electricity. A nuclear reactor produces heat through nuclear
fission in which atomic muclei break apart releasing large amounts
of energy. In the core of the reactor, a self-sustaining
nuclear reaction takes place.
The power level of an operating reactor is monitored by a variety
of thermal, flow, and nuclear instruments. Power output is controlled
by inserting or removing from the core a group of netron-absorbing control
rods. The position of these rods determines the power level at which
the chain reaction is just self-sustaining.
In the pressurized water reactor, the water collant operates at a pressure
150 atmospheres. It is pumped through the reactor core, where it is heated
to about 620oF. The superheated water is pumped through a steam generator
where, through heat exchangers, a secondary loop of water is heated and
converted to steam. The steam drives turbine generators, is condensed back to
water, and pumped back to the steam generator. The secondary loop is isolated
from the reactor core water and, therefore is not radioactive. A third stream of
water from a cooling tower is used to condense the steam. The reactor
pressure vessels are 49 feet high and 16.4 feet in diameter, with walls 10 in.
corrosion-resistant tubes. Finally generators produce electricity which is
delivered to a power grid by transmission lines.
During operation, and even after shutdown, this large 1000 megawatt power reactor
contains billions of curies of radioactivity. Radiation emitted from the reactor
during operation and from the fission products after shutdown is absorbed in thick
concrete shields around the reactor and primary collant system. Other safety
features include emergency core colling systems to prevent core overheating in the
event of malfunction of the main collant system and, a large steel and concrete
even of a leak.