Lesson Video: Radioactive Contamination Science

In this video, we will learn how to describe the ways that radioactive material can contaminate the environment.

12:55

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.

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