Environmental Engineering Reference
Radioactive substances found in
nature give off energy in the form of
radioactivity. In some cases, they may be
a danger to health, but on the whole, this is
not a matter of concern. Take, for instance, uranium
ore. This is rock that contains uranium, so it is radioactive, but it
does not release enough energy to run a generator. Also, if you
pile up the ore, it will not become a bomb. Something more is
needed to produce electric power or cause an explosion.
Actually, at least three things are needed for what is called
“useful” i ssion—i ssion that can be used to make electricity
or create an explosion. One thing is the right material. Useful
i ssion can occur only with certain materials, one of which is
uranium-235. Scientists describe such materials as i ssionable.
The right amount of i ssionable material is also needed. There
has to be enough to get the job done. These two things—the
right material and right amount of it—make possible the
third key requirement for useful i ssion. If the right amount of
material is brought together under suitable conditions, a chain
reaction can take place. The possibility of a chain reaction is
what makes i ssionable materials such useful sources of energy.
To see how a chain reaction works, let's look at uranium-235
(U-235). Suppose, as often happens, a free neutron—one that