Nuclear Fusion (Edexcel IGCSE Physics: Double Science)

• 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
• 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

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

Comparison of fusion and fission table

	Fusion	Fission
the process of...	nuclei joining together	nuclei splitting
nuclei are	small e.g. hydrogen	large e.g. uranium
occurs in	stars	nuclear reactors
produces	a large amount of energy larger nuclei (usually stable and not radioactive)	a large amount of energy smaller daughter nuclei (usually unstable and radioactive) 2 or 3 neutrons
requires	very high temperatures very high pressures	thermal neutrons to induce fission

 

• Nuclear fission reactors are an increasingly common method of electricity generation on Earth
• Nuclear fusion reactors are not yet a commercially viable method for generating electricity, but they are in development
• In the future, fusion reactors are likely to have several advantages over fission reactors

Advantages of fusion reactors 

• Nuclear fusion reactions are capable of generating more energy than fission reactions (per kilogram of fuel)
• The nuclear fuel required for fusion (isotopes of hydrogen found in water) is more abundant than the fuel required for fission (uranium and plutonium)
• Nuclear fusion produces no long-lived nuclear waste products

Disadvantage of fusion reactors

• The conditions for nuclear fusion are much harder to achieve and maintain on Earth than fission