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Electrochemical Properties of , Plutonium and Lanthanides in M elts

(1) R. Zakirov, V. Ignatiev, (2) V. Subbotin, A. Toropov

(1) RRC —Kurchatov Institute“, Moscow, 123182, RF (2) Institute of Technical Physics, Snezhinsk, 456770, RF zakirov@ imp.kiae.ru

Abstract - Today the evaluation of pyrochemical treatment capability request more experimental data and demonstrations then what has been done up to now. Much more calculated and experimental results are available on a thermodynamic of electrochemical processes in chloride melts compared to fluoride ones. New experimental data on electrochemical properties of 60LiF-40NaF and 15LiF- 58NaF-27BeF2 (mol. %) eutectic melts containing ZrF4, PuF3 and LnF3 (NdF3, LaF3, CeF3) are presented.

deposition potentials on solid Mo electrode on INTRODUCTION the basis of experimental results obtained.

Molten salt processes for irradiated EXPERIM ENTAL nuclear fuel have been studied internationally for several decades. Potential overall Preparation of major solvent constituents applications of pyrochemical processing include: Powdered lithium, sodium and beryllium • Fuel processing for recycle [1]; were used as initial components for • Fuel and fuel residues conditioning for preparation of LiF-NaF (60:40 mol.%) and disposal [2]; LiF-NaF-BeF2 (15:58:27 mol.%) mixtures. • Advanced waste processing, which could The content of metal (Ni, Fe, Cr, Cu, Mo, Ln) potentially include waste management options compounds impurities in powdered lithium, such as separation of heat generating or long- sodium and beryllium fluorides was less than lived wastes [3]; 0.01 % wt. (analysis by the ICP-AES method). • Fission product clean up for molten salt The powders of LiF, NaF and BeF2 were reactors (MSR), particularly as applied to mixed in prescribed proportion and dried at single stream Li,Na,Be/F transmuter system 500? for 3-4 h. Then the following order of without U-Th support [4]. operations was made in a separate test section Today the evaluation of pyrochemical for the chosen molten salt mixture preparation: treatment capability request more experimental • Heating of the starting powder mixture in -2 data and demonstrations, then what has been a glassy carbon crucible under vacuum (10 - -3 done up to now. It is not an easy task because 10 mm Hg) at gradual temperature increase the material to be treated is not completely from 300? up to 1100K during 8-10 h; defined and because many options for reducing • Double melting of the prepared fusion -2 -3 the long-lived radionuclide inventory are still cake at 1000? under vacuum (10 -10 mm under examination. Hg) for 4-5 h and mechanical removal of Note, that much less calculated and impurities from the frozen melt surface; experimental results are available on a • Transfer of glassy carbon crucible with thermodynamic of electrochemical processes fusion cake to electrochemical cell and pre- in fluoride melts compared to chloride ones. electrolysis of the melt (C=900?, vacuum 10-2- In this paper the experimental data on 10-3 mm Hg) using molybdenum cathode and electrochemical properties of 60LiF-40NaF graphite anode. and 15LiF-58NaF-27BeF2 (in mol. %) eutectic In the process of the potentiostatic pre- melts, containing zirconium, plutonium and electrolysis the cathode potential was kept at lanthanides fluorides are presented. the level of (œ1.2 V) versus molybdenum quasi Particularly, consideration includes the reference electrode. The pre-electrolysis plutonium trifluoride behavior in the Be- duration was approximately 3 h. The final containing solvent system: determination of value of the pre-electrolysis current was ∼ 2 the difference between plutonium and mA, surface area of the electrodes ∼5 cm2. beryllium deposition potentials on solid The fusion cake prepared in such a molybdenum electrode and evaluation of the manner with the mass about 75 g was used as difference between plutonium and neodymium solvent system in our experiments.

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The cell electrodes pass through the upper Preparation of ZrF4, PuF3 and LnF3 flange inside the cell through Teflon insulators. The cell electrodes were manufactured of a Zirconium tetrafluoride, plutonium and molybdenum (∅1mm wire), glassy carbon lanthanides trifluorides used in the experiments (∅2mm rod, SU-2000) and graphite. The cell were synthesized by a method based on direct electrodes were cleaned mechanically and fluorinating of metals or oxides by anhydrous degreased by a solvent before experiments. . The content of the basic The three-electrode scheme was used in substance in the specified metal fluorides was the electrochemical experiments with the no less than 99 wt.%. quasi-reference Mo electrode, the working Mo ZrF4, LaF3 and CeF3 were added to the electrode (cathode) and the auxiliary glassy molten salt mixture as a powder. In case of carbon (graphite) electrode (anode). The PuF3 and NdF3, its pressed pellet was placed to immersion depth of the working electrode was electrochemical cell on surface of the solvent equal to 5-7 mm, of the quasi reference fusion cake. Then the fusion cake was heated electrode œ 10 mm and of the auxiliary up to the operating temperatures (870-900K) at electrode œ 15mm. continuous flowing of high purity argon through the cell. For full dissolution of PuF3 M easurements procedure and NdF3 tablets the molten salt mixture was bubbled by high purity argon. To determine the electrochemical All operations with plutonium trifluoride properties of the fluoride melts constituents were carried out in a shielded glove box. following two methods were used [5,6]: • Cyclic voltammetry with linear potential Electrochemical cell design sweep, • Measurement (versus time) of the open A schematic drawing of the circuit potential (OCP) of cathode (versus Mo electrochemical cell used is shown in Fig. 1. quasi reference electrode) after transitory polarization of the electrochemical cell (hereafter OCP transient curves method). PI-50-1.1 potentiostate with a PR-8 programmator was used in our measurements.

8 XY- recorder N-307 was used for recording 8 the voltammograms and OCP transient curves. 5 A resistance furnace with thermoregulator was used for the cell heating. The salt melt 7 temperature was measured during experiment by a chromel-alumel thermocouple (its

3 9 junction was in the thermostat close to the nickel crucible). The precision of the 6 temperature control inside the cell during the 1 measurements was ±1 ?. 2 A position of current peaks of some metal 4 ions present in the melt on potential axis was Fig. 1. Schematic drawing of the cell for determined from the voltammograms. A value electrochemical studies in fluoride melts. of the deposition potential difference between 1- nickel crucible; 2- auxiliary electrode individual metals was qualitatively determined (graphite, glassy carbon); 3-working electrode from a position of current peaks on potential (Mo); 4-molten Li,Na/F or Li,Na,Be/F axis. More precisely (±20 mV) the deposition mixture; 5- quasi-reference electrode (Mo); 6- potential difference between the metals was thermocouple; 7-stainless steel vessel; 8-argon determined from the OCP transient curves (on input and output; 9- tube used for gas bubbling their horizontal plateaus). and tablets addition to the melt. RESULTS AND DISCUSSION The cell is installed in outer gas-tight vessel with flanges made of stainless steel. On LiF-NaF-ZrF4-LnF3 systems its bottom the massive copper thermostat is placed on alumina ring insulator. The nickel The main reason for experiments with crucible with the melt under investigation is LiF-NaF eutectic melt was to determine the placed inside of the thermostat. The volume of effect on zirconium and the nickel crucible is equal to 80 cm3. lanthanides electrodeposition from melts.

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Cyclic voltammograms (CV) of LiF-NaF (60:40 mol %) eutectic melt are presented in Fig. 2. One can see, that the preliminary procedures, including; melting under vacuum, mechanical removal of impurities and pre- electrolysis, resulted in high solvent purity.

Fig.4. OCP transient curve of Mo working electrode after electrolysis (current-15 mA, time-10 s) in LiF-NaF-ZrF4 melt. Electrodes: Mo (∅1mm)- cathode, Mo (∅1mm)-quasi Fig.2. Cyclic voltammogram of LiF-NaF reference, graphite- anode. C=1000?, argon eutectic melt. Electrodes: Mo ( 1mm)- ∅ working (0.25cm2), Mo (∅1mm)-quasi ref., -2 Cyclic voltammogram and OCP transient graphite œ auxiliary. C=1000?, P∼10 mm Hg. curve of a molten LiF-NaF mixture, containing

1 mol. % of NdF3 are shown in Figs. 5-6. Cyclic voltammogram of LiF-NaF eutectic melt containing 0.5 mol. % of ZrF4 is shown on Fig. 3. The clearly defined current peak corresponding to the reduction of zirconium ions on a molybdenum working electrode is observed on a cathode part of voltammogram at potential about (-1.10 V) versus Mo quasi reference electrode. Anodic current peak at potential (-0.90 V) correspond to this cathodic peak in the anodic area of the voltammogram and determined by Zr dissolution.

Fig.5. Cyclic voltammogram of a LiF-NaF + NdF3 (1 mol.%) melt. Electrodes: Mo - working, Mo -quasi reference, graphite œ auxiliary. C=1000?, P∼ 10-2 mm Hg.

Fig. 3. Cyclic voltammogram of a LiF-NaF + ZrF4 (0.5 mol.%) melt. Electrodes: Mo (∅1mm)- working, Mo (∅1mm)-quasi ref., graphiteœauxiliary. C=1000?, argon.

To confirm this conclusion OCP transient curve obtained after preliminary electrolysis of the melt is presented in Fig. 4. Fig. 6. OCP transient curve of a Mo working One can see, that at potential E = (-0.8 V) electrode after electrolysis (current-100 mA, there is a clearly defined extended plateau time-30 s) in a LiF-NaF-NdF3 melt. determined by Zr deposited on working Electrodes: Mo (∅1mm)- cathode, Mo electrode at electrolysis. (∅1mm)-quasi ref., graphite- anode. C=1000?, P∼ 10-2 mm Hg.

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As can seen, there are well enough formed anodic area of voltammogram. Complex current peaks on anodic area of voltammogram character of anodic current peak can be the corresponding, most probable, to dissolution of evidence that Be and Na are deposited on a a Nd - Mo alloy and oxidation of neodymium cathode simultaneously at electrolysis. ions. The clearly expressed extended plateau is observed at potential (-1.32 V) on OCP transient curve. Its stable value and duration are the evidence that neodymium is deposited on the cathode at electrolysis predominantly. It is not possible to determine difference in deposition potentials of neodymium and sodium from received curves, because neodymium reduction is hindered by the melt decomposition. There are no any peculiarities on cyclic voltammograms of a LiF-NaF melt containing Fig. 7. Cyclic voltammogram of a LiF-NaF- about 1 mol. % of LaF3 and CeF3 down to BeF2 melt. Electrodes: Mo (∅1mm)- working deposition of major solvent constituent (most 2 probable, sodium). (0.25cm ), Mo (∅1mm)-quasi reference, -2 Cyclic voltammogram of LiF-NaF eutectic graphite œ auxiliary. C=840?, P∼ 10 mm Hg. melt, containing 0.5 LaF3, 0.5 NdF3 and 0.25 ZrF4 (in mol. %), is similar to voltammogram OCP transient curve for LiF-NaF-BeF2 of molten LiF-NaF-ZrF4 mixture (see Fig. 3). eutectic melt is presented in Fig.8. Character of Only anodic current peak corresponding to potential plateau at (-1.40 V): stable value and dissolution of lanthanides alloy, probably duration, is the evidence that beryllium is formed at cathode polarization, and anodic deposited on the cathode at electrolysis. current peak corresponding to dissolution of zirconium are observed on voltammogram. So, it is possible to make the following preliminary conclusions from the analysis of voltammograms and OCP transient curves for molten LiF-NaF-ZrF4, LiF-NaF-LnF3 and LiF- NaF-LnF3-ZrF4 systems: • Deposition potentials of neodymium, lanthanum and cerium in LiF-NaF+LnF3 melt are close to deposition potential of sodium. Therefore there is a simultaneous deposition of Ln and Na on solid Mo electrode. • Difference of zirconium and lanthanides (alloys of lanthanides) deposition potentials in

LiF-NaF-LnF3-ZrF4 system is equal ∼0.4 V. This value is less than the difference of Fig. 8. OCP transient curve of a Mo electrode conditional standard electrode potentials of after electrolysis (current-180 mA, time-10 s) these metals in molten LiF-BeF mixture [7] 2 in a LiF-NaF-BeF2 eutectic melt. Electrodes: approximately by 0.2 V. Apparently this Mo - cathode, Mo -quasi reference, graphite- distinction is concerned with complexation of anode. C=840?, P∼ 10-2 mm Hg. zirconium tetrafluoride with sodium fluoride in LiF-NaF melt. It provide shift in zirconium LiF-NaF-BeF2 -- ZrF4 system deposition potential to electronegative values.

The LiF-NaF-BeF2 eutectic melt LiF-NaF-BeF2 system containing ZrF4 (0.5 mol. %) was studied to evaluate the effect of solvent on Cyclic voltammogram of LiF-NaF-BeF2 thermodynamic parameters of solute.CV and (15-58-27 mol. %) eutectic melt is shown in OCP transient curve for this system are shown Fig.7. Reduction of solvent constituents, in Fig.9-10. The cathodic current peak (E≈-1.1 apparently, at first of beryllium starts at V), apparently, corresponding to reduction of potential approximately (-1.30 V) (non-well beryllium forming an alloy with zirconium is formed current peak at E = -1.30V). Current appeared on cathodic area of voltammogram in peak corresponding to dissolution of metals, addition to current peak (E -0.95 V), evolved on a working electrode, is observed in ≈ corresponding to reduction of zirconium. Some

ATALANTE 2004 Nîmes (France) June 21-25, 2004 4 O22-09 anodic current peaks corresponding to dissolution of different alloys and zirconium, I, mA formed at cathode polarization of the salt IIIc system, occur on anodic area of CV. -80

-60 IIc -40 200 mV/S -20 Ic E, V 0 -0.30 -0.60 -0.90 -1.20 Ia -1.50 -1.80 20 40 IIIa

60 IIa

Fig. 11. Cyclic voltammogram of a LiF-NaF- BeF2 + PuF3 (0.2 mol.%) melt obtained 1 h after PuF3 addition. Electrodes: Mo (∅1mm)- working, Mo (∅1mm)-quasi ref., glassy Fig. 9. Cyclic voltammogram of a LiF-NaF- carbon œ auxiliary. C=893?, argon BeF2+ZrF4 (0.5 mol.%) melt. Electrodes: Mo (∅1mm)- working, Mo (∅1mm)-quasi ref., Two current peaks appeared in the graphite œ auxiliary. C=850?, argon. cathodic area of the voltammogram: Ic at the potential E∼ œ1.35 V and IIc at the potential E∼ œ1.50 V versus Mo quasi-reference electrode. Besides those peaks the most intense current peak at the potential E∼ œ1.60 V corresponding to beryllium electrodeposition on Mo cathode was observed. The anodic peak currents Ia at the potential E∼ -1.30 V, IIa at E∼ -1.45 V and IIIa at E∼ -1.50 V correspond to these cathodic peaks in the anodic area of the voltammogram. Three potential plateaus E∼ -1.55 V, E∼ - 1.45 V and E∼ -1.28 V corresponding to

potentials of the anodic peaks IIIa , IIa and Ia Fig. 10. OCP transient curve of a Mo are observed on the OCP transient curve of the electrode after electrolysis (current-50 mA, Mo electrode obtained in a few minutes after the voltammetric measurements (Fig.12). time-15 s) in LiF-NaF-BeF2-ZrF4 melt. Electrodes: Mo - cathode, Mo -quasi reference, graphite- anode. C=850?, argon. E, V -1.55 V -1.50 -1.45 V

In accordance with the voltammogram -1.28 V three clearness plateaus of potentials are observed on OCP transient curve: E =-1.02V -1.00 and E =-0.94V, corresponding to beryllium based alloys; E =-0.72V, corresponding to zirconium. The transition at E =-0.76V, -0.50 apparently, corresponds to zirconium based alloys. From data on Figs.9-10 it is follows, 0 τ, s that the difference of deposition potentials of 100 500 1000

Zr and Be is more than 0.3 V, that is in good Fig. 12. OCP transient curve of a Mo agreement with the difference of conditional electrode after electrolysis (current-50 mA, standard electrode potentials of zirconium and time-10 s) in LiF-NaF-BeF2 - PuF3 melt. beryllium in molten 2LiF-BeF2 mixture [7]. Electrodes: Mo - cathode, Mo -quasi ref., glassy carbon - anode. C=893?, argon. LiF-NaF-BeF2 - PuF3 system The following changes have occurred after CV of the LiF-NaF-BeF2 + PuF3 (0.2 complete dissolution of the plutonium mol.%) melt obtained 1 h after the plutonium trifluoride tablet (in 10 h) (Figs.13-14): trifluoride tablet addition is shown in Fig.11.

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a) The current peaks IIc and IIa increased The following changes have occurred on distinctly; the voltammograms and OCP transient curves b) The current peaks Ic and Ia did not change after addition of second plutonium trifluoride practically; tablet and its complete dissolution (by c) On the OCP transient curve the potential bubbling of high purity argon) (Figs.15-16): plateaus, corresponding to potentials of the • An overall displacement of the current current peaks IIa and Ia, are recorded distinctly, peaks to electropositive direction on the the potential plateau corresponding to potential potential axis occurred on the voltammogram of current peak IIIa is recorded badly. and a corresponding displacement of potential plateaus occurred on the OCP transient curve.

I, mA • The value of the cathodic peak current IIa

IIc increased twice, the value of cathodic peak -80 current Ia changed slightly. -60 • In the anodic area of the voltammogram -40 200 mV/S the peak currents IIa and Ia are recorded only, -20 Ic the peak currents III are not recorded even at E, V a 0 the current value more than 300 mA, when the -0.30 -0.60 -0.90 -1.20 -1.50 -1.80 20 Ia anodic effect becomes apparent on the glassy 40 carbon electrode. 60 IIa L) I, mA IIIc -200 I, mA -150 IIc

-240 IIIc -100 200 mV/S -160 -50 200 mV/S Ic E, V -80 IIc 0 Ic E, V -0.30 -0.60 -0.90 Ia -1.20 -1.50 -1.80 0 50 -0.30 -0.60 -0.90 -1.20 Ia -1.50 -1.80 80 100 IIIa 160 IIa 150 IIa M) 200

Fig. 13. Cyclic voltammograms of LiF-NaF- L) BeF2 melt, containing 0.2 mol. % PuF3.

Reverse potential a) - (-1.60V), b) - (-1.70V). I, mA Electrodes: Mo (∅1mm)- working, Mo IIIc -300 (∅1mm)-quasi ref., glassy carbon œ auxiliary. -200 IIc C=893?, argon. 200 mV/S -100 Ic E, V 0 -0.30 -0.60 -0.90 Ia -1.20 -1.50 -1.80 E, V 100 -1.58 V 200 -1.50 -1.47 V IIa -1.32 V 300

-1.00 M) Fig. 15. Cyclic voltammograms of LiF-NaF-

-0.50 BeF2 melt, containing 0.4 mol. % PuF3. Reverse potential a) - (-1.65V), b) - (-1.70V) Electrodes: Mo - working, Mo - quasi ref., 0 τ, s glassy carbon œ auxiliary. C=893?, argon. 100 200 300

On the OCP transient curve (Fig. 16) the Fig.14. OCP transient curve of a Mo working potential plateaus corresponding to the anodic electrode after electrolysis (current-150 mA, current peaks IIa and Ia are recorded only. The time-6 s) in LiF-NaF-BeF2 melt, containing duration of the potential plateaus is sufficiently 0.2 mol. % PuF3. . Electrodes: Mo (∅1mm)- long taking into account the short electrolysis cathode, Mo (∅1mm)-quasi reference, glassy time (5 s). carbon - anode. C=893?, argon.

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concentration in the melt: the more PuF3 E, V concentration in the melt, the higher is the values of current peaks. Moreover, the value of -1.50 -1.35 V cathode current peak IIc is in direct proportion -1.20 V to PuF3 concentration in the melt (Figs. 13 and

-1.00 15). Hence, it is logically to attribute the 3+ current peak IIc to Pu ions reduction on Mo electrode and the current peak IIa to dissolution -0.50 of metallic plutonium. As far as the difference in potentials of the cathodic and the anodic current peaks do not exceed 0.1 V (see Fig. 0 τ, s 11), than it is possible to assert that the process 100 500 1000 of plutonium deposition is reversible. Fig. 16. OCP transient curve of a Mo working The current peaks IIIc and IIIa (Figs.11 electrode after electrolysis (current-50 mA, and 13) are attributed to processes with time-5 s) in LiF-NaF-BeF2 melt, containing beryllium. Beryllium is known to form an 0.4 mol. % PuF3. Electrodes: Mo (∅1mm)- intermetallic compound with plutonium cathode, Mo (∅1mm)-quasi reference, glassy (PuBe13) [10], therewith the beryllium activity carbon - anode. C=893?, argon. in PuBe13 is lower, than activity of pure beryllium. Evidently, the anodic current peak The overall displacement of current peaks IIIa is referred to dissolution of PuBe13 and in the electropositive area of potentials on the beryllium. voltammograms and the corresponding At high content of PuF3 in the melt the displacement of potential plateaus on the OCP preferential deposition of plutonium is transient curves occurred after the melt occurred on cathode, although the formation of bubbling by high purity argon and complete solid solutions of plutonium and beryllium is dissolution of the second plutonium trifluoride also possible. For this reason, the anodic tablet. Nevertheless, the potential differences current peaks corresponded to dissolution of of current peaks on the voltammograms and beryllium or its alloys with plutonium (PuBe13) the difference of potential plateaus on the OCP are not recorded in the region of currents transient curves were not changed practically. investigated (up to 1 A/cm2). Apparently, the additional purification of the Taking into account, that the potential of melt from volatile impurities occurred, when pure beryllium versus Mo quasi-reference the melt was bubbled by high purity argon. electrode was equal to ∼ (-1.60 V) in the LiF- This operation resulted in the Redox potential NaF-BeF2 eutectic melt before addition of the shift to electronegative values. first plutonium trifluoride tablet and the The form of current peaks Ic and Ia plutonium potential is equal to ∼ (-1.45 V), it is (Fig.11) and the form of a potential plateau on possible to estimate the difference of the OCP transient curves, corresponding to the deposition potentials of plutonium and current peak I (Figs.12, 14,16), allow to a beryllium in the LiF-NaF-BeF2 eutectic melt suppose that the current peaks Ic and Ia (15:58:27 mol. %) as: ∆EPu-Be ≈ 0.15 V. This correspond to deposition and dissolution of value is a bit lesser than calculated difference some metal or alloy on the cathode. Taking of conditional electrode potentials of these into account that plutonium trifluoride was metals in 2LiF-BeF2 melt [7]. Possibly, that is added to the melt, it is possible to assume, that linked with the influence of the solvent the formation of plutonium-molybdenum alloy composition on thermodynamic properties of can occur on the cathode. The following plutonium trifluoride. features of the electrochemical curves point out to such a possibility: LiF-NaF-BeF2 - PuF3 - NdF3 system • The lengthy potential plateau on the OCP transient curves (N≈ - 1.32 V in Fig. 14 and N≈ The addition of ∼ 0.55 mol.% of - 1.20 V in Fig. 16); neodymium trifluoride to the LiF-NaF-BeF2 - • A weak dependence of the current peaks Ic PuF3 melt have not affected the form of and Ia on plutonium trifluoride concentration in electrochemical curves (Fig.3.12): they have the melt. remained the same as on the Figs. 15-16. The appearance of such current peaks for Basing on our data for zirconium chloride melts with UCl3 and PuCl3 was noted tetrafluoride, plutonium and neodymium in previous studies [8-9]. trifluoride, it is possible to suppose, that the For the values of current peaks IIc and IIa behavior of plutonium and fission products there is a good correlation with PuF3 (zirconium, lanthanides) in the LiF-NaF-BeF2

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eutectic melt is similar to their behavior in a ACKNOW LEDGEM ENT molten 2LiF-BeF2 mixture. Issuing from this data it is possible to estimate the difference of This effort is done within ISTC Task electrode potentials of plutonium and #1606 titled —Experimental study of molten neodymium in the LiF-NaF-BeF2 (15:58:27 salt technology for safe, low waste and mol.%) melt as ∆EPu-Nd ≈ 0.3 V. proliferation resistant treatment of plutonium Thus, it is possible to assert on the basis of and minor actinides in accelerator driven and experimental data gained, that electrolysis on critical systems“ supported by EU. solid cathode could be used for the fuel composition purification from corrosion REFERENCES products and zirconium and also for separation of actinides and lanthanides in the Li,Na,Be/F 1. W illit J.e.a., —Electrorefining of uranium system. and plutonium. A literature review“, J. Nucl. For more complete understanding of the Mater., 195(3), pp. 229-249 (1992). processes with plutonium ions in the LiF-NaF- 2. Sakamura Y. e.a, —Separation of actinides BeF2 melt it is necessary to investigate PuF3 from rare earth elements by electrorefining in behavior in different fluoride melts in detail LiCl-KCl eutectic salt“, J. Nucl. Sci. Techn., with use of standard reference electrode, and 35(1), pp.49-59 (1998). also other electrochemical methods as well as 3. A Roadmap for Developing Accelerator detailed physical & chemical analysis of Transmutation of Waste (ATW) Technology: A reaction products. Report to Congress. October 1999 4. IgnatievV., Feynberg O., Myasnikov A., CONCLUSIONS Zakirov A., —Neutronic Properties and Possible Fuel Cycle of a Molten Salt Transmuter“, A laboratory set up for electrochemical GLOBAL-03 proceedings, Nov.16-20,2003, investigations in fluoride melts containing New Orleans. plutonium trifluoride was prepared and tested. 5. Heineman W .R. and Kissinger P.T. In The difference of zirconium and beryllium, —Laboratory Techniques in Electroanalytical plutonium and beryllium deposition potentials Chemistry“, p.51-123, Marcel Dekker, (1996). in the LiF-NaF-BeF2 (15:58:27 mol. %) melt 6. Qiao H. et al. —Electrochemical formation were determined for the first time on the basis of Au2Na alloy and characteristics of (Au2Na + of experimental measurements. Au) reference electrode in a LiF-NaF-KF The difference of plutonium and eutectic melt. Electrochimica Acta, 47, pp. neodymium electrode potentials in the LiF- 4543-4549 (2002). NaF-BeF2 (15:58:27 mol. %) melt was 7. Baes C.F., Jr, —The chemistry and evaluated. thermodynamics of molten salt reactor fuel“, On the basis of voltammograms and OCP Nuclear Metallurgy, 15, pp.617-644 (1969). transient curves of Mo electrode after 8. Shirai O. e. a. —Electrochemical behavior electrolysis in molten LiF-NaF-BeF2, LiF- of actinide ions in LiCl-KCl eutectic melts“. J. NaF-BeF2 - PuF3 and LiF-NaF-BeF2 - PuF3- Alloys and Comp., 271-273, pp.685-688 NdF3 mixtures it was shown, that plutonium is (1998). deposited on molybdenum cathode earlier than 9. Serrano K. and Taxill P. —Electrochemical beryllium. The difference of plutonium and reduction of trivalent uranium ions in molten beryllium deposition potentials is equal chlorides“. J. Appl. Electroch., v.29, pp.497- approximately to 0.15 V. The presence of 503 (1999). neodymium trifluoride in the LiF-NaF-BeF2 - 10. Schonfeld, F. W . et al.: —Plutonium PuF3 melt had no effect on the shape of Constitutional Diagrams“, in: Progress in electrochemical curves. The evaluated value of Nuclear Energy, Series V, vol. 2 (Ed.: the plutonium and neodymium electrode Finniston and Howe), London, p.580 (1959). potentials difference in the LiF-NaF-BeF2 (15:58:27 mol.%) eutectic melt is equal approximately to 0.30 V. Further investigations are needed for determination of possible plutonium alloying with beryllium and molybdenum and its influence on plutonium deposition from fluoride melts.

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