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  1. Center for Advanced Energy Studies Computational and Experimental Studies of the Mark-IV Electrorefiner for Treatment of Used Nuclear Fuel Robert O. Hoover Michael F. Simpson Supathorn Phongikaroon Tae-Sic Yoo - Dept. of Chemical and Materials Engineering - Pyroprocessing Technology Dept. - University of Idaho, Idaho Falls - Idaho National Laboratory A research partnership between Boise State University, Idaho National Laboratory, Idaho State University and University of Idaho. November 16, 2011 CAES Colloquia Idaho Falls, ID

  2. Outline • Introduction • EBR-II Used Fuel Treatment Process & Mark-IV Electrorefiner • Mark-IV ER Computational Model • Motivation • Fundamental Theory • GUI Demonstration • 2D Distributions • Model Results • Electrochemical Zr Recovery • Motivation • Experimental Setup • Transparent Testing • Experimental Procedure • Results • Summary & Future Work

  3. Introduction • The Experimental Breeder Reactor-II (EBR-II) was a metallic fueled, sodium cooled fast reactor operated at Argonne National Laboratory-West (currently Idaho National Laboratory) from 1963-1994. • This reactor was fueled with a sodium- bonded, uranium-zirconium alloy fuel. • An electrochemical process was developed by Argonne National Laboratory to treat this stainless steel clad driver fuel. • This electrochemical process is currently being used at Idaho National Laboratory to treat the used EBR-II driver fuel. [a] S.X. Li & M.F. Simpson, Journal of Minerals & Metallurgical Processing, 22(4), 192-198 (2005).

  4. EBR-II Used Fuel Treatment Process Mark-IV Electrorefiner: Heart of the used fuel treatment process

  5. Mark-IV Electrorefiner (ER) • Sodium metal reacts with UCl3 to form NaCl. • 3Na + UCl3 3NaCl + U • Anode Basket • U  U3+ + 3e- • Cathode: U • U3+ + 3e-  U

  6. Modeling Motivation • Part of a joint International-Nuclear Energy Research Initiative (I-NERI) project. • Rigorous 3D model – Korea Atomic Energy Research Institute & Seoul National University • Simpler 2D model – Idaho National Laboratory & University of Idaho • Applied fundamental theories in: • Electrochemistry, thermodynamics, and kinetics. • Reactions and mass transfer across many different interfaces with the ER. • An invaluable tool • Optimizing operating parameters and • Determining the effect of different fuel inputs

  7. Fundamental Theory • Current due to surface overpotentials • Sum of partial currents • Total electrode potential • Equilibrium potential of half-cell reaction • Concentration of species i at electrode surface • Molar mass transfer of species i • Partial current

  8. Mathematical Method Guessing Variables Variables known from thermodynamic data and/or operating conditions Constraints: (1) Iij(Eij) = Iij(ηi,sj) (2) Etj = Eij + ηi,sj (3) ∑Iij = Icell

  9. Operating Parameters [a] S.X. Li and M.F. Simpson, Minerals and Metallurgical Processing, 22(4), 192 (2005). [b] M. Eisenberg, C.W. Tobias, Journal of the Electrochemical Society, 101, 305 (1954). [c] O. Shirai, H. Yamana, and Y. Arai, Journal of Alloys and Compounds, 408-412, 1267 (2006). [d] J.J. Roy, et. al, Journal of the Electrochemical Society, 143(8), 2487 (1996). [e] P. Masset, et. al, Journal of the Electrochemical Society, 152(6), A1109-A1115 (2005). [f] R.K. Ahluwalia, T.Q. Hua, and H.K. Geyer, Nuclear Technology, 133, 103-118 (2001).

  10. GUI Demonstration

  11. 2D Distributions – Model Development • Material Balance • Current Distribution Electroneutrality Movement of Ions

  12. 2D Distributions – Model Development • Species Flux • Laplace equation – potential distribution Ohm’s Law – Current Distribution

  13. Computational Procedure • Mark-IV ER Geometry • Four fuel dissolution baskets form each anode. • These anodes have unchanging geometry. • Cathode becomes coated with dendrites. • Radius grows as product is deposited. • All electrodes rotate and are modeled as smooth cylinders. Cathode Anode 1 Anode 2 Stirrer Baffles

  14. Computational Procedure • The outer shell, baffles, and stir rod are electrically insulated from the electrolyte. • Neumann boundary condition • Anodes and Cathode • Total: Φ = Et,a and Et,c • Boundary Conditions Φ = Et,c Φ = Et,a

  15. Computational Procedure • Mesh Generation • Current Distribution • Governing Equation • Conductivity

  16. GUI Results

  17. Anode Results • Model and experimental data match well with RMS error of 1.83%. • At the end of process, experimental potential flattens out, which is not captured by the model. • Plutonium is rapidly exhausted from the anode. • Uranium is the primary species being dissolved with zirconium dissolution increasing in relevance throughout.

  18. Cathode Results • Cathode data matches with an RMS error of 3.79%. • Cathode is modeled as a smooth cylinder. • There is no plutonium reduction. • Uranium deposition predominates with increasing zirconium reduction. • Zirconium deposition at the cathode depends upon the extent of zirconium dissolution at the anode.

  19. Primary Distributions Potential (V vs. Ag/AgCl) Current Density (A/m2) 10 hours

  20. Secondary Distribution • Ohmic and surface overpotentials • Boundary Condition: • Butler-Volmer Kinetics • Total Cathode Boundary Condition

  21. Secondary Distributions Potential Gradient Potential, Φ • Ohmic and surface overpotentials dominate. • Due to symmetry, half the ER is modeled. • Majority of current at the cathode flows directly opposite anode.

  22. Tertiary Distribution • Ohmic, surface, and concentration overpotentials • Boundary Condition: • Modified Butler-Volmer Kinetics • Concentration at the electrode surface depends upon : • Total Cathode Boundary Condition

  23. Tertiary Distribution Potential Gradient Potential, Φ • Ohmic, surface, and concentration overpotentials dominate. • Due to symmetry, half the ER is modeled. • Current is much more uniform around the cathode.

  24. Distribution Validation • Due to availability of Mark-IV data, the developed code has been modified using the same fundamental approach to reconstruct work published by Low et al. (2007)h on the deposition of copper from an aqueous Cu2SO4 solution in a Rotating Cylinder Hull (RCH) cell. • Modeled Two-Dimensional Region: Cu2+ (electrolyte) + 2e- Cu (cathode) Cathode: working electrode [h] C.T.J. Low, E.P.L. Roberts, and F.C. Walsh, Electrochimica Acta, 52, 3831-3840 (2007). Anode: counter electrode

  25. RCH Distribution Calculations • Laplace Equation • Non-electrode insulating boundaries • Neumann boundary condition • Counter electrode (Anode) boundary condition • Uniform at applied current density • Working electrode (Cathode) boundary condition • Depends upon importance of overpotentials

  26. Working Electrode Boundary Conditions • Primary • Ohmic overpotential • Secondary • Ohmic & surface overpotentials • Tertiary • Ohmic, surface, & concentration overpotentials

  27. Primary Current Distribution • Dimensionless Current Distribution at 750 rpm • Equation Fit obtained from the 2D model: Data from Low et al. (2007)h Theoretical analysis from Madore et al. (1992)j. Model from Low et al. (2007)h [h] C.T.J. Low, E.P.L. Roberts, and F.C. Walsh, Electrochimica Acta, 52, 3831-3840 (2007). [j] C. Madore, M. Matlosz, D. Landolt, J. Appl. Electrochem., 22(12), 1155 (1992).

  28. Secondary Current Distribution • Dimensionless Current Distribution at 1300 rpm Current Work Low et al. (2007)h [h] C.T.J. Low, E.P.L. Roberts, and F.C. Walsh, Electrochimica Acta, 52, 3831-3840 (2007).

  29. Tertiary Current Distribution Low, et al. (2007)h • Current Distribution at 750 rpm Current Work KAERI/SNU Work [h] C.T.J. Low, E.P.L. Roberts, and F.C. Walsh, Electrochimica Acta, 52, 3831-3840 (2007).

  30. Working Electrode Tertiary Current Distribution Comparison • The closer the data lies to the diagonal, the better the two sets of calculated data match. • Both data lie close to the diagonal. • The US 2D data tends to be slightly under the diagonal indicating that it slightly underpredicts the data calculated by KAERI’s 3D model. • There is more noise in the calculated data at higher current density.

  31. EBR-II Used Fuel Treatment Process

  32. Mark-IV Electrorefiner (ER) • Normal Operation • Cathode: U • U3+ + 3e-  U • Zr Recovery • Cathode: Zr • Zr4+ + 4e- Zr • Normal Operation • Anode Basket • U  U3+ + 3e- • Zr Recovery • Cd Pool Anode • Zr  Zr4+ + 4e-

  33. Zr Recovery Motivation • Zirconium constitutes a large amount of the EBR-II used driver fuel at greater than 10 wt%. • In the electrochemical modeling process, diffusion is a very important factor in the mass transfer both from the anode and to the cathode. • Diffusion coefficient data in the molten LiCl/KCl eutectic is either very sparse or highly variable in the literature depending on the species of interest. A = Electrode surface area Cb = Bulk concentration Cs = Surface concentration D = Diffusion coefficient F = Faraday’s constant I = Current z = Species charge δ = Diffusion layer [e] P. Masset, et al.,J. of the Electrochem. Soc., 152(6), A1109-A1115 (2005). [k] C.E. Thalmayer, et al., J. Inorg. Nucl. Chem., 26, 347-357 (1964). [m] D. Yamada, et al., J. of Alloys and Compounds, 444-445, 557-560 (2007). [n] G.J. Janz & N.P. Bansal, J. of Phys. and Chem. Ref. Data, 11(3), 505-693 (1982).

  34. Experimental Setup Fumehood • Thermocouple • Pt/Pt(II) quasi-reference electrode • Tantalum working electrode • Liquid cadmium counter electrode lead • Stainless steel tube for Ar purge • Magnesia or quartz crucible • Eutectic LiCl/KCl salt containing ZrCl4 • Cd-Zr pool (a) (b) (c) (d) (e) (f) (g) (h)

  35. Transparent Setup 51.57g LiCl/KCl salt 86.51 g cadmium Custom built Thermcraft furnace Quartz viewing windows 1700 W

  36. Transparent Testing • 500 °C • Quartz crucible • LiCl/KCl Eutectic Salt • 59/41 mol% • 45/55 wt% • LiCl: 99.99% • Rare Earth Products, Inc. • KCl: 99.999% • Rare Earth Products, Inc. • Cadmium metal • 99.95% Alfa Aesar • Al2O3 sheathed tantalum • 99.95% Alfa Aesar • 1.0 mm diameter 2 cm 0.7 cm

  37. Experimental Setup Cathode (WE) Anode (CE) Thermocouple Argon purge Reference Electrode • Working and counter electrodes • Alumina sheathed tantalum • Reference Electrode (Quasi) • Platinum: Pt(II)/Pt [p] [p] R.J. Gale & D.G. Lovering, Molten Salt Techniques, Vol. 2, p. 152, Plenum Press, New York (1984).

  38. Experimental Procedure Ar • Glovebox: Ar atmosphere • Weighed and loaded into MgO crucible: • Zr: 2.10 g 99.8% Alfa Aesar • Cd: 59.67 g 99.95% Alfa Aesar • LiCl: 14.05 g 99.99% Rare Earth Products • KCl: 17.17 g 99.999% Rare Earth Products • CdCl2: 1.54 g 99.996% Alfa Aesar • Fumehood • Crucible loaded into Ar purged furnace. • Heated to 500 °C. • Zr + 2CdCl2 ZrCl4 + 2Cd DG = -192.6 kJ/mol • Electrodes lowered into crucible and attached to potentiostat. • PAR VersaSTAT 4 potentiostat with VersaStudio software • Chronoamperometry run with potential stepped to -2.0 V and current recorded vs. time. LiCl, KCl, & ZrCl4 (3 wt%) Cd & Zr

  39. Chronoamperometryq • Diffusion equation: Fick’s second law • At a large potential, surface concentration becomes zero • Boundary Conditions • C(r0,t) = 0 • C(∞,t) = Cb • C(r,0) = Cb • Solution: Corrected Cottrell equationr • From this, and experimental current vs. time, diffusion coefficient, D, can be found. D = Diffusion Coefficient C = Concentration r = Distance from Electrode Surface t = time Cb Ion Concentration, C i = Current Density z = Ion Charge F = Faraday Constant r0 = Electrode radius Distance from Electrode, r [q] A.J. Bard & L.R. Faulkner, Electrochemical Methods: Fundamentals and Applications, pp. 162-163, John Wiley & Sons, Inc., New Jersey (2001). [r] N.P. Bansal & J.A. Plambeck, Canadian Journal of Chemistry,56, 155-156 (1978).

  40. Results • Applied Potential: -2.0 V vs. Pt(II)/Pt quasi-reference electrode • Two runs performed • Slopes = 0.19 & 0.14 • Intercepts = 0.82 & 0.81

  41. Results • Corrected Cottrell Equation with capacitive current • Literature Value • 1.13 10-5 cm2/s [m] [m] D. Yamada, T. Murai, K. Moritani, T. Sasaki, I. Takagi, H. Moriyama, K. Kinoshita, & H. Yamana,Journal of Alloys and Compounds, 444-445, 557-560 (2007).

  42. Summary • A 2D model of anode and cathode reactions occurring in the Mark-IV ER has been developed with calculated and experimental potential trends matching well. • Anode: 1.83% error • Cathode: 3.79% error • Primary, secondary, and tertiary potential and current distributions are calculated. • The model was used to simulate the aqueous deposition of copper in an RCH cell and shown to compare well with the 3D model data calculated by SNU/KAERI. • An experimental setup has been designed to test properties relevant to the electrochemical recovery of zirconium in molten salt. • Through use of a transparent furnace, a proposed method of visually examining the electrochemical process has been developed. • The diffusion coefficient of Zr4+ ions in the molten LiCl/KCl eutectic salt has been experimentally determined using chronoamperometry. • D = 2.06 10-5 cm2/s • This values differs slightly from the only published value of 1.13 10-5 cm2/s, which was determined using a capillary method [m]. [m] D. Yamada, T. Murai, K. Moritani, T. Sasaki, I. Takagi, H. Moriyama, K. Kinoshita, & H. Yamana,Journal of Alloys and Compounds, 444-445, 557-560 (2007).

  43. Future Work • Analysis of Zr-CdCl2 reaction completion/kinetics with ICP-MS data. • Monitor furnace exit gas for oxygen. • Fabricate Ag/AgCl reference electrode. • Further work in experimentally determining the Zr4+ diffusion coefficient via other methods, i.e. chronopotentiometry and/or cyclic voltammetry. • Further electrochemical experiments including chronopotentiometry, cyclic voltammetry, anodic stripping voltammetry, and/or potentiostatic electrodeposition to determine parameters important to the electrochemical recovery of Zr. • Electrodeposition experiments with transparent setup to analyze zirconium deposit morphology. • Experiments to optimize the process of Zr recovery. • Phase II of this work will explore the electrochemical recovery of Zr in the presence of uranium.

  44. Acknowledgements • This work was performed as part of two different I-NERI projects with University of Idaho, Idaho National Laboratory, Seoul National University (SNU), and Korea Atomic Energy Research Institute (KAERI). • I-NERI 2007-006-K: Development of Computational Models for Pyrochemical Electrorefiners of Nuclear Waste Transmutation Systems • I-NERI 2010-001-K: Investigation of Electrochemical Recovery of Zirconium from Spent Nuclear Fuels • Thanks to all those who have helped with this work including, but not limited to • Fellow students: • Riley Cumberland (NCSU), Michael Shaltry, Ammon Williams, and Jessica (JiHyun) Kim • Collaborators at SNU: • Prof. Il-Soon Hwang, Jaeyeong Park, Sungyeol Choi • Collaborators at KAERI: • Dr. Kwang-Rag Kim

  45. Journal Articles • R. Cumberland, R. Hoover, S. Phongikaroon, and M. Yim, Nuclear Engineering and Technology, accepted (2011). • S. Choi, J. Park, R.O. Hoover, S. Phongikaroon, M.F. Simpson, K.R. Kim, and I.S. Hwang, J. of Nucl. Matls., 416, 318-326 (2011). • R.O. Hoover, S. Phongikaroon, M.F. Simpson, and T. Yoo, Nuclear Technology, 173(2), 176-182 (2011). • R.O. Hoover, S. Phongikaroon, S.X. Li, M.F. Simpson, and T. Yoo, Nuclear Technology, 171(3), 276-284 (2010). • S. Phongikaroon, R. Hoover and E. Barker, Ind. & Eng. Chem. Res., 49(6), 2926-2931 (2010). • R. Hoover, S. Phongikaroon, S. Li, M. Simpson, and T. Yoo, J. of Eng. for Gas Turbines and Power, 131(5), 054503 (2009). • Conference Papers/Presentations • J. Park, R. Hoover, M. Kim, K.R. Kim, S. Choi, S. Phongikaroon, M. Simpson, T.S. Yoo, and I.S. Hwang, GLOBAL 2011, Makuhari, Japan, Dec. 11-16, 2011. • R.O. Hoover, S. Phongikaroon, M.F. Simpson, and T.S. Yoo, 2011 ANS Winter Meeting, Washington, D.C., Oct. 31-Nov. 3, 2011. • R.O. Hoover, S. Phongikaroon, M.F. Simpson, and T.S. Yoo, 2010 International Pyroprocessing Research Conference (IPRC), Dimitrovgrad, Russia, Nov. 29-Dec. 3, 2010. • R. Hoover, S. Phongikaroon, M.F. Simpson, and T.S. Yoo, 2010 AIChE Annual Meeting, Salt Lake City, UT, Nov. 7-12, 2010. • R. Hoover, S. Phongikaroon, M.F. Simpson, T. Yoo, and S.X. Li, 2009 ANS Winter Meeting, Washington, DC, Nov. 15-19, 2009. • R. Hoover, S. Phongikaroon, M.F. Simpson, T. Yoo, and S.X. Li, 2009 AIChE Annual Meeting, Nashville, TN, Nov. 8-13, 2009. • R. Hoover, S. Phongikaroon, M.F. Simpson, S.X. Li, and T. Yoo, 2009 International Workshop on Nuclear Pyroprocessing, Jeju Island, Korea, May 19-21, 2009. • R. Hoover, S. Phongikaroon, S.X. Li, M.F. Simpson, and T. Yoo, 2008 IPRC, Jeju Island, Korea, Aug. 24-27, 2008. • R. Hoover, S. Phongikaroon, M.F. Simpson, T. Yoo, and S.X. Li, ICONE 16, Orlando, FL, May 12-15, 2008. • R. Hoover, S. Phongikaroon, M.F. Simpson, S.X. Li, and T. Yoo, 32nd Annual Actinide Separations Conference, Park City, UT, May 12-15, 2008.