Environmental Engineering Reference
In-Depth Information
Mining of uranium
Uranium ore
Milling
Mill tailings
Yellow cake
Low-level
wastes
Chemical conversion
UF
6
Isotope separation
Depleted U
Enriched U
Low-level
wastes
Fuel fabrication
Fresh fuel
Low-level
wastes
Reactor operation
Spent fuel
Storage in water pool
Reprocessing
Fuel plus waste
High-level waste
Disposal in repository
Figure 6.6
Nuclear fuel cycle.
radioactive isotopes of radium, bismuth, and lead. These solids are pumped as a slurry to the tailings
heap, also called tailings dam. The tailings must be covered with clay or other impenetrable material
to protect humans and animals from radiation exposure.
6.5.2
Gasification and Enrichment
The U
3
O
8
concentrate is shipped from the mines to the enrichment facilities. The concentrate has the
normal isotope distribution, about 99.3%
238
U and 0.7%
235
U. With the exception of CANDU-type
heavy-water-moderated reactors, all other reactors need uranium enriched with
235
U.
For enrichment, a gaseous uranium compound is necessary. The concentrate is treated with
hydrogen fluoride gas and the uranium oxide is converted to uranium hexafluoride UF
6
. This is a
white solid that sublimates to a vapor at a pressure of 1 atmosphere at 56
◦
C. The gaseous UF
6
is
enriched by one of the following processes.
