The Nuclear Power Station

Energy from the atom

Deep inside a nuclear power station, the nucleus of an atom is split apart, releasing a huge amount of energy from a tiny amount of fuel. This module covers nuclear fission and the chain reaction, how a reactor is controlled and turns that energy into electricity, and how fission differs from nuclear fusion, the process that powers the Sun.

Fission and fusion words

Five ideas run through nuclear power:

What is nuclear fission?

What happens during nuclear fission in a reactor?

• A large nucleus absorbs a neutron and splits into smaller nuclei, releasing energy
• Two small nuclei join together to form a larger nucleus
• The fuel burns in oxygen like coal or gas
• Electrons are stripped from atoms to make a current

From fission to electricity

Put the stages of how a nuclear power station generates electricity into order.

• A neutron strikes a uranium-235 nucleus
• The nucleus splits, releasing energy and more neutrons
• The released energy heats water to make steam
• The steam drives a turbine
• The turbine turns a generator to produce electricity

Keeping it under control

Each fission releases more neutrons, which can split more nuclei: a chain reaction. Left alone it would run away, so a reactor controls it in two ways. The moderator (often water or graphite) slows the neutrons down so they are absorbed and keep the reaction going. Control rods (often boron) absorb neutrons: push them in to slow the reaction, pull them out to speed it up.

Match each reactor part to its job

Which describe fission?

Select the TWO statements that describe nuclear FISSION.

• It splits a large nucleus into smaller ones
• It can set off a chain reaction
• It joins two small nuclei together
• It is the process that powers the Sun

Fission versus fusion

Both release energy from the nucleus, but they are opposites.

How long must waste be stored?

A radioactive waste isotope has a half-life of 30 years. A sample starts with an activity of 800 Bq. What will its activity be after 90 years? Halve the activity once for each half-life that passes.

Complete the reactor

In a reactor, a slow _____ is absorbed by a large nucleus, which undergoes _____ and splits, releasing energy. The _____ slows the neutrons so the reaction continues, while the _____ absorb neutrons to control it. The heat produces steam that spins a _____.

Where does fusion happen?

Nuclear fusion powers the Sun. Why is it so hard to reproduce on Earth?

• It needs extremely high temperature and pressure to force nuclei together
• There are not enough neutrons available on Earth
• The hydrogen fuel is too rare to find
• It is banned by international law

Run the reactor

Three decisions about a nuclear reactor. Pick the best answer each time.

• The chain reaction is speeding up too much. What should the operators do?
• What is the job of the moderator in the reactor?
• Why do power stations use fission rather than fusion today?

Explain the difference

Explain the difference between nuclear fission and nuclear fusion. Include what happens to the nuclei in each, and one condition or feature of each.

• Fission: a large nucleus splits after absorbing a neutron
• Fusion: two small nuclei join together
• Give a condition or feature for each, such as a chain reaction or extreme temperature and pressure
• Say where each is used: power stations, or the Sun

Fission splits, fusion joins

Top answers keep fission and fusion crisp and separate: fission splits a large nucleus and can run a chain reaction; fusion joins small nuclei and needs extreme temperature and pressure. Never mix them up. And for half-life, just halve the quantity once for every half-life that passes, or read it straight off a decay curve. Split versus join, halve per half-life - top band.