Power Plants

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.

thick.The core houses some 82 metric tons of uranium oxide contained in the

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

containment building to retain any radioactive elements that might escape in the

even of a leak.