Sources of radiation Nuclear Fuel Cycle Conversion IAEA

Sources of radiation Nuclear Fuel Cycle - Conversion IAEA Day 4 – Lecture 6 (1) 1

Conversion IAEA 2

Conversion Ø Mills Ø Concentrate ores from ~1% to ~60% Ø Yellowcake (U 3 O 8 - really a mix of UO 2 and UO 3) Ø Ammonium Diuranate (ADU – (NH 4)2 U 2 O 7) Ø Conversion Output is UF 6 Ø Fluorine is used for two reasons: Ø Only one isotope Ø Physical properties are commercially viable IAEA 3

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 4

Conversion U 3 O 8 → UO 2 → UF 4 → UF 6 Ore – conversion - enrichment When UF 6 reacts with moisture in air, it creates deadly hydrogen fluoride (HF) UF 6 + 2 H 2 O →UO 2 F 2 + 4 HF Uranyl Fluoride Hydrofluoric Acid Chemical Hazard In the USA in 1986 an accident at a conversion facility resulted in the release of UF 6. A worker standing nearby was killed, not from any radiological hazard but from inhalation of HF produced by the reaction shown here. IAEA 5

Comparison of Dry and Wet Conversion DRY Process • • WET Process • • Pretreatment Prepared Feed and Calcination • • Reduction (NH ) Digestion Solvent Extraction Evaporation/Concentrate Denitration/Calcination Hydrofluorination Fluorination Distillation Product Loading and Shipping • • • Reduction (H 2 in steam) Hydrofluorination Fluorination • Product Loading and Shipping 3 IAEA 6

UF 6 Properties • UF 6 + 2 H 2 O UO 2 F 2 + 4 HF (hydorfluoric acid) • Any UF 6 leak into air will react with moisture and appear as a white cloud • When cooled to ambient temperatures, UF 6 is a solid at atmospheric pressures. • UF 6 cylinders are under a slight vacuum when allowed to reach ambient temperatures. • Any cylinder leak would tend to “self-seal” through the formation of UO 2 F 2 at the leak. IAEA 7

Product Loading and Shipping • UF 6 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 8

Conversion IAEA 9

Conversion Gore Oklahoma USA (closed) IAEA 10

Reference Ø International Atomic Energy Agency, Postgraduate Educational Course in Radiation Protection and the Safety of Radiation Sources (PGEC), Training Course Series 18, IAEA, Vienna (2002) IAEA 11