Environmental Engineering Reference
In-Depth Information
described in section 4. Regulations governing the transportation of used nuclear
fuel and high-level waste (HLW) are covered in section 5. Section 6 is devoted
to a description of the casks that have been used to transport used nuclear fuel
and HLW. For completeness, a brief description of the transportation methods
and requirements for other types of radioactive materials will be presented in
section 7. The chapter concludes with acknowledgments and references.
2
RADIOACTIVE MATERIAL, USED NUCLEAR FUEL,
AND HIGH-LEVEL WASTE
2.1
Radioactive Material and Radiation
Radioactive material is material that includes some radioactive atoms. A radioac-
tive atom is one whose nucleus is unstable and gives off energy in the form of
radiation in an effort to reach a stable configuration. Several types of radiation
can be emitted, but the most common ones in high-level radioactive waste are
alpha particles, beta particles, gamma rays, and sometimes neutrons. These types
of radiation are called ionizing radiation because they interact with matter by
knocking electrons out of their orbits and forming ions in the matter through
which they pass. Large amounts of ionizing radiation passing through a living
organism can ionize enough atoms to cause damage or even death. Thus, it
is important to protect people and other living things from highly radioactive
material when transporting it.
People are protected from radiation by placing a substance around the radioac-
tive material to absorb the radiation. The general term for this protective layer
is shielding , and many substances can be used as effective shielding. Alpha par-
ticles, which consist of two neutrons and two protons, are not very penetrating
and can be stopped by a sheet of paper. Beta particles, which are electrons, can
be stopped by less than a sixteenth of an inch of aluminum. Most gamma rays,
which are more penetrating than alphas or betas, can be stopped by 6 to 8 inches
of steel or a greater thickness of concrete. Neutrons are most effectively stopped
by materials made of molecules that contain hydrogen, such as water or plastic.
Figure 8.1 illustrates the penetrating power of the various types of radiation.
Transportation casks for highly radioactive material must be made of materials
that will protect people from all types of radiation being emitted.
2.2
Nuclear Fuel Cycle and Used Nuclear Fuel
Commercial nuclear power plants in the United States are fueled with uranium,
a naturally occurring radioactive metal found in the earth's crust. To prepare
fuel for the reactor, the uranium is mined, processed, enriched, and fabricated
into fuel elements. After the fuel has been used in the reactor, it is removed
and stored on site. Eventually, it will be buried or reprocessed and recycled.
 
 
 
 
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