Electrolytic production of metallic uranium from U3O8 in a 20-kg batch scale reactor&lt;/p&gt; &lt;/p&gt;

Jeong, Sang‐Mun; Park, S.-B.; Hong, Sun-Seok; Seo, Changwon; Park, S.-W.

doi:10.1007/s10967-006-0172-z

Cited by 64 publications

(23 citation statements)

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“…They concluded that a small pellet size, with a high anode surface area resulted in higher current efficiencies. Similar conclusions were drawn by Jeong et al 13 during which greater than 99% of 20 kg of U 3 O 8 were successfully reduced at potentials ranging from −2.47 V to −3.46 V (vs. Pt). The authors concluded that increasing in the size of the oxide pellets inhibited the penetration of electrolyte and thus led to an unreduced core.…”

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confidence: 88%

Electrochemical Reduction of UO₂ to U in LiCl-KCl Molten Salt Eutectic Using the Fluidized Cathode Process

et al. 2016

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The electrochemical reduction of UO 2 to U metal has been investigated in both Fluidized Cathode (FC) and Metallic Cavity Electrode (MCE) cell arrangements. Differences in the local concentration of O 2− where the reduction takes place influnces the reduction potential. The fleeting contact of UO 2 particle contact with the current collector in case of the FC results in much less O 2− buildup compared to MCE. Consequently, UO 2 reduction occurs over a range of potentials in the FC and may involve separate two 2-electron steps compared to one apparent 4-electron step in the MCE. It is proposed that there are three discrete periods during the FC reduction process. The first is an induction period during which reduced uranium particles gradually adhere to the tungsten current collector. The second is reduction associated with a rapid growth in electrode area and consequent increase in current. The third is a slower reduction of the remaining oxide in the melt. Complete reduction of metallic U is achieved at −2.2 V (vs. Ag/Ag + ) with an estimated faradaic current efficiency of >92%. There are significant drivers for pursuing the next generation of nuclear reactors. Generation IV reactors offer both advancements in reactor design and also feature fully integrated fuel reprocessing capabilities. There are six types of Generation IV nuclear reactors and power plants under development. These are: the very-high-temperature reactor (VHTR), the sodium-cooled fast reactor (SFR), the supercriticalwater-cooled reactor (SCWR), the gas-cooled fast reactor (GFR), the lead-cooled fast reactor (LFR), and the molten salt reactor (MSR). The key features of each are summarized in Table I. The fuel type used in the majority of these reactors is metal. Given that most current reactors employ metal oxide (MOX or UOX) fuel and the majority of legacy waste is also metal oxide, the conversion of metal oxides to metals is an important component in a future nuclear power flow sheet.High temperature molten salt reprocessing technology (pyroprocessing) 2 for spent nuclear fuel offers a range of advantages when compared to aqueous reprocessing techniques. This is due to: an improved proliferation resistance (local processing reduces the likelihood of material diversion, no separation of plutonium); using facilities with a smaller footprint; a shorter cooling period for irradiated fuel, and also improved criticality safety margins. Different process systems and salts have been studied in pyroprocessing, most of which are summarized by the Nuclear Energy Agency (NEA). Conceptual flow sheets for the pyrochemical treatment of used nuclear fuel are described by Argonne National Lab (ANL). 4 The spent nuclear fuel, in the form of oxide pellets, is decladded and chopped, then passed on for an electrolytic reduction step. The uranium is in the form of UO 2 ; hence, the reduction of UO 2 to U metal is being investigated here. The reduced species then undergo electrorefining, [5][6][7][8][9] where U product and other transuranic species are separated an...

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Electrochemical Reduction of UO₂ to U in LiCl-KCl Molten Salt Eutectic Using the Fluidized Cathode Process

et al. 2016

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“…[7][8][9][10][11][12][13] Almost all such studies have been carried out in LiCl melts containing 1-3 wt% Li 2 O at 650…”

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confidence: 99%

A Study of Graphite as Anode in the Electro-Deoxidation of Solid UO₂in LiCl-Li₂O Melt

Joseph

Sanil

Mohandas

et al. 2015

J. Electrochem. Soc.

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Electrochemical behavior of graphite in LiCl and LiCl melts containing up to 1 wt% Li 2 O was studied by using cyclic voltammetry and electrolysis, in the context of its probable use as anode in the electrochemical reduction of solid UO 2 in the molten salt at 650 • C. The lithium deposition and chlorine evolution potentials of LiCl melt were determined by CV of tantalum (cathodic polarization) and graphite (anodic polarization) working electrodes as −2.19 V and +1.21 V vs Ni/NiO reference electrode respectively. In LiCl-Li 2 O melts, carbon dioxide was formed on the graphite WE from > +0.75 V onwards and its current and potential range of formation increased with increase in the Li 2 O content of the melt. Cathodic polarization of a UO 2 disc WE in LiCl-1 wt% Li 2 O melt showed that the reduction of UO 2 to U occurs at −2.18 V and the lithium metal deposition on it at −2.36 V. Electro-reduction experiments carried out with a dense UO 2 pellet cathode and graphite anode in both LiCl and LiCl-Li 2 O melts proved that the surface of the pellet was reduced to U metal at ≥ −2. Nuclear energy is considered as a major source of electricity for the present and future demands of the modern world. Sodium cooled fast reactor with metal fuel is proposed as one of the future reactor systems in the Generation IV concept and such reactors are considered to be inherently safe, economically viable and resistant to nuclear proliferation.1 U-Pu-Zr alloy is used as the metal fuel and hence production of these metals is of importance in the context of nuclear electricity. These metals have been produced from their oxides by the conventional chemical processes for the past several decades and there has been a great deal of interest to develop more efficient methods of production of the metals directly from the oxides.Spent metal fuels are reprocessed by pyrometallurgical process, in which the major and minor actinides are recovered by an electrorefining process carried out in a molten bath of LiCl-KCl at 500• C. 2Most of the nuclear reactors use uranium oxide and mixed oxide of uranium and plutonium (MOX) as the fuel and the spent fuel containing UO 2 and PuO 2 along with other oxides and fission products can be processed to obtain U and Pu for preparation of metal fuel. Reprocessing of spent oxide fuels by the molten salt electrorefining process is difficult as the oxides do not dissolve in the molten chlorides.Hence an intermediate process is required to convert the spent-oxide fuel to a metal form, which can be subsequently electrorefined to separate the actinides of interest. Chemical reduction of the spent oxide fuel by lithium metal in molten LiCl at 650• C was reported in this context. 3 The process required handling of large quantities of highly reactive lithium metal. The process also demanded frequent change of the molten bath due to build up of Li 2 O and hence the use of large quantities of the molten salt. Obviously these factors raise issues of safety of handling and storage of hygroscopic salt and highly irradiated fu...

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“…Many authors have attributed observations of increased reduction kinetics to altering process variables that would result in increased O 2− transport out of the cathode assembly such as; decreasing the UO 2 pellet size, increasing the UO 2 porosity, rotating the cathode assembly, and changing the material of the cathode assembly. 5,6,18,26,44,47,66,87,88 These observations strongly suggest that the diffusion of O 2− out of the oxide pellet, through the metal phase, is the rate limiting step of the electrolytic reduction process.…”

Section: Experience With the Reduction Processmentioning

confidence: 99%

“…47,69 The reported rates of Li 2 O consumption during the reduction process vary widely between references; an inconsistency that is attributed to the previously mentioned difficulties in quantifying the concentration of Li and Li 2 O in the salt, the quantity of Li that is lost to side reactions, and the quantity of Li and Li 2 O that remain in the cathode basket. 6,42,72,84,127 The final aspect of the role of lithium in the electrolytic reduction of actinide oxides to be discussed is the underpotential deposition (UPD) of Li + . UPD is the formation of single monolayers of atoms on a foreign substrate at a potential more noble than is required to reduce successive bulk metal onto the initial monolayer.…”

Section: Before Reductionmentioning

confidence: 99%

Review—Metallic Lithium and the Reduction of Actinide Oxides

Merwin

Williamson

Willit

et al. 2017

J. Electrochem. Soc.

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Extensive research and process development has been conducted on the electrolytic reduction of actinide oxides in molten LiCl-Li 2 O. It is now accepted that the reduction of these metal oxides occurs via two separate reduction mechanisms: direct electro-chemical reduction and mediated chemical reduction by metallic lithium. The deposition of metallic lithium at the cathode (mediated chemical reduction mechanism) during the process is known to be essential in order to achieve high process throughputs and reduction yields, and yet a knowledge gap exists regarding the nature of metallic lithium in this system. This review summarizes the formation of lithium during the process and its dispersion into the molten salt electrolyte. Previously reported aspects of the physical chemistry of the LiCl-Li 2 O-Li system are presented with a specific focus on the dispersion of Li in the solution. Finally, issues regarding the effect of the presence of lithium on the electrolytic reduction process are discussed. Evidence shows that electrochemically generated metallic lithium is likely a significant source of experimental uncertainty, low current efficiency and Li 2 O consumption in the oxide reduction process. The reduction of uranium, plutonium and minor actinide oxides to a metallic form is an important nuclear fuel cycle process.2-9 The ability of metallic lithium to reduce various uranium oxides, importantly UO 2 and U 3 O 8 , has been known for many years.10 A molten salt metalothermic reduction process employing metallic lithium (Li) as a reductant dissolved in molten LiCl was first developed by Argonne National Laboratory (ANL) to consolidate a variety of forms of actinide oxides for integration into a single electrometallurgical reprocessing system. 11-13 An electrolytic process, often referred to as electro-deoxidation or simply oxide reduction, was subsequently developed as a more controllable method of reducing metal oxides. A feasibility study conducted by Poa et al. demonstrated that oxides of uranium and plutonium could be reduced electrochemically in molten salts as long as the reduction potential of the metal oxide in question was more noble than the cation of the electrolyte.14,15 This approach was further developed by Gourishankar et al. to better understand processes chemistry and develop the electrolytic cell technology. 13,[16][17][18][19][20] Independent research conducted by Fray, Farthing, and Chen (FFC) applied the principles of electrochemical reduction in molten salt electrolytes to a variety of metal oxide reduction processes. 21,22 The FFC process has been the subject of several literature reviews.23-25 While these review articles address the processes associated with the reduction of nuclear fuel in LiCl, they focus on the electro-deoxidation phenomena and the CaCl 2 -CaO system. Additionally, the process engineering of the electrolytic reduction of nuclear fuel, and experience in incorporating oxide fuel into pyroprocessing, has been the focus of a recent review article. 26 The current review wi...

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Electrolytic production of metallic uranium from U3O8 in a 20-kg batch scale reactor</p> </p>

Cited by 64 publications

References 0 publications

Electrochemical Reduction of UO₂ to U in LiCl-KCl Molten Salt Eutectic Using the Fluidized Cathode Process

Electrochemical Reduction of UO₂ to U in LiCl-KCl Molten Salt Eutectic Using the Fluidized Cathode Process

A Study of Graphite as Anode in the Electro-Deoxidation of Solid UO₂in LiCl-Li₂O Melt

Review—Metallic Lithium and the Reduction of Actinide Oxides

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Electrolytic production of metallic uranium from U3O8 in a 20-kg batch scale reactor</p> </p>

Cited by 64 publications

References 0 publications

Electrochemical Reduction of UO2 to U in LiCl-KCl Molten Salt Eutectic Using the Fluidized Cathode Process

Electrochemical Reduction of UO2 to U in LiCl-KCl Molten Salt Eutectic Using the Fluidized Cathode Process

A Study of Graphite as Anode in the Electro-Deoxidation of Solid UO2in LiCl-Li2O Melt

Review—Metallic Lithium and the Reduction of Actinide Oxides

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Electrochemical Reduction of UO₂ to U in LiCl-KCl Molten Salt Eutectic Using the Fluidized Cathode Process

Electrochemical Reduction of UO₂ to U in LiCl-KCl Molten Salt Eutectic Using the Fluidized Cathode Process

A Study of Graphite as Anode in the Electro-Deoxidation of Solid UO₂in LiCl-Li₂O Melt