Journal of the Korean Electrochemical Society (전기화학회지)

The Korean Electrochemical Society (한국전기화학회)
권호 표지
DOI QR코드

DOI QR Code

Electrolytic Reduction of 1 kg-UO2 in Li2O-LiCl Molten Salt using Porous Anode Shroud

Li2O-LiCl 용융염에서의 다공성 양극 슈라우드를 이용한1kg 우라늄산화물의 전해환원

  • Received : 2015.07.20
  • Accepted : 2015.08.25
  • Published : 2015.08.31
Download PDF
⟨ Previous Next ⟩

Abstract

The platinum anode for the electrolytic reduction process is generally surrounded by a nonporous ceramic shroud with an open bottom to offer a path for $O_2$ gas produced on the anode surface and prevent the corrosion of the electrolytic reducer. However, the $O^{2-}$ ions generated from the cathode are transported only in a limited fashion through the open bottom of the anode shroud because the nonporous shroud hinders the transport of the $O^{2-}$ ions to the anode surface, which leads to a decrease in the current density and an increase in the operation time of the process. In the present study, we demonstrate the electrolytic reduction of 1 kg-uranium oxide ($UO_2$) using the porous shroud to investigate its long-term stability. The $UO_2$ with the size of 1~4mm and the density of $10.30{\sim}10.41g/cm^3$ was used for the cathode. The platinum and 5-layer STS mesh were used for the anode and its shroud, respectively. After the termination of the electrolytic reduction run in 1.5 wt.% $Li_2O-LiCl$ molten salt, it was revealed that the U metal was successfully converted from the $UO_2$ and the anode and its shroud were used without any significant damage.

사용후핵연료 재활용을 위한 파이로프로세싱의 전해환원 공정에서는 $Li_2O-LiCl$ 용융염을 전해질로 사용하며 금속산화물 형태의 사용후핵연료를 음극, 백금을 양극으로 사용하여 금속전환체를 제조한다. 따라서, 음극에서는 금속산화물이 금속으로 전환되는 환원반응으로 인해 산소 이온이 생성되고, 양극에서는 그 산소이온이 산소 가스가 되는 산화반응이 발생한다. $650^{\circ}C$의 운전 온도에서 발생하는 양극의 산소 가스로 인한 금속 재질 장치의 부식을 막기 위해 양극을 둘러싸는 슈라우드(shroud)를 사용해 산소 가스를 포집하여 전해질로의 확산을 막는 동시에 장치 외부로 배출되도록 한다. 기존에는 슈라우드 자체의 부식과 산소 가스의 염 내 확산을 방지하기 위하여 세라믹을 사용하였으나 비다공성 재질로 인해 산소 이온의 백금 표면으로의 이동 경로를 제한하여 공정의 속도를 좌우하는 전류 크기를 낮춘다는 문제점이 있었다. 이러한 문제를 극복하기 위하여 스테인레스 스틸 mesh로 구성된 다공성 슈라우드의 사용이 수 그램 규모 실험을 통해 제안된 바 있다. 본 연구에서는 킬로그램 규모의 우라늄산화물 전해환원 운전을 통해 다공성 슈라우드의 안정성을 확인 하고자 하였다. 음극의 우라늄산화물로는 크기 1~4 mm, 밀도 $10.30{\sim}10.41g/cm^3$의 파쇄 펠렛 1 kg이 사용되었으며, 백금 전극과 다공성 슈라우드가 포함된 양극 모듈을 사용하였다. 전해환원 종료후 음극에서 우라늄 금속이 성공적으로 얻어졌으며, 백금 양극 및 다공성 슈라우드도 손상 없이 안정하게 사용되었다. $650^{\circ}C$에서의 LiCl의 점도와 동일한 물과 에틸렌글리콜의 혼합물에서 산소 가스를 주입하여 확인 결과 산소 버블이 다공성 슈라우드 외부로 유출되는 것은 관찰되지 않았다.

Keywords

References

  1. IAEA, International Status and Prospects of Nuclear Power (2008).
  2. IAEA, Spent Fuel Reprocessing Options, IAEATECDOC-1587 (2008).
  3. J. L. Willit, W. E. Miller and J. E. Battles, 'Electrorefining of uranium and plutonium - a literature review' J. Nucl. Mater., 195, 229 (1992). https://doi.org/10.1016/0022-3115(92)90515-M
  4. J. J. Laidler, J. E. Battles, W. E. Miller, J. P. Ackerman and E. L. Carls, 'Development of pyroprocessing technology' Prog. Nucl. Energ., 31, 131 (1997). https://doi.org/10.1016/0149-1970(96)00007-8
  5. R. W. Benedict and H. F. McFarlane, 'EBR-II spent fuel treatment demonstration project status' Radwaste Magazine, 5, 23 (1998).
  6. E. J. Karell and K. V. Gourishankar, 'Separation of actinides from LWR spent fuel using molten salt based electrochemical process' Nucl. Technol., 136, 342 (2001). https://doi.org/10.13182/NT136-342
  7. J. Konings, R. J. M. Serp, R. Malmbeck, J. Rebizant, C. Scheppler and J.-P. Glatz, 'Electrochemical behavior of plutonium ion in LiCl-KCl eutectic melts' J. Electroanal. Chem., 561, 143 (2004). https://doi.org/10.1016/j.jelechem.2003.07.027
  8. K. M. Goff, R. W. Benedict, K. L. Howden, G. M. Teske and T. A. Johnson, "Pyrochemical treatment of spent nuclear fuel", 364, Proc. of global 2005, Japan (2005).
  9. T. Inoue and L. Koch, 'Development of pyroprocessing and its future direction' Nucl. Eng. Technol., 40, 183 (2008). https://doi.org/10.5516/NET.2008.40.3.183
  10. M. F. Simpson and S. D. Herrmann, 'Modeling the pyrochemical reduction of spent $UO_2$ fuel in a pilot-scale reactor' Nucl. Technol., 162, 179 (2008). https://doi.org/10.13182/NT162-179
  11. J.-H. Yoo, C.-S. Seo, E.-H. Kim and H. Lee, 'A conceptual study of pyroprocessing for recovering actinides' Nucl. Eng. Technol., 40, 581 (2008). https://doi.org/10.5516/NET.2008.40.7.581
  12. S. Kitawaki, T. Shinozaki, M. Fukushima, T. Usami, N. Yahagi and M. Kurata, 'Recovery of U-Pu alloy from MOX using pyroprocess series' Nucl. Technol., 162, 118 (2008). https://doi.org/10.13182/NT08-A3937
  13. T. Koyama, Y. Sakamura, T. Ogata and H. Kobayashi, "Pyroprocess and metal fuel development for closing actinide fuel cycle with reduced waste burden", 40, Proc. of Global 2009, France (2009).
  14. T. Murakami, K. Uozumi, Y. Sakamura, M. Iizuka, H. Ohta, T. Ogata and T. Koyama, "Recent achievements and remaining challenges on pyrochemical reprocessing in CRIEPI", Proc. of the First ACSEPT International Workshop Lisbon, Portugal (2010).
  15. K.-C. Song, H. Lee, J.-M. Hur, J.-G. Kim, D.-H. Ahn and Y.-Z. Cho, 'Status of pyroprocessing technology development in Korea', Nucl. Eng. Technol., 42, 131 (2010). https://doi.org/10.5516/NET.2010.42.2.131
  16. T. Inoue, T. Koyama and Y. Arai, 'State of the art of pyroprocessing technology in Japan' Energy Procedia, 7, 405 (2011). https://doi.org/10.1016/j.egypro.2011.06.053
  17. K. Nagarajan, B. Prabhakara Reddy, S. Ghosh, G. Ravisankar, K. S. Mohandas, U. Kamachi Mudali, K. V. G. Kutty, K. V. Kasi Viswanathan, C. Anand Babu, P. Kalyanasundaram, P. R. Vasudeva Rao and B. Raj, 'Development of pyrochemical reprocessing for spent metal fuels' Energy Procedia, 7, 405 (2011). https://doi.org/10.1016/j.egypro.2011.06.053
  18. K. M. Goff, J. C. Wass, K. C. Marsden and G. M. Teske, 'Electrochemical reprocessing of used nuclear fuel' Nucl. Eng. Technol., 43, 335 (2011). https://doi.org/10.5516/NET.2011.43.4.335
  19. H. Lee, G.-I. Park, K.-H. Kang, J.-M. Hur, J.-G. Kim, D.-H. Ahn, Y.-Z. Cho and E. H. Kim, 'Pyroprocessing technology development at KAERI' Nucl. Eng. Technol., 43, 317 (2011). https://doi.org/10.5516/NET.2011.43.4.317
  20. G. Z. Chen, D. J. Fray and T. W. Farthing, 'Direct electrochemical reduction of titanium dioxide to titanium in molten calcium chloride' Nature, 407, 361 (2000). https://doi.org/10.1038/35030069
  21. K. Yasuda, T. Nohira, R. Hagiwara and Y. H. Ogata, 'Direct electrolytic reduction of solid $SiO_2$ in molten $CaCl_2$ for the production of solar grade silicon' Electrochim. Acta, 53, 106 (2007). https://doi.org/10.1016/j.electacta.2007.01.024
  22. S. M. Jeong, J. Y. Jung, C. S. Seo and S. W. Park, 'Characteristics of an electrochemical reduction of $Ta_2O_5$ for the preparation of metallic tantalum in a $LiCl-Li_2O$ molten salt' J. Alloy Compd., 440, 210 (2007). https://doi.org/10.1016/j.jallcom.2006.05.139
  23. S. I. Wang, G. M. Haarberg and E. Kvalheim, 'Electrochemical behavior of dissolved $Fe_2O_3$ in molten $CaCl_2-KF$' J. Iron Steel Res. Int., 16, 48 (2008).
  24. M. Gibilaro, J. Pivato, L. Cassayre, L. Massot, L. P. Chamelot and P. Taxil, 'Direct electroreduction of oxides in molten fluoride salts' Electrochim. Acta, 56, 5410 (2011). https://doi.org/10.1016/j.electacta.2011.02.109
  25. D. Wang, G. Qiu, X. Jin, X. Hu and G. Z. Chen, 'Electrochemical metallization of solid terbium oxide' Angew. Chem. Int. Edit., 45, 2384 (2006). https://doi.org/10.1002/anie.200503571
  26. X. Y. Yan and D. J. Fray, 'Production of niobium powder by direct electrochemical reduction of solid $Nb_2O_5$ in a eutectic $CaCl_2$-NaCl melt' Metall. Mater. Trans. B, 33, 685 (2002). https://doi.org/10.1007/s11663-002-0021-6
  27. Q. Xu, L.-Q. Deng, Y. Wu and T. Ma, 'A study of cathode improvement for electro-deoxidation of $Nb_2O_5$ in a eutectic $CaCl_2$-NaCl melt at 1073K' J. Alloy Compd., 396, 288 (2005). https://doi.org/10.1016/j.jallcom.2005.01.002
  28. S. M. Jeong, H. Y. Yoo, J.-M. Hur and C.-S. Seo, 'Preparation of metallic niobium from niobium pentoxide by an indirect electrochemical reduction in a $LiCl-Li_2O$ molten salt' J. Alloy Compd., 452, 27 (2008). https://doi.org/10.1016/j.jallcom.2007.02.057
  29. G. Z. Chen, E. Gordo and D. J. Fray, 'Direct electrolytic preparation of chromium powder' Metall. Mater. Trans. B, 35, 223 (2004). https://doi.org/10.1007/s11663-004-0024-6
  30. E. Gordo, G. Z. Chen and D. J. Fray, 'Toward optimisation of electrolytic reduction of solid chromium oxide to chromium powder in molten chloride salts' Electrochim. Acta, 49, 2195 (2004). https://doi.org/10.1016/j.electacta.2003.12.045
  31. B. Claux, J. Serp and J. Fouletier, 'Electrochemical reduction of cerium oxide into metal' Electrochim. Acta, 56, 2771 (2011). https://doi.org/10.1016/j.electacta.2010.12.040
  32. A. M. Abdelkader, K. Tripuraneni Kilby, A. Cox and D. J. Fray, 'DC Voltammetry of Electro-deoxidation of Solid Oxides' Chem. Rev., 113, 2863 (2013). https://doi.org/10.1021/cr200305x
  33. D. Wang, X. Jina and G. Z. Chen, 'Solid state reactions: an electrochemical approach in molten salts' Annu. Rep. Prog. Chem., Sect. C, 104, 189 (2008). https://doi.org/10.1039/b703904m
  34. Y. Sakamura, M. Kurata and T. Inoue, 'Electrochemical reduction of $UO_2$ in molten $CaCl_2$ or LiCl' J. Electrochem. Soc., 153, D31 (2006). https://doi.org/10.1149/1.2160430
  35. E.-Y. Choi, J. W. Lee, J. J. Park, J.-M. Hur, J.-K. Kim, K. Y. Jung and S. M. Jeong, 'Electrochemical reduction behavior of a highly porous SIMFUEL particle in a LiCl molten salt' Chem. Eng. J., 207, 514 (2012).
  36. E.-Y. Choi, J.-K. Kim, H.-S. Im, I.-K. Choi, S.-H. Na, J. W. Lee, S. M. Jeong and J.-M. Hur, 'Effect of the $UO_2$ form on the electrochemical reduction rate in a $LiCl-Li_2O$ molten salt' J. Nucl. Mater., 437, 178 (2013). https://doi.org/10.1016/j.jnucmat.2013.01.306
  37. E.-Y. Choi, J.-M. Hur, I.-K. Choi, S. G. Kwon, D.-S. Kang, S. S. Hong, H.-S. Shin, M. A. Yoo and S. M. Jeong, 'Electrochemical reduciton of porous 17 kg uranium oxide pellets by selection of an optimal cathode/anode surface area ratio' J. Nucl. Mater., 418, 87 (2011). https://doi.org/10.1016/j.jnucmat.2011.08.001
  38. E.-Y. Choi, C. Y. Won, J.-S. Cha, W. Park, H.-S. Im, S. S. Hong and J.-M. Hur, 'Electrochemical reduction of $UO_2$ in $LiCl-Li_2O$ molten salt using porous and nonporous anode shrouds' J. Nucl. Mater., 444, 261 (2014). https://doi.org/10.1016/j.jnucmat.2013.09.061

Cited by

  1. A preliminary study of pilot-scale electrolytic reduction of UO 2 using a graphite anode vol.49, pp.7, 2017, https://doi.org/10.1016/j.net.2017.05.004