Download Fuel Cycle Chemistry

Uranium Chemistry and the Fuel Cycle
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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
Why is U important in the fuel cycle: induced fission cross
Requires fissile isotopes
233U, 235U, 239Pu
section for 235U and 238U as function of the neutron energy.


Need in sufficient
concentration and
geometry
233U and 239Pu can be created in
neutron flux
235U in nature
1

Need isotope enrichment
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
2
Chemistry overview
• Uranium acid-leach
• Extraction and conversion
3
Fuel Fabrication
Enriched UF6
Calcination, Reduction
Pellet Control
40-60°C
UO2
Tubes
Fuel Fabrication
Other species for fuel
nitrides, 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
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•
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 5
* Goes to B site
Uraninite with oxidation
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
6
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
* 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
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Uranyl chemical bonding
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Uranyl (UO22+) linear molecule
Bonding molecular orbitals

sg2 su2 pg4 pu4
 Order of HOMO is unclear
* pg< pu< sg<< su proposed
 Gap for s based on 6p orbitals interactions

5fd and 5ff LUMO
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Bonding orbitals O 2p characteristics
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Non bonding, antibonding 5f and 6d
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Isoelectronic with UN2
Pentavalent has electron in non-bonding orbital
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Uranyl chemical bonding
• Linear yl oxygens from 5f characteristic
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6d promotes cis geometry
• yl oxygens force formal charge on U below 6
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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
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Uranium chemical bonding: oxidation states
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Tri- and tetravalent U mainly related to
organometallic compounds

Cp3UCO and Cp3UCO+
 Cp=cyclopentadiene
* 5f CO p backbonding
 Metal electrons to p
of ligands
* Decreases upon oxidation
to U(IV)
Uranyl(V) and (VI) compounds

yl ions in aqueous systems unique
for actinides
 VO2+, MoO22+, WO22+
* Oxygen atoms are cis to
maximize (pp)M(dp)
 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
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Multiple bond characteristics, 1 s
and 2 with p characteristics
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Uranium solution chemistry: U(III)
• Dissolution of UCl3 in water
• Reduction of U(IV) or (VI) at Hg cathode
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Evaluated by color change
 U(III) is green
• Very few studies of U(III) in solution
• No structural information
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Comparisons with trivalent actinides and lanthanides
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Uranium solution chemistry
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Tetravalent uranium

Forms in very strong acid
 Requires >0.5 M acid to prevent hydrolysis
 Electrolysis of U(VI) solutions
* Complexation can drive oxidation
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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 UO22+ with Zn or H2 or dissolution of UCl5
in water
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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
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No experimental information on structure
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Quantum mechanical predictions
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Hexavalent Uranium
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Large number of compounds prepared
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Crystallization
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Hydrothermal
Determination of hydrolysis constants
from spectroscopic and titration
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Determine if polymeric species form
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Polynuclear species present except at
lowest concentration
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Uranium speciation
• Speciation variation with uranium concentration
 Hydrolysis as example
 Precipitation at higher concentration
 Change in polymeric uranium species concentration
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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
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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
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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
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Ion exchange
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U(VI) anions in sulfate and carbonate solution
 UO2(CO3)34 UO2(SO4)34
Load onto anion exchange, elute with acid or NaCl
Solvent extraction
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Continuous process
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Not well suited for carbonate solutions
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Extraction with alkyl phosphoric acid, secondary and tertiary
alkylamines
 Chemistry similar to ion exchange conditions
Chemical precipitation
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Addition of base
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Peroxide
 Water wash, dissolve in nitric acid
 Ultimate formation of (NH4)2U2O7 (ammonium diuranate),
yellowcake
 heating to form U3O8 or UO3
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Uranium purification
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Tributyl phosphate (TBP) extraction
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Based on formation of nitrate species
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UO2(NO3)x2-x + (2-x)NO3- + 2TBP UO2(NO3)2(TBP)2
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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
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Mass
Size
Shape
Nuclear magnetic
moment
Angular momentum
• Massed based
separations utilize
volatile UF6
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UF6 formed from
reaction of U
compounds with F2
at elevated
temperature
• Colorless, volatile solid at room
temperature
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Density is 5.1 g/mL
Sublimes at normal atmosphere
Vapor pressure of 100 torr
 One atmosphere at 56.5 ºC
• Oh point group
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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
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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
mcv
r
 Radius (r)
qB
m mass, v velocity, q ion charge, B
magnetic field
2Vq
• For V acceleration potential v 
m
r
c
B
2Vm
q
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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
2
2
same energy
m352v352
 m349v349
* Ek=1/2 mv2
v349
m352
352


 1.00429
• For 235UF6 and 238UF6
v352
m349
349
 235UF6 and is 0.429 % faster on average
 why would UCl6 be much more complicated
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for enrichment?
Gaseous Diffusion
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235UF
6 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
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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
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Gaseous Diffusion
• Small enrichment in any given cell
 q=1.00429 is best condition
 Real barrier efficiency (eB) (qobserved  1)  e B (qideal  1)
 eB can be used to determine total barrier area
for a given enrichment
 eB = 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
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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 % 235U
 3.8 SWU for 0.25 % tails
 5.0 SWU for 0.15 % tails
• Determination of SWU

P product mass

W waste mass
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F feedstock mass

xW waste assay

xP product assay
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xF feedstock assay
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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
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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
p(r )
e
p (0)
mw 2 r 2
2 RT
 m molecular mass, r radius and w angular velocity
• With different masses for the isotopes, p can be solved for
each isotope
p x (r )
e
p ( 0)
m xw 2 r 2
2 RT
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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
q e
( m2  m1 )w 2 r 2
2 RT
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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
Need high tensile strength
* alloys of aluminum or titanium
* maraging steel
 Heat treated martensitic steel
* composites reinforced by certain glass,
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aramid, or carbon fibers
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Gas extracted from center post with 3
concentric tubes
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Product removed by top scoop
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Tails removed by bottom scoop
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Feed introduced in center
Mass load limitations
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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
Gas Centrifuge
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Centrifuges
US
Natanz
37
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
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
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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
40
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
41
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
42
Uranium-oxygen
• U3O8
 From oxidation of UO2 in air at 800 ºC
 a phase uranium coordinated to oxygen in
pentagonal bipyrimid
 b phase results from the heating of the a phase
above 1350 ºC
 Slow cooling
43
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
 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 UO22+
 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
44
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
H2 O

a-UO2(OH)2 [aUO3.H2O] forms in
hydrothermal
experiments
 b-UO3.H2O also
forms
45
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
46
47
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
48
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
49
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 UO22+
50
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
51
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
52
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
53
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
54
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 DG 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 DG for CeO2-x
compared to PuO2-x
55
Metallic Uranium
• Three different phase
 a, b, g 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
56
Metallic Uranium phases
 a-phase

Room temperature to 942 K

Orthorhombic

U-U distance 2.80 Å

Unique structure type
 b-phase

Exists between 668 and 775 ºC
a‐phase U-U distances in layer

Tetragonal unit cell
(2.80±0.05) Å and between layers
 g-phase
3.26 Å

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
57
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
58
Uranium-Aluminum Phase
Diagram
Uranium-Titanium Phase
Diagram
59
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
60
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
61
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?
62
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 UO22+
63
Pop Quiz
• What atomic orbitals form the molecular
orbitals for UO22+
64