Nuclear Energy

In this video Paul Andersen explains how nuclear energy is released during fission of radioactive uranium. Light water reactors, nuclear waste, and nuclear accidents are also discussed along with the future of nuclear energy.

Transcript Provided by YouTube:

00:04
Hi. It’s Mr. Andersen and this AP environmental sciences video 25. It is on nuclear energy.
00:09
You are probably familiar with the Richter Scale. It is a log scale by which we measure
00:13
the size of earthquakes. But you are not familiar with the INE Scale or the International Nuclear
00:17
Event Scale. It is also a log scale and we use it to measure the size of nuclear accidents.
00:23
We have only hit 7 twice. First time was in 1986 in Chernobyl. We had a collapse and a
00:28
meltdown of the reactor. Thirty-one people died from exposure to radiation. In 2011,
00:34
in Fukushima, we also hit a level 7. We had there of the reactors meltdown after an earthquake
00:39
and a tsunami. In the US the highest we have ever gone is a level 5, at Three Mile Island.
00:44
It released a little bit of radioactive material into the surrounding area. But it scared people.
00:50
These accidents scare people and radiation scares people because we cannot see it. And
00:54
so the amount of energy we are getting from nuclear reactors has remained static for decades.
00:59
But it is starting to be revisited again. And the reason why is there is also something
01:03
in the environment that is scary and it is also invisible. And that is carbon dioxide.
01:08
If we look at the amount of carbon dioxide being produced by nuclear power plants it
01:12
is on the level of the same as wind generation or hydro power. If we compare that to gas
01:17
and oil and coal there is way more carbon dioxide being created. So new technology and
01:23
a decrease in carbon emissions could see a resurgence of nuclear energy. Where is the
01:28
energy coming from? It comes from the fission of radioactive material, generally Uranium
01:33
235. So as it decays it breaks down into two fragments, barium and krypton. And as it does
01:39
that it gives off energy and it gives off neutrons that can trigger more fission in
01:44
more radioactive 235. So the way this is controlled, unlike in a weapon, it is controlled in a
01:50
reactor. Most of the reactors in play right now are light water reactors or normal water
01:54
reactors. What you do is you put fuel rods inside it and as they decay produces a little
02:01
bit of energy and that energy inside the water heats it up and we can use it to generate
02:05
steam and then generate electricity. Now when it melts down this goes out of control and
02:11
we get a release of that radiation into the environment. And so by having it in water
02:15
we can contain some of that energy. And we can also use control rods. These are actually
02:20
going to take in some of those neutrons and by lowering them between the fuel rods we
02:24
can slow down the reactor. Now the disadvantages are pretty apparent. Nuclear waste is going
02:29
to be created. It can be around of thousands and thousands of years, so we have to keep
02:33
track of that. Each of the radioactive materials have a different half life but it is going
02:37
to be on the order of thousands of years. And also we have these accidents where we
02:41
can have explosions, malfunctions and it releases that radiation into the environment. It can
02:46
cause things like thyroid cancer. Why do we still have it? Well the advantage is that
02:51
it creates a huge amount of energy and it can do that without increasing the amount
02:55
of carbon emissions in the environment. So if we look at uranium 235, now we are looking
03:00
just at the nucleus, and so we are looking at the protons and the neutrons. And so if
03:04
we were to hit one of those uranium atoms with a neutron, what it will do is it will
03:08
break in half. It breaks apart into these 2 fragments. And as it does that it releases
03:13
a certain amount of energy. You can see it is also liberating 3 of these neutrons. And
03:17
each of those have the potential to hit another uranium 235 and we can break it down. So it
03:23
is not an out of control chain reaction like this that we might see in a nuclear bomb,
03:29
but it goes slow over time. And so if we look at what those fuel rods are like, most of
03:34
the uranium is actually going to be uranium 238. A few of it is uranium 235. And so as
03:40
those neutrons are given off, by having it in water we can absorb some of that energy
03:45
and we can control that radiation. And also we can lower these control rods. They absorb
03:51
the neutrons and so we can slow it down. So if we look at a typical light-water reactor,
03:55
we are going to have the fuel rods and the control rods in the core. We are then going
03:58
to heat up a fluid. And that fluid is going to be in a closed system. So as it moves through
04:03
these pipes it returns back where it was. But it is bringing with it a huge amount of
04:07
heat. Now that heat moves into a separate loop. And so in this loop what we are doing
04:11
is heating up the water. It is forming steam up at the top and then that steam is moving
04:16
through a generator. So we are generating electricity. And then finally we still have
04:21
a lot of heat right here. Before we pump it back in we have to get rid of some of that
04:25
heat. And so we are going to do that by pumping the water in another loop into a cooling pond.
04:31
And so as along as we have energy contained within those fuel rods, we can generate electricity.
04:37
But what happens when we decay too much of that uranium 235? Now it becomes waste. It
04:43
is still radioactive, but it is not generating enough electricity for the plant to go. And
04:48
so now we have generated waste. So that is one form of nuclear waste. But we are also
04:52
generating a little bit of heat over here into the environment as well. And so how do
04:56
we deal with that waste? Well how do we deal with those fuel rods? We are going to put
05:00
them in a pool. And as we put them in a pool we are going to absorb some of that energy
05:04
here. But eventually we are going to have to put it in some kind of a container and
05:08
a lot of these are on these concrete slabs. And we have that nuclear waste contained inside
05:13
there. There is no real long range plan of what we are going to do with this nuclear
05:16
waste and it is going to be a problem that we will have to deal with generations down
05:20
the line. If we look at how long this could occur you have to understand what a half-life
05:24
is. A half-life is going to be the amount of time it takes for half of the material
05:29
to decay or to break apart. And so if we look at time 0, let’s say the half-life is one
05:35
year, at time 0 we would have 100 percent of the radioactive material. At time 1 we
05:41
would 50 percent of it. In other words half of it would have decayed. In another year
05:46
it would be half of that and a half of that and a half of that and a half of that. And
05:50
so in an AP environmental science class you should be able to calculate the half-life.
05:55
And let me give you a problem. Let’s say radium has a half-life of 1500 years. How
06:00
long will it take for 250 kilograms of the radium to decay down to less then 10 kilograms.
06:06
And so we are saying the mass of radium at the beginning is 250 kilograms at time 0.
06:12
And so in 1 half-life, in other words in 1500 years we would have decayed half of it down
06:17
to 125. In another 1500 years we would be down to 62.5. And you can just keep doing
06:23
this. And you can see at 7500 years we are less than 10 kilograms left. You can see a
06:28
lot of that is still going to be radioactive. Now what happens in accidents, something happens
06:33
where we are not able to contain this core. And so if we look at Chernobyl, they were
06:37
testing the reactor and it got out of control. It heated. We are having a melting or an explosion
06:44
that actually collapsed the roof. It released a lot of radiation. If we are looking at Fukushima,
06:48
it is like three levels of protection that failed. We have an earthquake but we also
06:53
have this giant tsunami. And if we are looking at Three Mile Island it was a problem with
06:57
a valve. But also a problem with user error as well. And so all of these, for the most
07:03
part, are human error. Either we had a mistake at the reactor or had a mistake in the design.
07:08
And what it does is it releases some of this radioactive material into the environment.
07:12
So for example radioactive iodine can cause thyroid cancer. So we eat it in our food.
07:18
It causes cancer years down the line. And we are going to see this wherever there is
07:22
a nuclear accident, we are going to have increases in thyroid cancer after that. So if we look
07:26
at these accidents, so this is Three Mile Island, here is Chernobyl. So we had the heyday
07:32
of nuclear reactor creation during this oil crisis. But then after these accidents you
07:37
can see the amount of reactors we have has remained static. And you can say even though
07:42
we could produce this amount of energy, we are producing less of that. And the reason
07:46
has to do with this fear of radiation and the fear of accidents as well. And so what
07:51
does the future hold for nuclear power? Well there are going to be increases in new technology.
07:56
Thorium reactors are going to be working much better than uranium light-water reactors.
08:00
And we can have these third generation reactors where we can actually reuse some of that waste.
08:06
And then finally we have to reduce carbon emissions. And nuclear energy is going to
08:10
be part of that discussion. So could you pause the video and fill-in the blanks? Let me do
08:14
that for you. Nuclear energy is the fission of something like uranium 235. We break it
08:19
apart into fragments. We also get energy in some neutrons that can cause fission in other
08:23
atoms. We have the fuel rods. That is where the radioactive material is. But we also have
08:28
these control rods. Disadvantages, nuclear waste. It takes a long time due to the half-life
08:34
of these radioactive materials for the waste to go away. We can have accidents that increase
08:38
the amount of cancer, thyroid cancer is an example of that. But the advantages again,
08:43
nuclear power can help us reduce the amount of carbon dioxide in the environment. Reduce
08:47
global warming. And that is why it is being revisited. And I hope that was helpful.


This post was previously published on YouTube.

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