Salt chemistry and Redox control Jinsuo Zhang 1,2 1) Virginia Tech - PowerPoint PPT Presentation

Salt chemistry and Redox control Jinsuo Zhang 1,2 1) Virginia Tech 2) Ohio State University

Research Team q PI: Dr. Jinsuo Zhang, Dr. Shaoqiang Guo q Students: Ryan Chesser, Yafei Wang (graduated from OSU, current Ph.D student of VT), Qiufeng Yang, Nik Shay (graduated), Bill Cohen (Graduated), Wentao Zhou (graduated), Evan Wu (graudated) q Visiting Scholar: Dr. Wei Wu All the experimental measurements presented were conducted at The Ohio State University Nuclear Materials and Fuel Nuclear Materials and Fuel 2 Cycle center Cycle center

Salt impurities/source term q Tritium q Noble Gas (Xe, Kr) q Noble metals (Nb, Mo, Tc, Ru, Rh, Ag, Cd, In, Sn, Zn, Ga, Ge, As ) q Halogens (I, Br) q Tellurium Group (Te, Sb, Se) q Barium, Strontium (Ba, Sr) q Rare earth/alkaline metals (Y, La, Ce, Pr, Nd, Pm, Gd, Tb, Dy, Ho, Er, Zr, Sm, Eu, Sr, Ba, Rb, Cs) q Actinide (U, Pu, Np) q Corrosion Products (Ni, Fe, Cr) Nuclear Materials and Fuel Nuclear Materials and Fuel 3 Cycle center Cycle center

What do we have to do q Review the available data q Measure fundamental data of element in the salt and liquid Bi q Develop chemical (redox) control method q Develop and design salt purification system in operation Nuclear Materials and Fuel Nuclear Materials and Fuel 4 Cycle center Cycle center

Measurement-experimental set up q A three-electrode system: working electrode (WE); Count electrode (CE) and Reference electrode (RE). q Glove box (purged with Argon): the O 2 and H 2 O was controlled below 4.0 during all experiments. q Electrochemical technology: CV, EIS, LP, etc q Properties measured: apparent potential, diffusion coefficient, activity coefficient, exchange current, Nuclear Materials and Fuel Nuclear Materials and Fuel 5 Cycle center Cycle center

Determining of reference potential Zone I: 5s current pulse is applied, and the potential of the W electrode becomes more negative due to the formation of a potassium layer on electrode surface. More negative potential at greater current due to the potential drop in electrolyte. 650 ˚ C Zone II: No current applied. Consistent potential represents K + /K potential. 𝐬𝐟𝐞𝐩𝐲 (V vs. Pt) 𝑭 𝐋 + 𝐋 Temperature (°C) Standard Deviation (mV) ⁄ Zone III: Potential returns back 650 -1.272 3.2 due to dissolution of K. 700 -1.270 2.9 750 -1.271 4.6 Electrolyte resistance of 0.12 Ω∙cm 2 at 650 ˚ C, 0.11 Ω∙cm 2 at 700 ˚ C and 0.09 Ω∙cm 2 at 750 ˚ C Nuclear Materials and Fuel Nuclear Materials and Fuel 6 Cycle center Cycle center

Measured CV signal Nuclear Materials and Fuel Nuclear Materials and Fuel 7 Cycle center Cycle center

Diffusion coefficient and Apparent potential of Dy and La Diffusion activation energy: 51.5 kJ/mol for Dy 3+ , 127 kJ/mol for La 3+ Both diffusion coefficient and apparent potential increases with temperature Nuclear Materials and Fuel Nuclear Materials and Fuel 8 Cycle center Cycle center

Fundamental data of Corrosion Products Nuclear Materials and Fuel Nuclear Materials and Fuel 9 Cycle center Cycle center

Exchange current density of Fe and Cr • Activation energy: 94.42 kJ/mol for Cr/Cr 2+ , and 87.69 kJ/mol for Fe/Fe 2+ in molten FLiNaK Nuclear Materials and Fuel Nuclear Materials and Fuel 10 Cycle center Cycle center

Redox Control q Cover gas control method q Metal control method q Dissolved salt control method q Refueling control method q Cathodic protection Nuclear Materials and Fuel Nuclear Materials and Fuel 11 Cycle center Cycle center

Dissolved Salt control method Tungsten electrode, 700 ˚ C, FLiNaK-EuF 3 -EuF 2 , 200 mV/s Nuclear Materials and Fuel Nuclear Materials and Fuel 12 Cycle center Cycle center

� Concentration ratio of Eu 3+ /Eu 2+ • Randles-Sevcik equation is not valid for system containing both members (e.g., both U 4+ and U 3+ )) of the redox couple: ./0 𝑗 " = 0.4463𝑜𝐺𝐷 , 𝐸 ./0 𝑜𝐺𝑤 𝑆𝑈 • Theory developed by Keightley et al. are adopted [1]: ./0 ./0 + 𝐷 , =>? ./0 789 𝐸 789 ;< 𝐸 ;< • 𝚥 ⃗ = 𝑜𝐺 𝐷 , 𝜓 𝜊; 𝜊 E @A ./0 ./0 + 𝐷 , =>? ./0 789 𝐸 789 ;< 𝐸 ;< [𝜓 2𝜊 I − 𝜊, 𝜊 E − • 𝚥 ⃖ = 𝑜𝐺 𝐷 , @A 𝜓 2𝜊 I − 𝜊, 𝜊 I − 𝜓 −𝜊, 𝜊 I ] 9 P/Q . RYZ Z • where 𝜓 𝑦, 𝛽 = tanh − tanh( 0 ) ; 𝜊 = 𝑜𝐺(𝐹 − 𝐹 ./0 )/𝑆𝑈 9R P/Q 0 S 0 [1] A.M. Keightley, et al, J. Electroanal. Chem. 322 (1992) 25-54. Nuclear Materials and Fuel Nuclear Materials and Fuel 13 Cycle center Cycle center

Determined concentration ratio Predicted coordinates of cyclic voltammetric peaks and the calculated concentration ratio. 𝒐𝑮 𝑫 𝐅𝐯 𝟑+ 𝑫 𝐅𝐯 𝟒+ .𝑬 𝐅𝐯 𝟑+ 0𝒋 𝒒 0 𝑺𝑼 𝑫 𝐅𝐯𝟒+ 𝒐𝑮 𝒅 ) 𝑺𝑼 (𝑭 𝟐/𝟑 − 𝑭 𝒒 𝑫 𝒄 . 𝑺𝑼 ∆𝑭 𝐪 𝑫 𝐅𝐯𝟑+ † Test # 𝑬 𝐅𝐯 𝟒+ 𝒐 𝟒 𝑮 𝟒 𝒘𝑬 𝒄 - 2.236 0 0.4463 1.109 - 650°C #1 2.814 1.31 0.5415 1.697 1.21 650°C #2 3.102 2.13 0.5596 1.988 1.96 650°C #3 3.075 2.04 0.5581 1.959 1.88 700°C #1 2.855 1.42 0.5447 1.741 1.29 700°C #2 3.067 2.02 0.5578 1.953 1.83 700°C #3 3.119 2.18 0.5605 2.003 1.98 750°C #1 2.740 1.13 0.5356 1.623 1.08 750°C #2 2.674 0.98 0.5299 1.558 0.93 750°C #3 2.842 1.39 0.5439 1.729 1.33 †Calculated by the determined diffusion coefficient. Nuclear Materials and Fuel Nuclear Materials and Fuel 14 Cycle center Cycle center

XPS examination • Eu 3+ /Eu 2+ ratio ≈ 2:1 Nuclear Materials and Fuel Nuclear Materials and Fuel 15 Cycle center Cycle center

Formal potential for Eu 3+ /Eu 2+ P 𝐹 ∗ = 𝐹 ./0 + @A ` ab Q • => 𝑚𝑜 ` cde Table Summary of formal standard potential from this work and references Total concentration of E * (V vs. F 2 /F - ) Temperature ( ° C) Salt Source Eu in salt 550 -3.94 or -3.82 † FLiNaK 0.072 mol/kg [1] 650 -3.836 ± 0.005 FLiNaK 0.048 mol/kg This work 700 -3.787 ± 0.009 FLiNaK 0.048 mol/kg This work 750 -3.732 ± 0.006 FLiNaK 0.048 mol/kg This work 800 -3.53 ± 0.01 LiF-CaF 2 0.100 mol/kg [2] 820 -3.46 ± 0.01 LiF-CaF 2 0.100 mol/kg [2] 840 -3.40 ± 0.01 LiF-CaF 2 0.100 mol/kg [2] 870 -3.33 ± 0.01 LiF-CaF 2 0.100 mol/kg [2] [1] W. Huang, et al. Electrochimi. Acta 147 (2014) 114-120. [2] L. Massot, et al. Electrochimi. Acta 54 (2009) 6361-6366 Nuclear Materials and Fuel Nuclear Materials and Fuel 16 Cycle center Cycle center

Redox potential window • Solid line: metal dissolution at limit activity of 10 -6 • Dotted line: reduction of oxidants. HF/H 2 =0.1: a mole ratio of HF/H 2 =0.1 at 1 atm total pressure • Double solid line: redox potential calculated based on measured apparent potential. All potentials calculated based on ∆𝐻 ° • of fluorides at supercooled state except gaseous MoF 5 , MoF 6 , WF 6 , and HF. Nuclear Materials and Fuel Nuclear Materials and Fuel 17 Cycle center Cycle center

Acceleration mechanisms of Cr Dissolution q Galvanic Corrosion q Direct reduction of Cr 2+ Anode: Cr (alloy 1) → Cr 0Y + 2e s Cathode (Ni): Cr 0Y + 2e s → Cr (alloy 2) Cathode (graphite): Cr 0Y + 3 7 C + 2e s → 1 7 Cr v C w q Disproportionation reaction of Cr 2 + Schematic of the direct reduction of the corrosion 3Cr 0Y → 2Cr wY + Cr products on the cathode during galvanic corrosion. Ox 3Cr 0Y + 3 7 C → 2Cr wY + 1 represents the residual 7 Cr v C w oxidants. Nuclear Materials and Fuel Nuclear Materials and Fuel 18 Cycle center Cycle center

Salt Purification Method q Bi-Li Extractor q Sacrificial Electrode Nuclear Materials and Fuel Nuclear Materials and Fuel 19 Cycle center Cycle center

Available Fundamental data in Liquid Nuclear Materials and Fuel Nuclear Materials and Fuel 20 Cycle center Cycle center

More fundamental data development based on phase diagram model Bi-Ce Nuclear Materials and Fuel Nuclear Materials and Fuel 21 Cycle center Cycle center

Fundamental data of Fission products in liquid Bi-Enthalpy of mixing Bi-Ce Nuclear Materials and Fuel Nuclear Materials and Fuel 22 Cycle center Cycle center

Activity coefficient of Fission products in liquid 873 K 973 K 923 K Nuclear Materials and Fuel Nuclear Materials and Fuel 23 Cycle center Cycle center

Purification model for Using Bi-Li ‚ 𝑜 E 𝑌 ~ • Š ‚ 𝐸 •E − 𝑌 •E • ‚ €•• 𝑍 •E | = 𝐶𝑗 „……† + 𝑇𝑏𝑚𝑢 „……† 𝐸 ~ • 𝐶𝑗 „……† + 𝑇𝑏𝑚𝑢 „……† 𝐸 •E E‹. Nuclear Materials and Fuel Nuclear Materials and Fuel 24 Cycle center Cycle center

One Example Nuclear Materials and Fuel Nuclear Materials and Fuel 25 Cycle center Cycle center

E-pO 2- diagram development Cerium species in LiF-BeF2 at 723K 0 -0.5 -1 Ce2O3 -1.5 CeF3 E(V) -2 -2.5 Ce -3 -3.5 -4 -2 0 2 4 6 8 10 12 14 pO (2-) Plutonium species in LiF-BeF2 at 723K 0 -0.5 PuF3 -1 Pu2O3 700C in FLiBe. 𝒃 𝐍 𝐨• of 10 -6 is used for the -1.5 calculation of related equilibrium lines E(V) -2 -2.5 Pu -3 Nuclear Materials and Fuel Nuclear Materials and Fuel -3.5 26 Cycle center Cycle center -4 -2 0 2 4 6 8 10 12 14 pO (2-)