Fission and fusion Flashcards
1
Q
What does natural uranium contain?
A
- Natural uranium consists of two isotopes, Uranium-258 and Uranium-235.
- The ‘enriched uranium’ used in fuel in a nuclear power station contains a greater proportion of the uranium-235 isotope than occurs naturally.
2
Q
When does fission occur?
A
- Fusion occurs when a large unstable nucleus is split up and energy released as heat.
- The heat is used to boil water to produce steam.
- The pressure of the steam acting on the turbine blades make it turn
- The rotating turbines turns the generator, producing electricity.
3
Q
What happens when uranium fissions?
A
When uranium fission, a chain reaction starts. A nuclear bomb is an example of a chain reaction that is not controlled.
4
Q
What happens to uranium-235 in a nuclear power station?
A
- In a nuclear power station, atoms of uranium-235 are bombarded with neutrons. This causes the nucleus to split, releasing energy.
- Extra neutrons emitted cause further uranium nuclei to split. This is described as a chain reaction and produces a large amount of energy.
5
Q
What happens in the diagram?
A
- A neutron is absorbed by the nucleus of a uranium-235 atom.
- the nucleus is now less stable than before.
- It splits into two parts and releases energy.
- Several neutrons are also produced - these may go on to strike the nuclei of other atoms causing further fission reactions.
6
Q
How can the output of a nuclear reactor can be controlled?
A
- A graphite moderator between the fuel rods slows down the fast-moving neutrons emitted during fission. Slow-moving neutrons are more likely to be captured by other uranium nuclei.
- Boron control rods can be raised or lowered. Boron absorbs neutrons, so fewer neutrons are available to split more uranium nuclei. This controls the rate of fission.
7
Q
Fusion bombs
A
Fusion bombs are started with a fission reaction which creates exceptionally high temperatures.
8
Q
When does nuclear fussion happen?
A
- Nuclear fusion happens when two light nuclei fuse together releasing large amounts of heat energy.
- In stars, fusion takes place under extremely high temperatures and pressures.
9
Q
What does fusion require?
A
- Fusion requires extremely high temperatures which have proved difficult to achieve and to manage safely on Earth and so its use for large-scale power generation remains a dream.
- Research in this area is very expensive so it is carried out as an international joint venture to share costs, expertise and benefits.
10
Q
How succesful are attempts to replicate fusion conditions?
A
- So far attempts to replicate these condition safety on Earth has been unsuccessful.
- Scientists are still trying to solve the safety and practical challenges presented.
- Cold Fusion is still not accepted as realistic since any results output impossible to verify so far.