|Program||Brown Science Prep|
|Developed by||Alex Meehan, Oyinkansola Osobamiro, Michelle Kim|
|Developer Type||Brown students|
Chain reaction modelStudents sit in a circle with you as leader. Explain that they have to pass a sound on (ie they can only start when the person before them starts doing it). Noise represents the energy being released by the reaction, and the ‘passing on’ represents the neutrons inducing fission. You start by rubbing hands together. You keep doing it as the others start. When the sound come back to you you change to snapping fingers. That then spreads round and back to you. You then change to hand clapping and then finally to feet stamping. You then go back to hand clapping, finger snapping and hand rubbing to simulate the control rods being incrementally lowered.
Things to encourage students to think about when coming up with Pros and Cons of using nuclear energy:
1.) Economic argument: why might it be better for the United States to invest in nuclear energy? Why might it be worse?
2.) Environmental argument: What are the benefits of using nuclear energy on the environment? What are the drawbacks? Which outweighs the other?3.) Are the risks greater than the benefits? Why or why not?
Overview / Purpose / Essential Questions
What is “nuclear energy” and where does it come from? What are the environmental and sociopolitical benefits/issues associated with this alternative form of energy?
Performance / Lesson Objective(s)
To learn about atoms, particles and the fundamental forces of physics
To learn how the processes of nuclear fission and fusion work through a series of physical activities intended to model themTo understand/be engaged in this debate of whether the world needs nuclear energy
The nuclear energy issue is relevant to energy sustainability and climate change. It is also important to understand the fundamental building blocks of the universe, i.e. particles and atoms, and how they interact at a fundamental level.
Atoms and Forces
This information is necessary for a basic understanding of
how nuclear fission and fusion work.
Most matter is made up of atoms (Note: it is not true that ‘everything is made up of atoms’--for example, photons aren’t and the majority of dark matter probably isn’t) . Atoms bind together into molecules, and then molecules bind together to form the objects we see in everyday life.
In nature, any atom you find will be one of 92 types of atoms, also known as elements (man has artificially created more types of atoms, so now this number is more like 118). So almost every substance on Earth -- metal, plastics, hair, clothing, leaves, glass -- is made up of combinations of the 92 atoms that are found in nature. Atoms are REALLY small. If you were to take a grapefruit and blow up each of its atoms to the size of a blueberry, the grapefruit would then have to be bigger than the earth.
Each atom consists of a cloud of electrons in orbitals surrounding a nucleus at the center. If the atom were the size of a football stadium, the nucleus would be the size of a small marble. The nucleus contains protons and neutrons. Protons, electrons, and neutrons are all examples of particles.
Protons are positively charged, electrons are negatively
charged, and neutrons are neutral. We know from our theory of electricity and
magnetism that similar charges repel, and that opposite charges attract (much
like the North and South poles of a bar magnet, although these are technically
different phenomena). For example, the electrons are kept in orbit around the
nucleus because there is an electromagnetic field of attraction between the
positive charge of the protons and the negative charge of the electrons.
So if like charges repel, and protons are clumped together really tightly in a ball at the center of the atom, you may be wondering-- how does the atom manage to stay together!? Why doesn’t it just fly apart, given that all the protons are repelling each other?
The answer is that there is more than just the attracting/repelling force between the charges (called electromagnetic force) at work here. There is also something called the strong nuclear force, which is attractive between neighbouring neutrons and protons. This force has a very short range, and (as the name indicates) it is very strong--in fact, it is the strongest type of force. The energy associated with the strong force is called the binding energy.
[Note: There are four fundamental forces. These four fundamental forces are strong nuclear, electro-magnetic, weak nuclear, and gravity. Many physicists are looking for a theory that will unite these into one or two types of fundamental force. ]
[Additional note: The strong nuclear force is a result of “gluon interactions” between nucleons (nucleons = neutrons and protons). The gluon is an example of what is called a ‘force carrier particle’. Although this is hard to understand intuitively, the basic idea is that forces are produced by the exchange of force carrier particles. In the case of electromagnetic force, the force carrier particle is the photon (light particle).]
In some atoms, the binding energy is great enough to hold the nucleus together. The nucleus of this kind of atom is said to be stable. In some atoms the binding energy is not strong enough to hold the nucleus together, and the nuclei of these atoms are said to be unstable. Unstable atoms will lose neutrons and protons as they attempt to become stable. This process of losing 0neutrons and protons is called radioactive decay. These emitted neutrons and protons are the radiation. Since these particles usually have high energy when they are radiated they can knock off electrons from atoms they hit. The loss of an electron can cause problems, including everything from cell death to genetic mutations (leading to cancer), in any living thing.
Uranium is a common element on Earth and has existed since the planet formed. While there are several varieties of uranium, uranium-235 (U-235) is the one most important to the production of both nuclear power and nuclear bombs. U-235 decays naturally by alpha radiation: It throws off an alpha particle, or two neutrons and two protons bound together. Most importantly, uranium can undergo induced fission, as explained in the next section.
Nuclear Fission and Nuclear Fission Power plants
We are now ready to understand how nuclear energy can be produced. There are two ways- nuclear fusion and nuclear fission. We will discuss fission first.
Fission is just a synonym for ‘splitting’. Fire a free neutron into a U-235 nucleus and the nucleus will absorb the neutron, become unstable and split immediately, releasing a Barium atom, a Krypton atom, three neutrons and a huge amount of energy. Furthermore, the type of energy it produces is carbon free unlike other forms of energy (such as burning natural gas) which release huge amounts of fossil fuels that negatively impact the environment. Forms of energy that release carbon dioxide enhance the greenhouse effect, so that more heat is trapped within the earth’s atmosphere, which causes global warming. (mentors if necessary go over some of the negative impacts of global warming, or have students brainstorm why this is bad in the debate activity) Furthermore, in the United States, we get the majority of our gas/oil from foreign sources. However, because nuclear fission produces so much energy, it can produce more kilowatts (a measurement of power or the rate that energy is used/transformed) for a lower cost than other energy alternatives including wind, solar and coal. Furthermore, the amount of space that nuclear power plants take up is significantly smaller than the amount of space that other sources of energy require to run. In addition, the waste that is produced by nuclear plants can be reprocessed to cut down on the amount of waste produced as well as the toxicity of the waste.
Though nuclear fission does not release carbon dioxide, it does consume huge amounts of uranium, thereby resulting in huge amounts dangerous radioactive waste that isn’t biodegradable. Governments have to figure out the best ways of storing the waste produced, which can be costly. Furthermore, though nuclear power plants take up a small amount of land acres, once they are used the land surrounding the nuclear power plant might no longer be usable due to the radioactive waste byproducts. Furthermore, in the United States, the majority of our Uranium is imported. In addition, while nuclear energy in and of itself is cost-effective building nuclear plants to make nuclear energy is extremely costly, as is building safe facilities for the radioactive waste collection, and training people how to effectively and safely use nuclear energy. This is a particularly troublesome issue, because even in the United States, the last nuclear plant was built in the 70s and significantly more plants would need to be built to have a more significant environmental impact. This takes a huge amount of time and cost, even though global warming is a problem right now.
Why does the absorbed neutron suddenly make the nucleus unstable, and cause it to split? Before the neutron arrived, the uranium atom had a very delicate balance between the strong nuclear force and the repulsive electromagnetic forces. Protons and neutrons were packed together very tightly, in a very specific geometric arrangement. When the new neutron enters, it upsets this delicate arrangement. The configuration becomes unstable, and the atom splits.
Now imagine a bunch of uranium atoms sitting side by side. One of them randomly undergoes spontaneous fission (i.e. undergoes naturally-occurring radioactive decay), and in the process ejects three neutrons. One of these neutrons hits another uranium atom, which causes induced fission. Another three neutrons are ejected from that atom, and one of those neutrons hits another uranium atom, which again causes induced fission. And the process repeats-- we have a chain reaction!
But wait... a chain reaction will result in a big explosion, and we’re trying to make a nuclear power plant, not a nuclear bomb. We still have two answer two questions:
1) How do nuclear power plants use the energy released from these fissions and convert it into electric power?
2) How do nuclear power plants control these chain reactions, and prevent themselves from becoming nuclear bombs?
The answers to 1) and 2) can be summarized as:
1) The fission process releases energy which heats water, which turns into steam and turns a turbine coupled to a generator which produces electricity
2) Control rods are lowered between the uranium rods. These
control rods absorb the neutrons and thus stop/slow the chain reaction. (If the
control rods are lowered completely, the reactor is shut down. When raised
fully, the chain reaction goes unchecked and the consequences are very
bad--although in reality there are usually safety features that prevent this
from happening). Coolant water is also used to prevent overheating and
meltdown. Meltdown is when the core gets too hot and the fuel rods melt,
leaking out into the coolant.
The potentials for nuclear energy harnessed as a nuclear
power plant are huge, particularly because, as some critics maintain, it also
provides an opportunity for developing economies to use a more cost-efficient
form of energy that doesn’t harm their environment if properly controlled.
However one drawback is that the cost it takes to set up such plants, and how they might actually be destructive to a developing nation’s economy. Furthermore, while there are trends and patterns between developing economies, each country is unique, and an economic policy that works for one nation might not work for another due to its own makeup. There’s a lot of short term sacrifice for the long term gain for nuclear power plant.
Summary of what went wrong at Fukushima in 2011, if you have time to explain some of it:
The tsunami following the earthquake quickly flooded the low-lying rooms in which the emergency generators were housed, cutting power to the critical pumps that must continuously circulate the coolant water. As the pumps stopped, the reactors overheated due to the normal high radioactive decay heat produced in the first few days after nuclear reactor shutdown.
As the water boiled away in the reactors and the water levels in the fuel rod pools dropped, the reactor fuel rods began to overheat severely and melt down.http://en.wikipedia.org/wiki/Fukushima_Daiichi_nuclear_disaster - cite_note-11
In the intense heat and pressure of the melting reactors, a reaction. between the nuclear fuel metal cladding and the remaining water surrounding them produced explosive hydrogen gas. As workers struggled to cool and shut down the reactors, several hydrogen-air chemical explosions occurred.
A more common concern is the impact that nuclear power plants have on wildlife. Most power plants have safety mechanism to prevent larger fishes from getting caught in the plant, but other animals like microscopic plankton, sea turtles, and seals can be particularly vulnerable.
Another concern is the impact that nuclear energy can have on human health. On one hand, studies done by the United States government to see if there is any correlation between proximity to a nuclear power plant and cancer rates have been inconclusive. However, severe exposure to radiation, while rare is fatal.
Wrap up / Conclusion
A debate on the pros and cons of nuclear energy will be the concluding activity for this lesson.
Supporting Web Information
(see above web information)
Pre Assessment Plan
quiz on general aspects of nuclear physics
Post Assessment Plan
conceptually similar quiz, focusing on points addressed in the lesson
|Audience(s)||High school students
|Grade Level(s)||High School
|Created||05/28/2013 08:55 PM|
|Updated||12/20/2018 11:54 AM|