The parts of a nuclear fission reactor

Transcription

1 P2 6.1a Student practical sheet The parts of a nuclear fission reactor Making uranium-235 split and produce energy is actually remarkably easy. The trick is to make it do so in a controllable way. Aim To explore the design of a nuclear fission reactor. Equipment scissors glue stick What you need to do 1 Below is a set of descriptions of what happens inside a nuclear reactor. There is also a set of descriptions of parts of a nuclear reactor. Cut out the 16 rectangles and sort them into eight pairs. 2 Now put each of the pairs of descriptions together with one of the questions, then answer the question. Use the information in the Student Book lesson P2 6.1 to help you. Questions 1 How can control rods slow down the rate of the chain reaction? (2 marks) 2 Why must fuel rods have a big surface area? (2 marks) 3 Why won t U-235 fission very well without a moderator? (2 marks) 4 How is the uranium spread out so that neutrons travel through a moderator before hitting other uranium nuclei? (2 marks) 5 Where does the primary coolant generate steam? (2 marks) 6 What device changes the energy in high-pressure steam into kinetic energy? (2 marks) 7 Which device turns kinetic energy into electrical energy? (2 marks) 8 What properties must the containment vessel have? (2 marks) Control rods: Absorb neutrons Electricity is generated when coils are turned within a magnetic field. Heat exchanger: Removes heat energy from the primary coolant and generates steam Primary coolant: Removes heat from the fuel rods The primary coolant needs to be cooled so that it can return to the reactor core to absorb more heat energy. Turbine: Uses steam to generate kinetic energy Uranium needs to be kept in a number of secure containers. High-pressure steam can make things move. Moderator: Slows fast neutrons down Concrete is a strong shield that both protects equipment and stops most radiation escaping. The neutrons from fissioning U-235 move too fast to make other U- 235 nuclei split To reduce the rate of the nuclear reaction, the number of neutrons must be reduced. Fuel rods: Contain enriched uranium Containment vessel: Contains all the radioactive part of the reactor After the U-235 has fissioned, heat is generated in the fuel rods. Generator: Uses kinetic energy to generate electricity Pearson Education Ltd Copying permitted for purchasing institution only. This material is not copyright free. 245

2 P2 6.1b Student worksheet Making a chain reaction work in a nuclear reactor A chain reaction can be controlled as long as you understand how it works. Part 1: What happens during a chain reaction If a neutron moving at the right speed is absorbed by a uranium-235 nucleus then the nucleus becomes unstable and quickly splits into two. This splitting is called fission. The nucleus gives out a lot of energy and some neutrons. The two parts the nucleus splits into are called daughter products. The speed that the neutrons come out of the nucleus with is too fast for them to be absorbed easily by another uranium-235 nucleus, so if we want to use them they need to be slowed down. This is why uranium-235 is put into fuel rods surrounded by a material called a moderator. The moderator slows the fast neutrons down. Now we can see the basic structure of the core of a nuclear fission reactor. With the moderator in place, neutrons from one fission event are slowed down by the moderator and then trigger another fission event. This is the chain reaction. Sheet 1 of Pearson Education Ltd Copying permitted for purchasing institution only. This material is not copyright free.

3 P2 6.1b Student worksheet Part 2: Slowing the chain reaction down To control the chain reaction, control rods are pushed into the core to absorb neutrons. If there are fewer neutrons about, then there will be fewer fission events so the chain reaction slows down. To speed the process up, the control rods are pulled out. Task Use the information above to label the image below and add descriptions of what is going on for the chain reaction to take place and be controlled. (6 marks) Sheet 2 of 2 Pearson Education Ltd Copying permitted for purchasing institution only. This material is not copyright free. 247

4 P2 6.1c Student worksheet Fuel rods, nuclear fission and enriching uranium Use the information below to answer the questions that follow. Spent fuel rods are highly radioactive when they are removed from the reactor. These spent fuel rods are classified as high-level waste because they emit high levels of radiation and generate heat. A 1000 MW nuclear power station needs about 500 kg of fuel each week, whilst the same energy is generated by burning around tonnes of coal. Because uranium-235 and uranium-238 both have 92 protons, their electron configuration is exactly the same. This means that chemically they are identical. To find out the number of neutrons that are in the nucleus of an isotope you subtract the atomic number from the mass number. In the case of uranium-238 this would mean = 146. So, uranium-238 has 146 neutrons in its nucleus. Uranium-235 can easily capture a neutron moving at the right speed, and this will make it split. Uranium-238 does not do this easily. Naturally occurring uranium consists of about 99% U-238 and 0.7% U-235. After enrichment, the amount of U-235 has been increased by using centrifugal processes. Enriched uranium has about 3% U-235 in it. Although uranium-235 undergoes fission quite easily, it is only when neutrons of the right speed are used. Unfortunately the neutrons from U-235 fission are moving too fast and have to be slowed down by using a moderator between the fuel rods. An alternative fuel, plutonium-239, can be used in nuclear fission reactors, but uranium 235 is much more common. Questions 1 What is the difference between atoms of uranium-235 and uranium-238? (1 mark) 2 Why is uranium-238 not suitable as a fuel? (1 mark) 3 What percentage of naturally occurring uranium is uranium-235? (1 mark) 4 What percentage of enriched uranium is uranium-235? (1 mark) 5 A fuel rod contains many millions of atoms. Why is it that neutrons from the fission of one U- 235 nucleus do not trigger fission in other U-235 nuclei in the same fuel rod? (3 marks) 6 How is the percentage of U-235 increased to produce enriched uranium? (1 mark) 7 Why is it impossible to chemically separate uranium-235 from uranium-238? (1 mark) 8 What is the other nuclear fuel that can be used in fission reactors? (1 mark) 9 How much coal is needed per day to power the same size of power station as a 1000 MW nuclear power station? (1 mark) 10 What sort of waste makes up high-level waste? (1 mark) 248 Pearson Education Ltd Copying permitted for purchasing institution only. This material is not copyright free.

5 P2 6.2a Student practical sheet Reviewing simulations One of the best ways to learn about a subject can be to review other people s presentations. Aim To understand how nuclear fusion works. Equipment access to the Internet What you need to do You will watch a series of videos and simulations using the computer. After you have watched each one, record your comments about the effectiveness of the video using the headings below. Remember, you are assessing these presentations for their suitability for use in teaching people about the fusion process. Clarity was the information clear? Bias do you feel that the information was given a slant that did not convey the whole truth? Accuracy was the science correct and were key items of information included? Text and soundtrack did the supporting text or soundtrack help understanding? Weblinks 1 Nuclear fusion (from Visionlearning website) 2 Nuclear fusion by laser (from Dailymotion website) 3 Deuterium tritium reaction (from YouTube) 4 Sun s energy (from YouTube) 5 The Universe: secrets of the sun 6 Nuclear fusion alternative energy (from YouTube) Using the evidence 1 When you have reviewed the videos, share your views with others in the class. Evaluation 2 Detail your understanding of the nuclear fusion process where deuterium fuses with tritium, using diagrams and text. (6 marks) Pearson Education Ltd Copying permitted for purchasing institution only. This material is not copyright free. 249

6 P2 6.2b Student worksheet Fission versus fusion Nuclear fusion has been in development since the 1950s whilst nuclear fission has been generating electricity in the UK since Use your understanding of nuclear fission and nuclear fusion to produce a table that identifies similarities and differences between the two processes. Include the types of atoms that are involved, waste management in energy production, conditions needed and risks associated with the use of the different technologies, etc. (14 marks) 250 Pearson Education Ltd Copying permitted for purchasing institution only. This material is not copyright free.

7 P2 6.2c Student worksheet Sun facts Below is a series of sets of three statements about the Sun. 1 Read through each set of statements and ring the one that you think is true. (10 marks) 2 Use books or the Internet to check which statements are actually the correct ones. Write a paragraph that puts all of these facts into a logical piece of text. (30 marks) Statement 1 Statement 2 Statement 3 Diameter km km km Surface temperature C C C Mass tons tons tons Age 100 million years 1.3 billion years 4.6 billion years Life expectancy 500 million years 3 billion years 10 billion years Make-up by mass at the moment Almost all hydrogen 72% hydrogen, 26% helium, 2% other 50% hydrogen, 40% helium, 10% uranium Mass of hydrogen fused each second 7 tons 7000 tons tons Element formed by fusing hydrogen helium uranium lithium Temperature of centre of the Sun 1.6 million C 5 million C 15.6 million C What will happen when the Sun gets older? turn into a black hole turn into a protostar turn into a white dwarf Pearson Education Ltd Copying permitted for purchasing institution only. This material is not copyright free. 251

8 P2 6.3a Student practical sheet The big poster Several billion years ago there was the Big Bang. All the rest is history! Aim To gain an understanding of the lives of stars and how they are made. Equipment access to the Internet 4 sheets of A3 paper coloured paper pencil crayons scissors glue stick What you need to do 1 You will be finding information from a variety of sources. Make sure that each piece of information is confirmed by a different source so that you can be fairly sure that it is accurate. 2 Plan and produce a poster on four pieces of A3 paper. They can be used however you like, e.g. a time line or large poster. 3 Find information on the following aspects: How the first stars were formed and how our star is different from the first stars. The life cycle of stars, in particular what happens to stars that are the same size as our Sun, a little bigger than our Sun and a lot bigger than our Sun. The timescale between now and the Big Bang, including significant landmarks in the formation of stars. What forces balance each other so that main sequence stars are stable. (15 marks) 252 Pearson Education Ltd Copying permitted for purchasing institution only. This material is not copyright free.

9 P2 6.3b Student worksheet Our Sun, a history By studying our local star, the Sun, we have been able to find out a lot about the way other stars behave. Answer the following questions through research and use the information to draw a labelled diagram of the Sun. You can use the information on the image here to help you. 1 What is the force that initially brings matter together to form a protostar? (1 mark) 2 Where does the energy come from to heat the hydrogen to make it start the fusion process? (1 mark) 3 What force balances the outwards pressure caused by the fusion process to keep the star stable during its main sequence? (1 mark) 4 What element is formed by the fusion of hydrogen? (1 mark) 5 Where does the energy come from when hydrogen fuses? (1 mark) 6 What fuel source will the Sun start to use when it has finished fusing the available hydrogen? (1 mark) 7 How much hydrogen does the Sun convert into energy every second? (1 mark) 8 In what form does energy from the Sun reach the Earth? (1 mark) 9 The Sun will eventually become a red giant. How large is it likely to become? (1 mark) 10 How old is the Sun and how much longer will its main sequence carry on for? (1 mark) Pearson Education Ltd Copying permitted for purchasing institution only. This material is not copyright free. 253

10 P2 6.3c Student worksheet Fact sheets What happens to a star when it runs out of fuel depends on how big it was during its mainsequence phase. Use the information below and any other research to produce three fact sheets: 1 A white dwarf 2 A neutron star 3 A black hole Your fact sheets should include physical data as well as information about how they are formed and a known or suspected example of one of these objects. Information When a star runs out of hydrogen to fuse together it starts to fuse heavier elements, creating elements up to iron in the periodic table. As this happens the star gets hotter. Exactly what happens next depends on the mass of the star. If the star is like our own Sun it will turn into a red giant star, which expands to many times the size of the original star. Eventually it will collapse in on itself and explode. The outer layers become a gas cloud called a planetary nebula. The core of the sun remains as a white dwarf. When it is young it has a temperature of C, but because there is no fuel to keep it hot, it will slowly cool. A white dwarf may be as heavy as the Sun but the size of the Earth because gravity has finally won the battle and crushed the matter that was a star into incredibly dense material. A teaspoon of white dwarf matter would weigh many tons on the Earth. If the star is more than 1.5 times larger than the Sun the expansion is far greater and the star becomes a red supergiant. When this type of star collapses, it produces a supernova. It is in a supernova that elements heavier than iron are produced. The explosion of the supernova spreads these elements across the galaxies. The core that is left behind becomes a neutron star. The neutron star is even more incredibly dense than a white dwarf. A neutron star can be heavier than our Sun but only 20 km across. A lump of neutron star would weigh a hundred million tons on the Earth. If the star is more than 3 three times heavier than the Sun then again it will go the supernova route but it will leave behind a black hole. A black hole has such a large gravitational field that the escape velocity is greater than the speed of light, so even light cannot escape. (15 marks) 254 Pearson Education Ltd Copying permitted for purchasing institution only. This material is not copyright free.

11 P2 6.4a Student practical sheet Planet building Aim To gain an understanding of how we think planets were formed. Equipment access to the Internet access to other forms of information What you need to do 1 You will explore a variety of sources of information. Using these you will put together a short presentation as part of a small group. Each group will have a different presentation to perform. 2 You can use paper, prepare an on-screen presentation or just give a talk to present the information you have gathered. 3 You will be listening to other presentations. You are to note down the important information. 4 You will be able to ask questions at the end of each presentation. 5 After all of the presentations have finished, you will be asked to summarise the key points that you have noted down. You may need to add others to your list. Presentation titles 1 Where do the elements come from to build planets? (5 marks) 2 Why are the outer planets gas giants? (5 marks) 3 Why is it that not all of the dust and gas that was around when the Sun formed got dragged into the Sun? (5 marks) 4 How old is the Earth? (5 marks) 5 Why is the Earth not covered by craters like the Moon? (5 marks) 6 How was the Moon formed? (5 marks) The presentations need to be made in this order. Pearson Education Ltd Copying permitted for purchasing institution only. This material is not copyright free. 255

12 P2 6.4b Student worksheet No life around the first stars The first stars are thought to have been extremely massive and so very short lived. They will have ended their lives as supernovae and spread vast amounts of the elements in the periodic table across the Universe. The first stars will have been formed almost entirely out of hydrogen because that was all there was about after the Big Bang. It is in the heart of a sun that the elements up to iron are created; then in the violent explosion of a supernova, the heavier elements are created. Use the information above with other information and images to produce a simple display that explains where the elements that make up our planet, and in fact our bodies, come from. (15 marks) P2 6.4c Student worksheet Time line Research the main events since the Big Bang. You must include at least the following key points: 1 When were the first atoms formed? 2 When were the first stars formed? 3 How are elements other than hydrogen formed? 4 When did the first stars form? 5 How old is the Universe? 6 What happened to the first stars? 7 When was the Solar System formed? 8 When did life begin on Earth? (16 marks) 256 Pearson Education Ltd Copying permitted for purchasing institution only. This material is not copyright free.