IAEA 1

Sources of radiation

Nuclear Fuel Cycle - Conversion

Day 4 – Lecture 6 (1)

IAEA 2

Conversion

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

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

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.

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

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.

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)

IAEA 9

Conversion

IAEA 10

Conversion

Gore Oklahoma USA (closed)

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)