The Uranium Fuel Cycle

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
Mining Processes

• World reserves
• 3.1 million tU

• Open-pit mining 30
• Underground mining 38 (55 in 1990)
• In situ leaching (ISL) 21

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