Childrens Illustrated Encyclopedia

385

The aToms ThaT make up everything in the universe are the

source of a huge amount of energy called nuclear energy. Nuclear

energy produces the searing heat and light of the sun, the deadly

explosions of nuclear weapons, and vast amounts of electricity in

nuclear power stations. Nuclear energy is based on the

fact that matter and energy are different forms of the

same thing, and one can be converted into the other. In

a nuclear reaction, a tiny amount of matter changes into

an enormous amount of energy. The nuclear reaction

occurs in the nuclei (centers) of atoms. This can happen

in two ways: when the nucleus of a heavy atom splits,

in a process called fission, and when two lightweight

nuclei join together, in a process called fusion.

In nuclear weapons, fission or fusion

occurs in a split second. In contrast,

nuclear power stations produce

electricity from fission reactions

that work at a controlled rate.

Experimental nuclear fusion

reactor near Oxford, England

Hydrogen

nucleus with two

extra neutrons

Nuclear fIssIoN

Nuclear power stations produce energy

from the fission of atoms of uranium

within uranium oxide pellets. The impact

of a particle called a neutron makes an

atom of uranium split, releasing heat

energy and two or three neutrons. The

neutrons strike other uranium atoms and

make them divide. soon, many atoms

split, producing a huge amount of energy.

Nuclear power sTaTIoN

a fission reaction becomes continuous

only if there is a certain amount of fuel

present, called the critical mass. In a

nuclear reactor, rods contain uranium

fuel. The fuel rods are placed close

together to provide the critical mass

that starts the reaction.

If neutrons travel too rapidly, they bounce

off uranium atoms without producing

fission. The fuel is surrounded by water,

which slows the neutrons down so they

produce fission. A material that slows

neutrons in a reactor is called a moderator.

Reactor core

contains pellets of

uranium dioxide fuel

held in fuel rods.

Two thimble-sized

pellets would

produce enough

electricity for one

person’s domestic

supply for one year.

Pump for

high-pressure

water system

Nuclear radIaTIoN

some waste from nuclear power stations is

radioactive—it produces deadly nuclear radiation

consisting of tiny particles or invisible waves that can

damage living cells. some radioactive waste may last

for thousands of years, so it is buried underground

in sealed containers. many people are concerned

about the dangers of nuclear waste and are

demanding an end to nuclear energy production.

The high-

pressure water

flows through pipes

in a steam generator,

which transfers its heat to

a separate water system.

The water in this second

system boils to form steam.

Steam spins turbines that drive

generators, producing electricity.

Pressurized water reactor (PWR)

Nuclear energy

Control rods absorb neutrons and

slow down the nuclear reaction. In an

emergency, the control rods drop into

the reactor core and shut off

the nuclear reaction.

Protective

clothing worn

when handling

nuclear waste

A third water circuit acts as a coolant,

changing the steam back into water, which

returns to the steam generator once again.

Water is pumped around the

reactor core at high pressure

in a sealed circuit. The nuclear

reactions heat the water to

more than 570°F (300°C),

but the high pressure keeps

it from turning into steam.

Find out more

atoms and molecules

chemistry

cold war

physics

radioactivity

science, history of

soviet union, history of

Hydrogen

nucleus with

extra neutron

Neutron

Helium

nucleus

Nuclear fusIoN

scientists are trying to build reactors that use nuclear fusion, a process

that produces less dangerous waste than nuclear fission (below).

Nuclear fusion occurs when hydrogen atoms smash together and join

to form heavier atoms of helium. however, nuclear fusion is extremely

difficult to achieve. hydrogen atoms must be held by a magnetic field

and heated to a temperature higher than that in the sun’s center for

fusion to occur.

Neutron hits

nucleus of

uranium atom.

Fission occurs,

releasing energy

and neutrons.

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