Video Transcript
In this video, we will learn how to
describe the ways that radioactive material can contaminate the environment.
Let’s begin by considering what it
means for something to be radioactive. Say that we have here a
substance. Any substance is made up of atoms,
and atoms fall into one of two categories. Some atoms are called stable. This means that they don’t tend to
change into another type of atom. We might think that all atoms are
like this, but actually some atoms are unstable. If we wait long enough, these
unstable atoms will decay, it’s called, into atoms of another type.
When a decay takes place, the
decaying atom gives off what’s called nuclear radiation. So a radioactive substance, whether
it be a solid, a liquid, or a gas, is any substance that has unstable atoms in
it. To be radioactive, a substance
doesn’t need to be made up of all unstable atoms or even a majority of unstable
atoms. Even if there’s just one unstable
atom in the entire substance, that substance is radioactive. Now, say that we had some big tank
of a liquid and that in this liquid there were no unstable atoms. That means if we were to put this
substance into the liquid and this substance, say it was a solid, dissolved and
mixed with the liquid, then by that mixing process, we would have contaminated this
liquid.
And then what’s more, because part
of what we added to the liquid is an unstable atom, this would be radioactive
contamination. In general, not all contamination
is radioactive, but in this instance it is. We’ve taken an unstable atom and
mixed it in to this liquid. Something important to realize is
that, as we said, unstable atoms eventually undergo decay. That means this atom will emit or
give off nuclear radiation. That radiation can be
dangerous. But keep in mind only a person who
is nearby this contaminated liquid will be likely to experience this radiation. A person far away would not be at
such risk.
But now imagine that a hole
develops in the container for this liquid. The liquid would flow out, spread
outside the container, and potentially move radioactive material closer to people
who are not near the container. Let’s consider for a moment the
containment of radioactive material. Say we have here three identical
containers. One contains a solid radioactive
material, one a liquid radioactive material, and one a radioactive gas. These containers could be buried
underground. Imagine that over time the walls of
the containers start to corrode, to break down. Eventually, each of the containers
develops a hole, a place where it can no longer contain its contents.
What happens next depends on the
state of matter of each material inside the containers. Even though the container of the
solid object has a hole in it, it may be that no radioactive material escapes. On the other hand, if the solid was
very brittle and flaked easily, then some radioactive bits of this substance might
possibly leak out. Moving on to our liquid, if a hole
develops in the bottom of the liquid’s container like this, we know this liquid will
come leaching out into the surrounding soil or rock. This radioactive liquid could mix
with groundwater contaminating it and then, through this mixture, be spread very far
away from the container.
Lastly, if the container of our gas
develops a hole, particles of this radioactive gas will easily escape and may find
their way through the soil and rock to the air. At this point, currents of air in
the atmosphere can spread these particles over long distances. The name typically given to
radioactive material stored this way is radioactive waste. This material is created through
processes like nuclear power generation. In a working nuclear power plant,
if we were to look inside the reactor, which by the way would not be a good idea
because of the radiation levels, we would see rods of solid radioactive material
being used to generate power. After a while, these rods become
what is called depleted.
At that point, they need to be
switched out with fresh radioactive material. The depleted rods, when they’re
removed from the reactor, are considered nuclear waste. That is, they’re still capable of
giving off nuclear radiation. As a result, they need to be
carefully contained, usually within concrete and steel containers. But there are other materials that
may need to be contained too, other nuclear waste. While these radioactive rods are
being removed from the reactor, anything they come in contact with, any containers
or equipment or movers, has a chance of receiving some of their radioactive
material.
For example, perhaps there’s a box
that’s used to transport the depleted rods. Maybe one of the rods rubs a bit on
the inside of the box and leaves some radioactive material behind. If that happens, the box itself is
contaminated. It too needs to be stored safely in
a container. Now, just to be clear, if nuclear
fuel gives off radiation, then a material that absorbs that radiation doesn’t itself
become contaminated. For something to be contaminated,
it has to actually mix with radioactive material. So, nuclear power generation
typically creates two types of nuclear waste. There’s the original radioactive
material that becomes depleted. And then there’s anything that that
material contaminates at any point in the process.
Generating nuclear power is a very
automated process. Still, people have to be involved
to some extent. A worker at a nuclear facility may
well wear protective clothing. This clothing shields the person
from certain types of nuclear radiation. In addition, a worker may use a
special breathing mask. This mask can help prevent
radioactive particles from being breathed in. The mask and the suit both help
this person avoid radioactive contamination. That is, they help keep radioactive
material from mixing with the person’s skin or getting inside the person’s body.
Nuclear waste is likely to be
contained in a storage facility that’s deep underground. What’s more, these facilities are
often far away from where any people live. Keeping nuclear waste far
underground in remote locations are two ways to make it less likely that the waste
will become dangerous to humans. Knowing all this about radioactive
contamination, let’s look at a few examples.
Which of the following most
correctly defines a radioactive object? (A) A radioactive object must have
emitted nuclear radiation. (B) A radioactive object must have
absorbed nuclear radiation. (C) A radioactive object must
contain atoms that can emit nuclear radiation.
Say that we have some object and we
want to determine if this object is radioactive. An object is radioactive if it’s
capable of emitting nuclear radiation. Nuclear radiation comes from atoms
as they change from one type of atom to another. So for an object to be able to give
off radiation, it has to have at least one of these unstable atoms. If it does, we know that at some
point, this object will give off nuclear radiation. Considering our three answer
options, option (A) says a radioactive object must have emitted nuclear
radiation. If an object gave off this
radiation in the past, then it was radioactive. But that doesn’t mean it still is
now.
On the other hand, an object that
has absorbed nuclear radiation isn’t necessarily able to emit radiation itself. As we’ve seen, it’s this emission
of radiation that defines a radioactive object. Our answer choice then is option
(C). A radioactive object must contain
atoms that can emit nuclear radiation.
Let’s look now at another
example.
Which of the following most
correctly describes what is meant by contamination? (A) The mixing of a substance with
other substances. (B) Chemical changes in a
substance. (C) Changes to the nuclei of atoms
in a substance.
To understand contamination, we
need to know that more than one substance must be involved. If we have some substance — say, a
cloud of gas — nothing that happens in this cloud by itself can contaminate the
gas. Contamination requires that some
other substance — say, another gas cloud — moves in and mixes with this one. That is, it’s only by mixing
substances that contamination can happen. We choose answer option (A). Note, by the way, that this
contamination may be radioactive contamination or not. Here, we’re speaking generally
about contamination and what it means. It’s the mixing of a substance with
one or more other substances.
Let’s look now at another
example.
An amount of water has a
radioactive gas dissolved in it. Which of the following would
produce a greater contamination risk? (A) Freezing the water. (B) Boiling the water.
Okay, so here we have a container
with this water in it. And we’re told that this water has
a radioactive gas dissolved in it. Now, if the gas was really
dissolved, the little pockets of gas would be so small we couldn’t see them. Here, we’ll represent this gas
dissolved in the water using these dots. We want to know whether freezing
this water or boiling it would produce a greater contamination risk. Let’s remember that contamination
involves the mixing of substances together.
So, for example, if our water, with
gas dissolved in it, were to mix with the air in the atmosphere, that would be
contamination. Or if it mixed with — say, the soil
in the ground — that would be contamination too. So, the way to decrease
contamination risk is to make it hard for this water to mix with any other
substance. We know if the water is frozen, it
will become a solid object. That way, it will be relatively
difficult for the block of ice to mix with any other substance.
But then, let’s think about boiling
the water with the radioactive gas. In that case, everything in the
water, including the radioactive gas, would be released into the atmosphere. Thanks to currents of air, this
material could be spread long distances. So, while freezing the water
contains contamination risk, boiling it makes it more likely that those water and
radioactive gas will mix with other substances. We choose answer option (B).
Let’s look now at one last
example.
Which of the following is the
safest way that nuclear waste can be stored? (A) In gas cylinders. (B) In barrels of liquid. (C) In solid blocks.
Considering these three answer
options, choice (A) tells us to think of a cylinder filled with a gas that contains
the nuclear waste, here shown in pink. In option (B), we imagine the
nuclear waste, these pink bars, submerged in a liquid that’s inside of a barrel. Finally, we imagine nuclear waste
stored in a solid block of material. In the cases of the gas cylinder
and the barrel of liquid, the chance that the nuclear waste will contaminate the gas
and the liquid is fairly high. That is, there’s a good chance that
some of the nuclear waste will mix in with the gas and the liquid.
On the other hand, nuclear waste
stored in a solid block of material may still contaminate that material, say, by
rubbing it. But it’s less likely that this will
happen. If somehow it were to happen that
each of these containers developed a leak, the gas inside the cylinder would easily
escape. The liquid inside the barrel would
tend quickly to flow out. But in the solid block, nothing
would tend to leave and contaminate the environment. So considering the safest way that
nuclear waste can be stored, we choose option (C). The safest way that nuclear waste
can be stored is in solid blocks.
Let’s finish this lesson now by
reviewing a few key points. In this video, we learned that a
substance is radioactive if it contains at least one unstable atom. We learned further that a substance
is contaminated if it mixes with other substances. Radioactive particles, whether in
solid, liquid, or gas form, can be spread through the environment. Radioactive waste, such as waste
produced at nuclear power plants, must be stored carefully to prevent
contamination. Lastly, we learned that proper
clothing, including masks, say for workers at a nuclear power facility, can help
prevent personal contamination. This is a summary of radioactive
contamination.
