1

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

§ Uraniumà Solution Chemistryà Separationà Fluorination and

enrichmentà 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

à 234: 0.005±0.001, 68.9 aà 235: 0.720±0.001, 7.04E8 aà 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

UO2Calcination, Reduction

Tubes

Pellet Control40-60°C

Fuel Fabrication

Other species for fuelnitrides, 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

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

coordination polyhedra§ Mineral deposits based on major anion

• Pyrochlore § A1-2B2O6X0-1

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

à B= Ti, Nb, Taà U(V) may be present when synthesized

under reducing conditions* XANES spectroscopy* Goes to B siteUraninite with oxidation

6

Aqueous solution complexes• Strong Lewis acid• Hard electron acceptor

§ F->>Cl->Br-I-

§ Same trend for O and N groupà 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

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

• U(III) and U(V)§ No data in solution

à 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

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

à Making or breaking yl oxygens

* UO22++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

§ sg2 su

2 pg4 pu

4

à Order of HOMO is unclear* pg< pu< sg<< su

proposedØ Gap for s based on 6p orbitals interactions

§ 5fd and 5f f 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

à Net negative 0.43 on oxygensà 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+

à Cp=cyclopentadiene * 5f CO p backbonding

Ø Metal electrons to p of ligands

* Decreases upon oxidation to U(IV)

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

actinidesà VO2

+, MoO22+, WO2

2+

* Oxygen atoms are cis to maximize (pp)M(dp)

à 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 pentavalentà Smaller effective charge on

pentavalent U§ Multiple bond characteristics, 1 s

and 2 with p characteristics

12

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

§ Evaluated by color changeà 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 acidà Requires >0.5 M acid to prevent hydrolysisà Electrolysis of U(VI) solutions

* Complexation can drive oxidation§ Coordination studied by XAFS

à Coordination number 9±1* Not well defined

à U-O distance 2.42 ŧ 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 2.7à 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

à 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

leachingà Removal of

carbonaceous or sulfur compounds

à 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)

Ø U(VI) soluble in sulfuricØ Anionic sulfate species

Ø Oxidizing conditions may be neededØ MnO2

Ø Precipitation of Fe at pH 3.8§ Carbonate leaching

à Formation of soluble anionic carbonate species

* UO2(CO3)34-

à Precipitation of most metal ions in alkali solutions

à Bicarbonate prevents precipitation of Na2U2O7

* Formation of Na2U2O7 with further NaOH addition

à Gypsum and limestone in the host aquifers necessitates carbonate leaching

17

Recovery of uranium from solutions• Ion exchange

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

4-

à 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

alkylaminesà Chemistry similar to ion exchange conditions

• Chemical precipitation§ Addition of base§ Peroxide

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

yellowcakeà heating to form U3O8 or UO3

18

Uranium purification• Tributyl phosphate (TBP) extraction

§ Based on formation of nitrate species

§ UO2(NO3)x2-x + (2-x)NO3

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

§ Process example of pulse column below

19

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

deviceà Critical mass decreases with increased

enrichment§ 20 % 235U critical mass for reflected device around

100 kgà Low enriched/high enriched uranium boundary

20

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

à One atmosphere at 56.5 ºC

• Oh point group§ U-F bond distance of 2.00 Å

21

Uranium Hexafluoride

• Very low viscosity § 7 mPoise

à Water =8.9 mPoiseà 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 (r)à m mass, v velocity, q ion charge, B magnetic

field• For V acceleration potential

qB

mcv

m

Vqv

2

q

Vm

B

c 2

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

à High intensities have beam spreading* Around 0.5 cm for 50 cm radius

§ Limits rate of production§ Low ion efficiency

à Loss of material• Caltrons used during Manhattan project

24

Calutron• Developed by Ernest Lawrence

§ Cal. U-tron• High energy use

§ Iraqi Calutrons required about 1.5 MW eachà 90 total

• Manhattan Project§ Alpha

à 4.67 m magnetà 15% enrichmentà Some issues with heat from

beamsà Shimming of magnetic fields to

increase yield§ Beta

à Use alpha output as feed* High recovery

25

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 energyà 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

à why would UCl6 be much more complicated for enrichment?

00429.1349

352

349

352

352

349

2349349

2352352

m

m

v

v

vmvm

26

Gaseous Diffusion• 235UF6

impacts barrier more often

• Barrier properties

§ Resistant to corrosion byUF6

à Ni and Al2O3

§ Hole diameter smaller than mean free pathà Prevent gas collision within barrier

§ Permit permeability at low gas pressureà 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 à purity greater than 99.9 percent à particle size less than 10 microns

à high degree of particle size uniformity

28

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 (eB)

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

à eB = 0.7 is an industry standard

§ Can be influenced by conditions§ Pressure increase, mean free path decrease

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

à 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

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 % 235Uà 3.8 SWU for 0.25 % tailsà 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

à 90 % enrichment§ Paducah and Portsmouth

à 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 w angular velocity• With different masses for the isotopes, p can be solved for

each isotope

RT

rm

ep

rp 2

22

)0(

)(

RT

rmx

x

ep

rp 2

22

)0(

)(

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

RT

rmm

eq 2

)( 2212

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

à Need high tensile strength* alloys of aluminum or titanium* maraging steel

Ø 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 pressureà 3.6E-4 atm for r = 10 cm

• Superior stage enrichment when compared to gaseous diffusion§ Less power need compared to

gaseous diffusion

à 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

37

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

à Reaction of excited state molecule§ Atomic photoionization

à Ionization of excited state molecule§ Photodissociation

à Dissociation of excited state molecule• AVLIS

§ Atomic vapor laser isotope separation• MLIS

§ Molecular laser isotope separation

40

Laser isotope separation

• AVLIS§ U metal vapor

à High reactivity, high temperature

à 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

à 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

§ UOà Solid UO unstable, NaCl structureà From UO2 heated with U metal

* Carbon promotes reaction, formation of UC§ UO2

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

à O2 presence responsible for UO2+x formationà 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 ºCà a phase uranium coordinated to oxygen in

pentagonal bipyrimid§ b phase results from the heating of the a phase

above 1350 ºCà Slow cooling

44

Uranium-oxygen• UO3

§ Seven phases can be prepared• A phase (amorphous)

à Heating in air at 400 ºC* UO4

.2H2O, UO2C2O4.3H2O, or

(HN4)4UO2(CO3)3

Ø Prefer to use compounds without N or C

• a-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 UO2

2+

• b-phase§ Ammonium diuranate or uranyl nitrate

heated rapidly in air at 400-500 ºC• g-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 a-UO3

.0.8 H2O

§ a-UO2(OH)2 [a-UO3

.H2O] forms in hydrothermal experiments

à b-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 UO22+

in structure§ Some layer

structures

47

48

UO2 Heat Capacity• Room temperature to 1000

K§ Increase in heat

capacity due to harmonic lattice vibrationsà 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

à Use of mass spectrometer to determine partial pressure for each species

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

à 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

à Rate increases with addition of NH4F, H2O2, or carbonates

* H2O2 reaction

Ø 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

à MyU1-yO2+x

à Evaluate by change of lattice parameter with change in y* δa/δy

Ø a is lattice parameter in ÅØ 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

à Varied if x is positive or negative

53

Solid solutions of UO2

• Tetravalent MyU1-yO2+x

§ Zr solid solutionsà Large range of systemsà y=0.35 highest valueà Metastable at lower temperature

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

* y=0.45 at 1100 ºC to y=0.36 at 1500 ºCà 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 solutionsà Continuous for y=0 to y=1à For x<0, solid solution restricted to y≤0.35

* Two phases (Ce,U)O2 and (Ce,U)O2-x

à x<-0.04, y=0.1 to x<-0.24, y=0.7à 0≤x≤0.18, solid solution y<0.5à Air oxidized hyperstoichiometric

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

• Tri and divalent§ Reducing atmosphere

à x is negativeà fccà Solid solution form when y is above 0à Maximum values vary with metal ion

§ Oxidizing atmosphereà Solid solution can prevent formation of U3O8

à 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

à Lower than the UO2+x system* x=0.05, y=0.3

Ø -270 kJ/mol for solid solution

Ø -210 kJ/mol for UO2+x

§ Th solid solutionà Increase in DG with

increasing yà Compared to UO2 difference

is small at y less than 0.1§ Ce solid solution

à Wide changes over y range due to different oxidation states

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

* Higher DG for CeO2-x

compared to PuO2-x

56

Metallic Uranium• Three different phase

§ , , a b g phasesà 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

• a-phase§ Room temperature to 942 K§ Orthorhombic § U-U distance 2.80 ŧ Unique structure type

• b-phase§ Exists between 668 and 775 ºC§ Tetragonal unit cell

• g-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

b-phase

a‐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

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

à Ru, Rh, Pd* Of interests for reprocessing

§ Solid solutions with:à 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+