Hi. It’s Mr. Andersen and this AP environmental sciences video 25. It is on nuclear energy.
You are probably familiar with the Richter Scale. It is a log scale by which we measure
the size of earthquakes. But you are not familiar with the INE Scale or the International Nuclear
Event Scale. It is also a log scale and we use it to measure the size of nuclear accidents.
We have only hit 7 twice. First time was in 1986 in Chernobyl. We had a collapse and a
meltdown of the reactor. Thirty-one people died from exposure to radiation. In 2011,
in Fukushima, we also hit a level 7. We had there of the reactors meltdown after an earthquake
and a tsunami. In the US the highest we have ever gone is a level 5, at Three Mile Island.
It released a little bit of radioactive material into the surrounding area. But it scared people.
These accidents scare people and radiation scares people because we cannot see it. And
so the amount of energy we are getting from nuclear reactors has remained static for decades.
But it is starting to be revisited again. And the reason why is there is also something
in the environment that is scary and it is also invisible. And that is carbon dioxide.
If we look at the amount of carbon dioxide being produced by nuclear power plants it
is on the level of the same as wind generation or hydro power. If we compare that to gas
and oil and coal there is way more carbon dioxide being created. So new technology and
a decrease in carbon emissions could see a resurgence of nuclear energy. Where is the
energy coming from? It comes from the fission of radioactive material, generally Uranium
235. So as it decays it breaks down into two fragments, barium and krypton. And as it does
that it gives off energy and it gives off neutrons that can trigger more fission in
more radioactive 235. So the way this is controlled, unlike in a weapon, it is controlled in a
reactor. Most of the reactors in play right now are light water reactors or normal water
reactors. What you do is you put fuel rods inside it and as they decay produces a little
bit of energy and that energy inside the water heats it up and we can use it to generate
steam and then generate electricity. Now when it melts down this goes out of control and
we get a release of that radiation into the environment. And so by having it in water
we can contain some of that energy. And we can also use control rods. These are actually
going to take in some of those neutrons and by lowering them between the fuel rods we
can slow down the reactor. Now the disadvantages are pretty apparent. Nuclear waste is going
to be created. It can be around of thousands and thousands of years, so we have to keep
track of that. Each of the radioactive materials have a different half life but it is going
to be on the order of thousands of years. And also we have these accidents where we
can have explosions, malfunctions and it releases that radiation into the environment. It can
cause things like thyroid cancer. Why do we still have it? Well the advantage is that
it creates a huge amount of energy and it can do that without increasing the amount
of carbon emissions in the environment. So if we look at uranium 235, now we are looking
just at the nucleus, and so we are looking at the protons and the neutrons. And so if
we were to hit one of those uranium atoms with a neutron, what it will do is it will
break in half. It breaks apart into these 2 fragments. And as it does that it releases
a certain amount of energy. You can see it is also liberating 3 of these neutrons. And
each of those have the potential to hit another uranium 235 and we can break it down. So it
is not an out of control chain reaction like this that we might see in a nuclear bomb,
but it goes slow over time. And so if we look at what those fuel rods are like, most of
the uranium is actually going to be uranium 238. A few of it is uranium 235. And so as
those neutrons are given off, by having it in water we can absorb some of that energy
and we can control that radiation. And also we can lower these control rods. They absorb
the neutrons and so we can slow it down. So if we look at a typical light-water reactor,
we are going to have the fuel rods and the control rods in the core. We are then going
to heat up a fluid. And that fluid is going to be in a closed system. So as it moves through
these pipes it returns back where it was. But it is bringing with it a huge amount of
heat. Now that heat moves into a separate loop. And so in this loop what we are doing
is heating up the water. It is forming steam up at the top and then that steam is moving
through a generator. So we are generating electricity. And then finally we still have
a lot of heat right here. Before we pump it back in we have to get rid of some of that
heat. And so we are going to do that by pumping the water in another loop into a cooling pond.
And so as along as we have energy contained within those fuel rods, we can generate electricity.
But what happens when we decay too much of that uranium 235? Now it becomes waste. It
is still radioactive, but it is not generating enough electricity for the plant to go. And
so now we have generated waste. So that is one form of nuclear waste. But we are also
generating a little bit of heat over here into the environment as well. And so how do
we deal with that waste? Well how do we deal with those fuel rods? We are going to put
them in a pool. And as we put them in a pool we are going to absorb some of that energy
here. But eventually we are going to have to put it in some kind of a container and
a lot of these are on these concrete slabs. And we have that nuclear waste contained inside
there. There is no real long range plan of what we are going to do with this nuclear
waste and it is going to be a problem that we will have to deal with generations down
the line. If we look at how long this could occur you have to understand what a half-life
is. A half-life is going to be the amount of time it takes for half of the material
to decay or to break apart. And so if we look at time 0, let’s say the half-life is one
year, at time 0 we would have 100 percent of the radioactive material. At time 1 we
would 50 percent of it. In other words half of it would have decayed. In another year
it would be half of that and a half of that and a half of that and a half of that. And
so in an AP environmental science class you should be able to calculate the half-life.
And let me give you a problem. Let’s say radium has a half-life of 1500 years. How
long will it take for 250 kilograms of the radium to decay down to less then 10 kilograms.
And so we are saying the mass of radium at the beginning is 250 kilograms at time 0.
And so in 1 half-life, in other words in 1500 years we would have decayed half of it down
to 125. In another 1500 years we would be down to 62.5. And you can just keep doing
this. And you can see at 7500 years we are less than 10 kilograms left. You can see a
lot of that is still going to be radioactive. Now what happens in accidents, something happens
where we are not able to contain this core. And so if we look at Chernobyl, they were
testing the reactor and it got out of control. It heated. We are having a melting or an explosion
that actually collapsed the roof. It released a lot of radiation. If we are looking at Fukushima,
it is like three levels of protection that failed. We have an earthquake but we also
have this giant tsunami. And if we are looking at Three Mile Island it was a problem with
a valve. But also a problem with user error as well. And so all of these, for the most
part, are human error. Either we had a mistake at the reactor or had a mistake in the design.
And what it does is it releases some of this radioactive material into the environment.
So for example radioactive iodine can cause thyroid cancer. So we eat it in our food.
It causes cancer years down the line. And we are going to see this wherever there is
a nuclear accident, we are going to have increases in thyroid cancer after that. So if we look
at these accidents, so this is Three Mile Island, here is Chernobyl. So we had the heyday
of nuclear reactor creation during this oil crisis. But then after these accidents you
can see the amount of reactors we have has remained static. And you can say even though
we could produce this amount of energy, we are producing less of that. And the reason
has to do with this fear of radiation and the fear of accidents as well. And so what
does the future hold for nuclear power? Well there are going to be increases in new technology.
Thorium reactors are going to be working much better than uranium light-water reactors.
And we can have these third generation reactors where we can actually reuse some of that waste.
And then finally we have to reduce carbon emissions. And nuclear energy is going to
be part of that discussion. So could you pause the video and fill-in the blanks? Let me do
that for you. Nuclear energy is the fission of something like uranium 235. We break it
apart into fragments. We also get energy in some neutrons that can cause fission in other
atoms. We have the fuel rods. That is where the radioactive material is. But we also have
these control rods. Disadvantages, nuclear waste. It takes a long time due to the half-life
of these radioactive materials for the waste to go away. We can have accidents that increase
the amount of cancer, thyroid cancer is an example of that. But the advantages again,
nuclear power can help us reduce the amount of carbon dioxide in the environment. Reduce
global warming. And that is why it is being revisited. And I hope that was helpful.