1

RFSS: Lecture 11 Uranium Chemistry and the Fuel Cycle

• Readings: Uranium chapter:§ http://radchem.nevada.edu/classes/

rdch710/files/uranium.pdf• 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§ 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

• Fission properties of uranium§ Defined importance of element

and future investigations§ Identified by Hahn in 1937§ 200 MeV/fission§ 2.5 neutrons

2

U Fuel Cycle Chemistry Overview

• Uranium acid-leach • Extraction and conversion

Understand fundamental chemistry of uranium and its applications to the nuclear fuel cycle

3

Fuel FabricationEnriched UF6

UO2Calcination, Reduction

Tubes

Pellet Control40-60°C

Fuel Fabrication

Other species for fuelnitrides, carbides

Other actinides: Pu, Th

4

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* From XANES spectroscopy* Goes to B siteUraninite with oxidation

5

Uranium solution chemistry overview• 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)

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

à Base information on lanthanide or pentavalent actinides • Uranyl(VI) most stable oxidation state in solution

§ Uranyl(V) and U(IV) can also be in solutionà 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* UO2

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

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

6

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

7

Uranium solution chemistry• Trivalent uranium

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

à Comparisons with trivalent actinides and lanthanides• 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 waterà U(V) is not stable but slowly oxidizes under suitable conditions

§ No experimental information on structure§ Quantum mechanical predictions

8

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• Hexavalent uranium as uranyl in solution

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

• Pentavalent has electron in non-bonding orbital

100

0.05

0.1

0.15

0.2

350 400 450 500 550

0.126 M UO22+

8 M HNO3

4 M HNO3

1 M HNO3

0.1 M HNO3

Abs

orba

nce

Wavelength (nm)

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Uranyl chemical bonding• yl oxygens force formal charge on U below 6

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

systemsà 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

12

Uranium speciation• Speciation variation with uranium concentration

§ Hydrolysis as example§ Precipitation at higher concentration

à Change in polymeric uranium species concentration

CHESS Calculation

13

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

§ 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

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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

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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

deviceà Critical mass decreases with increased enrichment

§ 20 % 235U critical mass for reflected device around 100 kgà 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

à 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

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 need for enrichment

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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

qBmcv

r

mVqv 2

qVm

Bc 2

r

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Uranium Enrichment: Electromagnetic Separation

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

• Requirements 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

qVm

Bc 2

r

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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

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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 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 averageà 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 by UF6

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

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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

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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 enrichmentà 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• Optimization of cells within cascades influences behavior of 234U

§ q=1.00573 (352/348)1/2 § Higher amounts of 234U, characteristic of feed

)1()1( idealBobserved qq e

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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

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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

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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

RTrm

eprp 2

22

)0()( w

RTrm

xx

eprp 2

22

)0()( w

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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 w

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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

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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

à 3.6E-4 atm for r = 10 cm• Superior stage enrichment when compared to gaseous

diffusion§ Less power need compared to gaseous

diffusionà 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

32

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

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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

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Laser isotope separation• AVLIS

§ U metal vaporà High reactivity, high

temperatureà 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

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Laser Isotope Separation

• MLIS (LANL method) SILEX (Separation of Isotopes by Laser Excitation) in Australia§ Absorption by UF6

§ Initial IR excitation at 16 micronà 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

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RFSS: Part 2 Lecture 11 Uranium Chemistry and the Fuel Cycle

• Readings: Uranium chapter:§ http://radchem.nevada.edu/classes/

rdch710/files/uranium.pdf• Chemistry in the fuel cycle

§ Uraniumà Solution Chemistryà Separationà Fluorination and enrichmentà Oxideà 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§ 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

• Fission properties of uranium§ Defined importance of element

and future investigations§ Identified by Hahn in 1937§ 200 MeV/fission§ 2.5 neutrons

37

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* UO2 has high surface area

38

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

39

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

40

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 experimentsà b-UO3

.H2O also forms

41

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

42

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

43

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

44

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+

45

Solid solutions with UO2

• Solid solution§ crystal structure unchanged by addition of

another compound§ mixture remains as single phase

à ThO2-UO2 is a solid solution• 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

46

Solid solutions with UO2

• Lattice parameter change in solid solution§ Changes nearly linearly with

increase in y and xà MyU1-yO2+xà Evaluate by change of

lattice parameter with change in y* δa/δy

Ø a is lattice parameter in Å

Ø 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 -0.3à Varied if x is positive or

negative

47

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 solution

à Continuous solid solutions for 0≤y≤1 and x=0

à 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

• Tri and tetravalent MyU1-yO2+x§ Cerium solid solutions

à 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-xà 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 fcc structureà Maximum values vary with metal

ion§ Oxidizing atmosphere

à 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

48

U-Zr oxide

system

49

Solid solution UO2• Oxygen potential

§ Zr solid solutionà Lower than the UO2+x system

* x=0.05, y=0.3Ø -270 kJ/mol for

solid solutionØ -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

50

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

51

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

52

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

53

Uranium-Aluminum Phase Diagram

Uranium-Titanium Phase Diagram

54

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

55

Review

• How is uranium chemistry linked with the fuel cycle

• What are the main oxidation states uranium• Describe the uranium enrichment process

§ Mass based§ Laser bases

• Understand the fundamental chemistry of uranium as it relates to: § Production§ Solution chemistry§ Speciation § Spectroscopy

56

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?• Describe the basic chemistry for the production of U metal• What are the natural isotopes of uranium• 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+

• What else could be used instead of 235U as the fissile isotope in a reactor?

• Describe two processes for enriching uranium. Why does uranium need to be enriched?

57

Questions

• Respond to PDF Quiz 11• Post comments on the blog

§ http://rfssunlv.blogspot.com/