Nuclear Fuel Cycle

1
Nuclear Fuel Cycle

• Chapter 10
• Dr. Steve Reese
• NE 112

2
The Big Picture

• Following the uranium
• Can be divided into two groups
• Front end (fabrication)
• Back end (post reactor)

3
Exploration

• Uranium is common in soil (1.8 g/ton)
• The trick is to find places were it is
  concentrated
• Fortunately, it is easy to find

4
Exploration

• Most of the worlds deposits have been found
• The amount is finite!

5
Mining

• Open pit or deep shaft mining are the two most
  common methods
• Because the concentration is typically very low
  (0.10) you need to move a large amount of soil
• First association between radiation and cancer

6
Milling

• Ore is converted to Yellow Cake (U3O8) by
• Crush ore into powder
• Dissolve in sulfuric acid
• Precipitated out
• 99.9 of the ore goes to waste material called
  tailings
• All of the radioactive progeny go into the
  tailings

7
Milling
8
Processing

• Need to convert yellow cake (U3O8) to uranium
  hexaflouoride (UF6)
• Primary reasonUF6 is a gas at 133.5?f
• Conversion done by
• Wet solvent extraction
• Dry hydrofluor reactions

9
Enrichment

• Natural U contains 0.71 235U
• Most reactors need 3 (except CANDU)
• Need to separate 235U from 238UNOT EASY!
• Gas diffusion
• Centrifuge
• Laser

10
Fuel Fabrication

• UF6 converted to UO2
• Ceramic pellets (MP 5000?F)
• Placed in zirconium tubes
• 0.4 in diameter
• 10 ft long

11
Fuel Fabrication

• Arranged in a 10 x 10 array
• Lots of QC/QA

12
Reactor Operations

• 235U becomes depleted over time
• Highly radioactive fission products trapped in
  the fuel and cladding
• Some Pu is created and burned as well
• Fuel good for 3 yrs
• Typically replace 1/3 of a core each year

13
Interim Storage

• Spent fuel is highly radioactive
• Stored in water for
• Cooling
• Shielding
• Moving to dry storage
• Risk of accidents
• Yucca mountain

14
Reprocessing

• Spent fuel contains about 0.8 235U and 0.7
  239Pu
• Fission products have short-lives
• In 500 yrs, the fission product activity will be
  less than the original ore!

15
Reprocessing

• Reprocessing prohibited in the US by the Carter
  Administration
• Many other countries are reprocessing despite
  what the US didimagine that?!

16
Final Disposition

• US charges a fee of 0.1 cents per kwh
• Money intended for the Yucca Mtn repository
• Current stock piles of spent fuel are filling up
• Yucca Mtn scheduled to open (by law) by 2000
• In realitymaybe 2010

17
Final Disposition

• Currently in the courts
• Some unique debates regarding modeling
• US will put in spent fueleveryone else only puts
  in the fission products

18
Another OptionFast Breeder Reactors

• Use 238U as fuel
• Remember 99.9 of U ore is 238U
• We have enough of this stuff just at Oak Ridge
  for 300 yrs of power!
• Optimizes 239Pu production
• Produces more fuel than it consumes!