Nuclear splits opinion more than any other energy source. It is low-carbon and extremely reliable, and it also produces waste that stays dangerous for thousands of years. Examiners are not looking for you to pick a side — they want to see you weigh both sides properly.
📘 What you need to know
Nuclear power generates electricity from the energy released by nuclear fission — splitting a heavy nucleus in two.
The fuels are uranium-235 (most common) and plutonium-239. Both are finite, so nuclear is non-renewable.
The five parts of the station: reactor, boiler, turbine, generator, condenser.
Main benefits: constant large-scale output, low running costs once built, and very low greenhouse gas emissions during generation.
Main costs: uranium mining damage, thermal pollution, the risk of accidents, radioactive waste, and very expensive decommissioning.
Named examples: Sweden over 40% nuclear electricity, Chernobyl 1986, Fukushima 2011.
What nuclear power is
Nuclear power is a method of generating electricity using the energy released from nuclear reactions — specifically nuclear fission. Fission is the splitting of the nucleus of a heavy atom such as uranium or plutonium. Splitting one nucleus releases an enormous amount of energy for a tiny amount of fuel.
Unlike solar or wind, nuclear power runs on finite resources. There is a limited supply of uranium ore in the ground, and it will eventually be used up. That is why nuclear sits in the non-renewable box even though it barely emits carbon dioxide.
The energy released heats water. From that point onwards a nuclear station works exactly like a coal station.
How a nuclear power station works
Once the heat exists, the rest is ordinary engineering. Learn the five parts and what each one does — short definition questions on this come up regularly.
Knowing that the reactor simply replaces the furnace makes the whole system easy to remember.
Part
What it does
Nuclear reactor
Provides thermal energy from fission chain reactions
Boiler
Uses that thermal energy to boil water and create steam
Turbine
Uses steam to turn thermal energy into kinetic energy
Generator
Transfers kinetic energy into electrical energy
Condenser
Cools the steam back into water so it can be reused
The benefits
1. Constant, low-cost energy
Once built, a nuclear power station produces large amounts of energy consistently, over decades. It does not care about wind speed or cloud cover, so it can supply reliable baseload electricity on a large scale. After the high initial construction costs, running costs are relatively low, partly because very small amounts of uranium are needed and large reserves are available.
2. Low-carbon energy
Unlike coal or gas, nuclear power does not emit CO2 during electricity generation. This is why it is treated as important in efforts to tackle climate change, and why several countries keep it despite the controversy. Over 40% of Sweden’s electricity comes from nuclear power, which is a large part of why its energy mix is so low-carbon.
3. Energy security
Nuclear reduces reliance on imported fossil fuels and adds a reliable, non-weather-dependent source to the mix. That is a diversification argument as much as an environmental one.
The costs
1. Environmental concerns
Uranium mining: extracting uranium causes habitat destruction and water pollution, and mining itself produces radioactive waste — before any electricity is generated.
Thermal pollution: stations use large amounts of water for cooling. Discharging heated water into rivers or lakes alters water temperature and chemistry, damaging local ecosystems.
2. Nuclear accidents
Accidents are rare but catastrophic. That combination is what makes them so hard to judge.
Chernobyl, 1986: a reactor explosion led to widespread contamination.
Fukushima, 2011: a tsunami disabled the cooling systems at a nuclear plant, causing radiation leaks.
3. Radioactive waste
Reactors produce radioactive waste that remains hazardous for thousands of years. It has to be sealed in specially designed containers and stored underground while the fission products are still radioactive. Safe storage is very expensive, and no country has fully solved the long-term problem. On top of that, the cost of decommissioning a plant at the end of its life is enormous.
BENEFITS — QUICK LIST
No greenhouse gases released during generation
Reliable large-scale output, available whenever needed
Small amounts of fuel; large uranium reserves
Low running costs once built
Reduces reliance on fossil fuels and improves energy security
COSTS — QUICK LIST
Finite uranium supply, so it is non-renewable
Radioactive waste hazardous for thousands of years
Safe storage of that waste is very expensive
Accidents can spread contamination over large areas
Decommissioning costs are very high
🤔 Why nuclear is so hard to evaluate fairly
Most energy sources cause steady, predictable harm: a coal station emits carbon dioxide every single day it runs. Nuclear is different. It causes almost no harm on a normal day, but carries a small chance of a very large harm, plus a waste problem that lands on people who are not born yet. Comparing “certain small damage” against “unlikely huge damage” is a genuine value judgement, not a calculation. That is exactly why exam questions ask you to discuss nuclear rather than to state whether it is good.
Making a judgement
An evaluation question wants a position, supported. A structure that works every time:
🧩 How to structure a nuclear evaluation
Define nuclear power in one line, including fission and its non-renewable status.
Two strong benefits with evidence — low-carbon generation, reliable large-scale supply, Sweden as an example.
Two strong costs with evidence — long-lived radioactive waste, accident risk, Chernobyl and Fukushima.
Compare to the alternative. Against coal, nuclear looks strong on emissions. Against wind and solar, its waste and cost look worse.
Judge and justify. For example: nuclear is a useful transition source where reliable low-carbon power is needed, provided waste storage is funded properly.
EXAM-STYLE
Explain why nuclear power is classed as non-renewable despite being low-carbon. [2]
Point 1
Nuclear fission uses uranium ore, of which there is a finite supply that cannot be replaced within a human lifespan.
Point 2
The renewable classification depends on whether the fuel is replaced, not on how much carbon dioxide is emitted, so a low-carbon source can still be non-renewable.
2 marks: finite fuel, and the classification ruleThe second point is the one most students miss. Say explicitly that renewable and low-carbon are different criteria.
EXAM-STYLE
Discuss whether a country should expand its nuclear power capacity. [6]
For
Nuclear emits no CO2 during generation, so it helps meet emissions targets. It runs constantly, unlike intermittent wind and solar, so it supports grid stability. It also reduces fossil fuel imports and improves energy security. Sweden gets over 40% of its electricity this way.
Against
Uranium is finite, so this is not a permanent solution. Waste stays hazardous for thousands of years and storage is costly. Accidents such as Chernobyl (1986) and Fukushima (2011) show contamination can spread widely. Construction and decommissioning are extremely expensive.
Judgement
Expansion is justified where a country needs reliable low-carbon power and has stable geology and strong regulation, but funding for waste storage and decommissioning must be secured first.
6 marks: balanced points both sides, examples, clear justified conclusionA discuss answer without a conclusion caps in the middle band. Always finish with a position.
💡 Exam tip
Say “no CO2 during generation”, not “no pollution”. Mining and waste are pollution too.
Learn the five station parts as a chain: reactor, boiler, turbine, generator, condenser.
Have your three named examples ready: Sweden over 40%, Chernobyl 1986, Fukushima 2011.
Thermal pollution is an easily forgotten disadvantage. Mentioning it separates you from most answers.
For “discuss” or “evaluate”, give both sides plus a justified conclusion. No conclusion means lost marks.
Use the phrase “rare but catastrophic” for accident risk — it captures the trade-off in three words.
⚠ Common mix-up
“Nuclear is renewable.” It is low-carbon, not renewable. Uranium ore is finite.
Fission confused with fusion. Fission splits a heavy nucleus. Fusion joins light nuclei and is not yet used commercially.
“Nuclear produces no pollution.” No air pollution during generation, but plenty of radioactive waste and mining damage.
Forgetting decommissioning. The cost of shutting a plant down is one of the biggest disadvantages.
Missing thermal pollution. Heated cooling water changes river temperature and chemistry.
One-sided answers. Nuclear questions almost always reward balance, whichever side you land on.
Up next: Storing Energy in Batteries — the last HL section, and the one that links energy to mining, geopolitics and trade.
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