Nuclear fission occurs when an unstable nucleus such as uranium splits after absorbing a neutron, releasing energy and more neutrons. These neutrons can trigger further fissions in a self-sustaining chain reaction. A nuclear power plant controls such a chain reaction to generate heat from uranium fuel rods, using this heat to boil water and drive turbines to produce electricity, without producing greenhouse gases. However, nuclear power also produces long-lasting radioactive waste and risks accidents that can kill people.

1. Lesson 6: Nuclear fission and power
What you need to know:
1. What is nuclear fission.
2. What is a chain reaction.
3. How a nuclear power station works.
Nuclear power is a very big topic in the news at the moment. The reason for this
is because it does not produce greenhouse gases and so does not add to the
problem of global warming. This is not to say that nuclear power is without its
problems!
A normal power station burns fossil fuels such as coal to produce heat. This heat
boils water that drives a turbine producing electricity. In a nuclear power station
the heat to boil the water comes from the decay of radioactive elements, such as
uranium.
Nuclear reactor Turbine Generator Electricity
and boiler
Radioactive elements have very unstable nuclei that decay very easily,
examples are uranium and plutonium. Nuclear fission occurs when a large
unstable nucleus (e.g. uranium) is hit by a neutron, which causes the large
unstable nucleus to split apart into two smaller nuclei, releasing lots of energy
and several neutrons. These neutrons can go on to hit other unstable nuclei,
releasing more energy and neutrons. These neutrons can go on to hit more
unstable nuclei releasing more energy and neutrons. This is called a chain
reaction.
Smaller
nucleus
Energy
Neutron
Unstable
nucleus
Smaller
nucleus
© Studydoctor 2009

2. Each one of these fission reactions releases many times the energy of an
equivalent chemical reaction, such as the burning of a fossil fuel. This means you
only need small amounts of a radioactive element to produce lots of energy.
In your exam you may be asked to explain nuclear fission and what a chain
reaction is. You may also be asked to draw a diagram showing a chain reaction.
If you have a piece of uranium and an uncontrolled chain reaction starts to
occur, all the energy can be released from the uranium very quickly. This is what
happens in a nuclear bomb.
Nuclear power plants use uranium-235 contained in fuel rods in their reactor
cores. Nuclear fission happens in these fuel rods and they become very hot. A
coolant is pumped through the reactor, making it become very hot. This coolant
is then used to turn water into steam, which drives the turbines producing
electricity.
In a nuclear power station, the energy stored within the uranium fuel rods is
released at a steady rate by controlling the chain reaction. Control rods are
made from the element boron. They absorb neutrons which prevent the
reaction from getting out of control. Moving the control rods in or out of the
reactor changes the amount of neutrons that are being absorbed and so can
either speed up or slow down the fission reactions.
In your exam you may be asked how a nuclear power station works.
Nuclear power stations have advantages over fossil fuel power stations:
1. They generate cheap energy.
2. Reduce the need to use fossil fuels.
Nuclear power stations do have disadvantages:
1. They produce nuclear waste that is difficult to dispose of.
2. Nuclear accidents have happened which have killed lots of people.
An example of this is the Chernobyl disaster.
In your exam you may be asked about the advantages and disadvantages of
nuclear power stations.
© Studydoctor 2009

3. Recap:
1. A radioactive element is an atom with an unstable nucleus that decays easily.
2. Nuclear fission occurs when an unstable nucleus is struck by a neutron, splitting the
nucleus into two smaller nuclei, releasing energy and several neutrons.
3. A chain reaction occurs when the neutrons released in fission reaction go on to hit
more unstable nuclei releasing more energy and neutrons.
4. A nuclear reactor works by controlling the chain reaction in nuclear fuel rods, to
release energy which can be used to generate electricity.
© Studydoctor 2009