TRANSPORTATION OF RADIOACTIVE MATERIALS - Environmentally Conscious Materials Handling - page 218

Ta b l e 8 . 1 Known Recoverable Resources of Uranium

Country Tonnes U Percentage of World's Uranium

Australia 1,143,000 24%

Kazakhstan 816,000 17%

Canada 444,000 9%

United States 342,000 7%

South Africa 341,000 7%

Namibia 282,000 6%

Source: World Nuclear Association 2008.

Uranium is typically mined from the ground in one of three ways:
1. Shaft mines—which are no longer used in the United States
2. Open pit mines or strip mines
3. In-situ leaching or solution mines
Shaft mines for uranium, and other materials such as coal, have proven to
be expensive and dangerous for miners. Open pit mines are more cost-effective
if the ore body is close to the surface, but they leave scars on the earth. In
solution mining, a solution designed to dissolve the uranium is pumped into the
ore body, and when the uranium has dissolved, the solution is pumped back to
the surface. This process does not disturb the surface, but some are concerned
about to potential for groundwater contamination. After it is mined, the uranium
is processed and the resulting material is U 3 O 8 , which is known as yellow cake .
Naturally occurring uranium consists primarily of two isotopes, U-235 (0.71
percent) and U-238 (99.29 percent). U-235 is the isotope that fissions and gener-
ates the power in a nuclear reactor. For power plants such as those in the United
States to operate efficiently, the uranium fuel should be about 5 percent U-235.
A process called enrichment is used to increase the U-235 content from 0.71 to
5 percent. The enriched uranium is converted to UO 2 and pressed into pellets,
which are, in turn, loaded into fuel pins. The fuel pins are assembled into bundles
and put into the reactor. Figure 8.3 shows a nuclear fuel assembly with spaces
for fuel pins.
In the reactor, the U-235 fissions (splits) when it is struck by a neutron,
resulting in two nuclei known as fission products, a few neutrons, and energy.
The neutrons that are released go on to strike other U-235 atoms, creating a
chain reaction that yields a steady supply of energy. When almost all of the
U-235 atoms have fissioned, the fuel can no longer sustain a chain reaction and
must be replaced. This used fuel is removed from the reactor and stored in a deep
pool of water at the reactor site. Eventually, it will be transported to a central
storage facility, a permanent repository, or a reprocessing/recycling facility.
Figure 8.4 shows the typical composition of used nuclear fuel. It contains
about 96 percent uranium, which is a mixture of U-238 and some U-235 atoms