Nuclear Fission & Fusion (Edexcel GCSE Physics): Flashcards
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Define nuclear fusion.
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Define nuclear fusion.
Nuclear fusion is when two small nuclei join together to produce a larger nucleus, releasing energy.
Define nuclear fission.
Nuclear fission is when one large (parent) nucleus splits into two smaller (daughter) nuclei, releasing energy.
Name three types of nuclear reaction that can release energy from the nucleus.
Fusion, fission and radioactive decay.
Why could harnessing nuclear energy safely help reduce our dependency on fossil fuels?
It can transfer large amounts of energy, reducing pollution and the emission of greenhouse gases compared with fossil fuels.
The nucleus of an atom stores an amount of energy roughly ______ times greater than the energy involved in chemical reactions.
The nucleus of an atom stores an amount of energy roughly one million times greater than the energy involved in chemical reactions.
The fusion of 1 kg of hydrogen releases how much energy, compared with burning coal?
An amount of energy equivalent to burning about 10 million kilograms of coal.
True or False?
Nuclear fusion occurs naturally on Earth.
False.
Fusion does not occur naturally on Earth; it occurs naturally in stars, although fusion reactors can be made artificially.
Which two isotopes fuse together in stars, and what element do they form?
Deuterium and tritium (isotopes of hydrogen) fuse to form helium, releasing energy.
Define nuclear fission.
Nuclear fission is the splitting of a large, unstable nucleus into two smaller nuclei.
Which element's isotopes are commonly used as fuel in nuclear power stations?
Isotopes of uranium, such as uranium-235.
What products are formed when a neutron collides with an unstable nucleus during fission?
Two smaller daughter nuclei, two or three neutrons, and gamma rays.
During induced fission, a ______ is absorbed by a uranium-235 nucleus to form uranium-236, which is unstable and splits almost immediately.
During induced fission, a neutron is absorbed by a uranium-235 nucleus to form uranium-236, which is unstable and splits almost immediately.
Why is uranium-235 unsuitable for producing energy in a power station without being induced to fission?
It has a very long half-life, so it has low activity and releases energy very slowly.
True or False?
Energy is transferred from the nuclear store to the kinetic store of the fission products.
True.
The fission products move away very quickly, transferring energy from the nuclear store to the kinetic store.
How is the energy released by nuclear fission eventually used to generate electricity?
It is used to heat water to produce steam, which generates electricity within the power station.
Define chain reaction.
A chain reaction is a process in which the neutrons released by each fission reaction go on to cause further fission reactions.
How many neutrons are needed to induce a uranium-235 nucleus to undergo fission, and how many neutrons does that fission produce?
One neutron induces the fission, which produces two or three neutrons.
What is the purpose of a control rod in a nuclear reactor?
To absorb neutrons, controlling the rate of fission.
What is the purpose of a moderator in a nuclear reactor?
To slow down neutrons so they are in thermal equilibrium with the moderator, allowing them to react efficiently with the uranium fuel.
Lowering the control rods further into the reactor ______ the rate of fission, because more neutrons are absorbed.
Lowering the control rods further into the reactor decreases the rate of fission, because more neutrons are absorbed.
True or False?
Raising the control rods decreases the rate of fission.
False.
Raising the control rods increases the rate of fission, since fewer neutrons are absorbed.
What two factors must be controlled to keep a nuclear reactor producing energy at the correct rate?
The number of free neutrons and the energy of the free neutrons.
How can a nuclear reactor be shut down using its control rods?
The control rods are lowered all the way into the reactor so no fission reaction can take place.
What is the role of the coolant in a nuclear power station?
It carries heat away from the reactor and is then used to heat a separate water source, producing steam.
Define nuclear reactor.
The reactor is the part of the power station that provides thermal energy from fission chain reactions.
The steam produced in a nuclear power station drives ______, which then turn generators to produce electricity.
The steam produced in a nuclear power station drives turbines, which then turn generators to produce electricity.
Why is a separate water source used to produce steam, rather than turning the coolant itself into steam?
To reduce the risk of contamination.
What is the purpose of the condenser in a nuclear power station?
To cool the steam back into water.
What does nuclear waste consist of?
The unusable fission products from the fission of uranium-235, and spent fuel rods.
True or False?
The daughter nuclei produced by fission are less radioactive than the original fuel.
False.
The daughter nuclei are more radioactive than the original fuel.
Why must nuclear waste be stored underground?
It remains radioactive for thousands of years, so it must be stored underground until it is no longer harmful.
Besides being highly radioactive, what other property makes spent fuel rods dangerous to handle?
They are extremely hot.
Why can nuclear power be frightening to people who do not understand it?
Because it is dangerous if not handled properly, yet it is invisible, which can be difficult for some people to comprehend.
True or False?
Increased education about nuclear energy has no effect on how society views it.
False.
With increased education, society can use this knowledge to inform their own decisions and opinions.
Define nuclear fusion.
Nuclear fusion is when two light nuclei join together to form a heavier nucleus, releasing energy.
Why has nuclear fusion proven very hard to reproduce on Earth?
It requires extremely high temperatures to maintain.
State Einstein's mass-energy equivalence equation, and define each term.
E = mc², where E = energy released (J), m = mass converted into energy (kg), c = speed of light (m/s).
Where does nuclear fusion occur naturally?
In the cores of stars, including the Sun.
Define nuclear fission.
Nuclear fission is the process in which large nuclei split into two smaller nuclei, releasing energy.
Fusion provides ______ energy per kg of fuel than fission.
Fusion provides more energy per kg of fuel than fission.
True or False?
The products of nuclear fusion are radioactive.
False.
The products of fusion are not radioactive, unlike fission products, which are radioactive and dangerous.
Why is nuclear fission used in power stations rather than nuclear fusion?
Fission is well controlled and achievable, whereas the conditions needed for fusion are very difficult to achieve on Earth.
Define high density in the context of nuclear fusion.
A high density of nuclei increases the number of collisions between them, which increases the chance of fusion occurring.
Define high kinetic energy in the context of nuclear fusion.
Nuclei need high kinetic energy (speed) to overcome the repulsive force between them and get close enough to fuse.
Why do protons repel each other?
Protons have a positive charge, so they exert a repulsive force on one another.
State the three conditions needed for nuclear fusion to take place.
Very high temperature of the fuel
Very high kinetic energy / speed of the nuclei
Very high density / pressure
Why is nuclear fusion not currently used as a source of power on Earth?
Achieving and containing the very high temperatures and pressures needed is difficult, so only a small, not-yet-useful amount of fusion takes place.
Physicists have not yet managed to produce ______ energy from fusion than the energy needed to start it.
Physicists have not yet managed to produce more energy from fusion than the energy needed to start it.
True or False?
Fusion currently produces more energy than is needed to start it.
False.
Physicists have not yet achieved a fusion reaction that produces more energy than is needed to start it.
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