How does nuclear power generate electricity, and do its low-carbon benefits outweigh the risks of waste and accidents?
How nuclear fission is used to generate electricity, the fuel cycle, the management of radioactive waste, and the advantages and disadvantages of nuclear power including safety and decommissioning.
A focused answer to AQA A-Level Environmental Science 3.3.2, covering how nuclear fission generates electricity, the fuel cycle, radioactive waste management, and the advantages and disadvantages of nuclear power.
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What this dot point is asking
AQA wants you to explain how nuclear fission generates electricity, outline the fuel cycle, explain how radioactive waste is managed, and evaluate the advantages and disadvantages of nuclear power, including safety and decommissioning. Command words are Describe, Explain and Evaluate, so a balanced judgement is expected on the longer items.
How nuclear fission generates electricity
The control of the chain reaction is the heart of reactor safety. Control rods of neutron-absorbing material (such as boron) are lowered into the core to absorb surplus neutrons and slow the reaction, and raised to speed it up. A moderator (such as water or graphite) slows the neutrons to the speed at which they most readily cause further fission. The enormous energy from fission comes from the conversion of a tiny amount of mass into energy, far more per kilogram of fuel than any chemical reaction, which is why nuclear fuel is so energy-dense.
The nuclear fuel cycle
The fuel cycle is the full path of the fuel:
- Mining and processing uranium ore, then enriching it to raise the proportion of fissile uranium-235 from about 0.7 percent to a few percent.
- Fabrication into fuel rods and use in the reactor to generate heat.
- Storage or reprocessing of the highly radioactive spent fuel afterwards, recovering usable uranium and plutonium where reprocessing is used.
Managing radioactive waste
The hazard falls over time according to the half-lives of the isotopes present: the activity halves each half-life, so a material with a long half-life stays dangerous for many half-lives, which is why some waste must be isolated for tens of thousands of years.
Advantages and disadvantages
Advantages:
- Very low carbon dioxide emissions in operation, helping decarbonise electricity.
- A large, reliable, continuous baseload output with very high energy density.
- Independent of the weather, unlike solar and wind.
Disadvantages:
- Produces hazardous radioactive waste that remains dangerous for thousands of years.
- A small but serious accident risk (Chernobyl 1986, Fukushima 2011) that can contaminate large areas.
- High build and decommissioning costs, long construction times, and finite uranium.
Exam-style practice questions
Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AQA 20194 marksDescribe how nuclear fission in a reactor is used to generate electricity.Show worked answer →
A 4-mark Describe rewards a clear sequence of stages. Markers look for the chain from fission to electricity.
A neutron strikes a uranium-235 nucleus, which splits (fission), releasing heat energy and further neutrons. Those neutrons cause more fissions, a self-sustaining chain reaction. Control rods absorb surplus neutrons to keep the reaction steady. The heat is carried away by a coolant and used to boil water into steam. The steam drives turbines connected to generators, producing electricity.
Full marks need the role of control rods and the steam-turbine-generator stage, not just the word fission.
AQA 20226 marksEvaluate the use of nuclear power as part of a low-carbon electricity supply, considering waste, safety and decommissioning.Show worked answer →
Evaluate requires advantages, disadvantages and a judgement that weighs them. Markers expect at least two of each plus a conclusion.
Advantages: very low carbon dioxide in operation, a large and reliable baseload output independent of weather, and very high energy density so little fuel is needed.
Disadvantages: high-level radioactive waste stays hazardous for thousands of years and lacks an operating permanent store in many countries; rare but severe accidents (for example Chernobyl in 1986 and Fukushima in 2011) can contaminate large areas; build costs are very high and slow; and decommissioning old reactors is expensive and technically difficult.
Judgement: nuclear offers reliable low-carbon power that complements intermittent renewables, but the unresolved waste and the cost and safety burdens mean its role depends on public acceptance and on whether long-term waste disposal can be guaranteed.
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