In the Name of God

In the Name of GodIn the Name of God

Isfahan University of TechnologyIsfahan University of Technology

Department of ChemistryDepartment of Chemistry

Nuclear Fuel Nuclear Fuel CycleCycle

By: Habib SoleimaniBy: Habib Soleimani

Supervisor: Dr. GhaziaskarSupervisor: Dr. Ghaziaskar

Contents:Contents:

DefinitionsDefinitions Uranium and its compounds Uranium and its compounds Uranium Mining and MillingUranium Mining and Milling Uranium ConversionUranium Conversion Uranium enrichmentUranium enrichment Fuel fabricationFuel fabrication Spent fuelSpent fuel Reprocessing Reprocessing

DefinitionsDefinitions

Radioactivity ( radioactive Radioactivity ( radioactive decay ):decay ):

1 Becquerel= 1 decays/S1 Becquerel= 1 decays/S

1 Curie= 37 billion decays/S1 Curie= 37 billion decays/S

Half-lifeHalf-life

DefinitionsDefinitions

Radiation: Radiation:

particlesparticles: : neutrons, alpha neutrons, alpha particles, and beta particles, and beta particlesparticles

energy energy : waves of : waves of pure energy, such as pure energy, such as gamma and X-rays. gamma and X-rays.

FissionFission

ElementElement

SySym-m-bolbol

AtomiAtomic c numbnumberer

Half-lifeHalf-life Decay Decay modemode

ActiniuActiniumm

AcAc 8989 22 y22 y αα

AstatineAstatine AtAt 8585 8.3 h8.3 h αα

FranciuFranciumm

FrFr 8787 22 min22 min αα

PlutoniuPlutoniumm

PuPu 9494 3.8 ×103.8 ×1055 yy

αα

PoloniuPoloniumm

PoPo 8484 138.4 d138.4 d αα

Thorium Thorium ThTh 9090 1.4 *101.4 *101010 yy

αα

UraniuUraniumm

U U 9292 4.5 *104.5 *1099 y y αα

UraniumUranium Uranium is present in the Earth’s crust at an Uranium is present in the Earth’s crust at an

average concentration of average concentration of 2 ppm2 ppm. Its natural . Its natural abundance is equal that of abundance is equal that of SnSn..

Acidic rocksAcidic rocks with high silicate, such as with high silicate, such as granitegranite, , have higher than average concentrations of have higher than average concentrations of uranium. uranium.

sedimentarysedimentary and and basicbasic rocks have lower than rocks have lower than average concentrations .average concentrations .

Isotopes: U-233, U-234, U-235, U-236, U-237, U-Isotopes: U-233, U-234, U-235, U-236, U-237, U-238 and U-239238 and U-239

Specific activity = 24.9 *10Specific activity = 24.9 *1033 Bq/g Bq/g All isotopes decay All isotopes decay by emission of α-radiation with

a radiation energy between 4.2 and 5.2 MeV.

Uranium CompoundsUranium Compounds

Uranium metalUranium metal Uranium dioxide ( UOUranium dioxide ( UO2 2 ))

Thriuranium octaoxide ( UThriuranium octaoxide ( U33OO88 ) )

Uranium tetrafluoride ( UFUranium tetrafluoride ( UF4 4 ))

Uranium hexafluoride ( UFUranium hexafluoride ( UF66 ) )

Uranium metalUranium metal

Uranium metal is heavy, silvery white, Uranium metal is heavy, silvery white, malleable, ductile, and softer than steel .malleable, ductile, and softer than steel .

d = 19 g/cmd = 19 g/cm33 , 1.6 times more dense than , 1.6 times more dense than leadlead..

it is subject to it is subject to surface oxidationsurface oxidation. . WaterWater attacks uranium metal slowly at room attacks uranium metal slowly at room

temperature and rapidly at higher temperature and rapidly at higher temperatures. temperatures.

Uranium metal Uranium metal powderpowder or or chipschips will ignite will ignite spontaneously in air at ambient temperature.spontaneously in air at ambient temperature.

Uranium metalUranium metal

Uranium dioxide ( UOUranium dioxide ( UO2 2 )) It is an It is an basic oxidebasic oxide.. Most commonly used as a nuclear reactor Most commonly used as a nuclear reactor fuelfuel. . It is a It is a stable ceramicstable ceramic that can be heated almost to its that can be heated almost to its

melting point, 5,212°F (2,878°C), without serious melting point, 5,212°F (2,878°C), without serious mechanical deterioration .mechanical deterioration .

It It does not reactdoes not react with with waterwater to any significant level. to any significant level.

At ambient temperatures, UOAt ambient temperatures, UO22 will gradually will gradually convertconvert to Uto U33OO88..

Particle density = 10.96 g/cmParticle density = 10.96 g/cm33 , , bulk density = 2.0 - 5.0 g/cm bulk density = 2.0 - 5.0 g/cm3 3

Uranium dioxide (UOUranium dioxide (UO22) will ) will ignite spontaneouslyignite spontaneously in in heated air and burn brilliantly .heated air and burn brilliantly .

Uranium dioxide ( UOUranium dioxide ( UO2 2 ))

Thriuranium octaoxide Thriuranium octaoxide ( U( U33OO88 ) )

It is an It is an amphoteric oxideamphoteric oxide.. Triuranium octaoxide (UTriuranium octaoxide (U33OO88) occurs naturally as the ) occurs naturally as the

olive-green-coloredolive-green-colored mineral mineral pitchblendepitchblende. . In the presence of In the presence of oxygenoxygen (O (O22), uranium dioxide ), uranium dioxide

(UO(UO22) and uranium trioxide (UO) and uranium trioxide (UO33) are oxidized to ) are oxidized to UU33OO88. .

It is generally considered for It is generally considered for disposaldisposal purposes purposes because, under normal environmental conditions, because, under normal environmental conditions, UU33OO8 8 is one of the is one of the most kinetically and most kinetically and thermodynamically stablethermodynamically stable forms of uranium. forms of uranium.

It is It is insolubleinsoluble in water in water Particle density = 8.3 g/cmParticle density = 8.3 g/cm33

bulk density = 1.5 - 4.0 g/cm bulk density = 1.5 - 4.0 g/cm33

Thriuranium octaoxide Thriuranium octaoxide ( U( U33OO88 ) )

Uranium tetrafluoride Uranium tetrafluoride ( UF( UF4 4 ))

Uranium tetrafluoride (UFUranium tetrafluoride (UF44) is a ) is a green green crystallinecrystalline solid. solid.

m.p.= 1,760°F (96°C)m.p.= 1,760°F (96°C) It is formed by the reaction It is formed by the reaction UFUF66 + H + H22 in a in a

vertical tube-type reactor or by the action vertical tube-type reactor or by the action HF+UOHF+UO22 . .

It is generally an It is generally an intermediateintermediate in the in the conversionconversion of UFof UF6 6 to either uranium oxide (Uto either uranium oxide (U33OO88 or UO or UO22) or ) or uranium metal.uranium metal.

Uranium tetrafluoride (UFUranium tetrafluoride (UF44) reacts slowly with ) reacts slowly with moisturemoisture at ambient temperature, forming UO at ambient temperature, forming UO2 2 and HF, which are very corrosive. and HF, which are very corrosive.

Bulk density = 2.0 - 4.5 g/cmBulk density = 2.0 - 4.5 g/cm33..

Uranium tetrafluoride Uranium tetrafluoride ( UF( UF4 4 ))

Uranium hexafluoride Uranium hexafluoride ( UF( UF66 ) )

Uranium hexafluoride (UFUranium hexafluoride (UF66) is the chemical ) is the chemical form of uranium that is used during the form of uranium that is used during the uranium uranium enrichment processenrichment process. .

Within a reasonable range of temperature Within a reasonable range of temperature and pressure, it can be a and pressure, it can be a solidsolid,, liquid liquid, or , or gasgas. .

Disadvantage: Disadvantage: UF UF66+2H+2H22O(g/l) 4HF(g)+UOO(g/l) 4HF(g)+UO22FF22

UFUF66 is not considered a preferred form for is not considered a preferred form for long-term long-term storagestorage or or disposaldisposal because of its because of its relative instability.relative instability.

Uranium hexafluoride Uranium hexafluoride ( UF( UF66 ) )

UF6 is characterised by an unusually high vapour pressure for a solid.

UF6 is not flammable and is inert in dry air.

TemperTemperat-ure at-ure ((ooC)C)

Vapor Vapor Pressure(mPressure(mbar)bar)

00 2424

2020 107 107

5656 1013.51013.5

6464 1516.51516.5

UFUF66

MiningMining

ExcavationExcavation : Excavation may be : Excavation may be undergroundunderground and and open pitopen pit mining . mining .

In situ leachingIn situ leaching (ISL) : (ISL) : oxygenatedoxygenated acidicacidic or or basicbasic groundwater is groundwater is circulated through a very porous circulated through a very porous orebody to dissolve the uranium and orebody to dissolve the uranium and bring it to the surface.bring it to the surface.

MillingMilling

The ore is first The ore is first crushedcrushed and and groundground to liberate to liberate mineral particles. mineral particles.

The The amphotericamphoteric oxide is then leached with oxide is then leached with sulfuric acidsulfuric acid ( ( LeachingLeaching):):

UOUO33(s) + 2H(s) + 2H++(aq)    UO(aq)    UO222+2+(aq) + H(aq) + H22O O

UOUO222+2+(aq) + 3SO(aq) + 3SO44

2-2-(aq)    UO(aq)    UO22(SO(SO44))334-4-(aq)(aq)

The The basicbasic oxide is converted by a similar oxide is converted by a similar process to that of a water soluble UOprocess to that of a water soluble UO22(CO(CO33))33

4-4-

(aq) ion.(aq) ion.

MillingMilling Two methods are used to concentrate and purify Two methods are used to concentrate and purify

the uranium: the uranium: ion exchangeion exchange and and solvent extractionsolvent extraction ( more common ).( more common ).

solvent extractionsolvent extraction : uses : uses tertiary aminestertiary amines in an in an organic organic kerosenekerosene solvent in a continuous solvent in a continuous process: process:

2 R2 R33N(org) + HN(org) + H22SOSO44(aq)   (R(aq)   (R33NH)NH)22SOSO44(org)(org)

2(R2(R33NH)NH)22SOSO44(org) + UO(org) + UO22(SO(SO44))334-4-(aq)(aq)

(R(R33NH)NH)44UOUO22(SO(SO44))33(org) + 2SO(org) + 2SO442-2-

(aq)(aq)

MillingMilling

The solvents are removed by The solvents are removed by evaporating in a evaporating in a vacuumvacuum . .

Ammonium diuranate, (NHAmmonium diuranate, (NH44))22UU22OO7 7 , , is is precipitatedprecipitated by adding by adding ammoniaammonia to neutralize the solution.to neutralize the solution.

Then Then

(NH(NH44))22UU22OO7 7 heat heat UU33OO88 (yellow (yellow

cake)cake)

Refining and converting Refining and converting UU33OO88 toUO toUO33

UU33OO88+HNO+HNO3 3 UOUO22(NO(NO33))22· 6H· 6H22O O Uranyl nitrate, UOUranyl nitrate, UO22(NO(NO33))22· 6H· 6H22O, is fed into a O, is fed into a

continuous solvent extractioncontinuous solvent extraction process. The process. The uranium is extracted into an organic phase uranium is extracted into an organic phase ((kerosenekerosene) with ) with tributyl phosphate (TBP)tributyl phosphate (TBP), and the , and the impurities remain again in the aqueous phase.impurities remain again in the aqueous phase.

Washing from Washing from kerosenekerosene with with dilute nitric aciddilute nitric acid and and

concentrated by evaporation to pure UOconcentrated by evaporation to pure UO22(NO(NO33))22· · 6H6H22O .O .

Then Then

UOUO22(NO(NO33))22· 6H· 6H22O O heat heat UOUO3 3 (pure)(pure)

Continuous solvent Continuous solvent extractionextraction

Converting UOConverting UO33 to UF to UF66

The UOThe UO33 is is reducedreduced with hydrogen in a kiln: with hydrogen in a kiln:

UOUO33(s) + H(s) + H22(g) UO(g) UO22(s) + H(s) + H22O(g) O(g)

thenthen

UOUO22(s) + 4HF(g)   (s) + 4HF(g)   UFUF44(s)(s) + 4H + 4H22O(g)O(g) The tetrafluoride is then fed into a The tetrafluoride is then fed into a fluidized fluidized

bedbed reactorreactor and reacted with gaseous fluorine and reacted with gaseous fluorine to obtain the hexafluoride:to obtain the hexafluoride:

UFUF44(s)(s) + F + F22(g)    UF(g)    UF66(g) (g)

Production of uranium Production of uranium metalmetal

Uranium metal is produced by Uranium metal is produced by reducing the uranium tetrafluoride reducing the uranium tetrafluoride with either with either calciumcalcium or or magnesiummagnesium, , both active both active group IIA metalsgroup IIA metals that are that are excellent reducing agents.excellent reducing agents.

UFUF44(s)(s) + 2Ca(s)   U(s) + + 2Ca(s)   U(s) + 2CaF2CaF22(s) (s)

EnrichmentEnrichment

Enriched uranium gradesEnriched uranium grades Highly Enriched Uranium ( HEU ): > 20% Highly Enriched Uranium ( HEU ): > 20% 235235UU 20% weapon-usable, 85% weapon-grade20% weapon-usable, 85% weapon-grade

Low Enriched Uranium ( LEU ): < 20% Low Enriched Uranium ( LEU ): < 20% 235235UU 12% - 19.75% used in 12% - 19.75% used in research reactorsresearch reactors 3% - 5% used in 3% - 5% used in Light Water ReactorsLight Water Reactors

Slightly enriched Uranium ( SEU ): 0.9% - 2% Slightly enriched Uranium ( SEU ): 0.9% - 2% 235235UU used in used in Heavy Water ReactorsHeavy Water Reactors instead of natural uranium instead of natural uranium

Recovered Uranium ( R U ):Recovered Uranium ( R U ): recovered from spent fuel of Light Water Reactorsrecovered from spent fuel of Light Water Reactors

Enrichment MethodsEnrichment Methods

Thermal DiffusionThermal Diffusion Gaseous DiffusionGaseous Diffusion The Gas CentrifugeThe Gas Centrifuge Aerodynamic ProcessAerodynamic Process Electromagnetic Isotope Electromagnetic Isotope

Separation( EMIS )Separation( EMIS ) Laser ProcessesLaser Processes Chemical MethodsChemical Methods Plasma SeparationPlasma Separation

Basic Facts of Separation Basic Facts of Separation PhysicsPhysics

Laser ProcessesLaser Processes

Atomic Vapor Atomic Vapor Laser Isotope Laser Isotope Separation Separation ((AVLISAVLIS))

Molecular Laser Molecular Laser Isotope Separation Isotope Separation ((MLISMLIS))

Diffusion CellDiffusion Cell

separation factor of asingle diffusion process step is

determined as follows:

00429.1

Gaseous Diffusion Gaseous Diffusion CascadeCascade

Separation factor & Separation factor & Separative power of Separative power of

centrifugecentrifuge

M1, M2 ; Molecular weight of the molecules to be separated

R ; gas constant D ; diffusion constant of the process gas ρ ; density of the process gas T ; temperature in degrees Kelvin d ; diameter of the rotor L ; length of the rotor V ; circumferential velocity of the rotor

R

Vmax

P1-centrifugeP1-centrifuge

Gas Centrifuge CascadeGas Centrifuge Cascade

Design of enrichment Design of enrichment plantsplants

Several centrifuges are therefore operated in parallel in the separation stages of a centrifuge cascade.

Centrifuge plants, are built of several operating units, which themselves consist of several cascades working in parallel.

Diffusion plants consist of a single large cascade with approximately 1,400 stages.

Fuel fabricationFuel fabrication

Enriched UFEnriched UF66 is converted into uranium is converted into uranium UOUO2 2 powder which is then processed into powder which is then processed into pelletpellet form: form:

UFUF66+H+H2 2 (g) (g) UFUF44(S(S))+2HF(g) +2HF(g)

UFUF44(S(S)+H)+H22O UOO UO22(S)(S)+2HF(g)+2HF(g)

Fuel fabricationFuel fabrication

The pellets are then fired in a The pellets are then fired in a high high temperaturetemperature sintering furnacesintering furnace (with H(with H22)) to create hard, to create hard, ceramicceramic pellets of enriched pellets of enriched uranium.uranium.

Fuel rods : Fuel rods : corrosion resistantcorrosion resistant metal alloy metal alloy ( ( zirconiumzirconium ). ).

Fuel bundle & fuel pelletFuel bundle & fuel pellet

Fuel assemblyFuel assembly

Chain reactionChain reaction

Nuclear reactorNuclear reactor

Spent fuelSpent fuel

Used fuel:Used fuel: About 95% U-238 About 95% U-238 About 1% U-235 that has About 1% U-235 that has not fissionednot fissioned About 1% About 1% plutonium plutonium 3% 3% fission productsfission products, which are highly , which are highly

radioactiveradioactive With other With other transuranictransuranic elements elements

formed in the reactor. formed in the reactor.

Spent fuel storageSpent fuel storage

Reprocessing Reprocessing

TheThe PUREX process is a PUREX process is a liquid-liquid liquid-liquid extractionextraction method used to reprocess method used to reprocess spent nuclear fuel, in order to spent nuclear fuel, in order to extract uranium and plutonium, extract uranium and plutonium, independent of each other, from the independent of each other, from the fission products.fission products.

PUREXPUREX is an acronym standing for is an acronym standing for PPlutonium and lutonium and UUranium ranium RRecovery by ecovery by ExExtraction. traction.

ReprocessingReprocessing

1.1. Dissolving of fuel into Dissolving of fuel into nitric acidnitric acid 2.2. Remove the fine insoluble solids Remove the fine insoluble solids 3.3. Organic solvent : 30% tributyl Organic solvent : 30% tributyl

phosphate (phosphate (TBPTBP) in odorless ) in odorless kerosenekerosene (or hydrogenated propylene(or hydrogenated propylene trimer) trimer)

4.4. The The extraction extraction of U(VI) and Pu(IV)of U(VI) and Pu(IV)5.5. ReductionReduction of Pu(IV) to Pu(III) of Pu(IV) to Pu(III) 6.6. Back extractionBack extraction (stripping) of U(VI) (stripping) of U(VI)

by a by a lowlow nitric acid concentrationnitric acid concentration

References:References: www.nrc.govwww.nrc.gov www.stpnoc.comwww.stpnoc.com www.urenco.comwww.urenco.com http://chemcases.comhttp://chemcases.com www.wikipedia.comwww.wikipedia.com www.jnfl.co.jpwww.jnfl.co.jp www.globalsecurity.comwww.globalsecurity.com http://daneshnameh.roshd.irhttp://daneshnameh.roshd.ir www.isotopetrace.comwww.isotopetrace.com

Uranium hexafluoride Uranium hexafluoride ( UF( UF66 ) )

With most metals and alloys (for example, Fe, Co, Cr, Al, Mg, high grade steel, brass) UF6 reacts slowly at room temperature to form metal fluorides and reacts somewhat faster at higher temperatures( grey, brown or green deposits).

Absolutely dry glass and dry quartz sand are not attacked by UF6.

Metals such as Ni and Pt and most of their alloys are practically resistant, even at 100 °C.

Synthetic polymers, for example Teflon and some copolymers,

demonstrate similar resistance towards UF6. ether, ester, ketone and saturated and unsaturated

hydrocarbons react at room temperature by fluorinating with UF6.

Refining and converting Refining and converting UU33OO88 to UF to UF66

Basic Facts of Separation Basic Facts of Separation PhysicsPhysics

The ability of the separation element to separate 235Uand 238U is described by its separation factor.

If N= concentration of If N= concentration of 235U; NF is its concentration in feed stream(F)

NP is its concentration in product stream(P)

NT is its concentration in Tails stream(T)

Basic Facts of Separation Basic Facts of Separation PhysicsPhysics

However, the separation factor alone does not describe fully the efficiency of a separation element.

To determine the "work” that must be applied for separation, P, NP, NF and NT must be given.

Mass balance : 0=P+T-F Isotope balance: 0=PNP +TNT -FNF

PNN

NNF

TF

TP

Separative Work and Separative Work and PowerPower

δU=PV(NP)+TV(NT)-FV(NF) The value function V(N) is determined

using mathematical methods so that the calculated separative work is independent of the 235U concentrations in the separation element and depends only on the archieved change in concentration and throughput.

Kg SW/S or SWU/S