Nuclear - Energy Policy Analysis: A Conceptual Framework - page 47

Figure 3.2 Pressurized Water Reactor

Switchyard

CONTAINMENT
STRUCTURE

Steam Line

Cooling
Towers

Control Rods

Generator

Steam
Generator

Pump

Turbine

Reactor

Reservoir

Condensor

Pump

Cooling Water

Water

Source: USEIA 2012.
Note: In a typical commercial pressurized light-water reactor the reactor core generates heat, pressurized-
water in the primary coolant loop carries the heat to the steam generator, inside the steam generator heat from
the primary coolant loop vaporizes the water in a secondary loop producing steam, the steam line directs the
steam to the main turbine causing it to turn the turbine generator, which produces electricity. The unused
steam is exhausted to the condenser where it is condensed into water. The resulting water is pumped out of
the condenser with a series of pumps, reheated, and pumped back to the steam generator. The reactors core
contains fuel assemblies which are cooled by water, which is force-circulated by electrically powered pumps.
Emergency cooling water is supplied by other pumps, which can be powered by on-site diesel generators.
Other safety systems, such as the containment cooling system, also need power.

ordinary water (H 2 O) to transfer the heat energy from reactor to turbine in the electricity genera-
tion process. In other reactor designs, the heat energy is transferred by heavy water (deuterium),
helium gas, or a liquid metal such as lead or sodium (USEIA 2011e).
In a PWR, superheated water in a primary cooling loop flows through a special heat exchanger
called a steam generator that is used to boil water and create steam in a secondary loop that turns
the turbine-generator. The two-loop design of a PWR keeps radioactivity isolated; only clean steam
is circulated through the turbine. This design helps minimize maintenance costs and radiation
exposure to plant personnel. In the BWR reactor design, water is boiled inside the reactor core
and then sent directly to the turbine-generator to produce electric power. The BWR is a simpler
design, but has the disadvantage that the turbine and more of the plant become radioactive over
time. In either a boiling-water or pressurized-water installation, steam under high pressure turns
a turbine whose shaft is connected to an electric generator (USEIA 2011e).
The fuel core for a nuclear power reactor can have up to 800 fuel assemblies. An assembly
consists of a group of sealed fuel rods, each filled with slightly enriched uranium oxide pellets,
supported by metal spacer-grids to brace the rods and maintain the proper distances between them.
During operation of the reactor, the concentration of U-235 in the fuel is decreased as those atoms
undergo nuclear fission to create heat energy. Some U-235 atoms are converted to atoms of fis-