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Nuclear Fuel Cycle: Mining, Enrichment, and Fuel Fabrication
Randall Fielding, INL Phone: (208)
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Presentation Summary Nuclear Electricity 7th Ed., Ian Hore-Lacy, Uranium Information Centre and World Nuclear Association
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Mining: Surveying Surveying Geological and satellite surveys
Very high level Aircraft surveys After areas of interest are seen with satellite a more detailed survey is done using planes and helicopters Surface surveys Prospector and his donkey
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Mining: Minerals of interest
Several uranium bearing minerals of interest for mining Grades usually vary from 0.5% % Mineral name Chemical Composition Uraninite UO2 Davidite (Fe, Ce, La, Y, U, Ca, Zr, Th) (Ti, Fe, Cr, V)3 (O,OH) Brannerite (U,Ca,Fe,Th,Y)3 Ti5O16 Carnotite K2 (UO2)2 (VO4) 2·3H2O Tyuyaminite Ca (UO2)2 (VO4) · 5-8 H2O Autunite Ca (UO2)2 (PO4)2 · H2O Torbernite Cu (UO2)2 (PO4)2 · 8-12 H2O Uranophane Ca (UO2)2 SiO3(OH)2 · 5H2O
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Mining: Types of mining
Open pit mine Most common Underground Must have adequate ventilation because of radon, sometimes necessitating remote equipment In-situ leaching (solution mining) Leaching solution pump down one hole and dissolved U3O8 pump up adjacent holes Somewhat experimental, ground water contamination concerns
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Mining: Milling During milling the U3O8 from the mine is concentrated
Incoming ore is crushed Roasted to dive off organics U3O8 is leached or recovered through Sx/ion exchange U3O8 is precipitated out, washed, dried, and packaged Finished product is termed “yellow cake”
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Enrichment: Conversion from U3O8 to UF6
Dry Hydrofluor Process UO2 UF4 UF6 U3O8 HF F2 Pure UF6 Reduction Hydofluorination Fluorination Distillation H2+N2 Wet Solvent Extraction Process UO3 U3O8 Solvent Heat Pure UF6 Digestion Sx Calcination Reduction HNO3 H2+N2 Hydro-fluorination Fluorination UO2 HF UF4 F2
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Enrichment: 235U Enrichment
Gaseous Diffusion 235U molecules are faster, hence diffuse through a hole in a barrier more quickly Centrifugal method Centrifugal forces compress the gas at the centrifuge wall, but thermal agitation separates lighter elements to the center of the chamber Atomic Vapor Laser Isotope Separation A laser selectively excites 235U atoms. UV light kicks some excited electrons free and ionizes the atoms. Ions are collected on a negatively charge Faraday cup.
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Fuel Fabrication: UO2 Production
Fuel manufacturers receive the UF6 which is solid at room temperature and convert it to UO2 Bubble UF6 gas through water to form UO2F2 UO2F2 is added to ammonia water to precipitate (NH4)2U2O2 (NH4)2U2O2 is calcined to form U3O8 U3O8 is reduced with H2 to form UO2
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Fuel Fabrication: Pellet Production
UO2 is crushed and ground to a fine powder and mixed with an organic binder (e.g.. polyvinyl alcohol) Powder is pressed into pellets and sintered Sintering Hydrogen 1650° C for 24 hours Final density: 94% theoretical density
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Fuel Fabrication: Pellet Production
Pellet final diameter: ~10 mm diameter Pellets are ground to final diameters Ends are be cupped and corners chamfered Grinding will reduce mechanical interaction during irradiation Each pellet is inspected
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Fuel Fabrication: Pellet Production
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Fuel Fabrication: Fuel Rod Production
Pellets are segregated into stacks and weighed Loaded into zirconium alloy tubes Pressurized to p.s.i. with helium and seal welded
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Fuel Fabrication: Assembly Fabrication
Fuel rods are then bundled into fuel assemblies
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Fuel Fabrication: Metal Fuel
Jacket hardware Bottom endplug welding Spacer wire wrap Inspections Sodium Loading Trimmings to casting furnace Trimmings to chemistry Fuels feedstock Alloy production Injection casting Break molds Trim slugs Inspection Load jackets with fuel Settle slugs Weld top endplug Bonding Furnace Weld inspection Final inspection Bonding Assembly hardware Fabricate fuel assemblies Final inspection Pull test Flow test
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Fuel Fabrication: Metal Fuel
Sodium bonded fuel Provides good heat conduction Metal fuel is compatible with Na LMFBR use sodium as the coolant
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Fuel Fabrication: Metal Fuel
Metal fuel is injection cast Alloys are melted under vacuum Evacuated molds are lowered into melt and furnace is pressurized Metal is forced up into the molds where it cools and solidifies Fuel slugs are then removed from the molds Remaining fabrication steps similar to UO2 fuel
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References: The Nuclear Fuel Cycle: Analysis and Management by R.G. Cochran and N. Tsoulfanidis Figures were found on (unless otherwise noted)
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