This chapter has covered the front end of the nuclear fuel cycle, from uranium ore in the ground to enriched uranium hexafluoride ready for fuel fabrication.
Key points to remember:
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Uranium mining is performed by three main methods: open pit (~24%), underground (~41%), and in situ leaching (~26%), with ~9% from by-products.
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Kazakhstan is the world’s largest uranium producer (~43%), followed by Canada (~15%), Namibia (~11%), and Australia (~9%).
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Milling converts uranium ore into yellowcake (UOC) through a process of comminution, leaching, extraction, and precipitation. Tailings contain ~85% of the original ore’s radioactivity.
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Conversion transforms yellowcake into UF₆ (hex) via UF₄ as an intermediate. UF₆ is chosen because fluorine is mono-isotopic and hex is gaseous above 56 degrees C.
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Gaseous diffusion enrichment exploits the slightly higher velocity of UF₆ molecules, with a maximum separation factor of sqrt(352/349) = 1.0043. It is now obsolete for new construction.
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Gas centrifuge enrichment exploits centrifugal force to concentrate heavier UF₆ molecules at the rotor wall, with separation factors of ~1.06-1.5 per stage. It is now the dominant commercial method.
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SWU (Separative Work Units) measure the effort of enrichment. The SWU formula uses the value function V(x) = (2x-1) ln(x/(1-x)).
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Safety considerations at the front end include: radiation protection (especially radon in underground mining), chemical hazards of UF₆, criticality control at enrichment, environmental management of tailings, and nuclear proliferation/safeguards.