Nuclear Fusion (Edexcel GCSE Physics): Revision Note

Nuclear Fusion

• 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, including the Sun, use nuclear fusion to produce energy

  • Therefore, fusion reactions are very important to life on Earth

• In most stars, hydrogen atoms are fused together to form helium and produce lots of energy

Two hydrogen nuclei are fusing to form a helium nuclei

• The energy produced during nuclear fusion comes from a very small amount of the particle’s mass being converted into energy

• Albert Einstein described the mass-energy equivalence with his famous equation:

E = mc²

• Where:

  • E = energy released from fusion in Joules (J)

  • m = mass converted into energy in kilograms (kg)

  • c = the speed of light in metres per second (m/s)

• 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

Fusion vs 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 very dangerous

• Fusion is the opposite of that: it 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

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

Comparison of Nuclear Fusion and Fission Table