Actinides/lanthanides separation in molten salt media: application to the liquid fuel reprocessing of molten salt fast reactor (MSFR)

Transcription

1 First SACSESS International Workshop Warsaw, April 2015 Actinides/lanthanides separation in molten salt media: application to the liquid fuel reprocessing of molten salt fast reactor (MSFR) Davide Rodrigues, Sylvie Delpech CNRS/IN2P3 Univ. Paris Sud, IPN d Orsay, 15 Rue Georges Clemenceau Orsay Unité mixte de recherche CNRS-IN2P3 Université Paris-Sud Orsay cedex Tél. : Fax :

2 1. Forum GEN IV International Forum focused on research and development of nuclear reactor stimulated by the U.S Department of Energy (DOE) [1] GEN IV Forum established concrete targets for focusing research and development efforts: Sustainability (1), safety and reliability (2), economics (3) and proliferation resistance (4) GIF concept selection: Gas-Cooled Fast Reactor (GFR) Sodium-Cooled Fast Reactor (SFR) Very-High-Temperature Reactor (VHTR) Supercritical-Water Reactor (SCWR) Lead-Cooled Fast Reactor (LFR) Molten Salt Reactor (MSR) [1] Forum GEN IV website: 2

3 1. Forum GEN IV International Forum focused on research and development of nuclear reactor stimulated by the U.S Department of Energy (DOE) [1] GEN IV Forum established concrete targets for focusing research and development efforts: Sustainability (1), safety and reliability (2), economics (3) and proliferation resistance (4) GIF concept selection: Molten Salt Reactor (MSR) It s the only one concept to use a liquid fuel, to operate with Th/U fuel cycle and to have an integrated reprocessing [1] Forum GEN IV website: 3

4 2. Molten Salt Reactor history Molten Salt Reactor (MSR) was first developed by Oak Ridge National Laboratory in the 50 s Aircraft Reactor Experiment (ARE) in 1954 Molten Salt Reactor Experiment (MSRE) from 1965 to Graphite moderator (5 years of lifetime) - Thermal Neutron Spectrum Molten Salt Breeder Reactor (MSBR) - High flow of fuel reprocessing (4000 liters per day) NaF-ZrF 4 -UF 4 LiF-BeF 2 -ZrF 4 -UF mol% LiF-BeF 2 -ThF 4 -UF mol% MSRE Reactor (8.5MWth) Inside of MSRE wall protection (8.5MWth) 4

5 3. Molten Salt Fast Reactor concept Reference concept of Forum GEN IV in 2010 Molten Salt Fast Reactor (MSFR) in 2006 Liquid fuel Cycle 232 Th / 233 U: t 1/2 Th (233) = 22 Minutes t 1/2 Pa (233) = 27 Days Fast spectrum: no graphite moderator Operating temperature: C LPSC design [2] LPSC design [2] Fertile blanket (LiF-ThF 4 ): fissile nuclei production Low flow of fuel reprocessing (40 liters per day) LiF-ThF 4 -(UF 4 /UF 3 ) mol% Reprocessing objectives: - Uranium recovery (used to launch the MSFR) - Waste management (actinide burner) - Lanthanides removal which have a low solubility in the liquid fuel and also neutron poison [2] E. Merle-Lucotte, M. Allibert, M. Brovchenko, V. Ghetta, D. Heuer, P. Rubiolo, Preliminary Design Assessment of the Molten Salt Fast Reactor, Actes de la conférence European Nuclear Conference ENC2012, Manchester, UK (2012) 5

6 4. Fuel reprocessing Reaction balance of the reprocessing: 2 LnF H 2 O Ln 2 O HF 6

7 1. Steps 2.A and 2.B Principle scheme: (MS) (MS) The chemical reaction for the reductive extraction: MF z (MS) + z R (LM) z RF (MS) + M (LM) (LM) (LM) (LM) The reducing agent (R) selected, is lithium The nature of the solvent metal (LM) chosen is bismuth The particularity of the reprocessing scheme proposed for MSFR treatment is to use the same technique to extract actinides in the first step (2.A) and lanthanides in the second one (2.B) Actinides extraction must to be selective and with a high efficiency Lanthanides extraction must to be only with a high efficiency 7

8 2. Analytical description Extraction efficiency: Solvation in the molten salt: HSC Database Lebedev Database [4] Database established by extrapolation of literature results [3] Two kinds of parameters: - Constant (thermodynamical and solvation) - Adjustable log ɣ(li) Bi = Adjustable parameters of the process: - Mole fraction of lithium in bismuth liquid pool - Volume ratio between metallic phase and salt phase [3] S. Delpech, Possible routes for pyrochemical separation: Focus on the reductive extraction in fluoride media, Pure Appl. Chem., vol. 85, no. 1, p (2013) [4] V.A. Lebedev, "Selectivity of Liquid Metal Electrodes in Molten Halides", Chelyabinsk: Metallurgiya, (1993) 8

9 3. Extraction efficiency calculations Influence of the mole fraction of the reducing agent in Bi: Ratio of liquid phases mole number: Selective and quantitative extraction of actinides (2.A): x(li) Bi < Quantitative extraction of lanthanides (2.B): x(li) Bi > 0.1 It s possible to perform the two extraction steps (actinides and lanthanides) by changing the concentration of Li in Bi in the two steps For the steps 2.A (actinides extraction): For the steps 2.B (lanthanides extraction): x(li) Bi = 0.1 % x(li) Bi = 10 % 9

10 1. Cyclic voltammetry Electroactivity domain of the salt with W and Bi working electrode: 0,4 Li (0) Li (I) 2 j (A/cm ) Bi (0) Bi (III) 0,2 Li (0)Bi Li (I) Cl- Ei 0 Bi (0) Cl2(g) Ei Bi (III) Production of the metallic phase Bi-Li in LiF-LiCl -0,2 Li (0)Bi -0,4-3 Li (0) Li (I) -2 Li (I) LiF-LiCl T = 800 K Working Electrode (Bi) and (W) Reference Electrode Ag/AgCl Scan Rate 100 mv/s -1 E (V/Ref.) 0 Electroactivity domain of the salt X Coulometry X ICP-AES analysis of the bismuth 1 Coulometry current set at -0.5 A 10

11 2. Coulometry Coulometry current set at -0.5 A during 8 hours and 20 minutes: LiF-LiCl T = 800 K Working Electrode (Bi) Reference Electrode Ag/AgCl Scan Rate 100 mv/s Theoretical calculations: Q = n x z x F = I x t Q = C Theo. (% mol) ICP analysis (% mol) Bi Li Faraday efficiency 73.6 % X Electroactivity domain of the salt Coulometry ICP-AES analysis of the bismuth 11

12 3. Composition salt influence Different bismuth-lithium pool production in various molten salt: Molten salt ICP-AES analysis (% mol) Faraday efficiency (%) E or I set LiF-LiCl + ThF 4 * Lithium 1.33 / Thorium V/Ref. LiF-LiCl** Lithium 12.4 / 9.4 / / 93.8 / / -0.4 / -0.4 A LiF-ThF 4 Lithium 0.17 / Thorium V/Ref. LiCl-KCl Lithium 17.0 / Potassium A LiCl-CaCl 2 Lithium 1.63 / Calcium A LiF-CaF 2 [6] Lithium 6.1 / Calcium A * mol/kg of ThF 4 ** 3 experiments Even if the reduction potential of an element occurs at a more cathodic potential compare to lithium reduction on a bismuth liquid electrode, this element will be reduced simultaneously The molten salt selected is LiF-LiCl for the bismuth pool production Electroactivity domain of the salt Coulometry ICP-AES analysis of the bismuth [6] M. Gibilaro and al., On the use of liquid metals as cathode in molten fluorides", J. Elect. Chem., 726, p (2014) 12

13 1. Bi-Li / LiF-ThF 4 + UF 4 + NdF 3 Contacting Bi-Li pool with the salt phase LiF-ThF 4 at 600 C in two steps: Experimental device: Glassy carbon crucible 20 (U / Nd) (%) 15 4 Li Bi + UF 4 4 LiF + U Bi 10 Step 1: addition of UF 4 to simulate the actinide Step 2: addition of NdF 3 to simulate the lanthanide 3 Li Bi + NdF 3 3 LiF + Nd Bi 5 Step 2: Bi-Li (12.4 mol%) mol% of NdF Time (min) Step 1: Bi-Li (12.4 mol%) mol% of UF 4 13

14 2. Bi-Li / LiF-ThF 4 + UF 4 + NdF 3 Contacting Bi-Li pool with the salt phase LiF-ThF 4 at 600 C for simulate four stages: 50 (U / Nd) (%) 40 4 Li Bi + UF 4 4 LiF + U Bi 30 Stage 2 Stage 3 Stage 4 20 Stage 1 3 Li Bi + NdF 3 3 LiF + Nd Bi Time (min) 14

15 3. Comparison 1 / 4 stages Extraction efficiency of U and Nd with 1 and 4 stages: Analytical description U Nd 1 stage (Theo.)* stage (Exp.) Stages number for 95% efficiency (blue number) stages (Theo.) (blue number) stages (Exp.) * with bibliographic database and extractions condition X Determination of activity coefficient of M in the fuel salt No data in LiF-ThF 4 salt 15

16 1. Speciation of thorium Speciation of thorium by adding lithium fluoride in LiCl-KCl: LiCl-KCl ThF 4 ( mol/kg) Working electrode (W) S = 0.50 cm 2 Scan rate 100 mv/s Measuring the solvation effect on the equilibrium potential of Th(IV)/Th system Open circuit potential evolution of a Th working electrode prepared by electrodeposition The equilibrium potential measured corresponds to the potential of Th(IV)/Th redox system 16

17 2. Mathematical analysis [8] Simulation of the experimental section: Nernst relation: Potential for each addition of LiF Initial potential (x(lif) = 0) Complexation reaction and equilibrium constant: The equilibrium constants bi can be performed by fitting the variation of (a M,F ) as a function of the total concentration of fluoride ions [7] [7] F. Séon, "Réactions d échange de l'ion oxyde dans l'eutectique LiCl-KCl a 470 C: application a la chloruration sélective d'oxydes métalliques en milieu chlorures fondus", Thèse de doctorat, Université de Pierre et Marie Curie, France (1981) [8] S. Delpech et al., "Electrochemistry of thorium fluoride in LiCl-KCl eutectic melts", Elect. Chem. Ac., vol. 144, p (2014) 17

18 3. Extraction efficiency M log M/Li log ɣ (MF Z ) MS Th (IV) U (IV) U Bi + 3UF 4 4UF 3 Nd (III) *ɣ(lif) MS = 0.90 Theoretical extraction efficiency decrease and closer from experimental efficiency 18

19 Bi-Li pool production: Great control of the lithium mole fraction in Bi Use of LiF-LiCl necessary to produce pure bismuth-lithium pool Perspective: X Stability of the bismuth-lithium pool in LiF-ThF 4 will be studied Extraction experiments: Realization of extraction of U and Nd but also extraction of Th in 1 stage and 4 stages Low value of the extraction efficiency Development of a methodology for activity coefficient calculation: Calculation of activity coefficient for Th, U and Nd in the fuel salt Perspective: X Calculation of ɣ(lif) MS T=600 C LiF-ThF 4 -UF 4 ( mol%) The low value requires a lot of stages to attempt a high efficiency: Reprocessing by reductive extraction? Another way: Reprocessing by electrolysis? 19

20 Thank you for your attention 20

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