The Physics Question Bank

10 GCSE Physics questions about the nuclear power station, from Foundation to Higher, each with a full worked solution.

Inside a nuclear reactor, uranium nuclei absorb neutrons and split, releasing a huge amount of energy and more neutrons that split more nuclei – a controlled chain reaction. The energy heats water to make steam, which spins a turbine and generator just like in a coal or gas power station. There is no carbon dioxide from the reactor, but the used fuel stays dangerously radioactive for thousands of years.

Course: Combined Science + Separate Physics  |  Tier: Foundation + Higher  |  Topics: Atomic Structure · Energy

Equations you’ll use

Quantity	Symbol	Unit
power	P	watts (W)
energy transferred	E	joules (J)
time	t	seconds (s)
efficiency	–	no unit (decimal or %)
activity	A	becquerels (Bq)

Equations: E = P t  |  efficiency = useful power output ÷ total power input  |  1 GW = 1000 MW = 1 000 000 000 W

Use FIFA for every calculation

• F – Formula: write the equation as it appears on the sheet.
• I – Insert: put in the numbers (convert to standard units first).
• F – Fix: rearrange to make the unknown the subject.
• A – Answer: calculate and always give the unit.

Foundation: aim for Q1–8.   Higher: aim for Q4–10.

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Questions

Q1 (F) A nuclear power station has an electrical power output of 1200 MW. Calculate the energy it supplies in 1 minute.

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Convert first: 1200 MW = 1 200 000 000 W; 1 minute = 60 s
F: E = P t
I: E = 1 200 000 000 × 60
F: E is already the subject
A: 7.2 × 10¹⁰ J

Q2 (F) Nuclear waste contains iodine-131, which has a half-life of 8 days. A sample has an activity of 6400 Bq. Calculate its activity after 32 days.

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Step 1 – number of half-lives: 32 ÷ 8 = 4
Step 2 – halve 4 times: 6400 → 3200 → 1600 → 800 → 400
A: 400 Bq

Q3 (F) The reactor transfers 3400 MW of power to heat the water. The electrical output is 1200 MW. Calculate the efficiency of the power station.

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F: efficiency = useful power output ÷ total power input
I: efficiency = 1200 ÷ 3400
F: efficiency is already the subject
A: 0.352… = 0.35 (35%)

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Q4 (F · S only) Describe what happens when a uranium-235 nucleus undergoes fission. [3 marks]

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• The uranium-235 nucleus absorbs a neutron and becomes unstable.
• It splits into two smaller nuclei (daughter nuclei), roughly equal in size.
• It releases two or three neutrons, gamma rays and energy (mostly as kinetic energy of the products).

Q5 (F/H) Caesium-137 in nuclear waste has a half-life of 30 years. A sample of waste has an activity of 2.4 × 10⁶ Bq. Calculate its activity after 90 years.

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Step 1 – number of half-lives: 90 ÷ 30 = 3
Step 2: 2 400 000 ÷ 2³ = 2 400 000 ÷ 8
A: 300 000 Bq (3.0 × 10⁵ Bq)

Q6 (F/H) 1 kg of uranium-235 can release about 8.0 × 10¹³ J by fission. Burning 1 kg of coal releases about 2.4 × 10⁷ J. Calculate the mass of coal that releases the same energy as 1 kg of uranium-235, in tonnes.

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A: mass of coal = 8.0 × 10¹³ ÷ 2.4 × 10⁷ = 3.3 × 10⁶ kg
1 tonne = 1000 kg, so = 3300 tonnes (2 s.f.)

Q7 (H · HT) Calculate the net decline in the activity of a caesium-137 sample after 150 years, expressed as a ratio. (half-life = 30 years)

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Step 1 – number of half-lives: 150 ÷ 30 = 5
Step 2: fraction left = (½)⁵ = 1/32
A: the activity falls to 1/32 of its starting value – a ratio of 1 : 32 (final : initial).

Q8 (H · S only) Each fission of uranium-235 releases about 3.2 × 10⁻¹¹ J. Calculate the number of fissions each second needed to produce the reactor’s 3400 MW of thermal power, to 2 significant figures.

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Convert first: 3400 MW = 3.4 × 10⁹ W, so 3.4 × 10⁹ J is released every second
A: fissions per second = 3.4 × 10⁹ ÷ 3.2 × 10⁻¹¹ = 1.06 × 10²⁰ = 1.1 × 10²⁰ fissions per second (2 s.f.)

Q9 (H · S only) Explain how a chain reaction happens in a nuclear reactor and how it is kept under control. [4 marks]

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• Each fission releases two or three neutrons.
• These neutrons can be absorbed by other uranium nuclei, causing more fissions – a chain reaction.
• Control rods are lowered into the reactor to absorb some of the neutrons, so that on average only one neutron from each fission causes another fission.
• Lowering the rods further absorbs more neutrons and slows the reaction; raising them speeds it up. This controls the rate of energy release.

Q10 (H) Evaluate the use of nuclear power stations, rather than coal-fired power stations, to generate the UK’s electricity. [6 marks]

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Model answer – points for and against, then a conclusion:
• Nuclear power releases no carbon dioxide while generating, so it does not add to global warming; coal releases CO₂ and sulfur dioxide (acid rain).
• Nuclear fuel releases a huge amount of energy per kilogram (millions of times more than coal), so little fuel is needed.
• Nuclear power is reliable – it can run all the time, whatever the weather.
• But nuclear fuel is still non-renewable.
• It produces radioactive waste, some with very long half-lives, which must be stored safely for thousands of years.
• Nuclear power stations are very expensive to build and to decommission, take a long time to start up, and there is a small risk of a major accident.
• Conclusion: nuclear is much better than coal for reducing carbon emissions and gives a reliable supply, but the long-term problem of waste and the high cost must be weighed against this.

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⚠️ Where students lose marks

• Confusing fission (splitting a large nucleus) with fusion (joining small nuclei).
• Saying control rods “slow down” or “absorb heat” – they absorb neutrons.
• Halving the activity the wrong number of times – work out time ÷ half-life first.
• Saying nuclear power is renewable because it releases no CO₂ – uranium is non-renewable.

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