Fig. 1 shows a comparison board at a science museum. It compares a fission reactor with a fusion reactor. Both are nuclear energy sources, but the fission r...
Question 1 Report
Fig. 1 shows a comparison board at a science museum. It compares a fission reactor with a fusion reactor. Both are nuclear energy sources, but the fission reaction splits a heavy nucleus whereas fusion joins light nuclei. Visitors are asked to consider the source of fuel and the long-term radioactive waste before choosing which technology may be more useful.
(a) Name the reaction shown in the right-hand box. [1]
(b) Give one similarity between fission and fusion. [1]
(c) Describe one advantage of fusion fuel compared with uranium fuel. [1]
(d) Explain one reason why fusion may produce less long-lived radioactive waste than fission. [2]
Fig. 1 is a binding-energy-per-nucleon graph used by a research team choosing possible reactor fuels. The vertical axis shows how strongly nucleons are held in a nucleus. Deuterium and tritium are light hydrogen isotopes. Iron is near the highest point on the graph. The team wants a reaction with an energy output that is useful for generating electricity.
(a) Name the type of nuclear reaction represented by moving from deuterium towards helium. [1]
(b) Describe how Fig. 1 shows that energy is released in this reaction. [2]
(c) Explain why fission of a very heavy nucleus can also release energy. [2]
Answer Details
First question set
- (a) The right-hand box shows light nuclei joining, so the reaction is nuclear fusion. [1]
- (b) Both fission and fusion are nuclear reactions that release energy. In each case, the change is in atomic nuclei, not an ordinary chemical reaction. [1]
- (c) Fusion fuel is more plentiful: hydrogen isotopes can be obtained from abundant water, and lithium can be used to breed tritium. This is an advantage over finite uranium fuel. [1]
- (d) Fission produces large quantities of radioactive fission fragments, whereas fusion does not. Also, although fusion reactors can make surrounding materials radioactive by neutron activation, these materials generally have shorter half-lives. Therefore fusion produces less long-lived radioactive waste. [2]
Second question set
- (a) Moving from deuterium towards helium represents fusion, because small nuclei join to make a heavier nucleus. [1]
- (b) The graph rises from deuterium and tritium towards helium. The product therefore has a higher binding energy per nucleon; the increase in binding energy is released as energy. [2]
- (c) A very heavy nucleus can split into medium-mass nuclei. These products have a greater binding energy per nucleon, shown by moving upwards on the graph, so energy is released. [2]
Exam reminder: Both fusion of light nuclei and fission of very heavy nuclei release energy because the products are more tightly bound per nucleon.
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