• •

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

19

• •

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

20

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

21

• • • •

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

23

• • •

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

24

• • •

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

27

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

28

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

31

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