Download Fuel Cycle Chemistry - UNLV Radiochemistry

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Readings: Uranium chapter:

http://radchem.nevada.edu/classes/r
dch710/files/uranium.pdf
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

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
CHEM 312: Lecture 12 Part 1
Uranium Chemistry and the Fuel
Cycle
Fission properties of uranium
 Defined importance of
element and future
investigations
 Identified by Hahn in 1937
 200 MeV/fission
 2.5 neutrons
1
U Fuel Cycle Chemistry Overview
• Uranium acid-leach
• Extraction and conversion
Understand fundamental chemistry of uranium and
its applications to the nuclear fuel cycle
2
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
3
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
* From XANES spectroscopy
4
* Goes to B site
Uraninite with oxidation
Uranium solution chemistry overview
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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)
U(III) and U(V)

No data in solution
 Base information on lanthanide or pentavalent actinides
• 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
• 5f electrons have strong influence on actinide chemistry

For uranyl, f-orbital overlap provide bonding
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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
Trivalent uranium
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Very few studies of U(III) in solution
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No structural information
 Comparisons with trivalent actinides and lanthanides
Tetravalent uranium
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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
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O exchange examined by NMR
Pentavalent uranium
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Extremely narrow range of existence

Prepared by reduction of UO22+ with Zn or H2 or dissolution of UCl5 in water
 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
Hexavalent uranium as uranyl in solution
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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
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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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0.126 M UO
2+
2
0.2
8 M HNO
3
4 M HNO
0.15
3
1 M HNO
Absorbance
3
0.1 M HNO
3
0.1
0.05
0
350
400
450
Wavelength (nm)
500
10
550
Uranyl chemical bonding
• 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
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Lower frequency for pentavalent U
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Weaker bond
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Uranium speciation
• Speciation variation with uranium concentration
 Hydrolysis as example
 Precipitation at higher concentration
 Change in polymeric uranium species concentration
CHESS Calculation
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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
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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 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
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
c 2Vm
r
 Higher mass, larger radius
B
q
• Requirements 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 by UF6
 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 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
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Ideal barrier, Rproduct =Rtail(352/349)1/2; q= 1.00429
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Gaseous Diffusion
• Small enrichment in any given cell
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q=1.00429 is best condition
(qobserved  1)  e B (qideal  1)
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Real barrier efficiency (eB)
 eB can be used to determine total barrier area for a given
enrichment
 eB = 0.7 is an industry standard
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Can be influenced by conditions
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Pressure increase, mean free path decrease
 Increase in collision probability in pore
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Increase in temperature leads to increase velocity
 Increase UF6 reactivity
• Normal operation about 50 % of feed diffuses
• Gas compression releases heat that requires cooling
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Large source of energy consumption
• Optimization of cells within cascades influences behavior of 234U
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q=1.00573 (352/348)1/2
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Higher amounts of 234U, characteristic of feed
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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
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Generally small levels of tails and product removed
• Separative work unit (SWU)
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Energy expended as a function of amount of U processed
and enriched degree per kg
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3 % 235U
 3.8 SWU for 0.25 % tails
 5.0 SWU for 0.15 % tails
• Determination of SWU
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P product mass
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W waste mass
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F feedstock mass
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xW waste assay
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xP product assay
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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
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
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Low center pressure
 3.6E-4 atm for r = 10 cm
Superior stage enrichment when compared to gaseous
diffusion
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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
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Tend to have no non-natural U isotopes
Gas Centrifuge
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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
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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 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
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Readings: Uranium chapter:

http://radchem.nevada.edu/classes/r
dch710/files/uranium.pdf
Chemistry in the fuel cycle

Uranium
 Solution Chemistry
 Separation
 Fluorination and enrichment
 Oxide
 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
 234: 0.005±0.001, 68.9 a
 235: 0.720±0.001, 7.04E8 a
 238: 99.275±0.002, 4.5E9 a
CHEM 312: Part 2 Lecture 12
Uranium Chemistry and the Fuel
Cycle
Fission properties of uranium
 Defined importance of
element and future
investigations
 Identified by Hahn in 1937
 200 MeV/fission
 2.5 neutrons
36
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
* UO2 has high surface area
37
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
38
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
39
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
40
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
41
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
42
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
43
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+
44
Solid solutions with UO2
• Solid solution
 crystal structure unchanged by addition
of another compound
 mixture remains as single phase
 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 fluoritetype 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
45
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
46
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
•
•
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 structure
 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
47
and 0.5, x = 0.5-y
U-Zr
oxide
system
48
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
49
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
50
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
51
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
52
Uranium-Aluminum Phase
Diagram
Uranium-Titanium Phase
Diagram
53
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
54
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
55
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 UO22+
• 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?
56
Questions
• Provide comments in the blog
• Respond to PDF Quiz 12
57