1

Uranium Chemistry and the Fuel Cycle • Chemistry in the fuel cycle

Uranium Solution Chemistry Separation Fluorination and

enrichment Metal

• Focus on chemistry in the fuel cycle Speciation (chemical

form) Oxidation state Ionic radius and

molecular size

• Utilization of fission process to create heat Heat used to turn turbine

and produce electricity • Requires fissile isotopes

233U, 235U, 239Pu Need in sufficient

concentration and geometry

• 233U and 239Pu can be created in neutron flux

• 235U in nature Need isotope enrichment

Why is U important in the fuel cycle: induced fission cross section for 235U and 238U as function of the neutron energy.

2

Nuclear properties of Uranium • Fission properties of

uranium Defined importance

of element and future investigations

Identified by Hahn in 1937

200 MeV/fission 2.5 neutrons

• Natural isotopes 234,235,238U Ratios of isotopes established

234: 0.005±0.001, 68.9 a 235: 0.720±0.001, 7.04E8 a 238: 99.275±0.002, 4.5E9 a

• 233U from 232Th

need fissile isotope initially

3

Chemistry overview • Uranium acid-leach • Extraction and conversion

4

Fuel Fabrication Enriched UF6

UO2 Calcination, Reduction

Tubes Pellet Control

40-60°C

Fuel Fabrication

Other species for fuel nitrides, carbides Other actinides: Pu, Th

5

Uranium chemistry • Uranium solution

chemistry • Separation and

enrichment of U • Uranium separation

from ore Solvent extraction Ion exchange

• Separation of uranium isotopes Gas centrifuge Laser

• 200 minerals contain uranium Bulk are U(VI) minerals

U(IV) as oxides, phosphates, silicates Classification based on polymerization of

coordination polyhedra Mineral deposits based on major anion

• Pyrochlore A1-2B2O6X0-1

A=Na, Ca, Mn, Fe2+, Sr,Sb, Cs, Ba, Ln, Bi, Th, U

B= Ti, Nb, Ta U(V) may be present when

synthesized under reducing conditions

* XANES spectroscopy * Goes to B site

Uraninite with oxidation

6

Aqueous solution complexes • Strong Lewis acid • Hard electron acceptor

F->>Cl->Br-≅I-

Same trend for O and N group based on electrostatic force as dominant factor

• Hydrolysis behavior U(IV)>U(VI)>>>U(III)>U(V)

• Uranium coordination with ligand can change protonation behavior HOCH2COO- pKa=17, 3.6 upon complexation of UO2

Inductive effect * Electron redistribution of coordinated ligand * Exploited in synthetic chemistry

• U(III) and U(V) No data in solution

Base information on lanthanide or pentavalent actinides

7

Uranium solution chemistry

• Uranyl(VI) most stable oxidation state in solution Uranyl(V) and U(IV) can also be in solution

U(V) prone to disproportionation Stability based on pH and ligands Redox rate is limited by change in species

Making or breaking yl oxygens * UO2

2++4H++2e-U4++2H2O

• yl oxygens have slow exchange Half life 5E4 hr in 1 M HClO4

• 5f electrons have strong influence on actinide chemistry For uranyl, f-orbital overlap provide bonding

8

Uranyl chemical bonding • Uranyl (UO2

2+) linear molecule • Bonding molecular orbitals

σg2 σu

2 πg4 πu

4

Order of HOMO is unclear * πg< πu< σg<< σu

proposed Gap for σ based on 6p orbitals interactions

5fδ and 5fφ LUMO Bonding orbitals O 2p characteristics Non bonding, antibonding 5f and 6d Isoelectronic with UN2

• Pentavalent has electron in non-bonding orbital

9

10

Uranyl chemical bonding • Linear yl oxygens from 5f characteristic

6d promotes cis geometry • yl oxygens force formal charge on U below 6

Net charge 2.43 for UO2(H2O)52+, 3.2 for fluoride systems

Net negative 0.43 on oxygens Lewis bases

* Can vary with ligand in equatorial plane * Responsible for cation-cation interaction * O=U=O- - -M * Pentavalent U yl oxygens more basic

• Small changes in U=O bond distance with variation in equatoral ligand • Small changes in IR and Raman frequencies

Lower frequency for pentavalent U Weaker bond

11

Uranium chemical bonding: oxidation states • Tri- and tetravalent U mainly related to

organometallic compounds Cp3UCO and Cp3UCO+

Cp=cyclopentadiene * 5f CO π backbonding

Metal electrons to π of ligands

* Decreases upon oxidation to U(IV)

• Uranyl(V) and (VI) compounds yl ions in aqueous systems unique

for actinides VO2

+, MoO22+, WO2

2+

* Oxygen atoms are cis to maximize (pπ)M(dπ)

Linear MO22+ known for

compounds of Tc, Re, Ru, Os * Aquo structures unknown

Short U=O bond distance of 1.75 Å for hexavalent, longer for pentavalent Smaller effective charge on

pentavalent U Multiple bond characteristics, 1 σ

and 2 with π characteristics

12

Uranium solution chemistry: U(III) • Dissolution of UCl3 in water • Reduction of U(IV) or (VI) at Hg cathode

Evaluated by color change U(III) is green

• Very few studies of U(III) in solution • No structural information

Comparisons with trivalent actinides and lanthanides

13

Uranium solution chemistry • Tetravalent uranium

Forms in very strong acid Requires >0.5 M acid to prevent hydrolysis Electrolysis of U(VI) solutions

* Complexation can drive oxidation Coordination studied by XAFS

Coordination number 9±1 * Not well defined

U-O distance 2.42 Å O exchange examined by NMR

• Pentavalent uranium Extremely narrow range of existence Prepared by reduction of UO2

2+ with Zn or H2 or dissolution of UCl5 in water

UV-irradiation of 0.5 M 2-propanol-0.2 M LiClO4 with U(VI) between pH 1.7 and 2.7 U(V) is not stable but slowly oxidizes under suitable conditions

No experimental information on structure Quantum mechanical predictions

14

Hexavalent Uranium • Large number of compounds prepared

Crystallization Hydrothermal

• Determination of hydrolysis constants from spectroscopic and titration Determine if polymeric species form Polynuclear species present except at

lowest concentration

15

Uranium speciation • Speciation variation with uranium concentration Hydrolysis as example Precipitation at higher concentration

Change in polymeric uranium species concentration

16

Uranium purification from ores: Using U chemistry in the fuel cycle

• Preconcentration of ore Based on density of ore

• Leaching to extract uranium into aqueous phase Calcination prior to

leaching Removal of

carbonaceous or sulfur compounds

Destruction of hydrated species (clay minerals)

• Removal or uranium from aqueous phase Ion exchange Solvent extraction Precipitation

• Use of cheap materials

Acid solution leaching * Sulfuric (pH 1.5)

U(VI) soluble in sulfuric Anionic sulfate species

Oxidizing conditions may be needed MnO2

Precipitation of Fe at pH 3.8 Carbonate leaching

Formation of soluble anionic carbonate species

* UO2(CO3)34-

Precipitation of most metal ions in alkali solutions

Bicarbonate prevents precipitation of Na2U2O7

* Formation of Na2U2O7 with further NaOH addition

Gypsum and limestone in the host aquifers necessitates carbonate leaching

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Recovery of uranium from solutions • Ion exchange

U(VI) anions in sulfate and carbonate solution UO2(CO3)3

4-

UO2(SO4)34-

Load onto anion exchange, elute with acid or NaCl • Solvent extraction

Continuous process Not well suited for carbonate solutions Extraction with alkyl phosphoric acid, secondary and tertiary

alkylamines Chemistry similar to ion exchange conditions

• Chemical precipitation Addition of base Peroxide

Water wash, dissolve in nitric acid Ultimate formation of (NH4)2U2O7 (ammonium diuranate),

yellowcake heating to form U3O8 or UO3

18

Uranium purification • Tributyl phosphate (TBP) extraction

Based on formation of nitrate species UO2(NO3)x

2-x + (2-x)NO3- + 2TBP UO2(NO3)2(TBP)2

Process example of pulse column below

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Uranium enrichment

• Once separated, uranium needs to be enriched for nuclear fuel Natural U is 0.7 % 235U

• Different enrichment needs 3.5 % 235U for light water reactors > 90 % 235U for submarine reactors 235U enrichment below 10 % cannot be used for a

device Critical mass decreases with increased

enrichment 20 % 235U critical mass for reflected device around

100 kg Low enriched/high enriched uranium

boundary

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Uranium enrichment • Exploit different

nuclear properties between U isotopes to achieve enrichment Mass Size Shape Nuclear magnetic

moment Angular momentum

• Massed based separations utilize volatile UF6 UF6 formed from

reaction of U compounds with F2 at elevated temperature

• Colorless, volatile solid at room temperature Density is 5.1 g/mL Sublimes at normal atmosphere Vapor pressure of 100 torr

One atmosphere at 56.5 ºC • Oh point group

U-F bond distance of 2.00 Å

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Uranium Hexafluoride

• Very low viscosity 7 mPoise Water =8.9 mPoise Useful property for enrichment

• Self diffusion of 1.9E-5 cm2/s • Reacts with water UF6 + 2H2O UO2F2 + 4HF

• Also reactive with some metals • Does not react with Ni, Cu and Al Material made from these elements

22

Uranium Enrichment: Electromagnetic Separation

• Volatile U gas ionized Atomic ions with charge +1 produced

• Ions accelerated in potential of kV Provides equal kinetic energies Overcomes large distribution based on

thermal energies • Ion in a magnetic field has circular path Radius (ρ)

m mass, v velocity, q ion charge, B magnetic field

• For V acceleration potential

qBmcv

=ρ

mVqv 2

=

qVm

Bc 2

=ρ

23

Uranium Enrichment: Electromagnetic Separation

• Radius of an ion is proportional to square root of mass Higher mass, larger radius

• For electromagnetic separation process Low beam intensities High intensities have beam spreading

* Around 0.5 cm for 50 cm radius Limits rate of production Low ion efficiency Loss of material

• Caltrons used during Manhattan project

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Calutron • Developed by Ernest Lawrence Cal. U-tron

• High energy use Iraqi Calutrons required about

1.5 MW each 90 total

• Manhattan Project Alpha

4.67 m magnet 15% enrichment Some issues with heat from

beams Shimming of magnetic fields

to increase yield Beta

Use alpha output as feed * High recovery

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Gaseous Diffusion • High proportion of world’s enriched U 95 % in 1978 40 % in 2003

• Separation based on thermal equilibrium All molecules in a gas mixture have same average

kinetic energy lighter molecules have a higher velocity at

same energy * Ek=1/2 mv2

• For 235UF6 and 238UF6

235UF6 and is 0.429 % faster on average why would UCl6 be much more complicated

for enrichment?

00429.1349352

349

352

352

349

2349349

2352352

===

=

mm

vv

vmvm

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Gaseous Diffusion • 235UF6

impacts barrier more often • Barrier properties Resistant to corrosion byUF6

Ni and Al2O3 Hole diameter smaller than mean free path

Prevent gas collision within barrier Permit permeability at low gas pressure

Thin material • Film type barrier Pores created in non-porous membrane Dissolution or etching

• Aggregate barrier Pores are voids formed between particles in sintered

barrier • Composite barrier from film and aggregate

27

Gaseous Diffusion Barrier • Thin, porous filters • Pore size of 100-1000 Å • Thickness of 5 mm or less tubular forms, diameter of 25 mm

• Composed of metallic, polymer or ceramic materials resistant to corrosion by UF6, Ni or alloys with 60 % or more Ni, aluminum

oxide Fully fluorinated hydrocarbon polymers

purity greater than 99.9 percent particle size less than 10 microns high degree of particle size uniformity

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Gaseous Diffusion • Barrier usually in tubes UF6 introduced

• Gas control Heater, cooler, compressor

• Gas seals • Operate at temperature above 70 °C and pressures below

0.5 atmosphere • R=relative isotopic abundance (N235/N238) • Quantifying behavior of an enrichment cell q=Rproduct /Rtail Ideal barrier, Rproduct =Rtail(352/349)1/2; q= 1.00429

29

Gaseous Diffusion • Small enrichment in any given cell q=1.00429 is best condition Real barrier efficiency (εB)

εB can be used to determine total barrier area for a given enrichment

εB = 0.7 is an industry standard Can be influenced by conditions Pressure increase, mean free path decrease

Increase in collision probability in pore Increase in temperature leads to increase velocity

Increase UF6 reactivity • Normal operation about 50 % of feed diffuses • Gas compression releases heat that requires cooling Large source of energy consumption

)1()1( −=− idealBobserved qq ε

30

Gaseous Diffusion • Simple cascade Wasteful process High enrichment at

end discarded • Countercurrent Equal atoms

condition, product enrichment equal to tails depletion

• Asymmetric countercurrent Introduction of tails

or product into nonconsecutive stage

Bundle cells into stages, decrease cells at higher enrichment

31

Gaseous Diffusion • Number of cells in each stage and balance of tails and product

need to be considered • Stages can be added to achieve changes in tailing depletion

Generally small levels of tails and product removed • Separative work unit (SWU)

Energy expended as a function of amount of U processed and enriched degree per kg

3 % 235U 3.8 SWU for 0.25 % tails 5.0 SWU for 0.15 % tails

• Determination of SWU P product mass W waste mass F feedstock mass xW waste assay xP product assay xF feedstock assay

32

Gaseous Diffusion

• Optimization of cells within cascades influences behavior of 234U q=1.00573 (352/348)1/2 Higher amounts of 234U, characteristic of

feed • US plants K-25 at ORNL 3000 stages 90 % enrichment

Paducah and Portsmouth Reactor U was enriched

* Np, Pu and Tc in the cycle

33

Gas centrifuge • Centrifuge pushes heavier 238UF6 against wall with center

having more 235UF6 Heavier gas collected near top

• Density related to UF6 pressure Density minimum at center

m molecular mass, r radius and ω angular velocity • With different masses for the isotopes, p can be solved for

each isotope

RTrm

ep

rp 2

22

)0()( ω

=

RTrm

xx

ep

rp 2

22

)0()( ω

=

34

Gas Centrifuge • Total pressure is from

partial pressure of each isotope Partial pressure

related to mass • Single stage separation

(q) Increase with mass

difference, angular velocity, and radius

• For 10 cm r and 1000 Hz, for UF6 q=1.26

Gas distribution in centrifuge

RTrmm

eq 2)( 22

12 ω−

=

35

Gas Centrifuge • More complicated setup than diffusion Acceleration pressures, 4E5 atmosphere from

previous example High speed requires balance Limit resonance frequencies High speed induces stress on materials Need high tensile strength

* alloys of aluminum or titanium * maraging steel Heat treated martensitic steel

* composites reinforced by certain glass, aramid, or carbon fibers

36

Gas Centrifuge • Gas extracted from center post with 3 concentric tubes Product removed by top scoop Tails removed by bottom scoop Feed introduced in center

• Mass load limitations UF6 needs to be in the gas phase Low center pressure

3.6E-4 atm for r = 10 cm • Superior stage enrichment when

compared to gaseous diffusion Less power need compared to

gaseous diffusion 1000 MWe needs 120 K

SWU/year * Gas diffusion 9000

MJ/SWU * centrifuge 180 MJ/SWU

• Newer installations compare to diffusion Tend to have no non-natural U

isotopes

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Centrifuges

Natanz US

38

Laser Isotope Separation

• Isotopic effect in atomic spectroscopy Mass, shape, nuclear spin

• Observed in visible part of spectra • Mass difference in IR region • Effect is small compared to transition energies 1 in 1E5 for U species

• Use laser to tune to exact transition specie Produces molecule in excited state

• Doppler limitations with method Movement of molecules during excitation

• Signature from 234/238 ratio, both depleted

39

Laser Isotope Separation

• 3 classes of laser isotope separations Photochemical Reaction of excited state molecule

Atomic photoionization Ionization of excited state molecule

Photodissociation Dissociation of excited state molecule

• AVLIS Atomic vapor laser isotope separation

• MLIS Molecular laser isotope separation

40

Laser isotope separation • AVLIS U metal vapor

High reactivity, high temperature

Uses electron beam to produce vapor from metal sample

• Ionization potential 6.2 eV • Multiple step ionization 238U absorption peak

502.74 nm 235U absorption peak

502.73 nm • Deflection of ionized U by

electromagnetic field

41

Laser Isotope Separation • MLIS (LANL method) SILEX (Separation of

Isotopes by Laser Excitation) in Australia Absorption by UF6 Initial IR excitation at 16 micron

235UF6 in excited state Selective excitation of 235UF6 Ionization to 235UF5 Formation of solid UF5 (laser snow) Solid enriched and use as feed to another

excitation • Process degraded by molecular motion\ Cool gas by dilution with H2 and nozzle

expansion

42

Nuclear Fuel: Uranium-oxygen system • A number of binary uranium-oxygen compounds

UO Solid UO unstable, NaCl structure From UO2 heated with U metal

* Carbon promotes reaction, formation of UC UO2

Reduction of UO3 or U3O8 with H2 from 800 ºC to 1100 ºC * CO, C, CH4, or C2H5OH can be used as reductants

O2 presence responsible for UO2+x formation Large scale preparation

* UO4, (NH4)2U2O7, or (NH4)4UO2(CO3)3 * Calcination in air at 400-500 ºC * H2 at 650-800 ºC * UO2has high surface area

43

Uranium-oxygen • U3O8 From oxidation of UO2 in air at 800 ºC

α phase uranium coordinated to oxygen in pentagonal bipyrimid

β phase results from the heating of the α phase above 1350 ºC Slow cooling

44

Uranium-oxygen • UO3

Seven phases can be prepared • A phase (amorphous)

Heating in air at 400 ºC * UO4

.2H2O, UO2C2O4.3H2O, or

(HN4)4UO2(CO3)3 Prefer to use compounds

without N or C � α-phase

Crystallization of A-phase at 485 ºC at 4 days

O-U-O-U-O chain with U surrounded by 6 O in a plane to the chain

Contains UO22+

� β-phase Ammonium diuranate or uranyl nitrate

heated rapidly in air at 400-500 ºC � γ-phase prepared under O2 6-10 atmosphere at

400-500 ºC

45

Uranium-oxygen • UO3 hydrates

6 different hydrated UO3 compounds

• UO3.2H2O

Anhydrous UO3 exposed to water from 25-70 ºC

Heating resulting compound in air to 100 ºC forms α-UO3

.0.8 H2O

α-UO2(OH)2 [α-UO3

.H2O] forms in hydrothermal experiments β-UO3

.H2O also forms

46

Uranium-oxygen single crystals • UO2 from the melt of

UO2 powder Arc melter used Vapor deposition

• 2.0 ≤ U/O ≤ 2.375 Fluorite structure

• Uranium oxides show range of structures Some variation

due to existence of UO2

2+ in structure Some layer

structures

47

48

UO2 Heat Capacity • Room temperature to 1000

K Increase in heat

capacity due to harmonic lattice vibrations Small

contribution to thermal excitation of U4+ localized electrons in crystal field

• 1000-1500 K Thermal expansion

induces anharmonic lattice vibration

• 1500-2670 K Lattice and electronic

defects

49

Vaporization of UO2 • Above and below the melting

point • Number of gaseous species

observed U, UO, UO2, UO3, O, and

O2 Use of mass

spectrometer to determine partial pressure for each species

For hypostiochiometric UO2, partial pressure of UO increases to levels comparable to UO2

O2 increases dramatically at O/U above 2

50

Uranium oxide chemical properties • Oxides dissolve in strong mineral acids

Valence does not change in HCl, H2SO4, and H3PO4 Sintered pellets dissolve slowly in HNO3

Rate increases with addition of NH4F, H2O2, or carbonates * H2O2 reaction

UO2+ at surface oxidized to UO2

2+

51

Solid solutions with UO2

• Solid solutions formed with group 2 elements, lanthanides, actinides, and some transition elements (Mn, Zr, Nb, Cd) Distribution of metals on UO2 fluorite-type cubic

crystals based on stoichiometry • Prepared by heating oxide mixture under reducing

conditions from 1000 ºC to 2000 ºC Powders mixed by co-precipitation or mechanical

mixing of powders • Written as MyU1-yO2+x x is positive and negative

52

Solid solutions with UO2

• Lattice parameter change in solid solution Changes nearly linearly with increase in y and x

MyU1-yO2+x Evaluate by change of lattice parameter with

change in y * δa/δy a is lattice parameter in Å Can have both negative and positive

values δa/δy is large for metals with large ionic radii δa/δx terms negative and between -0.11 to -0.3

Varied if x is positive or negative

53

Solid solutions of UO2

• Tetravalent MyU1-yO2+x Zr solid solutions

Large range of systems y=0.35 highest value Metastable at lower temperature

Th solid solution Continuous solid solutions for 0≤y≤1 and x=0 For x>0, upper limit on solubility

* y=0.45 at 1100 ºC to y=0.36 at 1500 ºC Also has variation with O2 partial pressure

* At 0.2 atm., y=0.383 at 700 ºC to y=0.068 at 1500 ºC

54

Solid solutions of UO2 • Tri and tetravalent MyU1-yO2+x

Cerium solid solutions Continuous for y=0 to y=1 For x<0, solid solution restricted to y≤0.35

* Two phases (Ce,U)O2 and (Ce,U)O2-x x<-0.04, y=0.1 to x<-0.24, y=0.7 0≤x≤0.18, solid solution y<0.5 Air oxidized hyperstoichiometric

* y 0.56 to 1 at 1100 ºC * y 0.26-1.0 1550 ºC

• Tri and divalent Reducing atmosphere

x is negative fcc Solid solution form when y is above 0 Maximum values vary with metal ion

Oxidizing atmosphere Solid solution can prevent formation of U3O8 Some systematics in trends

* For Nd, when y is between 0.3 and 0.5, x = 0.5-y

55

Solid solution UO2 • Oxygen potential

Zr solid solution Lower than the UO2+x system

* x=0.05, y=0.3 -270 kJ/mol for

solid solution -210 kJ/mol for

UO2+x Th solid solution

Increase in ∆G with increasing y

Compared to UO2 difference is small at y less than 0.1

Ce solid solution Wide changes over y

range due to different oxidation states

Shape of the curve is similar to Pu system, but values differ

* Higher ∆G for CeO2-x compared to PuO2-x

56

Metallic Uranium • Three different phase α, β, γ phases

Dominate at different temperatures

• Uranium is strongly electropositive Cannot be prepared

through H2 reduction • Metallic uranium

preparation UF4 or UCl4 with Ca or

Mg UO2 with Ca Electrodeposition from

molten salt baths

57

Metallic Uranium phases � α-phase

Room temperature to 942 K Orthorhombic U-U distance 2.80 Å Unique structure type

� β-phase Exists between 668 and 775 ºC Tetragonal unit cell

� γ-phase Formed above 775 ºC bcc structure

• Metal has plastic character Gamma phase soft, difficult fabrication Beta phase brittle and hard

• Paramagnetic • Temperature dependence of resistivity • Alloyed with Mo, Nb, Nb-Zr, and Ti

β-phase

α‐phase U-U distances in layer (2.80±0.05) Å and between layers

3.26 Å

58

Intermetallic compounds • Wide range of intermetallic compounds and solid solutions in alpha and

beta uranium Hard and brittle transition metal compounds

U6X, X=Mn, Fe, Co, Ni Noble metal compounds

Ru, Rh, Pd * Of interests for reprocessing

Solid solutions with: Mo, Ti, Zr, Nb, and Pu

59

Uranium-Aluminum Phase Diagram

Uranium-Titanium Phase Diagram

60

Chemical properties of uranium metal and alloys

• Reacts with most elements on periodic table Corrosion by O2, air,

water vapor, CO, CO2 • Dissolves in HCl Also forms hydrated

UO2 during dissolution • Non-oxidizing acid results in

slow dissolution Sulfuric, phosphoric,

HF • Exothermic reaction with

powered U metal and nitric • Dissolves in base with

addition of peroxide peroxyuranates

61

Review • How is uranium chemistry linked with the fuel cycle • What are the main oxidation states of the fission products and

actinides • Describe the uranium enrichment process • What drives the speciation of actinides and fission products in fuel • Understand the fundamental chemistry of the fission products and

actinides Production Solution chemistry Speciation Spectroscopy

62

Questions

1. What drives the speciation of actinides and fission products in spent nuclear fuel? What would be the difference between oxide and metallic fuel?

2. Describe two processes for enriching uranium. Why does uranium need to be enriched? What else could be used instead of 235U?

3. What are the similarities and differences between lanthanides and actinides?

4. What are some trends in actinide chemistry?

63

Questions • What are the different types of conditions used for separation of U

from ore • What is the physical basis for enriching U by gas and laser

methods? • What chemistry is exploited for solution based U enrichment • Describe the basic chemistry for the production of Umetal • Why is U alloyed? • What are the natural isotopes of uranium • Provide 5 reactions that use U metal as a starting reagent • Describe the synthesis and properties of the uranium halides • How is the O to U ratio for uranium oxides determined • What are the trends in U solution chemistry • What atomic orbitals form the molecular orbitals for UO2

2+

64

Pop Quiz

• What atomic orbitals form the molecular orbitals for UO2

2+