SELECTIVE REDUCTION OF ACTIVE METAL CHLORIDES FROM MOLTEN LiCl-KCl USING LITHIUM DRAWDOWN

MICHAEL F. SIMPSON 한국원자력학회 2012 Nuclear Engineering and Technology Vol.44 No.7

In support of optimizing electrorefining technology for treating spent nuclear fuel, lithium drawdown has been investigated for separating actinides from molten salt electrolyte. Drawdown reaction selectivity is a major issue that requires investigation,since the goal is to remove actinides while leaving the fission products and other components in the salt. A series of lithium drawdown tests with surrogate fission product chlorides was run to obtain selectivity data with non-radioactive salts, develop a predictive model, and draw conclusions about the viability of using this process with actinide-loaded salt. Results of tests with CsCl, LaCl3, CeCl3, and NdCl3 are reported here. Equilibrium was typically achieved in less than 10 hours of contact between lithium metal and molten salt under well-stirred conditions. Maintaining low oxygen and water impurity concentrations (<10ppm) in the atmosphere was observed to be critical to minimize side reactions and maintain stable salt compositions. An equilibrium model has been formulated and fit to the experimental data. Good fits to the data were achieved. Based on analysis and results obtained to date, it is concluded that clean separation between minor actinides and lanthanides will be difficult to achieve using lithium drawdown.

Electrochemical Impedance Spectroscopy and Cyclic Voltammetry Methods for Monitoring SmCl₃ Concentration in Molten Eutectic LiCl-KCl

Shaltry, Michael R.,Allahar, Kerry N.,Butt, Darryl P.,Simpson, Michael F.,Phongikaroon, Supathorn Korean Radioactive Waste Society 2020 방사성폐기물학회지 Vol.18 No.1

Molten salt solutions consisting of eutectic LiCl-KCl and concentrations of samarium chloride (0.5 to 3.0 wt%) at 500℃ were analyzed using both cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The CV technique gave the average diffusion coefficient for Sm³⁺ over the concentration range. Equipped with Sm³⁺ diffusion coefficient, the Randles-Sevcik equation predicted Sm³⁺ concentration values that agree with the given experimental values. From CV measurements; the anodic, cathodic, and half-peak potentials were identified and subsequently used as a parameter to acquire EIS spectra. A six-element Voigt model was used to model the EIS data in terms of resistance-time constant pairs. The lowest resistances were observed at the half-peak potential with the associated resistance-time constant pairs characterizing the reversible reaction between Sm³⁺ and Sm²⁺. By extrapolation, the Voigt model estimated the polarization resistance and established a polarization resistance-concentration relationship.

Basis for a Minimalistic Salt Treatment Approach for Pyroprocessing Commercial Nuclear Fuel

Simpson, Michael F.,Bagri, Prashant Korean Radioactive Waste Society 2018 방사성폐기물학회지 Vol.16 No.1

A simplified flowsheet for pyroprocessing commercial spent fuel is proposed in which the only salt treatment step is actinide drawdown from electrorefiner salt. Actinide drawdown can be performed using a simple galvanic reduction process utilizing the reducing potential of gadolinium metal. Recent results of equilibrium reduction potentials for Gd, Ce, Nd, and La are summarized. A description of a recent experiment to demonstrate galvanic reduction with gadolinium is reviewed. Based on these experimental results and material balances of the flowsheet, this new variant of the pyroprocessing scheme is expected to meet the objectives of minimizing cost, maximizing processing rate, minimizing proliferation risk, and optimizing the utilization of geologic repository space.

DEVELOPMENT OF ELECTROREFINER WASTE SALT DISPOSAL PROCESS FOR THE EBR- II SPENT FUEL TREATMENT PROJECT

MICHAEL F. SIMPSON,PRATEEK SACHDEV 한국원자력학회 2008 Nuclear Engineering and Technology Vol.40 No.3

The results of process development for the blending of waste salt from the electrorefining of spent fuel with zeolite-A are presented. This blending is a key step in the ceramic waste process being used for treatment of EBR-II spent fuel and is accomplished using a high-temperature v-blender. A labscale system was used with non-radioactive surrogate salts to determine optimal particle size distributions and time at temperature. An engineering-scale system was then installed in the Hot Fuel Examination Facility hot cell and used to demonstrate blending of actual electrorefiner salt with zeolite. In those tests, it was shown that the results are still favorable with actinide-loaded salt and that batch size of this v-blender could be increased to a level consistent with efficient production operations for EBR-II spent fuel treatment. One technical challenge that remains for this technology is to mitigate the problem of material retention in the v-blender due to formation of caked patches of salt/zeolite on the inner v-blender walls.

SELECTIVE REDUCTION OF ACTIVE METAL CHLORIDES FROM MOLTEN LiCl-KCl USING LITHIUM DRAWDOWN

Simpson, Michael F.,Yoo, Tae-Sic,Labrier, Daniel,Lineberry, Michael,Shaltry, Michael,Phongikaroon, Supathorn Korean Nuclear Society 2012 Nuclear Engineering and Technology Vol.44 No.7

In support of optimizing electrorefining technology for treating spent nuclear fuel, lithium drawdown has been investigated for separating actinides from molten salt electrolyte. Drawdown reaction selectivity is a major issue that requires investigation, since the goal is to remove actinides while leaving the fission products and other components in the salt. A series of lithium drawdown tests with surrogate fission product chlorides was run to obtain selectivity data with non-radioactive salts, develop a predictive model, and draw conclusions about the viability of using this process with actinide-loaded salt. Results of tests with CsCl, $LaCl_3$, $CeCl_3$, and $NdCl_3$ are reported here. Equilibrium was typically achieved in less than 10 hours of contact between lithium metal and molten salt under well-stirred conditions. Maintaining low oxygen and water impurity concentrations (<10 ppm) in the atmosphere was observed to be critical to minimize side reactions and maintain stable salt compositions. An equilibrium model has been formulated and fit to the experimental data. Good fits to the data were achieved. Based on analysis and results obtained to date, it is concluded that clean separation between minor actinides and lanthanides will be difficult to achieve using lithium drawdown.

DEVELOPMENT OF ELECTROREFINER WASTE SALT DISPOSAL PROCESS FOR THE EBR- II SPENT FUEL TREATMENT PROJECT

Simpson, Michael F.,Sachdev, Prateek Korean Nuclear Society 2008 Nuclear Engineering and Technology Vol.40 No.3

The results of process development for the blending of waste salt from the electrorefining of spent fuel with zeolite-A are presented. This blending is a key step in the ceramic waste process being used for treatment of EBR-II spent fuel and is accomplished using a high-temperature v-blender. A labscale system was used with non-radioactive surrogate salts to determine optimal particle size distributions and time at temperature. An engineering-scale system was then installed in the Hot Fuel Examination Facility hot cell and used to demonstrate blending of actual electrorefiner salt with zeolite. In those tests, it was shown that the results are still favorable with actinide-loaded salt and that batch size of this v-blender could be increased to a level consistent with efficient production operations for EBR-II spent fuel treatment. One technical challenge that remains for this technology is to mitigate the problem of material retention in the v-blender due to formation of caked patches of salt/zeolite on the inner v-blender walls.

SEPARATION OF CsCl FROM LiCl-CsCl MOLTEN SALT BY COLD FINGER MELT CRYSTALLIZATION

Versey, Joshua R.,Phongikaroon, Supathorn,Simpson, Michael F. Korean Nuclear Society 2014 Nuclear Engineering and Technology Vol.46 No.3

This study provides a fundamental understanding of a cold finger melt crystallization technique by exploring the heat and mass transfer processes of cold finger separation. A series of experiments were performed using a simplified LiCl-CsCl system by varying initial CsCl concentrations (1, 3, 5, and 7.5 wt%), cold finger cooling rates (7.4, 9.8, 12.3, and 14.9 L/min), and separation times (5, 10, 15, and 30 min). Results showed a potential recycling rate of 0.36 g/min with a purity of 0.33 wt% CsCl in LiCl. A CsCl concentrated drip formation was found to decrease crystal purity especially for smaller crystal formations. Dimensionless heat and mass transfer correlations showed that separation production is primarily influenced by convective transfer controlled by cooling gas flow rate, where correlations are more accurate for slower cooling gas flow rates.

Water Sorption/Desorption Characteristics of Eutectic LiCl-KCl Salt-Occluded Zeolites

Allison Harward,Levi Gardner,Claire M. Decker Oldham,Krista Carlson,유 태식,Guy Fredrickson,Michael Patterson,Michael F. Simpson 한국방사성폐기물학회 2022 방사성폐기물학회지 Vol.20 No.3

Molten salt consisting primarily of eutectic LiCl-KCl is currently being used in electrorefiners in the Fuel Conditioning Facility at Idaho National Laboratory. Options are currently being evaluated for storing this salt outside of the argon atmosphere hot cell. The hygroscopic nature of eutectic LiCl-KCl makes is susceptible to deliquescence in air followed by extreme corrosion of metallic cannisters. In this study, the effect of occluding the salt into a zeolite on water sorption/desorption was tested. Two zeolites were investigated: Na-Y and zeolite 4A. Na-Y was ineffective at occluding a high percentage of the salt at either 10 or 20wt% loading. Zeolite-4A was effective at occluding the salt with high efficiency at both loading levels. Weight gain in salt occluded zeolite-4A (SOZ) from water sorption at 20% relative humidity and 40℃ was 17wt% for 10% SOZ and 10wt% for 20% SOZ. In both cases, neither deliquescence nor corrosion occurred over a period of 31 days. After hydration, most of the water could be driven off by heating the hydrated salt occluded zeolite to 530℃. However, some HCl forms during dehydration due to salt hydrolysis. Over a wide range of temperatures (320–700℃) and ramp rates (5, 10, and 20℃ min−1), HCl formation was no more than 0.6% of the Cl− in the original salt.

Enhanced electrochemical reduction of rare earth oxides in simulated oxide fuel via co-reduction of NiO in Li₂O–LiCl salt

Lee, Min-Woo,Choi, Eun-Young,Jeon, Sang-Chae,Lee, Jeong,Park, Sung-Bin,Paek, Seungwoo,Simpson, Michael F.,Jeong, Sang Mun Elsevier 2016 Electrochemistry communications Vol.72 No.-

<P><B>Abstract</B></P> <P>Rare earth oxides in spent oxide fuel from nuclear plants have poor reducibility in the electrochemical reduction process due to their high oxygen affinity and thermodynamic stability. Here, we demonstrate that the extent of their reduction can be enhanced via co-reduction of NiO in a Li<SUB>2</SUB>O–LiCl electrolyte for the electrochemical reduction of a simulated oxide fuel (simfuel). First, the electrochemical behaviors of Nd<SUB>2</SUB>O<SUB>3</SUB>, NiO, and Nd<SUB>2</SUB>O<SUB>3</SUB>–NiO were studied by cyclic voltammetry and voltage control electrolysis. Then, the electrochemical reduction of the simfuel containing UO<SUB>2</SUB> and rare earth oxides (Nd<SUB>2</SUB>O<SUB>3</SUB>, La<SUB>2</SUB>O<SUB>3</SUB>, and CeO<SUB>2</SUB>) was conducted in molten LiCl salt with 1wt.% Li<SUB>2</SUB>O via the co-reduction of NiO. The extent of reduction of the rare earth oxides was found to be significantly improved.</P> <P><B>Highlights</B></P> <P> <UL> <LI> NiO enhances electrochemical reduction of rare earth oxides in molten Li<SUB>2</SUB>O–LiCl. </LI> <LI> There is a 300% increase in the reduction of La<SUB>2</SUB>O<SUB>3</SUB> in simulated fuel by co-reduction of NiO. </LI> <LI> Improved reduction of Nd<SUB>2</SUB>O<SUB>3</SUB> and La<SUB>2</SUB>O<SUB>3</SUB> due to the formation of NdNi<SUB>5</SUB> and LaNi<SUB>5</SUB>. </LI> </UL> </P>

Electrochemical Synthesis of Graphene/MnO₂ Nano-Composite for Application to Supercapacitor Electrode

Jeong, Kwang Ho,Lee, Hyeon Jeong,Simpson, Michael F.,Jeong, Sang Mun American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.5

<P>Graphene/MnO2 nano-composite was electrochemically synthesized for application to an electrode material for electrochemical supercapacitors. The nanosized needle-like MnO2 was obtained by use of a graphene substrate. The prepared composite exhibited an ideal supercapacitive behavior. A capacitance retention of 94% was achieved with a 4 h deposition time (an initial capacitance of 574 mF/cm(2) at a scan rate of 20 mV/s) and the retention declined with further deposition time. The results demonstrate enhanced contact between the electrode and electrolyte and improved power density as an electrochemical capacitor.</P>