iaea sources of radiation nuclear fuel cycle - conversion day 4 – lecture 6 (1) 1
TRANSCRIPT
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IAEA 1
Sources of radiation
Nuclear Fuel Cycle - Conversion
Day 4 – Lecture 6 (1)
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IAEA 2
Conversion
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IAEA 3
Mills Concentrate ores from ~1% to ~60% Yellowcake (U3O8 - really a mix of UO2 and UO3) Ammonium Diuranate (ADU – (NH4)2U2O7)
Conversion Output is UF6
Fluorine is used for two reasons: Only one isotope Physical properties are commercially viable
Conversion
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IAEA 4
Uranium Hexafluoride
• Key compound in Nuclear Fuel Cycle• Solid for storage• Liquid for feeding/withdrawing• Gas for processing
• Solid is white, dense, crystalline• Reacts with water vapor to produce
toxic and corrosive hydrofluoric acid
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IAEA 5
UF6 + 2H2O →UO2F2 + 4HF
When UF6 reacts with moisture in air, it creates deadly hydrogen fluoride (HF)
Conversion
Uranyl Fluoride Hydrofluoric AcidChemical Hazard
U3O8 → UO2 → UF4 → UF6
Ore – conversion - enrichment
In the USA in 1986 an accident at a conversion facility resulted in the release of UF6. A worker standing nearby was killed, not from any radiological hazard but from inhalation of HF produced by the reaction shown here.
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IAEA 6
Comparison of Dryand Wet Conversion
DRY Process
• Pretreatment• Prepared Feed and Calcination• Reduction (NH3)• Hydrofluorination• Fluorination• Distillation• Product Loading and Shipping
WET Process
• Digestion• Solvent Extraction• Evaporation/Concentrate• Denitration/Calcination
• Reduction (H2 in steam)• Hydrofluorination• Fluorination
• Product Loading and Shipping
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IAEA 7
UF6 Properties
• UF6 + 2H2O UO2F2 + 4HF (hydorfluoric acid)
• Any UF6 leak into air will react with moisture and
appear as a white cloud
• When cooled to ambient temperatures, UF6 is a
solid at atmospheric pressures.
• UF6 cylinders are under a slight vacuum when
allowed to reach ambient temperatures.• Any cylinder leak would tend to “self-seal” through
the formation of UO2F2 at the leak.
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IAEA 8
Product Loading and Shipping
• UF6 product is 99.99% pure
• Packaged in 10 and 14 ton cylinders• Allowed to cool for 5 days to solidify• Overfill is the highest safety concern
• Product (source material) is shipped to the Gaseous Diffusion Plants for enrichment (special nuclear material)
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IAEA 9
Conversion
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IAEA 10
Conversion
Gore Oklahoma USA (closed)
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IAEA 11
Reference
International Atomic Energy Agency, Postgraduate Educational Course in Radiation Protection and the Safety of Radiation Sources (PGEC), Training Course Series 18, IAEA, Vienna (2002)