P6 nuclear-power-and-fission


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P6 nuclear-power-and-fission

  1. 1. Lesson 6: Nuclear fission and powerWhat 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. 2. Each one of these fission reactions releases many times the energy of anequivalent chemical reaction, such as the burning of a fossil fuel. This means youonly 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 chainreaction 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 tooccur, all the energy can be released from the uranium very quickly. This is whathappens in a nuclear bomb.Nuclear power plants use uranium-235 contained in fuel rods in their reactorcores. Nuclear fission happens in these fuel rods and they become very hot. Acoolant is pumped through the reactor, making it become very hot. This coolantis then used to turn water into steam, which drives the turbines producingelectricity.In a nuclear power station, the energy stored within the uranium fuel rods isreleased at a steady rate by controlling the chain reaction. Control rods aremade from the element boron. They absorb neutrons which prevent thereaction from getting out of control. Moving the control rods in or out of thereactor changes the amount of neutrons that are being absorbed and so caneither 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. 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