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The Uranium Fuel Cycle

This overview delves into the stages of the uranium fuel cycle, from mining to disposal. It covers processes like milling, enrichment, and reprocessing, as well as the challenges and solutions in transport, storage, and disposal. With insights on world reserves and mining methods, it provides a comprehensive look at the entire cycle. Explore the complexities of service periods, storage options, and the open versus closed fuel cycle approaches. Gain an understanding of the technologies involved and the ongoing debates surrounding uranium fuel management.

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The Uranium Fuel Cycle

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  1. The Uranium Fuel Cycle Robert Tsai November 21, 2006

  2. Overview • Front end • Mining • Milling • Enrichment / fuel fabrication • Service period • Back end • Transport and storage • Disposal (open fuel cycle) • Reprocessing (closed fuel cycle)

  3. World reserves: 3.1 million tU Open-pit mining: 30% Underground mining: 38% (55% in 1990) In situ leaching (ISL): 21% Mining Processes

  4. Milling – Uranium Extraction • Grinding (~100 microns) • Acid (H2SO4) or alkaline (Na2CO3 / NaHCO3) leach • Solid / liquid separation of slurry • Purification (simple or extensive) • Precipitation – diuranate salt (e.g. Na2U2O7) • Drying Uranium oxide concentrate (UOC) (predominantly U3O8)

  5. Milling – Uranium Conversion • Dissolving of U3O8 in HNO3 • Calcination (strong heating) → UO3 • Reduction with H2 → UO2 • Hydrofluorination (HF) → UF4 • Fluorination (F2) → UF6 • In most cases, end-use requires conversion to UF6 for enrichment • However, certain reactors (CANDU) can use “natural” UO2

  6. Enrichment • Natural uranium: 235U: 0.7%, 238U: 99.3% • Reactor-grade: 235U increased to 3-5% • Necessary to sustain fission chain reaction • Methods • Gas diffusion (GD) • High-speed gas centrifugation (GC) • 5% of power requirements for GD • Laser technology (still in development) • Afterward, UF6 converted back to UO2 for mechanical processing (fuel rods)

  7. Service Period • Fission process depletes fuel • 235U → 92Kr, 141Ba • 238U → 239U → 239Pu • PWRs and BWRs reloaded bet/1-2 years, 1/4-1/3 of assemblies replaced • Complicated optimization problem • Maximize core reactivity • Top priority to safety / operational limitations

  8. Transport and Storage • At Reactor (AR) storage • Handle intense radioactivity of freshly-discharged fuel • Wet (cooling ponds) vs. dry • Transport via heavily-shielded flasks • Away From Reactor (AFR) storage • Similar set-up to AR facilities • NRC has repeatedly confirmed storages’ safety, minimal environmental impact

  9. Disposal (Open Fuel Cycle) • No permanent disposal procedures have been implemented in the world • Plans for 2010? • Consensus: burial deep underground after period of interim storage • Safeguards: vitrification, corrosion-resistant canisters, constant monitoring (106 years) • U.S. waste: Yucca Mountain in Nevada

  10. Reprocessing (Closed Fuel Cycle) • Similar process as with fresh feed • Benefits • Resource conservation • Decreased waste load • Use of ex-military material • Uranium + plutonium → MOX fuel • Major challenge: build-up of by-products

  11. Conclusions • Front end • Well developed and understood process • Gas centrifugation: best available enrichment technology • Future of lasers questionable • Back end • Underground disposal viable but will always have critics • Reprocessing necessary but has limitations

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