Transcript Fuel Cycle Chemistry
• •
Uranium Chemistry and the Fuel Cycle
Chemistry in the fuel cycle
Uranium
Solution Chemistry cycle
form) Separation Fluorination and enrichment
Metal Focus on chemistry in the fuel Speciation (chemical Oxidation state
• • • •
Utilization of fission process to create heat
Heat used to turn turbine and produce electricity Requires fissile isotopes
233 U, 235 U, 239 Pu
233 neutron flux 235 Need in sufficient concentration and geometry U and 239 Pu can be created in
U in nature Need isotope enrichment
Why is U important in the fuel cycle: induced fission cross section for 235 U and 238 U as function of the neutron energy.
1
•
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
234,235,238 U
233
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 U from 232 Th need fissile isotope initially
2
•
Chemistry overview
Uranium acid-leach
•
Extraction and conversion
3
Fuel Fabrication
Enriched UF 6 Calcination, Reduction UO 2 Pellet Control 40-60°C 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
• •
200 minerals contain uranium
Bulk are U(VI) minerals
U(IV) as oxides, phosphates, silicates
coordination polyhedra Mineral deposits based on major anion Pyrochlore
A 1-2 B 2 O 6 X 0-1
A=Na, Ca, Mn, Fe 2+ , Sr,Sb, Cs, Ba,
B= Ti, Nb, Ta U(V) may be present when
* *
XANES spectroscopy Goes to B site
5 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
HOCH
2 COO pKa=17, 3.6 upon complexation of UO Inductive effect 2
*
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
*
UO 2 2+ +4H + +2e -
U 4+ +2H 2 O yl oxygens have slow exchange
Half life 5E4 hr in 1 M HClO 4 5f electrons have strong influence on actinide chemistry
For uranyl, f-orbital overlap provide bonding
7
• • •
Uranyl chemical bonding
Uranyl (UO 2 2+ ) linear molecule Bonding molecular orbitals
s
g 2
s
u 2
p
g 4
p
u 4
5f
d
Order of HOMO is unclear
* p
g <
p
u <
s
g <<
s
u proposed
Gap for and 5f
f
LUMO
s
based on 6p orbitals interactions
Bonding orbitals O 2p characteristics
Non bonding, antibonding 5f and 6d Isoelectronic with UN 2 Pentavalent has electron in non-bonding orbital
8
9
• • • •
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 UO
2 (H 2 O) 5 2+ Net negative 0.43 on oxygens , 3.2 for fluoride systems
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
10
Uranium chemical bonding: oxidation states
• •
Tri- and tetravalent U mainly related to organometallic compounds
Cp 3 UCO and Cp 3 UCO +
Cp=cyclopentadiene
*
5f CO
p
backbonding
Metal electrons to of ligands
p *
Decreases upon oxidation to U(IV) Uranyl(V) and (VI) compounds
yl ions in aqueous systems unique for actinides
VO 2 + , MoO 2 2+ , WO 2 2+
*
Linear MO 2 2+ compounds of Tc, Re, Ru, Os
*
Oxygen atoms are cis to maximize (p
p
)
M(d
p
) known for Aquo structures unknown
Short U=O bond distance of 1.75 Å for hexavalent, longer for pentavalent
Smaller effective charge on pentavalent U Multiple bond characteristics, 1
s
and 2 with
p
characteristics
11
Uranium solution chemistry: U(III)
• • • •
Dissolution of UCl 3 in water Reduction of U(IV) or (VI) at Hg cathode
Evaluated by color change
U(III) is green Very few studies of U(III) in solution No structural information
Comparisons with trivalent actinides and lanthanides
12
• •
Uranium solution chemistry
Tetravalent uranium
Forms in very strong acid
Requires >0.5 M acid to prevent hydrolysis
Electrolysis of U(VI) solutions
*
Complexation can drive oxidation
Coordination studied by XAFS
Coordination number 9±1
*
Not well defined
U-O distance 2.42 Å
O exchange examined by NMR Pentavalent uranium
Extremely narrow range of existence
Prepared by reduction of UO 2 2+ in water with Zn or H 2 or dissolution of UCl 5 UV-irradiation of 0.5 M 2-propanol-0.2 M LiClO 4 with U(VI) between pH 1.7 and 2.7
U(V) is not stable but slowly oxidizes under suitable conditions No experimental information on structure Quantum mechanical predictions
13
• •
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
14
•
Uranium speciation
Speciation variation with uranium concentration
Hydrolysis as example
Precipitation at higher concentration
Change in polymeric uranium species concentration
15
• • • •
Uranium purification from ores: Using U chemistry in the fuel cycle
Preconcentration of ore
Based on density of ore Leaching to extract uranium into aqueous phase
Calcination prior to leaching
Removal of carbonaceous or sulfur compounds
Destruction of hydrated species (clay minerals) Removal or uranium from aqueous phase
Ion exchange
Solvent extraction Precipitation Use of cheap materials
*
Acid solution leaching Sulfuric (pH 1.5)
U(VI) soluble in sulfuric
Anionic sulfate species
Oxidizing conditions may be needed
MnO 2 Precipitation of Fe at pH 3.8
Carbonate leaching
Formation of soluble anionic carbonate species
*
UO 2 (CO 3 ) 3 4-
Precipitation of most metal ions in alkali solutions
Bicarbonate prevents precipitation of Na
*
2 U 2 O 7 Formation of Na NaOH addition 2 U 2 O 7 with further
Gypsum and limestone in the host aquifers necessitates carbonate leaching
16
• • •
Recovery of uranium from solutions
Ion exchange
U(VI) anions in sulfate and carbonate solution
UO 2 (CO 3 ) 3 4-
UO 2 (SO 4 ) 3 4 Load onto anion exchange, elute with acid or NaCl Solvent extraction
Continuous process
Not well suited for carbonate solutions
Extraction with alkyl phosphoric acid, secondary and tertiary alkylamines
Chemistry similar to ion exchange conditions Chemical precipitation
Addition of base
Peroxide
Water wash, dissolve in nitric acid
Ultimate formation of (NH 4 ) 2 U 2 O 7 (ammonium diuranate), yellowcake
heating to form U 3 O 8 or UO 3
17
•
Uranium purification
Tributyl phosphate (TBP) extraction
Based on formation of nitrate species
UO 2 (NO 3 ) x 2-x + (2-x)NO 3 + 2TBP
UO 2 (NO 3 ) 2 (TBP) 2 Process example of pulse column below
18
Uranium enrichment
• •
Once separated, uranium needs to be enriched for nuclear fuel
Natural U is 0.7 % 235 U Different enrichment needs
3.5 % 235 U for light water reactors
> 90 % 235 U for submarine reactors
235 device
U enrichment below 10 % cannot be used for a Critical mass decreases with increased enrichment 20 % 235 U critical mass for reflected device around 100 kg
Low enriched/high enriched uranium boundary
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• •
Uranium enrichment
Exploit different nuclear properties between U isotopes to achieve enrichment
Mass
Size Shape Nuclear magnetic moment Angular momentum Massed based separations utilize volatile UF 6
UF 6 formed from reaction of U compounds with F 2 at elevated temperature
• •
Colorless, volatile solid at room temperature
Density is 5.1 g/mL
Sublimes at normal atmosphere Vapor pressure of 100 torr
One atmosphere at 56.5 ºC O h
point group U-F bond distance of 2.00 Å
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Uranium Hexafluoride
• • • • •
Very low viscosity
7 mPoise
Water =8.9 mPoise
Useful property for enrichment Self diffusion of 1.9E-5 cm 2 /s Reacts with water
UF 6 + 2H 2 O
UO 2 F 2 + 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
Radius (
r
)
m mass, v velocity, q ion charge, B magnetic field For V acceleration potential
v
2
Vq m
r
c B
2
Vm q
r
mcv
22
qB
• • •
Uranium Enrichment: Electromagnetic Separation
Radius of an ion is proportional to square root of mass
Higher mass, larger radius For electromagnetic separation process
Low beam intensities
High intensities have beam spreading
*
Around 0.5 cm for 50 cm radius Limits rate of production
Low ion efficiency
Loss of material Caltrons used during Manhattan project
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• • •
Calutron
Developed by Ernest Lawrence
Cal. U-tron High energy use
Iraqi Calutrons required about 1.5 MW each
90 total Manhattan Project
Alpha
4.67 m magnet
15% enrichment
Some issues with heat from beams Shimming of magnetic fields to increase yield Beta
Use alpha output as feed
*
High recovery
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• • •
Gaseous Diffusion
High proportion of world’s enriched U
95 % in 1978 40 % in 2003 Separation based on thermal equilibrium
All molecules in a gas mixture have same average kinetic energy
lighter molecules have a higher velocity at same energy
m
2 352
v
352
m
2 349
v
349
For
235 UF
*
6 E k =1/2 mv 2 and 238 UF 6
v
349
v
352
m
352
m
349
235 UF 6 and is 0.429 % faster on average
352 349 1 .
00429
why would UCl 6 for enrichment?
be much more complicated
25
• • • • •
Gaseous Diffusion
235 UF 6 Barrier properties
Resistant to corrosion byUF 6
impacts barrier more often
Ni and Al 2 O 3 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
26
• • • •
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 UF 6 ,
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
UF 6 introduced Gas control
Heater, cooler, compressor Gas seals Operate at temperature above 70 °C and pressures below 0.5 atmosphere R=relative isotopic abundance (N 235 /N 238 ) Quantifying behavior of an enrichment cell
q=R product /R tail
Ideal barrier, R product =R tail (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 (
e
B )
(
q observed
1 ) e
B
(
q ideal
e
B can be used to determine total barrier area for a given enrichment
e
B = 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 UF 6 reactivity Normal operation about 50 % of feed diffuses Gas compression releases heat that requires cooling
Large source of energy consumption
29 1 )
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
30
• • • •
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 % 235 U
3.8 SWU for 0.25 % tails 5.0 SWU for 0.15 % tails Determination of SWU
P product mass
W waste mass F feedstock mass x W x P x F waste assay product assay feedstock assay
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Gaseous Diffusion
• •
Optimization of cells within cascades influences behavior of 234 U
q=1.00573 (352/348) 1/2
Higher amounts of 234 U, 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
32
Gas centrifuge
• • •
Centrifuge pushes heavier 238 UF 6 having more 235 UF 6
against wall with center Heavier gas collected near top Density related to UF 6
pressure Density minimum at center
p
(
r
)
p
( 0 )
e m
w 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
)
p
( 0 )
e m x
w 2
r
2 2
RT
33
• • •
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
(
m
2
m
1 ) w 2
r
2 2
RT
34
•
Gas Centrifuge
More complicated setup than diffusion
Acceleration pressures, 4E5 atmosphere from previous example High speed requires balance Limit resonance frequencies High speed induces stress on materials
Need high tensile strength
*
alloys of aluminum or titanium
*
maraging steel
Heat treated martensitic steel
*
composites reinforced by certain glass, aramid, or carbon fibers
35
• • • •
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
UF 6 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 MW e 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
36
Natanz
Centrifuges
US
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
38
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
39
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
238 U absorption peak 502.74 nm
235 U 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 UF 6
Initial IR excitation at 16 micron
235 UF 6 in excited state Selective excitation of 235 UF 6
Ionization to 235 UF 5 Formation of solid UF 5 (laser snow) Solid enriched and use as feed to another excitation Process degraded by molecular motion\
Cool gas by dilution with H 2 and nozzle expansion
41
•
Nuclear Fuel: Uranium-oxygen system
A number of binary uranium-oxygen compounds
UO
Solid UO unstable, NaCl structure From UO 2
*
heated with U metal Carbon promotes reaction, formation of UC
UO 2
Reduction of UO 3 ºC
*
CO, C, CH 4 , or C 2 H 5 OH can be used as reductants O 2 presence responsible for UO 2+x formation Large scale preparation
* *
UO 4 , (NH 4 ) 2 U 2 O 7 , or (NH 4 ) 4 UO 2 (CO 3 ) 3 Calcination in air at 400-500 ºC
* *
or U 3 O 8 with H H 2 at 650-800 ºC UO 2 has high surface area 2 from 800 ºC to 1100
42
•
Uranium-oxygen
U 3 O 8
From oxidation of UO
2 in air at 800 ºC
a
phase uranium coordinated to oxygen in pentagonal bipyrimid
b
phase results from the heating of the
a
above 1350 ºC
Slow cooling phase
43
Uranium-oxygen
•
UO 3
Seven phases can be prepared
•
A phase (amorphous)
Heating in air at 400 ºC
*
UO 4 .
2H 2 O, UO 2 C 2 O 4 .
3H 2 O, or (HN 4 ) 4 UO 2 (CO 3 ) 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 UO 2 2+
b
-phase
Ammonium diuranate or uranyl nitrate heated rapidly in air at 400-500 ºC
g
-phase prepared under O 2 6-10 atmosphere at 400-500 ºC
44
Uranium-oxygen
• •
UO 3
hydrates 6 different hydrated UO 3 compounds UO 3 .
2H 2 O Anhydrous UO 25-70 ºC 3 exposed to water from
Heating resulting compound in air to 100 ºC forms
a
-UO 3 .
0.8 H 2 O
a
-UO 2 (OH) 2 [
a
UO
3 .
b
H 2 O] forms in hydrothermal experiments -UO 3 .
H 2 O also forms
45
• • •
Uranium-oxygen single crystals
UO 2 UO 2
from the melt of 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 UO 2 2+ in structure Some layer structures
46
47
• • •
UO
2
Heat Capacity
Room temperature to 1000 K
Increase in heat capacity due to harmonic lattice vibrations
Small contribution to thermal excitation of U 4+ localized electrons in crystal field 1000-1500 K
Thermal expansion induces anharmonic lattice vibration 1500-2670 K
Lattice and electronic defects
48
Vaporization of UO
2
• •
Above and below the melting point Number of gaseous species observed
U, UO, UO 2 , UO 3 , O, and O 2
Use of mass spectrometer to determine partial pressure for each species For hypostiochiometric UO 2 , partial pressure
levels comparable to UO 2 O increases dramatically at O/U above 2
49
•
Uranium oxide chemical properties
Oxides dissolve in strong mineral acids
Valence does not change in HCl, H 2 SO 4 , and H 3 PO 4
Sintered pellets dissolve slowly in HNO 3
Rate increases with addition of NH
*
4 F, H 2 O 2 , or carbonates H 2 O 2 reaction
UO 2 + at surface oxidized to UO 2 2+
50
Solid solutions with UO
2
• • •
Solid solutions formed with group 2 elements, lanthanides, actinides, and some transition elements (Mn, Zr, Nb, Cd)
Distribution of metals on UO 2 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 M y U 1-y O 2+x
x is positive and negative
51
Solid solutions with UO
2
•
Lattice parameter change in solid solution
Changes nearly linearly with increase in y and x
M y U 1-y O 2+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 UO
2
•
Tetravalent M y U 1-y O 2+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 O 2
*
1500 ºC partial pressure At 0.2 atm., y=0.383 at 700 ºC to y=0.068 at
53
• •
Solid solutions of UO
2 Tri and tetravalent M y U 1-y O 2+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)O 2 and (Ce,U)O 2-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 U 3 O 8
Some systematics in trends
*
For Nd, when y is between 0.3 and 0.5, x = 0.5-y
54
•
Solid solution UO
2 Oxygen potential
Zr solid solution
Lower than the UO 2+x system
*
x=0.05, y=0.3
-270 kJ/mol for solid solution
-210 kJ/mol for UO 2+x Th solid solution
Increase in
D
G with increasing y Compared to UO 2
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
D
G for CeO compared to PuO 2-x 2-x
55
• • •
Metallic Uranium
Three different phase
a, b, g
phases
Dominate at different temperatures Uranium is strongly electropositive
Cannot be prepared through H 2 reduction Metallic uranium preparation
UF 4 or UCl 4 with Ca or Mg
UO 2 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
Tetragonal unit cell
g
-phase
Formed above 775 ºC
bcc structure Metal has plastic character
a ‐phase U-U distances in layer (2.80±0.05) Å and between layers
Gamma phase soft, difficult fabrication
3.26 Å
Beta phase brittle and hard Paramagnetic Temperature dependence of resistivity Alloyed with Mo, Nb, Nb-Zr, and Ti
57 b -phase
•
Intermetallic compounds
Wide range of intermetallic compounds and solid solutions in alpha and beta uranium
Hard and brittle transition metal compounds
U 6 X, 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 O 2 , air, 2 Dissolves in HCl
Also forms hydrated UO 2 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 235 U?
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 UO 2 2+
63
Pop Quiz
•
What atomic orbitals form the molecular orbitals for UO 2 2+
64