1. 1 Fuel Cycle Chemistry Chemistry in the fuel cycle §Uranium àSeparation àFluorination §Fission products Advanced Fuel Cycle §Fuel development §Separations Environmental behavior §Waste forms Focus on chemistry and radiochemistry in the fuel cycle

2. 2 Reactor basics Utilization of fission process to create heat §Heat used to turn turbine and produce electricity Requires fissile isotopes § 233 U, 235 U, 239 Pu §Need in sufficient concentration and geometry 233 U and 239 Pu can be created in neutron flux 235 U in nature §Need isotope enrichment induced fission cross section for 235 U and 238 U as function of the neutron energy.

3. 3 Uranium chemistry Separation and enrichment of U Uranium separation from ore §Solvent extraction §Ion exchange Separation of uranium isotopes §Gas centrifuge §Laser

4. 4

5. 5 Mining Uranium is reduced (tetravalent) Introduction of oxygen produces hexavalent uranium 222 Rn daughter Ore mining or solution mining §solution mining uses injection of sulfuric acid to dissolve U and solution is removed §not all solution is removed §minerals are solubilized §seepage into aquifer (Dresden, Sachsen)

6. 6 Acid-Leach Process for U Milling U ore Crushing & Grinding Water Acid Leaching Slurry H 2 SO 4 Steam NaClO 3 40-60°C Separation Tailings Solvent Extraction Recovery, Precipitation Drying (U 3 O 8 ) Organic Solvent NH 4 +

7. 7 Uranium Ore http://www.cogema.fr/photos_gb/

8. 8 Yellowcake production http://www.cogema.fr/photos_gb/

9. 9 U Fluorination U ore concentrates Conversion to UO 3 UO 2 H 2 Reduction UF 4 U metal UF 6 HNO 3 Solvent extraction purification HF Mg MgF 2 F2F2

10. 10 Fuel Fabrication Enriched UF 6 UO 2 Calcination, Reduction Tubes Pellet Control 40-60°C Fuel Fabrication

11. 11 Aside: Fluorination of UO 2 by NH 4 HF 2 Degradation of TRISO Fuel and Kernel Matrices using Ammonium Bifluoride §Chemical treatment of TRISO Concept: Fluorination of graphite, SiC and actinide kernel by NH 4 HF 2 Solid-solid reactions have been observed between ammonium bifluoride and oxides of vanadium, zirconium, thorium, uranium, and plutonium Reaction with uranium dioxide at 25 °C §UO 2 (s) + 4 NH 4 HF2(s) → (NH 4 ) 4 UF 8 ∙2H 2 O(s)

12. 12 Fluorination of UO 2 : Ball Mill at 25 °C UO 2 + 4 NH 4 HF 2 → (NH 4 ) 4 UF 8 ∙2H 2 O ~50 g finely-divided (30  m) UO 2 and 10% excess NH 4 HF 2 20 minutes in a ball mill →

13. 13 U enrichment Utilizes gas phase UF 6 §Gaseous diffusion àlighter molecules have a higher velocity at same energy *E k =1/2 mv 2 àFor 235 UF 6 and 238 UF 6 235 UF 6 impacts barrier more often

14. 14 Gas centrifuge Centrifuge pushed heavier 238 UF 6 against wall with center having more 235 UF 6 §Heavier gas collected near top Enriched UF 6 converted into UO 2 §UF 6 (g) + 2H 2 O  UO 2 F 2 + 4HF Ammonium hydroxide is added to the uranyl fluoride solution to precipitate ammonium diuranate §2UO 2 F 2 + 6NH 4 OH  (NH 4 ) 2 U 2 O 7 + NH 4 F + 3 H 2 O Calcined in air to produce U 3 O 8 and heated with hydrogen to make UO 2 Final Product

15. 15 Fission Product Chemistry Chemistry dictated by oxidation state §Importance of isotopes related to half life àShorter half-lives important in reactor maintenance àLonger lived isotopes important waste treatment and disposal *Dose and heat

16. 16

17. 17

18. 18 Radionuclide Inventories Fission Products §generally short lived (except 135 Cs, 129 I)  ß,  emitters §geochemical behavior varies Activation Products §Formed by neutron capture ( 60 Co)  ß,  emitters §Lighter than fission products §can include some environmentally important elements (C,N) Actinides §alpha emitters, long lived

19. 19 Fission products Kr, Xe §Inert gases §Xe has high neutron capture cross section Lanthanides §Similar to Am and Cm chemistry §High neutron capture cross sections Tc §Redox state (Tc 4+, TcO 4 - ) I §Anionic § 129 I long lived isotope

20. 20 Cesium and Strontium High yield from fission Both beta §Some half-lives similar Similar chemistry §Limited oxidation states §Complexation §Reactions Can be separated or treated together

21. 21

22. 22 Alkali Elements 1st group of elements §Li, Na, K, Rb, Cs §Single s electron outside noble gas core §Chemistry dictated by +1 cation àno other cations known or expected §Most bonding is ionic in nature àCharge, not sharing of electron §For elemental series the following decrease àmelting of metals àsalt lattice energy àhydrated radii and hydration energy àease of carbonate decomposition

23. 23 Solubility Group 1 metal ions soluble in some non- aqueous phases Liquid ammonia §Aqueous electron àvery high mobility Amines Tetrahydrofuran Ethylene glycol dimethyl ether Diethyl ether with cyclic polyethers

24. 24 Complexes Group 1 metal ions form oxides §M 2 O, MOH Cs forms higher ordered chloride complexes Cs perchlorate insoluble in water Tetraphenylborate complexes of Cs are insoluble §Degradation of ligand occurs Forms complexes with ß-diketones Crown ethers complex Cs Cobalthexamine can be used to extract Cs Zeolites complex group 1 metals In environment, clay minerals complex group 1 metal ions

25. 25

26. 26 Group 2 Elements 2nd group of elements §Be, Mg, Ca, Sr, Ba, Ra §Two s electron outside noble gas core §Chemistry dictated by +2 cation àno other cations known or expected §Most bonding is ionic in nature àCharge, not sharing of electron §For elemental series the following decrease àmelting of metals *Mg is the lowest àease of carbonate decomposition àCharge/ionic radius ratio

27. 27 Complexes Group 2 metal ions form oxides §MO, M(OH) 2 Less polarizable than group 1 elements Fluorides are hydroscopic §Ionic complexes with all halides Carbonates somewhat insoluble in water CaSO 4 is also insoluble (Gypsum) Nitrates can form from fuming nitric acid Mg and Ca can form complexes in solution Zeolites complex group 2 metals In environment, clay minerals complex group 2 metal ions

28. 28

29. 29

30. 30 Trivalent Actinides Am, Cm §Am does have oxidation states 3-6 §most prevalent state is 3+ Similar chemical behavior §Trivalent lanthanides can be used as homologs §Thermodynamic data can be interchanged Alpha emitters §Produced through neutron capture

31. 31

32. 32 A=241 Isotopes

33. 33 Solution chemistry Oxidation states §Am (3-6) àAm 3+, AmO 2 +, AmO 2 2+ can be made àAm 4+ rapidly disproportionates in solution except concentrated fluoride or phosphate §Cm (3 and 4) àCm 4+ is a strong oxidizing agent àCm 4+ can be stabilized in high fluoride concentrations forming CmF 5 - or CmF 6 2-

34. 34 Trivalent State In solution forms §Carbonates §Hydroxides §Organic complexes Easily separated from other actinides by redox properties Behaves similar to trivalent lanthanides

35. 35

36. 36

37. 37

38. 38 Absorption and fluorescence process of Cm 3 + Optical Spectra HGFHGF 7/2A Z Fluorescence Process Excitation Emissionless Relaxation Fluorescence Emission

39. 39

40. 40 Waste from Reactor For a typical 1000 MWe reactor §30 tons of spent fuel are produced each year §4-11 m 3 of HLW §up to 400 m 3 of non-HLW Medium Level Waste or Low Level Waste Generally waste not from spent fuel Only LLW in USA (no MLW) Radionuclide Inventory Concerned about: §amount §half-live §decay mode

41. 41

42. 42 Power Plants Spent Fuel §Actinides, Fission, Activation Products Radionuclides from Fuel (in Kg) IsotopeStartingEnding∆ 235 U337.9-25.1 236 U04.04 238 U967942.9-24.1 237 Np00.750.75 Am, Cm00.20.2 Pu09.059.05 FP035.135.1

43. 43

44. 44

45. 45 Solvent Extraction: PUREX Based on separating aqueous phase from organic phase Used in many separations §U, Zr, Hf, Th, Lanthanides, Ta, Nb, Co, Ni §Can be a multistage separation §Can vary aqueous phase, organic phase, ligands §Uncomplexed metal ions are not soluble in organic phase §Metals complexed by organics can be extracted into organic phase §Considered as liquid ion exchangers

46. 46 Extraction Reaction Phases are mixed Ligand in organic phase complexes metal ion in aqueous phase §Conditions can select specific metal ions àoxidation state àionic radius àstability with extracting ligands Phase are separated Metal ion removed from organic phase §Evaporation §Back Extraction

47. 47 Effect of nitric acid concentration on extraction of uranyl nitrate with TBP

48. 48 Reactions Tributyl Phosphate (TBP) §(C 4 H 9 O) 3 P=O §Resonance of double bond between P and O §UO 2 2+ (aq) + 2NO 3 - (aq) + 2TBP (org) UO 2 (NO 3 ) 2. 2TBP (org) §Consider Pu 4+

49. 49

50. 50

51. 51 Extraction Systems Automatic systems are available §Separation of solutions based on density àOrganic usually lower density than water *Chlorinated hydrocarbons tend to be denser than water §Need to achieve phase separation before solution extraction

52. 52 Single Solvent Extraction Stage

53. 53

54. 54

55. 55 Aside: Third phase formation Brief review of third phase formation Related prior research Laboratory methods Np third phase behavior Comparison with U and Pu Spectroscopic observations

56. 56 Third Phase Formation In liquid-liquid solvent extraction certain conditions cause the organic phase to split  PUREX separations using tributyl phosphate (TBP)  Possible with future advanced separations Limiting Organic Concentration (LOC) – highest metal content in phase prior to split Light phase – mostly diluent Heavy phase – extractant and metal rich  Problematic to safety!

57. 57 Actinide Third Phases Light Phase Heavy Phase Aqueous Phase U(VI) Pu(IV) Np(IV)Np(VI) Pu(VI)

58. 58 Importance to Safety Increased risk of criticality Phase inversion Difficulty in process fluid separations Carry-over of high concentration TBP to heated process units  Possible contribution to Red Oil event at Tomsk, Russia

59. 59 Phase Inverted Plutonium Inverted Organic Aqueous Heavy Organic Light Organic

60. 60 Prior Research  Majority of work focused on defining LOC boundary (reviewed by Rao and Kolarik) -Effects of temp., concs., acid, diluent, etc.  Recent work on possible mechanisms -Reverse micelle evidence from neutron scattering (Osseo-Asare; Chiarizia) -Spectroscopic studies -UV, IR, EXAFS (Jensen)

61. 61 Reverse Micelle Theory Classical Stoichiometry Possible Reverse Micelle UO 2 2+ + 2NO 3 - + 2TBP  UO 2 (NO 3 ) 2 ▪ 2TBP

62. 62 Role of the Metal LOC behavior well known for U(VI), U(IV), Pu(IV), and Th(IV) Little data available on Pu(VI) No data on any Np systems Mixed valence systems not understood

63. 63 Mixed Systems Observed effect of Pu(VI) in HPT vs. C 12 Large impact of presence of Pu(VI) in HPT -Indications heavy phase enriched in Pu(VI) Opposite found with U(VI) inhibiting phase separation in U(IV) system (Zilberman 2001)  Suggests possible role of trinitrato species AnO 2 (NO 3 ) 3 -

64. 64 Neptunium Study Unique opportunity to examine trends in the actinides [LOC curve for U(IV) vs Pu(IV)] §- Effective ionic charge §- Ionic radii §- Stability constants for trinitrato species Never been investigated Ease of preparing both tetravalent and hexavalent nitrate solutions

65. 65 Neptunium Methods Worked performed at Argonne National Laboratory, Argonne, IL Stock prepared from nitric acid dissolution of 237 Np oxide stock Anion exchange purification -Reillex HPQ resin, hydroquinone (Pu reductant), hydrazine (nitrous scavenger) Np(IV) reduction with hydrogen peroxide reduction Np(VI) oxidation with concentrated HNO 3 under reflux Np(VI) nitrate salt Np(IV) nitrate

66. 66 LOC Behavior Np(VI) near linear Np(IV) slight parabolic  Appears between linear U(IV) and parabolic Pu(IV) Both curves similar resemblance to distribution values Purex systems §  Suggests possible link with metal- nitrate speciation

67. 67 Np Third Phase Boundaries

68. 68 Comparison with Other Actinides UNpPu An (IV)0.08 (Wilson 1987) 0.150.27 (Kolarik 1979) An (VI)No 3Φ (Chiarizia 2003) 0.170.10 LOC in 7M HNO 3 / 1.1M TBP/dodecane 20-25 °C, M

69. 69 Organic Nitric Acid Balance available TBP and organic H + Np(IV) = mixture of the monosolvate (TBP · HNO 3 ) and hemisolvate (TBP · 2HNO 3 ) species Np(VI) = hemisolvate  Agrees with literature data on U(VI) and Th(IV) acid speciations

70. 70 Valence Trends – An (IV) General trend = decreasing LOC as ionic radii increases  Lowest charge density = lowest LOC Np intermediate between U and Pu Literature Th(IV) data consistent with trend

71. 71 Valence Trends – An(VI) An(VI) = LOC increases as ionic radii decreases  Opposite trend for An(IV), including Th(IV) Charge density using effective cationic charge and 6- coordinate radii  No evidence of correlation with charge density within error of effective charge data Oxo group interactions not fully considered §  Future work required

72. 72 Spectral Study Methods Look for spectral trends in Np(VI) system Examined trends for: -LOC -Metal loading -Nitrate loading (using NaNO 3 ) 5 mm quartz cuvette with Cary 5 Spectrometer

73. 73 LOC Spectra

74. 74 Metal Loading

75. 75 Nitrate Effects AqueousOrganic [H + ] = 4M, [Np(VI)] = 0.03M

76. 76 Valence Scoping Experiments Examined various mixes of Pu(IV)/Pu(VI) Solutions prepared by method of slow addition of concentrated HNO 3 to heated syrupy Pu nitrate solution Use UV-Vis peak analysis for determination of initial aqueous composition Perform mole balance on aqueous phase before and after contact for organic content of each valence species (some samples)

77. 77 Spectrum – Mixed Valence Phases

78. 78 Third phase conclusions Third phase behavior measured in Np LOC trends consistent with U and Pu Np(IV) LOC trends with charge density No clear correlation for Np(VI) Spectroscopic evidence suggests possible role of trinitrato species in third phase

79. 79 The Department is engaged in the review and approval process for the NGNP Acquisition Strategy §Critical Decision from the Deputy Secretary is expected to be issued in a matter of weeks We expect to be able to make awards for NGNP in 2005 Expected NGNP to be gas cooled reactor §TRISO fuel §Prismatic àBased on discussion amongst current researchers àNot official Research coupled with Gen IV, AFCI, nuclear hydrogen and NERI §NERI program covers all areas §Increase university participation Current and Future Fuel Cycles: US Approach and R&D Programs Next Generation Nuclear Plant

80. 80 US DOE Advanced Fuel Cycle Initiative Advanced Fuel Cycle Initiative §Administered by the Office of Nuclear Energy, Science and Technology Stems from National Energy Policy Development Group, May 2001 §Support expansion of nuclear energy in the United States §Develop advanced nuclear fuel cycles and next generation technologies §Develop advanced reprocessing and fuel treatment technologies

81. 81 AFCI Mission and Goals Mission §Develop technologies for the transition to a stable, long-term, and politically acceptable advanced fuel cycle àWaste àProliferation resistance àEconomics àSafety *Transition from once-through fuel cycle to an advanced closed fuel cycle ØCurrent focus on aqueous reprocessing; additional research on pyroprocessing Goals §Develop advanced, proliferation-resistant fuel cycle technologies for current and next-generation reactors §Develop a recommendation on the need for a second repository in the 2007- 2010 timeframe àRepository and proliferation needs related to separation àNear term focus on utilization of existing reactors for transmutation àReduce cost of geologic disposal by enhancing performance of Yucca Mountain *Heat loading

82. 82 AFCI Research National Program on Development of New Nuclear Fuel Cycle §Combines universities, national laboratories, and industry §Long term view àTo be deployed in the future àTraining next generation of researchers àDevelopment of new facilities *“Super Atalante” for separations and fuel §Development of fuel cycle that combines separations and fuel design àUtilization of separated material for fuel in new or existing reactors Address pressing nuclear issues facing the United States: §nuclear energy and waste management concerns §declining US nuclear infrastructure àFacilities and researchers §global nuclear leadership àCooperation with international partners *France *Russia

83. 83

84. 84 AFCI Research Separations §Aqueous-organic §Electrochemical separations in molten salt §TRISO fuel àReprocessing and repository behavior of Pu, Np, Am fuel Fuel §Inert matrix for existing light water reactors §Advanced fuels with transuranic elements àOxides, carbides §TRISO fuel àSilica carbide coated fuel for gas reactors àProduction of coated Pu, Np, Am oxides Reactors §Advanced light water reactors §Gas reactors àHigh temperature for H 2 production àTRISO fuel deep burn reactors *Pu, Np, Am kernel ØReactor physics and system analysis

85. 85 Overview of AFC reactors

86. 86 AFCI separations Bulk U separations §Precipitation §Electrochemistry àDisposal or re-enrichment Separation of actinides and fission products by group §Transuranics (Np, Pu, Am, Cm) àSolvent extraction àFor incorporation into fuel *Discussion of Am and Cm separation ØFuel fabrication §Fission products àCs, Sr *Separate disposal àLanthanides *Separation from actinides

87. 87 Separation Primarily solvent extraction based on PUREX §Organic phase tributylphosphate in dodecane àSome inclusion of other organic ligand *Acetohydroxamic acid §Aqueous phase nitric acid at varying concentrations §Other processes also examined àPyroprocessing àFluoride volatility

88. 88 Current Extraction Scheme UREX §PUREX modification §addition of the acetohydroxamic acid (AHA) reduces Pu àTetravalent Np and Pu forms aqueous phase AHA complexes §U and Tc extracted CCD-PEG §Cs and Sr extracted with chlorinated cobalt dicarbollide/polyethylene glycol (CCD/PEG ) NPEX §Np, Pu §Nitric acid, acetohydroxamic acid, CH 3 COOH TRUEX §Remaining fission products except lanthanides §TBP with Diphenyl-N,N-dibutylcarbamoyl phosphine oxide (CMPO), oxalic acid CYANEX-301 §Am and Cm §TBP, CYANEX-301

89. 89 Separation flowsheet CCD-PEG Tc, U TRUEXCYANEX-301 UREX Cs, Sr NPEX Pu, Np FPAm, Cm Cs, Sr, Np, Pu, Am, Cm, FP, Ln Np, Pu, Am, Cm, FP, Ln Am, Cm, FP, Ln Am, Cm, Ln Ln

90. 90 High Level Waste and AFC Separation coupled to extension of repository utility §Separation of heat generating isotopes §Separation of long lived actinides Need 6000 MT reprocessing capacity High Level Waste

91. 91 Expect US Repository Need in 2100

92. 92 Current AFCI Direction Stress research for recommendation on second repository in 2007-2010 §explore new alternative approaches to provide confidence in selection §advanced recycle research facility Investigate other advanced aqueous processes Defer building and construction Increase systems analysis and modeling Align separations with current US non-proliferation policy §May need to emphasize group actinide separations àRemove U, keep rest of actinides as group FY 2005 Budget at $ 68 M

93. 93 Evaluation of Fuel Cycles 6 cases were studied for 3 growth rates (0%, 1.8%, 3.8%) §Once through LWR §LWR + Inert Matrix Fuel (IMF)(TRU) recycle in LWR àstart separations in 2025 §LWR + MOX (Np, Pu, Am) one pass in LWR àstart separations in 2025 §LWR + IMF (Pu, Np) + Fast Reactor (FR) (TRU) §LWR + MOX (Pu, Np) one pass + FR (TRU) §LWR + FR (TRU)

94. 94 Pu Inventory

95. 95 Repository Heat Loading

96. 96 Implementation of Fuel Cycle Separation facility identified as limiting factor §Early large scale separation enterprise §reactor capacity for recycled materials is not issue àDelay in separation causes large inventory delay in 2 nd tier reactor Exact separation scheme open to debate §Ideally only fission products go to repository §Separation and storage of Cm àDecay of 244 Cm will leave 245 Cm §Time before separation àAnalysis supports both 5 year and 30 year waiting period *Different results based on heat loading and proliferation ØIssue is decay of 241 Pu ØNeed to prevent placement of 241 Am, 238,240 Pu and 237 Np in repository

97. 97 Separation Needs Both repository and proliferation resistance needs to be addressed §Repository àReduction of heat loading *Separation of Cs, Sr *Removal of 241 Pu and 241 Am àEnvironmental behavior of 237 Np §Proliferation àBuild up of fissile isotopes in fuel cycle àSeparation of Pu during reprocessing *Procedure should not produce separated Pu stream

98. 98 Separations Current extraction research (Scheme 1) §U and Tc with UREX àU precipitation as nitrate §Cs and Sr with CCD-PEG §Np, Pu with NPEX §Remaining fission products except lanthanides with TRUEX §Am and Cm with CYANEX-301 and TPB àAm and Cm separation New concept separation discussed (Scheme 2) §U §Cs, Sr, and long lived fission products §No Pu or Np/Pu separation àActinide group separation Future separation research and development ongoing §Am and Cm treatment àSeparation both from recycle or just Cm Mass separation can be applied to either scheme §Initial U separation needed for both schemes

99. 99 Waste Forms and Packaging Components of Waste §Radioactive Isotopes §Other Materials Waste Forms §Materials §Characteristics §Properties and analysis Spent Fuel

100. 100

101. 101 Components of Waste Radioactive elements common in radioactive waste §monovalent:Cs §divalent:Sr, Co §trivalent:Am, Cm §tetravalent:Zr, Tc, Th, U, Pu §heptavalent:Np, Pu §hexavalent:U, Pu §septvalent:Tc Non radioactive elements need to be considered §B, lanthanides, Si, Cu, Fe, Ni, Ti, Zr, C, H, O Each elements behave differently in the environment and needs to be considered separately

102. 102 Waste Placement and Packaging A disposal site will contain packaged waste Waste will have different sections and components §Waste Form àForm of the material containing the radioactive waste §Canister àPrimary container of the waste form *Consider robust canister §Overpack àBarrier surrounding canisters for up to 1 meter àMay not be used

103. 103 Waste Placement and Packaging §Backfill àMaterial placed into gallery àDifferent possible backfill materials *Bentonite, crushed geologic material ØHigh exchange capacity or low permeability §Sleeve for removal may be included §Drip shield àDivert water from package

104. 104 Waste Package Requirements From 10CFR60 “Substantially complete” (assuming anticipated processes and events) containment for 300 to 1000 years after repository closure Release rate after 1000 years < 10 ppm/year for inventory at 1000 years Retrievability at any time up to 50 years after emplacement starts

105. 105 Waste Forms In US, two existing high level waste forms §Spent fuel àZircaloy clad à≈5% UO 2 §Borosilicate glass àSiO 2 -B 2 O 3 -Na 2 O à1-30% waste in the glass A number of other waste forms are being considered

106. 106 Waste Forms Ceramics §For disposal of weapons grade Pu §Very durable material §Based on TiO 2, ZrO 2 §Up to 20% incorporation of waste àFor Weapons grade Pu, up to 10% Pu §Zeolite ceramics examined for disposal of liquid metal reactor waste àHigh Na contain precluded normal ceramics and glass

107. 107 Zeolite

108. 108 Waste Forms Other Glass §Developed as potential candidates àPb-Fe phosphate àLanthanide borosilicate *For weapons grade Pu àMonazite àSulfur glass *For Hanford waste Waste loading determines volume, radiation dose, and thermal property of glass

109. 109 Glass Inorganic product of fusion §Cooled to a rigid condition §No crystallization àAmorphous material §Any substance with rapid cooling

110. 110 Glass Structure Compound forming structural network §Oxides of Si, B, and P Modifiers §Decrease melting temperature §Add favorable processing properties àCan degrade stability, increase solubility *Oxides of Na, K, Ca, Ba Intermediates §Can be present in waste §May act as network former, increase durability àOxides of Al, Fe

111. 111 Thermal Stability of Glass Devitrification §Formation of crystals in glass §Lower chemical stability àIncreased leaching §Reduced waste loading Phase separation §Liquid-liquid phase separation during formation

112. 112 Glass Radiation Stability Atomic displacement by heavy particle radiation §Volume change àDensity changes by 1% àDepends upon glass chemical composition §Crystallization àConcern over stored energy in glass leading to cracking or crystallization Ionizing effect from ß and  Chemical effects §Disordering àBreaking of bonds causes increased corrosion §Radiolytic processes in aqueous medium in contact with glass

113. 113 Glass Corrosion Formation of altered phase on glass surface Can inhibit diffusion of radionuclide out of glass Two possible method of radionuclide release §Diffusion of radionuclide out of glass àDepends upon chemical behavior of radionuclide §Corrosion of glass with release of radionuclide àRelease depends upon glass àSecondary phase formation varies for radionuclide

114. 114 Need to consider colloids Chemical changes in near field can also effect glass dissolution Basic Dissolution Rate Equation Rate=Sk(1-(Q/K)  S=surface area, k=rate coefficient, Q= activity, K=K sp   =stoichiometric number for rate-limiting reaction

115. 115 Spent Fuel Barrier §Zr cladding àZr corrosion *Zr + 2H 2 O -> ZrO 2 + 2H 2 àWeakening of cladding àDrop in thermal conductivity Radiation §Atomic Displacement §Neutron activation of Zr and Ni 3 phases of release §Gap release, grain release, UO 2 dissolution

116. 116 Geochemistry Principles which control the behavior of dissolved groundwater constituents Behavior based on equilibrium concepts Provide insight into behavior Groundwater Constituents Concentration Units §Molality (m) (mol/kg solute) §Molarity (M) (mol/L) for dilute concentrations (<0.2 M), m≈M §Mass concentration (g/L, mg/L) §Equivalent (valence per unit) Used for resins or humic substances (moles H + /g) Often written in milliequivalents/g (meq/g)

117. 117 Speciation and Transport

118. 118 Temperature Effects Temperature effects can be described by enthalpy (∆H) and entropy (∆S) Gibbs Free Energy (∆G) relates ∆H and ∆S ∆G=∆H-T∆S ∆G=-RTlnß T in K, R=8.314 J/molK Temperature effect on ß can be described as:

119. 119 Oxidation-Reduction Charge of ions in solution §Fe, Mn, Co, As, Cr, U, Np, Pu are some redox sensitive metal ions Eh-pH diagrams can show the oxidation states §based on oxygen and hydrogen §Eh is also written as pE O 2 (g) + 4H + + 4e 2 H 2 O 2H + + 2e H 2 (g) At 25 °C pE = 20.8 - pH + 0.25 logP O2 pE = - pH - 0.5 logP H2

120. 120 Eh-pH diagram for Gohy Groundwater

121. 121 Am and Cm at ORNL WAG-5 site pH near 7 Carbonate system Use modified Gohy data §FA stability less than HA [FA(III)] =2 µmol/L [An 3+ ] t = [Cm 3+ ] + [Am 3+ ] = 20 pmol/L aqueous carbonate concentration evaluated from the measured alkalinity ionic strength at 0.02 M

122. 122 Data of WAG-5 Site Specieslogß AnFA(III)6.09±0.12 An(OH)FA(II)13.04±0.20 An(OH) 2 FA(I)17.24±0.30 An(CO 3 )FA(I)12.74±0.30 Also carbonate and hydrolysis data LC = 0.279pH - 1.01 §maximum =1, minimum = 0

123. 123 Speciation Calculation for WAG-5 Site