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