In the Name of God Isfahan University of Technology Department of Chemistry

Nuclear Fuel Cycle By: Habib Soleimani Supervisor: Dr. Ghaziaskar

Contents: Definitions Definitions Uranium and its compounds Uranium and its compounds Uranium Mining and Milling Uranium Mining and Milling Uranium Conversion Uranium Conversion Uranium enrichment Uranium enrichment Fuel fabrication Fuel fabrication Spent fuel Spent fuel Reprocessing Reprocessing

Definitions Radioactivity ( radioactive decay ): Radioactivity ( radioactive decay ): 1 Becquerel= 1 decays/S 1 Becquerel= 1 decays/S 1 Curie= 37 billion decays/S 1 Curie= 37 billion decays/S Half-life Half-life

Definitions Radiation: Radiation: particles: neutrons, alpha particles, and beta particles particles: neutrons, alpha particles, and beta particles energy : waves of pure energy, such as gamma and X-rays. energy : waves of pure energy, such as gamma and X-rays.

Fission

Element Element Sym- bol Atomic number Half-life Half-life Decay mode Actinium Ac Ac y 22 y α   Astatine At At h 8.3 hα Francium Fr Fr min 22 min α   Plutonium Pu Pu ×10 5 y 3.8 ×10 5 yα Polonium Po Po d dα Thorium Th Th *10 10 y 1.4 *10 10 yα Uranium U *10 9 y 4.5 *10 9 yα

Uranium Uranium is present in the Earth’s crust at an average concentration of 2 ppm. Its natural abundance is equal that of Sn. Uranium is present in the Earth’s crust at an average concentration of 2 ppm. Its natural abundance is equal that of Sn. Acidic rocks with high silicate, such as granite, have higher than average concentrations of uranium. Acidic rocks with high silicate, such as granite, have higher than average concentrations of uranium. sedimentary and basic rocks have lower than average concentrations. sedimentary and basic rocks have lower than average concentrations. Isotopes: U-233, U-234, U-235, U-236, U-237, U-238 and U-239 Isotopes: U-233, U-234, U-235, U-236, U-237, U-238 and U-239 Specific activity = 24.9 *10 3 Bq/g Specific activity = 24.9 *10 3 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 Compounds Uranium metal Uranium metal Uranium dioxide ( UO 2 ) Uranium dioxide ( UO 2 ) Thriuranium octaoxide ( U 3 O 8 ) Thriuranium octaoxide ( U 3 O 8 ) Uranium tetrafluoride ( UF 4 ) Uranium tetrafluoride ( UF 4 ) Uranium hexafluoride ( UF 6 ) Uranium hexafluoride ( UF 6 )

Uranium metal Uranium metal is heavy, silvery white, malleable, ductile, and softer than steel. Uranium metal is heavy, silvery white, malleable, ductile, and softer than steel. d = 19 g/cm 3, 1.6 times more dense than lead. d = 19 g/cm 3, 1.6 times more dense than lead. it is subject to surface oxidation. it is subject to surface oxidation. Water attacks uranium metal slowly at room temperature and rapidly at higher temperatures. Water attacks uranium metal slowly at room temperature and rapidly at higher temperatures. Uranium metal powder or chips will ignite spontaneously in air at ambient temperature. Uranium metal powder or chips will ignite spontaneously in air at ambient temperature.

Uranium metal

Uranium dioxide ( UO 2 ) It is an basic oxide. It is an basic oxide. Most commonly used as a nuclear reactor fuel. Most commonly used as a nuclear reactor fuel. It is a stable ceramic that can be heated almost to its melting point, 5,212°F (2,878°C), without serious mechanical deterioration. It is a stable ceramic that can be heated almost to its melting point, 5,212°F (2,878°C), without serious mechanical deterioration. It does not react with water to any significant level. It does not react with water to any significant level. At ambient temperatures, UO 2 will gradually convert to U 3 O 8. At ambient temperatures, UO 2 will gradually convert to U 3 O 8. Particle density = g/cm 3, bulk density = g/cm 3 Particle density = g/cm 3, bulk density = g/cm 3 Uranium dioxide (UO 2 ) will ignite spontaneously in heated air and burn brilliantly. Uranium dioxide (UO 2 ) will ignite spontaneously in heated air and burn brilliantly.

Uranium dioxide ( UO 2 )

Thriuranium octaoxide ( U 3 O 8 ) It is an amphoteric oxide. It is an amphoteric oxide. Triuranium octaoxide (U 3 O 8 ) occurs naturally as the olive-green- colored mineral pitchblende. Triuranium octaoxide (U 3 O 8 ) occurs naturally as the olive-green- colored mineral pitchblende. In the presence of oxygen (O 2 ), uranium dioxide (UO 2 ) and uranium trioxide (UO 3 ) are oxidized to U 3 O 8. In the presence of oxygen (O 2 ), uranium dioxide (UO 2 ) and uranium trioxide (UO 3 ) are oxidized to U 3 O 8. It is generally considered for disposal purposes because, under normal environmental conditions, U 3 O 8 is one of the most kinetically and thermodynamically stable forms of uranium. It is generally considered for disposal purposes because, under normal environmental conditions, U 3 O 8 is one of the most kinetically and thermodynamically stable forms of uranium. It is insoluble in water It is insoluble in water Particle density = 8.3 g/cm 3 bulk density = g/cm 3 Particle density = 8.3 g/cm 3 bulk density = g/cm 3

Thriuranium octaoxide ( U 3 O 8 )

Uranium tetrafluoride ( UF 4 ) Uranium tetrafluoride (UF 4 ) is a green crystalline solid. Uranium tetrafluoride (UF 4 ) is a green crystalline solid. m.p.= 1,760°F (96°C) m.p.= 1,760°F (96°C) It is formed by the reaction UF 6 + H 2 in a vertical tube-type reactor or by the action HF+UO 2. It is formed by the reaction UF 6 + H 2 in a vertical tube-type reactor or by the action HF+UO 2. It is generally an intermediate in the conversion of UF 6 to either uranium oxide (U 3 O 8 or UO 2 ) or uranium metal. It is generally an intermediate in the conversion of UF 6 to either uranium oxide (U 3 O 8 or UO 2 ) or uranium metal. Uranium tetrafluoride (UF 4 ) reacts slowly with moisture at ambient temperature, forming UO 2 and HF, which are very corrosive. Uranium tetrafluoride (UF 4 ) reacts slowly with moisture at ambient temperature, forming UO 2 and HF, which are very corrosive. Bulk density = g/cm 3. Bulk density = g/cm 3.

Uranium tetrafluoride ( UF 4 )

Uranium hexafluoride ( UF 6 ) Uranium hexafluoride (UF 6 ) is the chemical form of uranium that is used during the uranium enrichment process. Uranium hexafluoride (UF 6 ) is the chemical form of uranium that is used during the uranium enrichment process. Within a reasonable range of temperature and pressure, it can be a solid, liquid, or gas. Within a reasonable range of temperature and pressure, it can be a solid, liquid, or gas. Disadvantage: UF 6 +2H 2 O(g/l) 4HF(g)+UO 2 F 2 Disadvantage: UF 6 +2H 2 O(g/l) 4HF(g)+UO 2 F 2 UF 6 is not considered a preferred form for long-term storage or disposal because of its relative instability. UF 6 is not considered a preferred form for long-term storage or disposal because of its relative instability.

Uranium hexafluoride ( UF 6 ) UF 6 is characterised by an unusually high vapour pressure for a solid. UF 6 is not flammable and is inert in dry air. Temperat- ure ( o C) Vapor Pressure(mbar)

UF 6

Mining Excavation : Excavation may be underground and open pit mining. Excavation : Excavation may be underground and open pit mining. In situ leaching (ISL) : oxygenated acidic or basic groundwater is circulated through a very porous orebody to dissolve the uranium and bring it to the surface. In situ leaching (ISL) : oxygenated acidic or basic groundwater is circulated through a very porous orebody to dissolve the uranium and bring it to the surface.

Milling The ore is first crushed and ground to liberate mineral particles. The ore is first crushed and ground to liberate mineral particles. The amphoteric oxide is then leached with sulfuric acid ( Leaching): The amphoteric oxide is then leached with sulfuric acid ( Leaching): UO 3 (s) + 2H + (aq) UO 2 2+ (aq) + H 2 O UO 3 (s) + 2H + (aq) UO 2 2+ (aq) + H 2 O UO 2 2+ (aq) + 3SO 4 2- (aq) UO 2 (SO 4 ) 3 4- (aq) UO 2 2+ (aq) + 3SO 4 2- (aq) UO 2 (SO 4 ) 3 4- (aq) The basic oxide is converted by a similar process to that of a water soluble UO 2 (CO 3 ) 3 4- (aq) ion. The basic oxide is converted by a similar process to that of a water soluble UO 2 (CO 3 ) 3 4- (aq) ion.

Milling Two methods are used to concentrate and purify the uranium: ion exchange and solvent extraction ( more common ). Two methods are used to concentrate and purify the uranium: ion exchange and solvent extraction ( more common ). solvent extraction : uses tertiary amines in an organic kerosene solvent in a continuous process: solvent extraction : uses tertiary amines in an organic kerosene solvent in a continuous process: 2 R 3 N(org) + H 2 SO 4 (aq) (R 3 NH) 2 SO 4 (org) 2 R 3 N(org) + H 2 SO 4 (aq) (R 3 NH) 2 SO 4 (org) 2(R 3 NH) 2 SO 4 (org) + UO 2 (SO 4 ) 3 4- (aq) 2(R 3 NH) 2 SO 4 (org) + UO 2 (SO 4 ) 3 4- (aq) (R 3 NH) 4 UO 2 (SO 4 ) 3 (org) + 2SO 4 2- (aq) (R 3 NH) 4 UO 2 (SO 4 ) 3 (org) + 2SO 4 2- (aq)

Milling The solvents are removed by evaporating in a vacuum. The solvents are removed by evaporating in a vacuum. Ammonium diuranate, (NH 4 ) 2 U 2 O 7, is precipitated by adding ammonia to neutralize the solution. Ammonium diuranate, (NH 4 ) 2 U 2 O 7, is precipitated by adding ammonia to neutralize the solution. Then Then (NH 4 ) 2 U 2 O 7 heat U 3 O 8 (yellow cake) (NH 4 ) 2 U 2 O 7 heat U 3 O 8 (yellow cake)

Refining and converting U 3 O 8 toUO 3 U 3 O 8 +HNO 3 UO 2 (NO 3 ) 2 · 6H 2 O U 3 O 8 +HNO 3 UO 2 (NO 3 ) 2 · 6H 2 O Uranyl nitrate, UO 2 (NO 3 ) 2 · 6H 2 O, is fed into a continuous solvent extraction process. The uranium is extracted into an organic phase (kerosene) with tributyl phosphate (TBP), and the impurities remain again in the aqueous phase. Uranyl nitrate, UO 2 (NO 3 ) 2 · 6H 2 O, is fed into a continuous solvent extraction process. The uranium is extracted into an organic phase (kerosene) with tributyl phosphate (TBP), and the impurities remain again in the aqueous phase. Washing from kerosene with dilute nitric acid and concentrated by evaporation to pure UO 2 (NO 3 ) 2 · 6H 2 O. Washing from kerosene with dilute nitric acid and concentrated by evaporation to pure UO 2 (NO 3 ) 2 · 6H 2 O. Then Then UO 2 (NO 3 ) 2 · 6H 2 O heat UO 3 (pure) UO 2 (NO 3 ) 2 · 6H 2 O heat UO 3 (pure)

Continuous solvent extraction

Converting UO 3 to UF 6 The UO 3 is reduced with hydrogen in a kiln: The UO 3 is reduced with hydrogen in a kiln: UO 3 (s) + H 2 (g) UO 2 (s) + H 2 O(g) UO 3 (s) + H 2 (g) UO 2 (s) + H 2 O(g) then then UO 2 (s) + 4HF(g) UF 4 (s) + 4H 2 O(g) UO 2 (s) + 4HF(g) UF 4 (s) + 4H 2 O(g) The tetrafluoride is then fed into a fluidized bed reactor and reacted with gaseous fluorine to obtain the hexafluoride: The tetrafluoride is then fed into a fluidized bed reactor and reacted with gaseous fluorine to obtain the hexafluoride: UF 4 (s) + F 2 (g) UF 6 (g) UF 4 (s) + F 2 (g) UF 6 (g)

Production of uranium metal Uranium metal is produced by reducing the uranium tetrafluoride with either calcium or magnesium, both active group IIA metals that are excellent reducing agents. Uranium metal is produced by reducing the uranium tetrafluoride with either calcium or magnesium, both active group IIA metals that are excellent reducing agents. UF 4 (s) + 2Ca(s) U(s) + 2CaF 2 (s) UF 4 (s) + 2Ca(s) U(s) + 2CaF 2 (s)

Enrichment

Enriched uranium grades Highly Enriched Uranium ( HEU ): > 20% 235 U Highly Enriched Uranium ( HEU ): > 20% 235 U 20% weapon-usable, 85% weapon-grade 20% weapon-usable, 85% weapon-grade Low Enriched Uranium ( LEU ): < 20% 235 U Low Enriched Uranium ( LEU ): < 20% 235 U 12% % used in research reactors 12% % used in research reactors 3% - 5% used in Light Water Reactors 3% - 5% used in Light Water Reactors Slightly enriched Uranium ( SEU ): 0.9% - 2% 235 U Slightly enriched Uranium ( SEU ): 0.9% - 2% 235 U used in Heavy Water Reactors instead of natural uranium used in Heavy Water Reactors instead of natural uranium Recovered Uranium ( R U ): Recovered Uranium ( R U ): recovered from spent fuel of Light Water Reactors recovered from spent fuel of Light Water Reactors

Enrichment Methods Thermal Diffusion Thermal Diffusion Gaseous Diffusion Gaseous Diffusion The Gas Centrifuge The Gas Centrifuge Aerodynamic Process Aerodynamic Process Electromagnetic Isotope Separation( EMIS ) Electromagnetic Isotope Separation( EMIS ) Laser Processes Laser Processes Chemical Methods Chemical Methods Plasma Separation Plasma Separation

Basic Facts of Separation Physics

Laser Processes Atomic Vapor Laser Isotope Separation (AVLIS) Atomic Vapor Laser Isotope Separation (AVLIS) Molecular Laser Isotope Separation (MLIS) Molecular Laser Isotope Separation (MLIS)

Diffusion Cell

separation factor of a single diffusion process step is determined as follows:

Gaseous Diffusion Cascade

Separation factor & Separative power of centrifuge M 1, M 2 ; 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

P1-centrifuge

Gas Centrifuge Cascade

Design of enrichment plants 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 fabrication Enriched UF 6 is converted into uranium UO 2 powder which is then processed into pellet form: Enriched UF 6 is converted into uranium UO 2 powder which is then processed into pellet form: UF 6 +H 2 (g) UF 4 (S)+2HF(g) UF 6 +H 2 (g) UF 4 (S)+2HF(g) UF 4 (S)+H 2 O UO 2 (S)+2HF(g) UF 4 (S)+H 2 O UO 2 (S)+2HF(g)

Fuel fabrication The pellets are then fired in a high temperature sintering furnace (with H 2 ) to create hard, ceramic pellets of enriched uranium. The pellets are then fired in a high temperature sintering furnace (with H 2 ) to create hard, ceramic pellets of enriched uranium. Fuel rods : corrosion resistant metal alloy ( zirconium ). Fuel rods : corrosion resistant metal alloy ( zirconium ).

Fuel bundle & fuel pellet

Fuel assembly

Chain reaction

Nuclear reactor

Spent fuel Used fuel: Used fuel: About 95% U-238 About 95% U-238 About 1% U-235 that has not fissioned About 1% U-235 that has not fissioned About 1% plutonium About 1% plutonium 3% fission products, which are highly radioactive 3% fission products, which are highly radioactive With other transuranic elements formed in the reactor. With other transuranic elements formed in the reactor.

Spent fuel storage

Reprocessing The PUREX process is a liquid-liquid extraction method used to reprocess spent nuclear fuel, in order to extract uranium and plutonium, independent of each other, from the fission products. The PUREX process is a liquid-liquid extraction method used to reprocess spent nuclear fuel, in order to extract uranium and plutonium, independent of each other, from the fission products. PUREX is an acronym standing for Plutonium and Uranium Recovery by Extraction. PUREX is an acronym standing for Plutonium and Uranium Recovery by Extraction.

Reprocessing 1. Dissolving of fuel into nitric acid 2. Remove the fine insoluble solids 3. Organic solvent : 30% tributyl phosphate (TBP) in odorless kerosene (or hydrogenated propylene trimer) 4. The extraction of U(VI) and Pu(IV) 5. Reduction of Pu(IV) to Pu(III) 6. Back extraction (stripping) of U(VI) by a low nitric acid concentration

References:

Uranium hexafluoride ( UF 6 ) 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 UF 6. 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 UF 6. ether, ester, ketone and saturated and unsaturated hydrocarbons react at room temperature by fluorinating with UF 6.

Refining and converting U 3 O 8 to UF 6

Basic Facts of Separation Physics The ability of the separation element to separate 235 Uand 238 U is described by its separation factor. If N= concentration of If N= concentration of 235 U; N F is its concentration in feed stream(F) N P is its concentration in product stream(P) N T is its concentration in Tails stream(T)

Basic Facts of Separation Physics 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, N P, N F and N T must be given. Mass balance : 0=P+T-F Isotope balance: 0=PN P +TN T -FN F

Separative Work and Power δU=PV(N P )+TV(N T )-FV(N F ) The value function V(N) is determined using mathematical methods so that the calculated separative work is independent of the 235 U concentrations in the separation element and depends only on the archieved change in concentration and throughput. Kg SW/S or SWU/S