432 CHAPTER 17 Nonrenewable Energy Resources
Jack Fletcher/NG Image Collection Patrick Landmann/Photo Researchers
b. The uranium pellets are loaded into long fuel rods, which are
grouped into square fuel assemblies.a. Uranium dioxide pellets contain about 3 percent uranium-235,
the fission fuel in a nuclear reactor. Each pellet contains the
energy equivalent of 1 ton of coal.
A typical nuclear power plant has four main parts: a
reactor core, a steam generator, a turbine, and a condenser
(}ÕÀiʣǰ£x). Nuclear fission occurs in the reactor core,
and the heat produced by fission is used to produce steam
from liquid water in the steam generator. Steam drives a
turbine that generates electricity, and the condenser cools
the steam, converting it back to liquid water.Nuclear Energy and Fossil Fuels
Worldwide, nuclear power production is steadily in-
creasing. In part, this is due to concerns about climate
change, but it is primarily driven by an increasing de-
mand for energy. According to the Nuclear Energy
Institute, in 2012, 30 countries around the world were
operating 435 nuclear power plants, producing 373
gigawatts. Another 66 plants were under construction in
14 countries, including China and India.
Supporters of nuclear energy argue that we should
generate more because nuclear energy affects the environ-
ment less than fossil fuels such as coal (/>Liʣǰ£). The
combustion of coal to generate electricity is responsible
for more than one-third of the air pollution in the United
States and contributes to acid precipitation and climate
warming. In comparison, nuclear energy emits few pollut-
ants into the atmosphere. Nuclear energy can also provide
power without producing climate- altering CO 2.energy equivalent of 1 ton of coal
(}ÕÀiʣǰ£{>). The pellets are
then placed in closed pipes, often
as long as 3.7 m (12 ft), called fuel
rods. The fuel rods are grouped
into square fuel assemblies, gen-
erally made up of 200 rods each
(}ÕÀiʣǰ£{L). A typical nuclear reactor contains 150
to 250 fuel assemblies.
U-235 atoms can spontaneously undergo fission
(or decay), releasing neutrons at high velocities. When
enough U-235 atoms are placed near each other, a chain
reaction can occur as each decay releases neutrons that
cause at least one additional atom to undergo fission.
Nuclear power generation requires careful control of the
rate of this chain reaction.
The fission of U-235 releases an enormous amount
of heat, which is used to transform water into steam. The
steam, in turn, is used to generate electricity. Operators
of a nuclear power plant can start or stop and increase or
decrease the fission reactions in the reactor to produce
the desired amount of heat. Nuclear bombs make use of
uncontrolled fission reactions. If the control mechanism
in a nuclear power plant were to fail, a bomblike nuclear
explosion could not take place because nuclear fuel has
such a low percentage of U-235 compared to bomb-grade
material.
nuclear reactor
A device that initiates
and maintains a
controlled nuclear
fission chain reaction
to produce energy for
electricity.1À>ÕÊvÕiÊUÊ}ÕÀiʣǰ£{Ê