Fission and Fusion
4 marks · NormalThe nuclear reaction below shows a fusion reaction that occurs in stars:
Explain what happens to the total mass of the products compared to the reactants in this reaction, and state what happens to the 'missing' mass.
Describe one reason why nuclear fusion does not produce long-lived radioactive waste, unlike nuclear fission reactors.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) — · must show Product mass less than reactant mass; missing mass converted to energy
(b) — · must show Fusion's products (e.g., helium, neutrons) are stable and non-radioactive, unlike fission's radioactive waste
Common mistakes: Not linking mass loss to energy; Suggesting fusion forms heavy nuclei that are radioactive
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States that total mass of products is less than reactants.
B2 (a) · 1 mark · Explains the missing mass is released as (nuclear) energy.
B3 (b) · 1 mark · Fusion produces stable nuclei (e.g., helium), not radioactive waste.
M1 (b) · 1 mark · Clearly compares waste from fission versus fusion.
Worked solution
a) In this fusion reaction, the combined mass of the helium nucleus and the neutron produced is less than the total mass of the deuterium and tritium nuclei that started the reaction. The missing mass is converted into energy and released (often as kinetic energy and electromagnetic radiation).
b) Fusion reactions like this do not create large, unstable nuclei, but instead produce stable nuclei such as helium and single neutrons. As a result, fusion does not generate long-lived radioactive waste as fission does.