Fission and fusion

Question 1

What does natural uranium contain?

Answer 1

• 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.

Question 2

When does fission occur?

Answer 2

• 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.

Question 3

What happens when uranium fissions?

Answer 3

When uranium fission, a chain reaction starts. A nuclear bomb is an example of a chain reaction that is not controlled.

Question 4

What happens to uranium-235 in a nuclear power station?

Answer 4

• 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.

Question 5

What happens in the diagram?

Answer 5

• 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.

Question 6

How can the output of a nuclear reactor can be controlled?

Answer 6

• 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.

Question 7

Fusion bombs

Answer 7

Fusion bombs are started with a fission reaction which creates exceptionally high temperatures.

Question 8

When does nuclear fussion happen?

Answer 8

• 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.

Question 9

What does fusion require?

Answer 9

• 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.

Question 10

How succesful are attempts to replicate fusion conditions?

Answer 10

• 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.