaluation of the corrosion behavior by using more sophisticated analytical equipment. 4. Discussion Fig. 3. EDX line scan on cross-section of CLAM after 5000 h exposure (before cleaned). cern for refractory metals exposed to liquid LiPb is the penetration of the liquid along the grain boundaries. The formation of a liquid channel from the surface of the refractory metals was observed on the cross-section. Further investigation on the microstructure is needed to definitely conclude about LiPb penetration along the matrix grain boundaries SiC f /SiC composites Corrosion tests of CLAM steel in flowing liquid LiPb at 480 Care performed up to about 5000 h to evaluate the kinetics of the dissolution attack. The exposed specimens are analyzed by SEM and EDX. The results show that CLAM is attacked by flowing liquid LiPb and Fe, Cr metallic element depleted in the surface are dissolved, which is similar to the results obtained after 2500 h exposure [12]. The observed attack is uniform, which is consistent with the corrosion results of other RAFMs exposed in LiPb [16,17]. The compatibility of refractory metals W, Mo, Nb specimens with static LiPb is investigated experimentally. Their dissolution rates and solubilities in LiPb are very low up to 600 C [15]. But from the test presented in this paper, the W and Mo suffered much more weight loss compared with Nb, and a thin reaction zone is visible on the surface of all the three refractory metals. It means beside dissolution effect, the liquid metal penetration and compound formation are important factors to be taken into consideration. Due to the protective SiC coating at the surface of SiC f /SiC composites made by CVD method, there were no reaction products at the surface from the SEM and EDX analysis. But as the signal of the corrosion of SiC f /SiC composites in liquid LiPb, the silicon con- Fig. 4. Cross-sections of refractory metal specimens after 500 h exposure (after cleaned).

4 Q. Huang et al. / Fusion Engineering and Design 84 (2009) Fig. 5. EDX line scans on cross sections of refractory metal specimens after 500 h exposure (after cleaned). centration existed in LiPb after exposure need to be investigated carefully. Moreover, the effects of the temperature and liquid flow velocity on the corrosion behavior of the material should be evaluated in further study. 5. Summary Different materials were tested in the facilities built in ASIPP to evaluate their compatibility with flowing or static LiPb. The spec- imens of CLAM steel showed good compatibility after exposed to liquid LiPb with flowing speed of 0.08 m/s at 480 C for more than 5000 h in DRAGON-I loop. It is necessary to carry out the corrosion experiment on CLAM steel for much longer time at higher flowing velocity. The results of refractory metals tested in SiC capsule showed that W and Mo were not stable at 700 C compared to the results obtained at 600 C which was presented in Ref. [15], only the Nb specimen showed almost no change in weight. As for SiC f /SiC composites, preliminary analysis indicated that no liquid LiPb penetration and reaction with the liquid observed at 700 C, and it was stable and compatible with static isothermal LiPb at this temperature for 500 h. Further study will focus on the effects of temperature, flowing velocity and longer exposure time on the corrosion behavior of the materials in order to investigate the compatibility and feasibility of the candidate materials to be used as the structural materials at elevated temperature for fusion reactor blankets and/or their auxiliary systems. Acknowledgements Fig. 6. The surface morphology of the SiC f /SiC composite specimen after 500 h exposure (before cleaned). This work was supported by the National Natural Science Foundation of China with Grant No , and , the National Basic Research Program of China with the Grant No. 2008cb717802, and the Knowledge Innovation Program of Chinese Academy of Sciences. We would like to thank the great help from the members of FDS Team in this research.

5 246 Q. Huang et al. / Fusion Engineering and Design 84 (2009) References [1] Y. Wu, FDS Team, Conceptual design activities of FDS series fusion power plants in China, Fusion Eng. Des. 81 (2006) [2] Y. Wu, the FDS Team, Design status and development strategy of China liquid lithium lead blankets and related material technology, J. Nucl. Mater (2007) [3] Y. Wu, the FDS Team, Design concept and testing strategy of a dual functional lithium lead test blanket module in ITER and EAST, Nucl. Fusion 47 (2007) [4] Y. Wu, the FDS Team, Design analysis of the China dual-functional lithium lead (DFLL) test blanket module in ITER, Fusion Eng. Des. 82 (2007) [5] Q. Huang, C. Li, Y. Li, M. Chen, M. Zhang, L. Peng, et al., Progress in development of China low activation martensitic steel for fusion application, J. Nucl. Mater (2007) [6] Q. Huang, C. Li, Y. Li, S. Liu, Y. Song, L. Peng, et al., Research and development status of China liquid Li-Pb blanket materials, Chin. J. At. Energy Sci. Tech. 41 (2007) [7] Q. Huang, C. Li, Y. Li, M. Zhang, S. Liu, Y. Wu, et al., R&D status of China low actavition martensitic steel, Chin. J. Nucl. Sci. Eng. 27 (2007) [8] Q. Huang, Y. Wu, J. Li, F. Wan, J. Chen, G. Luo, et al., Status and strategy of fusion materials development in China, J. Nucl. Mater. (2008), doi: /j.jnucmat [9] Y. Wu, J. Qian, J. Yu, The fusion-driven hybrid system and its material selection, J. Nucl. Mater (2002) [10] B. Riccardi, L. Giancarli, A. Hasegawa, Y. Katoh, A. Kohyama, R. Jones, et al., Issues and advances in SiC f /SiC composites development for fusion reactors, J. Nucl. Mater (2004) [11] Q. Huang, M. Zhang, Z. Zhu, S. Gao, Y. Wu, Y. Li, et al., Corrosion experiment in the first liquid metal LiPb loop of China, Fusion Eng. Des. 82 (2007) [12] M. Zhang, Q. Huang, Y. Wu, Z. Zhu, S. Gao, Y. Song, et al., Corrosion behavior of CLAM in liquid LiPb Alloy at 480 C, Mater. Sci. Forum (2007) [13] S. Gao, M. Zhang, Z. Zhu, Q. Huang, C. Li, Y. Li, et al., Preliminary experiment study on the corrosion of China low activation martensitic steel in liquid lithium lead, Chin. J. Nucl. Sci. Eng. 27 (2007) [14] G. Benamati, C. Fazio, I. Ricapito, Mechanical and corrosion behaviour of EURO- FER 97 steel exposed to Pb-17Li, J. Nucl. Mater (2002) [15] H. Feuerstein, H. Grabner, J. Oschinski, S. Horn, Compatibility of refractory metals and beryllium with molten Pb-17Li, J. Nucl. Mater (1996) [16] H. Glasbrenner, J. Konys, Z. Voß, Corrosion behaviour of low activation steels inflowing Pb-17Li, J. Nucl. Mater. 281 (2000) [17] K. Splichal, M. Zmitko, Corrosion behaviour of EUROFER in Pb-17Li at 500 C, J. Nucl. Mater (2004)