Environmental Engineering Reference
In-Depth Information
eration could take 30 years. The United Kingdom's power generation mix
has less CO 2 emitted per megawatt-hour by one third compared to United
States. The U.K. has moved away from extensive coal power generation in
the past few decades and is aggressively pushing renewable energy and
cogeneration.
Nuclear power is quietly reappearing in the United States and
around the world. Major U.S. utilities have applied for site permits for
new reactors, and interest is also growing through Europe.
The nuclear plants now operating in the U.S. are light water reactors,
which use water as both a moderator and coolant. These are sometimes
called Generation II reactors. In these Generation II Pressurized Water
Reactors, the water circulates through the core where it is heated by the
nuclear chain reaction. The hot water is turned into steam at a steam gen-
erator and the steam is used by a turbine generator to produce electric
power.
The Generation III reactors Evolutionary Pressurized Reactor has ex-
panded safety features such as 2 separate 51 inch thick concrete walls with
the inner one lined with metal. Each of the walls is strong enough to with-
stand the force of a large commercial airplane.
The reactor vessel is on top of a 20 foot concrete slab with a leaktight
core catcher. In the event of a meltdown the molten core would collect
there and cool down. Four safeguard buildings are also used with inde-
pendent pressurizers and steam generators. Each of these buildings is able
to provide emergency cooling for the reactor core.
A dozen utilities around the country have started the process of ap-
plying to build nuclear plants. These would be Generation III and III+ de-
signs.
In 2000, 10 countries including the U. S. evaluated more than 100
Generation IV designs and after 2 years picked six. Fourth generation
nuclear plants replace the water coolants and moderators to allow high-
er temperatures with the potential to create hydrogen as well as electric
power. Tests show that electrolysis is almost twice as efficient at the high
temperatures.
One of the Generation IV designs is a melt-down proof pebble-bed
reactor. It uses grains of uranium encased in balls of graphite for fuel.
Helium gas is heated as it circulates through a vessel of the pebbles. It is
then used to turn a turbine generator. A heat exchanger is used to transfer
heat from the helium to produce hydrogen. This type of reactor is fail-safe,
if the cooling system fails the reactor shuts down on its own. The hot he-
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