Fusion (WJEC GCSE Physics)

• Small nuclei can react to release energy in a process called nuclear fusion
• Nuclear fusion is defined as:

When two light nuclei join to form a heavier nucleus

• This process requires extremely high temperatures to maintain
  • This is why nuclear fusion has proven very hard to reproduce on Earth

• Stars use nuclear fusion to produce energy
• In stable stars, hydrogen nuclei fuse together to form helium and produce lots of energy

Nuclear Fusion of Hydrogen

Two hydrogen nuclei fuse to form a helium nucleus

• The amount of energy released during nuclear fusion is huge:
  • The energy from 1 kg of hydrogen that undergoes fusion is equivalent to the energy from burning about 10 million kilograms of coal

Comparing Fusion & Fission

• Fission is the process in which large nuclei are split into two smaller nuclei, releasing energy in the process
  • This is the process that produces energy in nuclear power stations, where it is well-controlled
  • Fission provides less energy per kg of fuel than fusion
  • The products of fission are radioactive and hence are very dangerous and difficult to store and dispose of
  • In fission reactors, shielding is required for the containment of energetic neutrons and gamma rays

• Fusion involves taking smaller nuclei and bringing them together to form a bigger nucleus
  • The conditions for fusion are very difficult to achieve on Earth, so nuclear fusion is currently only known to occur in the cores of stars
  • Fusion provides more energy per kg of fuel than fission
  • The products of fusion are not radioactive and are therefore much safer than the products of fission reactions
  • Fusion reactors require very high temperatures and pressure which are difficult to achieve and control

• The following table summarises some of the key differences between fusion and fission:

Comparison of Nuclear Fusion and Fission Reactions