Modifying U/Pu separation chemistry in Purex processes Robin Taylor. Date: 02/12/09

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1 Developments in actinide separations for processing past, present & future nuclear fuels Modifying U/Pu separation chemistry in Purex processes Robin Taylor Date: 0/1/09

2 Purex reprocessing plant Fuel preparation (disassemble, declad, shear) Dissolution in HNO 3 Solvent extraction of U & Pu (+Np+Tc) into TBP/kerosene solvent separation from fission products Separation of Pu from bulk U stream Purification of U & Pu streams (if required) Conversion to solid oxide products Waste management Slide

3 Basis of U/Pu separation = reductive stripping Extraction Stripping U,Pu extractable Pu UO NO 3 + NO 3 + TBP + TBP Pu( NO ) UO ( NO TBP ).TBP D 100 U(VI) 10 Pu(IV) Distributi on Ratio D = U,Pu inextractable X [ X ] [ X ] solv aq Redox reactions Pu(IV) + reductant Pu(III) + products Pu(III) + HNO Pu(IV) + products HNO + stabiliser products HNO3 (M) Pu(III) inextractable Slide 3 Pu(III)

4 U/Pu separation Key process stage Magnox reprocessing Ferrous sulphamate Thorp reprocessing Uranous (IV) nitrate / hydrazine Advanced reprocessing Complex chemistry Slide 4

5 Magnox Reprocessing Magnox Reprocessing Linked series of plants Reprocessing commissioned 1964 Al/Mg clad U metal fuel from UK Magnox reactors Low burnup & short cooled fuel Salt containing flowsheet (Fe, S, Na) Waste treatment infrastructure Slide 5

6 New flowsheet for PS4 in Magnox Reprocessing Objective to minimise solid wastes arising from Magnox Reprocessing Ferrous sulphamate added in PS4 (U/Pu split) major contributor 10 s M savings over plant lifetime achievable + ultimate disposal liability + avoid new ILW store? Question was how can we reduce FeSM usage in PS4? Options Low Iron flowsheet Partially replace FeSM with HAN Low Acid flowsheet Reduce acidity in PS4 (reduced FeSM) Needed a better understanding of existing PS4 chemistry Slide 6

7 PS4 U/Pu separation contactor 0% TBP/OK 13 M HNO 3 [Pu] < 0. g/l [U] ~ 60 g/l 18 U recovery Pu backwash 1 5 ºC 5 ºC [U] ~ 45 g/l [Pu] < 1E-6 g/l 0.5 M HNO 3 [Pu] ~ 1.5 g/l [U] < E-4 g/l Solvent Aqueous Fe(II)SM Fe + + Pu 4+ Fe Promote 3+ + Pu 3+ NH SO3H + HNO H SO NO + H O... + N + H O NO + HNO3 + H O 3HNO Pu 3+ + HNO + H + Prevent Pu Slide

8 The Box Effect complex reaction cycles Super-stoichiometric consumption of Ferrous ions to reduce Pu 4+ ions [Pu(IV)(TBP) (NO 3 ) 4 ] (D~6) [Pu(III)(TBP) 3 (NO 3 ) 3 ] (D~0.0) [HNO 3 TBP] (D~0.1) Pu(IV) + Fe(II) Pu(III) + Fe(III) Pu(III) + NO + H + Pu(IV) + HNO HNO 3 + HNO NO + H O [HNO TBP] (D~10) [HNO TBP] NO + HO] NH SO 3 H + HNO fast fast H SO 4 + N + H O Fe(II) + NO + H + Fe(III) + HNO Aqueous AqueousOrganic Organic [Pu(III)(TBP) + 3 (NO 3 ) 3 ]+ NO + H + [Pu(IV)(TBP) (NO 3 ) 4 ] + HNO Slide 8

9 What about engineering? SX contacting equipment in Magnox reprocessing = Mixer-settlers Mixer Settler SINGLE STAGE Solvent & aqueous streams flow counter-current to each other BATTERY 1 STAGES Slide 9

10 Modelling existing plant flowsheet (Mk 9) Process model required Solvent extraction algorithms (major species) Chemical kinetics (aqueous & solvent phases) Mass transfer and/or stage efficiencies Physico-chemical data Mixer-settler details nd order effects (radiolysis, DBP, entrainment) Sensitivity tests on model Validation against lab flowsheet trials Validation against single stage experiments Validation against plant data Validation against pilot plant trials (1960 s) Confidence to extend to low Iron flowsheets designs Slide 10

11 Validation against plant performance Fe(III) in Aq Prod Plant data 0.04 Model transformed 0.03 Factor X Model Time (hours) Slide 11

12 Fe/Pu/HAN chemistry & reactions Alternatively partially replace FeSM with HAN as it is known that: HAN can reduce Pu(IV) HAN can reduce Fe(III) Savannah River tested a FeSM/HAN flowsheet Reduction of Pu(IV) by HAN is slow unless H+ < 1 M HNO 3 Pu 4+ + NH 3 OH + Pu 3+ + H + + H O N Fe catalyses the reduction of Pu(IV) by HAN because: HAN reduces Fe(III) Fe 3+ + NH 3 OH + Fe + + H + + H O + 0.5N HAN can also scavenge HNO HNO + NH 3 OH + H + + H O + N O HAN can also generate HNO autocatalytically (!) Confusing literature Slide 1

13 -phase (single stage) experiments 4.5E-04 Could the Box Effect be suppressed simply by reducing the acid concentrations within PS4? Therefore could lower concentrations of FeSM be used to maintain 80 ppm Pu(III) DBP concentration (without HAN)? 4.0E E E-04.5E-04.0E E E E E Total HNO 3 (M) [U] =.5 g/l [U] = 5 g/l [U] = 50 g/l Mass Transfer DBP Rate of consumption of ferrous as a) function of uranium concentration ([Pu] = 1.4 g/l, 4M HNO3, 0.17 M FeSM, 0% TBP/OK ) and b) a function of acidity for conditions of (pre-equilibrium) [Pu] = 1.4 g/l, 0.17 M FeSM, 0% TBP/OK; data in the presence of DBP and at lower stirrer efficiency are also Slide 13 shown.

14 Deciding factor Low Fe vs. Low Acid % Fe(II) % Fe(II) Conditions: [Fe] = M, [HAN] = 0.76 M, [H + ] = days = 14.4 mins DEG C 5 DEG C 35 DEG C 45 DEG C 55 DEG C 0.01 days = 14.4 mins Time (days) [Fe] = M, [HAN] = 0.76 M, [H + ] = 1.9 M Bengtsson Lehman Fox Time (days) - d[fe(iii)] [Fe(III)][NH3 OH =k dt + [H ] [Fe(II)] - d[fe(iii)] k [Fe(III)] [NH = dt c [Fe(II)] [H a = 1.5, b = 1 & c = 1.5 Experimental kinetics under process conditions: Ambient T similar to slower rate High E a = 175 kj/mol Requirement for elevated temperature Considered not implementable on plant Proceed with Low Acid flowsheet a ] + OH ] + ] b Slide 14 LEHMAN - d[fe(iii)] K [Fe(III)] [NH3 OH ] BENGTSSON = dt + 4 [Fe(II)] [H ]

15 Aqueous Acid Profiles [H+](aq) 3.5 Aqueous Acid Profiles for Various Flowsheets 3.5 Low Acid F/S Mark 9b F/S Mark 9c F/S Mark 10 F/S Stage Slide 15

16 Base Case Low Acid Flowsheet Solvent Product: U, Np, some Tc in TBP/OK Active Feed: U, Pu i n T BP/ OK Np, T c Impurities Solve nt Feed: TBP/OK PS4 Plutonium Backwash PS4 Uranium Strip Strip Acid: Reductant: HN O 3 Fe rr ous Sulp hama te: Redu ced by 40% und er LA FS Split (C onditioning) Acid:HNO 3 : Changed from C oncentrate d to Dilu te un der LAFS Aqueous Product: Pu, some Tc in HNO 3, Resid ual FeSM an d its reaction products 40% Reduction in FeSM usage in PS4 Slide 16

17 Next generation processing & actinide recycle GenIII & transition to GenIV based fuel cycles Actinide recycle as: Limited U reserves need to maximise energy potential of SF Extend capacities of geological repositories Reduce radiotoxicity of wastes in repositories Proliferation resistance & nuclear security concerns Advanced Fuel Cycle plants need to demonstrate: Reduced wastes & environmental impact Reduced costs Greater flexibility Greater proliferation resistance Industrially deployable processes U + Pu (Np) recycle modified PUREX technology Minor actinide recycle Slide 17

18 Complexant based stripping Based on greater affinity of charge dense An(IV) ions to form hydrophilic complexes with aqueous ligands Temperature insensitive ambient T operations Fast kinetics No Pu(III) so no stabiliser required Stable species no catalytic cycles Suitable for high Pu feeds (MOX/FR fuels) No dilution of U enrichment Equilibrium processes rather than kinetic Decompose aqueous phase complexants to gases (CHON molecules) Slide 18

19 Hydroxamic acids Bidentate O,O donor ligands Selective for An(IV) ions Strong hydrophilic complexes in acid solutions Unstable w.r.t. acid hydrolysis Redox active CHON decomposable Slide 19

20 Stability constants Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu U(IV) Np(IV) Pu(III) Th Pa U(VI) Np(V) Pu(IV) Am Cm Bk Cf Es Fm Md No Lr Set of Ln(III), An(III,IV,V,VI) logβ 1-4 SX, UV/vis, luminescence methods I= T= C See Ln contraction & Gd break Likely steric constraints (decrease in logk 4 from Ho(III) onwards) Follow expected trends in logβ 1 AnO + < An(III) < AnO + < An(IV) log10(1 st stability constant) An(III) An(IV) Ln(III) Ln(III) K /ionic radius (pm -1 ) 1:1 1: H Ce(III) Nd(III) Eu(III) Dy(III) Yb(III) Pu(III) Am(III) Cm(III) Np(IV) Pu(IV) Np(V) Slide 0 U(VI)

21 Aqueous phase speciation (0.1 M AHA) : Np-AHA complex dominates % species Di-nitrate dominates av. AHA coordination 10 0 No hydrolysis [HNO 3 ] (M) % free % mono-nitrate % di-nitrate % mono-hydrolysed % di-hydrolysed 1:1 AHA 1: AHA 1:3 AHA av. AHA number Slide 1

22 Solvent extraction behaviour D Pu(IV) [HNO 3 ] aq,init Low D An(IV) at low HNO 3 Study 3 Study 4 Study 5 ref. [36] 0.1 M AHA ref. [36] 0.3 M AHA Studies 3-5 (T = 5 C; [AHA] = 0.5 M; AHA:Pu = 4:1 390:1; S/A = 1:1; Karraker at (a) 0.1 M AHA; AHA:Pu = 7470:1 and (b) 0.3 M AHA; AHA:Pu = 410:1 (S/A = 1); DPu(IV) [Pu(IV)]aq,init (g/l) D Pu(IV) remains low with high [Pu] Effect of initial Pu(IV) concentration on the Pu(IV) distribution coefficient (T = 5 C; [XHA] = 0.5 M; [HNO 3 ] aq,init = 1.0 M Example Separation Factors SF U/Pu = 585 at 0. M HNO 3 ; 0.5 M AHA SF U/Np = 11 at 0.6 M HNO 3 ; 0.1 M AHA SF U/Np = 498 at 0.6 M HNO 3 ; 1 M AHA Selective stripping conditions Low HNO 3 Excess AHA Ambient temperature Short residence times Slide

23 Solvent extraction models (HNO 3 ) a (TBP) b HNO 3 =H + +NO 3 - An 4+ +ino 3- =An(NO 3 ) i (4-i)+ HLH + HL L - An 4+ +L - =An(L) j (4-j)+ An(NO 3 ) 4 (TBP) An(NO 3 ) 4 (TBP) HNO 3 Can model as an extension of simple An(IV)-HNO 3 -TBP/OK system With AHA complexation in aqueous phase Ionic strength effects included (SIT) Extraction of An(IV)- AHA complexes into TBP predicted An 4+ +OH - =AnOH 3+ AnL j (NO 3 ) (4-j) (TBP) D An( IV ) = { NO 3 } [ TBPf ] 1 1+ K1 [ H 3 + ( K { NO } + K { NO } { H } + K [ L ] ) + X 3 + β1[ NO ] 3 X, HNO3 ] + β [ NO 3 ] 3 + β ' 1 [ L ] + β ' X, AHA, [ L ] Slide 3

Flowsheet testing MOX & FR feeds 3 AHA tests from 18 100 g/l Pu (40 wt.

24 Flowsheet testing MOX & FR feeds 3 AHA tests from g/l Pu (40 wt.%) in Aqueous Feed 30% TBP HA HA HS HAR 30% TBP SP1 HAF U,Pu,Np,Tc HNO 3 SP U Pu AHA trials general layout URX PuS PuS PuS AP Np,Pu Solvent Aqueous UV-Vis flow cell AHA HNO 3 Solvent flow Aqueous flow Slide 4

25 Pu/AHA Flowsheet Trials: Key results Trial 1 Trial Trial 3 [Pu] in HAF (g/l) Solvent loading (%) [Pu] in HAR (g/l) Pu % recovery >99.97 > > U % recovery > > > [Pu] in product AP (g/l) [U] in product SP (g/l) U stream Pu DF E+06 Pu stream U DF 1.30E Pu in U product (µgpu/kgu)* Slide 5

26 Hot testing AHA based processes Argonne National Lab. UREX Process (USA) 30% TBP n-dodecane HAF AHA HAR To SX cycles CCD-PEG TRUEX TALSPEAK HA HS 1C All TRU+FP % U+95%Tc U Ion exchange column Tc (Option Tc Rejection) Dil.HNO 3 Cs+Sr TRU FP Pu (Raff) U product U Finishing Slide 6

27 Conclusions New flowsheet for 40+ year old Magnox reprocessing plant operational multi-m savings due to reduction in wastes Criticality safety case issues in maloperations key aspect Use of AHA enables move to complexant based stripping of Np+Pu rather than reductive stripping Substantial benefits in flowsheet operations Likely future reprocessing technology U/Pu separation is key point in flowsheet Fundamental process chemistry is key to underpinning flowsheet development Slide 7

28 Acknowledgements NNL (Past & present) Danny Fox (NDA) Mike Carrott Howard Sims Mark Sarsfield Chris Mason Chris Maher Dave Woodhead Steve Percival Richard Cooke Cécile Roube (AREVA) Iain Denniss Iain May (LANL) Chris Jones (UofM) Eddie Birkett (Sellafield Ltd.) Sellafield Ltd Nigel Donaldson Debbie Keighley Jeff Hobbs Bill Carr Steve Cope Magnox Technical NDA Neil Smart EC FPVI EUROPART Charles Madic Collaborations Colin Boxall (U of Lancaster) Fabrice Andrieux (U of Lancaster) Greg Choppin (FSU, USA) Sergey Sinkov (PNNL, USA) Boris Zilberman (KRI, Russia) AEA-T Harwell Slide 8

Neptunium behaviour in PUREX and GANEX processes

Neptunium behaviour in PUREX and GANEX processes C. Gregson, M. Carrott, D. Woodhead, R. Taylor SNEC 2014, Manchester Challenges in Np separations chemistry Background Neptunium extraction in an Advanced