Nuclear energy at HL: Nuclear energy is the same for SL and HL. At HL you weigh it through its economic and risk trade-offs against other low-carbon options.
Nothing extra here — just understand the pros and cons of nuclear energy.
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How nuclear power works
Big idea: Nuclear fission releases enormous amounts of energy from small amounts of fuel, providing low-carbon baseload electricity.
The fission process
- Fuel: Usually uranium-235 or plutonium-239
- Fission: Neutrons split heavy nuclei, releasing energy and more neutrons
- Chain reaction: Released neutrons split more nuclei; controlled by moderators and control rods
- Heat generation: Energy heats water to steam, which drives turbines
- Energy density: 1 kg uranium = ~20,000 kg coal equivalent
Types of nuclear power
- Conventional fission reactors: Current technology; uses enriched uranium
- Breeder reactors: Create more fuel than they consume; can use thorium
- Fusion (future): Fusing light nuclei (hydrogen); no commercial plants yet
- Small modular reactors (SMRs): Emerging technology; smaller, potentially safer
Nuclear power produces no direct CO₂ emissions during operation, making it attractive for climate mitigation — but waste and safety remain concerns.
Exam tip: Nuclear is often classified separately from both fossil fuels and renewables. Understand why — its non-renewable (finite uranium) but low-carbon.
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Advantages and disadvantages
Big idea: Nuclear power is controversial — it offers low-carbon baseload electricity but raises concerns about safety, waste, cost, and proliferation.
Advantages
- Low carbon emissions: No CO₂ during operation; lifecycle emissions similar to renewables
- High energy density: Small fuel volume produces large amounts of electricity
- Reliable baseload: Runs continuously regardless of weather; ~90% capacity factor
- Small land footprint: Much less land than solar or wind for same output
- Long operating life: Plants can run 40-60+ years
Disadvantages
- Radioactive waste: High-level waste remains dangerous for thousands of years; no permanent disposal solution
- Safety risks: Accidents (Chernobyl, Fukushima) can have catastrophic consequences
- High costs: Expensive to build; often over budget and delayed
- Proliferation: Technology and materials can potentially be used for weapons
- Uranium mining: Causes environmental damage similar to other mining
- Decommissioning: Costly and complex process at end of plant life
Nuclear accidents are rare but severe. The debate often comes down to comparing small probability × high consequence risks against certain, ongoing climate change impacts.
Exam tip: Nuclear power divides people across the EVS spectrum. Technocentrists often support it; many ecocentrists oppose it. Be ready to explain both perspectives.
IB-style question — Nuclear energy [1]
A new 1200 MW nuclear plant runs at 90% capacity for a full year. Calculate the electricity it generates in one year, in GWh. (Hint: GWh = MW x 8760 hours x capacity factor / 1000.) [1]
How to answer it, step by step
- Set up the calculation
• Hours in a year = 8760
• Energy = 1200 x 8760 x 0.90 - Compute and convert
• = 9,460,800 MWh
• Divide by 1000 = 9461 GWh (accept ~9460)
Final answer
Examiner tip: show the multiplication line — a correct method still scores even if the final rounding differs slightly.
IB-style question — Nuclear energy [2]
Outline two reasons why some governments view nuclear power as a low-carbon alternative to fossil fuels, despite public concern. [2]
How to answer it, step by step
- State the carbon advantage
• Fission releases no CO2 during operation
• Replaces coal/gas that emit greenhouse gases - Add a supply advantage
• High, steady output (good base-load)
• Small fuel mass yields huge energy
Final answer
Examiner tip: "low-carbon" refers to the operating phase — name CO2 directly rather than just saying "clean".