🏠 Home
FractionRush AQA GCSE Physics 4.1
AQA GCSE Physics 4.1

Non-renewable Energy Sources

Fossil fuels and nuclear energy: how they work, environmental impact, energy security

Learning Objectives

⚑ Describe how fossil fuels (coal, oil, natural gas) release energy to generate electricity
☒️ Explain how nuclear fission releases energy and how this is used in power stations
🌍 Evaluate the environmental impacts of fossil fuels including greenhouse gases and pollution
πŸ”’ Discuss energy security and why nations depend on non-renewable sources
βš–οΈ Compare the advantages and disadvantages of fossil fuels vs nuclear power
πŸ“Š Perform calculations involving energy output, efficiency and fuel consumption

πŸ“š Core Theory

πŸ”‹ What are Non-renewable Energy Sources?

Non-renewable energy source: A resource that is used up faster than it can be replaced naturally, meaning it will eventually run out.

The three main fossil fuels are coal, oil (crude oil / petroleum), and natural gas (mainly methane, CHβ‚„). They are called fossil fuels because they formed over millions of years from the remains of ancient plants and animals that were compressed and heated deep underground.

Nuclear fuels β€” primarily uranium-235 (U-235) and plutonium-239 β€” are also non-renewable. They exist in limited quantities in Earth's crust and cannot be replenished on a human timescale.

Globally, non-renewable sources provide roughly 80–85% of all primary energy. Although renewable alternatives are growing rapidly, fossil fuels and nuclear power remain central to electricity generation in most countries, including the UK.

Non-renewables release stored chemical energy (fossil fuels) or stored nuclear energy (uranium) as heat, which drives turbines to generate electricity.
FuelTypeEnergy stored asTypical use
CoalFossil fuelChemical (carbon bonds)Power stations
OilFossil fuelChemical (hydrocarbons)Transport, heating
Natural gasFossil fuelChemical (CHβ‚„)Heating, power stations
Uranium-235Nuclear fuelNuclear binding energyNuclear power stations

πŸ”₯ How Fossil Fuel Power Stations Work

All fossil fuel power stations follow the same basic principle: burning fuel β†’ heat β†’ steam β†’ turbine β†’ generator β†’ electricity. This sequence is sometimes called the thermal generation cycle.

  1. Combustion: Fuel is burned in a furnace or boiler. The chemical energy stored in the fuel is converted to thermal (heat) energy.
  2. Steam production: The heat boils water to produce high-pressure steam.
  3. Turbine: Steam rushes through turbine blades, making them spin β€” thermal energy β†’ kinetic energy.
  4. Generator: The spinning turbine rotates electromagnets inside coils of wire, inducing an alternating current β€” kinetic energy β†’ electrical energy.
  5. Cooling: Steam is condensed back to water and recycled. Waste heat is released via cooling towers.
Efficiency = (Useful energy output Γ· Total energy input) Γ— 100%
Ξ· = (Euseful Γ· Einput) Γ— 100%

Typical efficiencies: coal ~35–40%, natural gas (combined cycle) ~55–60%, oil ~38–42%.

Coal produces the most COβ‚‚ per unit of energy. Natural gas produces roughly half as much COβ‚‚ as coal for the same energy output, making it a "transitional" fuel in many energy policies.

Differences between fossil fuels:

  • Coal: Solid; highest carbon content; most polluting; cheapest historically but declining rapidly.
  • Oil: Liquid; easily transported by pipeline and tanker; primarily used for transport fuel (petrol/diesel).
  • Natural gas: Gas (mostly methane); burns most cleanly of the three; widely used for domestic heating and electricity.

☒️ Nuclear Energy and Fission

Nuclear fission: The splitting of a large, unstable atomic nucleus (e.g. uranium-235) into two smaller nuclei, releasing a large amount of energy and 2–3 neutrons.

Inside a nuclear reactor, uranium-235 nuclei absorb slow-moving neutrons and split apart. This releases enormous amounts of thermal energy (heat) plus more neutrons, which trigger further fissions in a controlled chain reaction.

Key components of a nuclear reactor:

  • Fuel rods: Contain enriched uranium-235 pellets.
  • Control rods: Made of boron or cadmium; absorb neutrons to slow or stop the chain reaction.
  • Moderator: Usually water or graphite; slows neutrons to the speed needed for fission.
  • Coolant: Water or carbon dioxide; carries heat away from the reactor core to produce steam.
  • Containment vessel: Thick steel and concrete shield prevents radiation escaping.
Energy released: E = mcΒ²
where m = mass defect (kg), c = speed of light = 3 Γ— 10⁸ m/s
(Note: mass defect is tiny but cΒ² is enormous β†’ huge energy release)

One kilogram of uranium-235 releases roughly 83 million times more energy than one kilogram of coal. This is why nuclear power stations use very small quantities of fuel to generate enormous amounts of electricity.

After fossil fuel combustion, the rest of the process is identical: heat β†’ steam β†’ turbine β†’ generator β†’ electricity.

Nuclear power produces no direct COβ‚‚ emissions during operation, making it attractive as a low-carbon electricity source. However, mining and processing uranium does involve some carbon emissions.

🌍 Environmental Impact

Fossil fuels and climate change:

  • Burning fossil fuels releases carbon dioxide (COβ‚‚) β€” a greenhouse gas that traps heat in Earth's atmosphere, contributing to global warming and climate change.
  • Coal combustion also releases sulfur dioxide (SOβ‚‚) and nitrogen oxides (NOβ‚“), which cause acid rain, damaging ecosystems, buildings and human health.
  • Particulate matter (soot, fine particles) from coal causes respiratory disease.
  • Oil spills during extraction and transport cause catastrophic damage to marine ecosystems.
  • Natural gas is mainly methane β€” a powerful greenhouse gas itself if it leaks during extraction (known as fugitive emissions).
Greenhouse effect: COβ‚‚ and other gases in the atmosphere absorb infrared radiation emitted by Earth's surface, re-radiating it back and warming the planet.

Nuclear power and the environment:

  • No COβ‚‚ produced during operation β€” very low lifecycle carbon emissions.
  • Produces radioactive waste that remains dangerous for thousands of years β€” safe long-term storage is a major challenge.
  • Risk of accidents (e.g. Chernobyl 1986, Fukushima 2011) releasing radioactive material β€” though modern reactors have extensive safety systems.
  • Uranium mining causes habitat destruction and some radioactive dust release.
  • Thermal pollution: warm water released into rivers/sea from cooling can affect aquatic life.
The major trade-off: fossil fuels damage the climate through COβ‚‚; nuclear avoids COβ‚‚ but creates long-lived radioactive waste and carries accident risk.

πŸ”’ Energy Security and Resource Depletion

Energy security: A country's ability to reliably access sufficient, affordable energy to meet its needs, now and in the future.

Non-renewable fuels are unevenly distributed around the world. Countries that lack domestic reserves must import fuel, creating political and economic vulnerabilities:

  • Prices can spike due to geopolitical events (wars, trade disputes, OPEC decisions).
  • Supply disruptions can cause power shortages and economic damage.
  • Countries with large fossil fuel reserves gain significant political power.

Resource depletion concerns: At current consumption rates, proven reserves are estimated to last approximately:

FuelEstimated reserves remainingKey producers
Coal~130–150 yearsUSA, Russia, China, Australia
Oil~50–55 yearsMiddle East, USA, Russia
Natural gas~50–60 yearsRussia, Iran, Qatar, USA
Uranium~130 years (conventional)Kazakhstan, Canada, Australia

Advantages of non-renewables for energy security:

  • Reliable β€” can generate electricity on demand, regardless of weather or time of day (unlike wind/solar).
  • Existing infrastructure is already built and paid for.
  • High energy density β€” small volume of fuel produces large amounts of energy (especially nuclear).
  • Can be stockpiled β€” fuel stored in advance provides buffer against supply disruptions.
The UK's energy policy balances energy security (keeping the lights on reliably) with environmental goals (reducing COβ‚‚). This creates tension between continuing to use non-renewables and transitioning to renewables.

✏️ Worked Examples

Example 1: A coal-fired power station burns 500 kg of coal per second. Coal releases 30 MJ of energy per kilogram. If the power station has an efficiency of 38%, calculate the useful electrical power output in MW.
1 Find the total power input
Power input = energy per kg Γ— mass per second
Power input = 30 Γ— 10⁢ J/kg Γ— 500 kg/s
Power input = 1.5 Γ— 10¹⁰ W = 15,000 MW
2 Apply the efficiency equation
Efficiency = (Useful power output Γ· Total power input) Γ— 100%
38% = (Useful power output Γ· 15,000 MW) Γ— 100%
3 Rearrange and solve
Useful power output = (38 Γ· 100) Γ— 15,000 MW
Useful power output = 0.38 Γ— 15,000 MW
Useful power output = 5,700 MW
βœ… Useful electrical power output = 5,700 MW (5.7 Γ— 10Β³ MW or 5.7 Γ— 10⁹ W)
Example 2: A nuclear power station generates 1,200 MW of electrical power with an efficiency of 33%. (a) Calculate the total thermal power produced in the reactor. (b) How much waste (thermal) power is released to the environment per second?
1 Part (a): Find total thermal power input
Efficiency = Useful power out Γ· Total power in
0.33 = 1,200 MW Γ· Total power in
Total power in = 1,200 MW Γ· 0.33
2 Calculate total thermal power
Total thermal power = 1,200 Γ· 0.33 = 3,636 MW (β‰ˆ 3,600 MW to 2 sig. figs.)
3 Part (b): Find wasted thermal power
Wasted power = Total power in βˆ’ Useful power out
Wasted power = 3,636 MW βˆ’ 1,200 MW = 2,436 MW
4 Energy wasted per second
Power = Energy Γ· Time, so Energy per second = Power Γ— 1 s
Wasted energy per second = 2,436 Γ— 10⁢ J/s Γ— 1 s = 2.44 Γ— 10⁹ J
βœ… (a) Total thermal power β‰ˆ 3,636 MW  |  (b) Wasted power β‰ˆ 2,436 MW (2.44 Γ— 10⁹ J every second)
Example 3: A gas-fired power station uses natural gas with an energy density of 55 MJ/kg. It operates at 55% efficiency and needs to supply 880 MW of electrical power. Calculate the mass of gas burned per hour.
1 Find total power input needed
Efficiency = Useful output Γ· Input
Total power input = Useful power Γ· Efficiency
Total power input = 880 MW Γ· 0.55 = 1,600 MW = 1.6 Γ— 10⁹ W
2 Find energy input needed per hour
1 hour = 3,600 s
Energy per hour = Power Γ— Time = 1.6 Γ— 10⁹ W Γ— 3,600 s
Energy per hour = 5.76 Γ— 10ΒΉΒ² J
3 Find mass of gas burned per hour
Mass = Energy Γ· Energy per kg
Mass = 5.76 Γ— 10ΒΉΒ² J Γ· 55 Γ— 10⁢ J/kg
Mass = 5.76 Γ— 10ΒΉΒ² Γ· 5.5 Γ— 10⁷ = 104,727 kg β‰ˆ 105,000 kg
βœ… Mass of natural gas burned per hour β‰ˆ 105,000 kg (1.05 Γ— 10⁡ kg)
Example 4 (6-mark evaluate question): Evaluate the use of nuclear power as an alternative to coal for generating electricity in the UK. Consider reliability, environmental impact, and energy security.
1 Reliability
Both nuclear and coal can generate electricity on demand, 24/7, regardless of weather β€” a major advantage over wind and solar. Nuclear plants typically run at very high capacity factors (~90%), making them extremely reliable base-load generators.
2 Environmental impact β€” in favour of nuclear
Nuclear produces no direct COβ‚‚ during operation; coal is the most carbon-intensive fuel (~820 g COβ‚‚/kWh vs ~12 g COβ‚‚/kWh for nuclear lifecycle). Replacing coal with nuclear would dramatically cut the UK's greenhouse gas emissions and reduce acid rain (no SOβ‚‚ or NOβ‚“ from nuclear).
3 Environmental impact β€” against nuclear
Nuclear produces radioactive waste that must be safely stored for up to 100,000 years. Risk of catastrophic accidents (Chernobyl, Fukushima) causing widespread radioactive contamination. Decommissioning old plants is extremely expensive.
4 Energy security
Nuclear: uranium is imported (mainly Kazakhstan, Canada, Australia) but the high energy density means large stockpiles can be stored, reducing supply vulnerability. Coal: UK has domestic coal reserves but mining is largely shut down; imported coal is subject to price volatility. Nuclear provides greater long-term energy security due to smaller fuel volumes needed.
βœ… Conclusion: Nuclear is preferable to coal on climate and air quality grounds, and offers comparable reliability and better energy security. The key drawbacks are radioactive waste management, high construction costs, and public concern about safety. Overall, nuclear is widely considered a better option than coal for the UK's low-carbon energy future.

🎲 Practice Questions

Question 1: Which of the following correctly describes why fossil fuels are called "non-renewable"?

Question 2: In a coal power station, what is the correct order of energy transfers?

Question 3: What is the purpose of control rods in a nuclear reactor?

Question 4: A power station has a total power input of 2,000 MW and a useful electrical output of 700 MW. Calculate its efficiency as a percentage. Give your answer to 2 significant figures.

Question 5: Which environmental problem is most directly linked to burning coal in power stations?

πŸ† Challenge Questions

These are exam-style questions worth 4–6 marks each. Work out your answer before revealing the mark scheme.

Challenge 1 [5 marks]: An oil-fired power station burns 200 kg of oil per second. Oil has an energy density of 45 MJ/kg. The power station produces 3,500 MW of electrical power.
(a) Calculate the total power input from burning oil. [2 marks]
(b) Calculate the efficiency of the power station. [2 marks]
(c) State one way that the wasted energy is released to the environment. [1 mark]

Challenge 2 [6 marks]: A student claims: "Nuclear power stations should replace all coal power stations in the UK because they are better for the environment." Evaluate this claim. You should consider: COβ‚‚ emissions, waste products, safety, and reliability.

Challenge 3 [4 marks]: A country currently imports 70% of its natural gas. Explain why this could be a concern for energy security, and suggest two ways the country could reduce this vulnerability.

Challenge 4 [5 marks]: A nuclear power station produces 1,000 MW of electrical power at 32% efficiency. It runs continuously for 365 days.
(a) Calculate the total electrical energy produced in one year, in joules. [2 marks]
(b) Calculate the total thermal energy input from the reactor in one year. [2 marks]
(c) Give one advantage and one disadvantage of nuclear power compared to a natural gas station of equal electrical output. [1 mark]