Nuclear Fission & Fusion Flashcards
All 38 cards in this deck
Name the three types of nuclear reaction that can be a source of energy.
Nuclear fission, nuclear fusion and radioactive decay.
True or false? Radioactive decay is a source of energy as well as fission and fusion.
True. All three nuclear reactions release energy.
In a nuclear reaction, where does the released energy come from?
A loss of mass — the products have less total mass than the starting nuclei, and the lost mass appears as energy ().
True or false? A kilogram of nuclear fuel releases far more energy than a kilogram of coal.
True. Nuclear reactions release much more energy per kilogram than chemical reactions such as burning.
What is nuclear fission?
The splitting of a large unstable nucleus into two smaller daughter nuclei, releasing neutrons and energy.
Which particle must be absorbed by a uranium-235 nucleus to make it undergo fission?
A neutron.
What are the three products of the fission of a uranium-235 nucleus?
Two daughter nuclei, two or more neutrons, and a release of energy.
What must balance on both sides of a nuclear fission equation?
The total mass number (top numbers) and the total atomic number (bottom numbers).
What are the steps of a chain reaction in uranium-235?
e.g. starting with one neutron and one U-235 nucleus
- The U-235 nucleus absorbs the neutron and splits into two daughter nuclei, releasing energy.
- Two or more neutrons are released by the fission.
- Each of these neutrons can be absorbed by another U-235 nucleus, causing further fissions — the reaction spreads.
What is meant by a controlled chain reaction?
On average only one neutron from each fission goes on to cause another fission, so the number of fissions per second stays constant.
What is the job of the moderator in a nuclear reactor?
It slows down the fast neutrons so they are more likely to be absorbed and cause further fission.
What is the job of the control rods in a nuclear reactor?
They absorb neutrons, so fewer neutrons are available to cause fission.
True or false? The control rods slow down the neutrons in a nuclear reactor.
False. The moderator slows neutrons down; the control rods absorb them.
What are the steps by which pushing the control rods further in slows the chain reaction?
e.g. the reactor core is getting too hot
- The rods are lowered further into the core.
- They absorb more of the neutrons.
- Fewer neutrons are available, so fewer fissions happen each second and less energy is released.
True or false? Removing the control rods from the core speeds up the chain reaction.
True. Fewer neutrons are absorbed, so more neutrons cause fission.
In a nuclear reactor, what energy transfer happens immediately after fission?
Kinetic energy of the fission fragments is transferred to thermal energy of the coolant.
What are the steps in generating electricity from the chain reaction in a nuclear power station?
e.g. a reactor fuelled with uranium-235
- Fission heats the coolant, which carries thermal energy out of the reactor.
- The hot coolant boils water in a boiler to make steam.
- The steam turns a turbine, which turns a generator to produce electricity.
What can be said about the daughter nuclei (products) of nuclear fission?
They are radioactive.
How is high-level radioactive waste from a nuclear power station dealt with?
It is sealed in containers and stored securely, often buried deep underground.
True or false? Radioactive waste from a nuclear power station is safe after a few years.
False. Some waste stays dangerously radioactive for thousands of years, so it must be stored for a very long time.
Give an advantage of nuclear power relating to the atmosphere.
It produces no carbon dioxide (or other greenhouse gases) while generating electricity.
Give two disadvantages of using nuclear power to generate electricity.
It produces radioactive waste that is hard to dispose of, and there is a risk of an accident releasing radioactive material.
True or false? Nuclear power stations release carbon dioxide as they generate electricity.
False. No CO is released during generation, although building and fuel processing do produce some.
Why is public perception a disadvantage of nuclear power?
Many people fear nuclear accidents, radiation and links with weapons, so they oppose new power stations.
True or false? Nuclear fuel is a renewable energy resource.
False. Uranium is non-renewable — supplies are limited.
Give an advantage of nuclear power compared with wind or solar power.
It gives a reliable, constant supply of electricity that does not depend on the weather.
What is nuclear fusion?
Two small nuclei joining together to create a larger nucleus, with a release of energy.
Where does the energy released in nuclear fusion come from?
The new nucleus has less mass than the two small nuclei combined; this lost mass is released as energy.
What is the energy source of stars such as the Sun?
Nuclear fusion — hydrogen nuclei fusing to form helium.
What is the difference between nuclear fission and nuclear fusion?
Fission is a large nucleus splitting into two smaller nuclei; fusion is two small nuclei joining to make a larger one.
True or false? Both nuclear fission and nuclear fusion release energy.
True. Both involve a loss of mass that appears as energy.
True or false? Fusion is the reaction used in nuclear power stations today.
False. Power stations use fission; no practical fusion power station exists yet.
Why does nuclear fusion not happen at low temperatures and pressures?
Nuclei are positively charged, so electrostatic repulsion pushes them apart before they can join.
What conditions are needed for nuclear fusion to occur?
Extremely high temperature and extremely high pressure.
Why is a very high temperature needed for fusion?
It gives the nuclei enough energy (high speed) to overcome the electrostatic repulsion between them.
Why is a very high pressure needed for fusion?
It forces the nuclei close together so that collisions are frequent enough for them to fuse.
Why is it difficult to build a practical, economic fusion power station?
The extremely high temperatures and pressures are very hard and expensive to produce and contain, so at present more energy is put in than is got out.
True or false? The repulsion that must be overcome in fusion is between the protons in the nuclei.
True. Both nuclei are positively charged, so they repel each other electrostatically.