Energy - Environmental Science - page 298

Light-water reactors (LWRs) like the one dia-
grammed in Figure 13-17 produce 85% of the world's
nuclear-generated electricity (100% in the United
States). Control rods are moved in and out of the reactor
core to absorb neutrons, thereby regulating the rate of
fission and amount of power produced. A coolant, usu-
ally water, circulates through the reactor's core to re-
move heat to keep fuel rods and other materials from
melting and to produce steam for generating electric-
ity. The greatest danger in water-cooled reactors is a
loss of coolant, which would allow the nuclear fuel to
overheat, melt down, and possibly release radioactive
materials to the environment. An LWR includes an
emergency core cooling system as a backup to help
prevent such meltdowns.
A containment vessel with strong, thick walls sur-
rounds the reactor core. It is designed to keep radio-
active materials from escaping into the environment in
case of an internal explosion or core meltdown within
the reactor, and to protect the core from external threats
such as a plane crash.
Water-filled pools or dry casks with thick steel walls
are used for on-site storage of highly radioactive spent
fuel rods, which are removed when reactors are refu-
eled. Spent-fuel pools or casks are located in a separate
building that is not nearly as well protected as the re-
actor core and are much more vulnerable to a head-on
crash from a plane or terrorist attack. The long-term
goal is to transport spent fuel rods and other long-
lived radioactive wastes to an underground facility for
long-term storage.
The overlapping and multiple safety features of a
modern nuclear reactor greatly reduce the chance of a
serious nuclear accident. At the same time, these safety
features make nuclear power plants very expensive to
build and maintain.
Nuclear power plants, each with one or more reac-
tors, are merely one part of the nuclear fuel cycle (Fig-
ure 13-18, p. 300). Unlike other energy resources, nu-
clear energy produces highly radioactive materials that
must be stored safely for 10,000-240,000 years until
their radioactivity falls to safe levels. In addition, once
a nuclear reactor comes to the end of its useful life (after
40-60 years), it cannot be shut down and abandoned
like a coal-burning plant. It contains large quantities of
intensely radioactive materials that must be kept out of
the environment for many thousands of years.
In evaluating the safety and economic feasibility of nu-
clear power, energy experts and economists caution us to look
at the entire nuclear fuel cycle, not just the nuclear plant itself.

T rade-Offs

Synthetic Fuels

Advantages

Disadvantages

Large potential
supply

Low to moderate
net energy yield

Higher cost than
coal

Vehicle fuel Requires mining

50% more coal

High
environmental
impact

Moderate cost
(with large
government
subsidies)

Increased surface
mining of coal

High water use

Lower air
pollution when
burned than coal

Higher CO 2
emissions than
coal

Figure 13-16 Trade-offs: advantages and disadvantages of
using synthetic natural gas (SNG) and liquid synfuels produced
from coal. Critical thinking: pick the single advantage and dis-
advantage that you think are the most important.

13-3 NONRENEWABLE NUCLEAR
ENERGY

Science: How Does a Nuclear Fission
Reactor Work?
In a conventional nuclear reactor, isotopes of uranium
and plutonium undergo controlled nuclear fission.
The resulting heat produces steam that in turn spins
turbines to generate electricity.
To evaluate the advantages and disadvantages of nu-
clear power, we must know how a conventional nu-
clear power plant and its accompanying nuclear fuel
cycle work. In the reactor of a nuclear power plant, the
rate of fission in a nuclear chain reaction (Figure 2-6,
p. 28) is controlled and the heat generated is used to
produce high-pressure steam, which spins turbines
that generate electricity.

What Happened to Nuclear Power?
After more than 50 years of development and
enormous government subsidies, nuclear power has
not lived up to its promise.