7.9 Nuclear Issues

A free GCSE Physics lesson for AQA (8463) from OBA School: background radiation and dose in sieverts, radon, nuclear waste, accidents, and weighing up radiation risks. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

• Name natural and man-made sources of background radiation and explain why the dose varies
• Use radiation dose in sieverts and millisieverts to compare risks
• Explain why radon gas is a hazard and how it can be reduced
• Explain why nuclear waste must be stored securely for a long time, linking hazard to half-life
• Evaluate the risks and benefits of nuclear power and other uses of radiation

Key words

• Background radiation: Ionising radiation that is always around us, from natural and man-made sources.
• Radiation dose: A measure of the risk of harm to the body from the radiation it absorbs. Unit: sievert (Sv).
• Millisievert (mSv): 1/1000 of a sievert: 1000 mSv = 1 Sv.
• Radon: A radioactive gas that seeps out of rocks such as granite. It emits alpha particles.
• Nuclear waste: Radioactive material left over from nuclear power, medicine and industry. High-level waste comes from used fuel.
• Risk: How likely it is that harm will happen, together with how serious the harm would be.

Background radiation

A Geiger counter clicks even with no source nearby. This background radiation comes from:

• natural sources: radon gas from the ground, rocks and building materials, cosmic rays from space, and radioactive isotopes in food and drink (and so in our own bodies)
• man-made sources: medical X-rays and tracers, fallout from past nuclear weapons tests and accidents, and the nuclear industry

The dose a person gets depends on where they live (areas on granite release much more radon) and what they do: aircrew receive more cosmic rays, and miners and some medical staff are exposed at work.

Key fact: Most background radiation is natural, and the largest single part is usually radon gas.

Radiation dose in sieverts

Radiation dose measures the risk of harm from the radiation absorbed by the body. It takes into account the amount and type of radiation. It is measured in sieverts (Sv); doses are usually small, so millisieverts (mSv) are used: 1000 mSv = 1 Sv.

Worked example: comparing doses

How many chest X-rays give the same dose as one year of average background radiation?
2.7 mSv ÷ 0.02 mSv = 135

Answer: about 135 chest X-rays

Exam tip: The bigger the dose, the bigger the risk of cancer. Very large doses kill cells and cause radiation sickness. Small doses carry a small risk, but the risk is never zero.

Radon gas

Radon is a radioactive gas made when uranium in rocks decays. It seeps out of the ground and can collect in houses, especially in cellars and poorly ventilated rooms. Radon emits alpha particles. When it is breathed in, the alpha particles are emitted inside the lungs, where they strongly ionise cells and increase the risk of lung cancer.

• improve ventilation under the floor and in the house
• seal cracks in floors and walls
• fit a radon sump: a pipe under the floor with a fan that pumps the gas out into the open air before it enters the house

Key fact: Radon is dangerous because it is inside the body when breathed in. The same alpha particles from outside would be stopped by the dead layer of skin.

Nuclear waste and accidents

Used fuel rods are very radioactive and hot. They are kept in deep water tanks for months to cool and to let short-lived isotopes decay. Unused uranium and plutonium can be removed to be used again. What remains contains many isotopes with long half-lives, so it stays dangerous for thousands of years. It is sealed (for example, melted into glass and put in steel containers) and stored securely, and may be buried deep underground in stable rock.

Worked example: how long must waste be stored?

A waste isotope has a half-life of 30 years. How long until its activity falls to about 1/1000 of its starting value?
2¹⁰ = 1024, so about 10 half-lives are needed
10 × 30 = 300 years

Answer: about 300 years

Serious accidents are rare but can spread radioactive material over a wide area: at Chernobyl (Ukraine, 1986) a reactor exploded and burned, and at Fukushima (Japan, 2011) an earthquake and tsunami knocked out cooling, so damaged reactors released radioactive material. People nearby were evacuated and land and food were monitored for years. Modern reactors have extra safety systems, such as automatic shutdown and cooling that works without power.

Weighing up the risks

The harm from radiation depends on the dose, the type of radiation, whether the source is inside or outside the body, and how long the exposure lasts. A source with a short half-life is very active for a short time; one with a long half-life is less active but stays hazardous for much longer.

• no carbon dioxide released while generating electricity; Nuclear power: drawbacks long-lived radioactive waste must be stored securely for thousands of years
• reliable: works whatever the weather; Nuclear power: drawbacks small risk of a serious accident spreading radioactive material
• a little fuel releases a huge amount of energy; Nuclear power: drawbacks very expensive to build and to take apart (decommission) at the end

Exam tip: In “evaluate” questions, give points for and against, use any data you are given (for example, compare doses), and finish with a justified conclusion.

Common mistakes

• Saying most background radiation comes from nuclear power stations. Their share is tiny; most is natural.
• Saying radon is dangerous because it gives off gamma rays. It is an alpha emitter and is dangerous when breathed in.
• Thinking waste with a long half-life is “more radioactive”. It has a lower activity, but stays hazardous for much longer.
• Saying any dose will cause cancer. The risk rises with dose; small doses carry a small risk.

Revision questions

Try these, then check your answers below each one.

Question 1. For most people in the UK, what is the largest source of background radiation? (Choose from: radon gas, nuclear power stations, medical X-rays, cosmic rays.)

Answer: radon gas

Working: Radon gas from rocks gives about half of the average yearly background dose.

Question 2. One long-haul flight gives a dose of 0.05 mSv. How many such flights give the same dose as a yearly background dose of 2.7 mSv?

Answer: 54 flights

Working: 2.7 ÷ 0.05 = 54 flights.

Question 3. True or false? Radon is dangerous mainly because it emits alpha particles inside the lungs when it is breathed in.

Answer: True

Working: True. Inside the lungs, the alpha particles are next to living cells and cause heavy ionisation, increasing the risk of cancer.

Related lessons

• Previous lesson: 7.8 Nuclear Fusion
• Next lesson: 8.1 Vectors and Scalars
• In this chapter: 7.1 Atoms and Radiation
• In this chapter: 7.2 The Discovery of the Nucleus
• In this chapter: 7.3 Changes in the Nucleus

Continue in the full course

This lesson is section 7.9 (AGCPH0709) of our free GCSE Physics course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Physics course.