Fission and Fusion

Question 1

What isotopes does natural uranium consist of?

Answer 1

Uranium-238 and uranium-235

Question 2

What does enriched uranium contain?

Answer 2

Used as a fuel in nuclear power stations and contains more uranium-235 than naturally occurs.

Question 3

What happens during a fission reaction?

Answer 3

• Large unstable nucleus is split up and energy is released as heat
• Atoms of uranium-235 are bombarded with neutrons
• Causes the neutrons to split and releases energy
• Extra neutrons are emitted and cause further nuclei to split, causing a chain reaction and making a large amount of energy
• 235-U-92 + 1-n-0 —> 90-Kr-36 + 143-Ba-56 + 3(1-n-0) + gamma rays

Question 4

How can the output of a nuclear reactor be controlled?

Answer 4

• Graphite moderator between the fuel rods can slow down the fast-moving neutrons emitted during fission. This increases the output as slow-moving neutrons are more likely to be captured by uranium nuclei
• Boron control rods can be lowered as boron absorbs neutrons so fewer neutrons are available to split more uranium nuclei. This decreases the output

Question 5

What is nuclear fusion?

Answer 5

• Two light nuclei fuse together releasing large amounts of heat energy
• Needs extremely high temperatures and pressures, happens in stars where two hydrogen isotopes fuse together to form a helium isotope
• Fusion bombs are started off with a fission reaction to induce required high temperatures