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How do we get energy from atoms?. Atoms contain huge amounts of energy, and there are two ways in which this energy can be released. nucleus. One way is to split atomic nuclei in a process called nuclear fission . Another way is to join nuclei together in a process called nuclear fusion .
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How do we get energy from atoms? Atoms contain huge amounts of energy, and there are two ways in which this energy can be released. nucleus One way is to split atomic nuclei in a process called nuclear fission. Another way is to join nuclei together in a process called nuclear fusion. electrons The energy that holds particles together in a nucleus is much greater than the energy that holds electrons to a nucleus. This is the why the energy released during nuclear reactions (involving nuclei splitting apart or joining together) is much greater than that for chemical reactions (involving electrons).
Einstein and E = mc2 In 1905, Albert Einstein made the connection between energy and matter. Einstein made the prediction that a small amount of matter could release a huge amount of energy. He expressed this in, what is probably the most famous equation in physics, E = mc2.
Proof of Einstein’s theory In 1933, work by Irène and Frédéric Joliot-Curie proved Einstein’s prediction. They produced a photograph, which showed the creation of two particles (mass) when a particle of light (carrying energy) was destroyed. This was the first proof of the conversion of energy into mass. However, the strongest evidence of Einstein’s theory came with discoveries about nuclear fission and fusion reactions, in which huge amounts of energy are released from atoms.
What is nuclear fission? Nuclear fission occurs when a stable isotope is struck by a neutron. The isotope absorbs the neutron, becomes unstable and then splits apart, releasing large amounts of energy. Unlike natural radioactive decay, fission is not a natural event. Isotopes that undergo fission include uranium-235 and plutonium-239. These isotopes can both be used in nuclear reactors and in nuclear weapons. The fission of 1 kilogram of uranium-235 releases more energy than burning 2 million kilograms of coal!
How is uranium used in nuclear reactors? There are two major isotopes of uranium – 238 and 235. Uranium-238 is the major isotope, but it does not undergo nuclear fission. Only 0.7% of naturally-occurring uranium is uranium-235, which does undergo nuclear fission. Before it can be used as the fuel in nuclear power stations, uranium needs to be enriched until it has 3% uranium-235. The enriched fuel is made into rods which are used in the reactor.
fission + + + + + + neutron neutrons uranium235 uranium 236 strontium90 xenon144 What are the products of fission? When fission of uranium-235 occurs, it splits into two smaller nuclei, known as daughter nuclei. Many possible daughter nuclei may be formed in a fission process. One example is shown below.
90 143 1 235 1 n n U Kr Ba 3 + + + 92 0 36 56 0 Where does the energy come from? Barium and krypton are often the daughter nuclei formed by the fission of uranium-235. The decay equation for this is: In this decay equation, the number of protons and the mass numbers on both sides of the equation balance. However, the particles after decay have slightly less mass than the particles before decay. The mass that has been lost has turned into energy.
Strontium-90 half-life = 28 years Yttrium-90 half-life = 64 hours Zirconium-90 (stable) What happens to the daughter nuclei? Some of the daughter nuclei produced during nuclear fission are stable isotopes, but many are unstable and radioactive. An example of an unstable daughter nucleus produced by nuclear fission is strontium-90. Unstable daughter nuclei will decay into other radioactive isotopes. The decay process continues until a stable isotope is formed. This is called a decay series.
Why do fuel rods have to be replaced? Eventually, the uranium-235 in fuel rods is used up and they have to be replaced. The spent fuel rods contain fission products, many of which are radioactive. Some waste isotopes are short lived, while others will remain radioactive for thousands of years. Plutonium-239 is formed when uranium-238 is bombarded by neutrons. This highly toxic material can be used as a nuclear fuel and to make nuclear weapons. Other significant waste isotopes include strontium-90 and iodine-131, which are easily absorbed by the body. Why does nuclear waste have to carefully controlled?
How is nuclear waste dealt with? Spent fuel rods are sent to a reprocessing plant to recover any usable uranium and plutonium. Many of the isotopes in the remaining waste have no practical purpose and are too dangerous to be released to the environment. Strict regulations are followed when handling and storing nuclear waste. Some waste can be stored in cement inside reinforced steel drums. Long-term storage of nuclear waste is a major problem. Why is it so difficult to find suitable sites?
+ + + + What is a chain reaction? Nuclear fission results in a chain reaction because each time a nucleus splits it releases more neutrons, which can go on and cause more fission reactions to occur... and so on. This is why a chain reaction releases a lot of energy so rapidly. If a chain reaction is uncontrolled, heat builds up very quickly. A chain reaction must be controlled to maintain a steady output of heat.
How are neutrons controlled? For nuclear fission to start in a reactor, a uranium-235 atom must absorb a low speed neutron. High speed neutrons are not as readily absorbed by uranium nuclei. water carrying away heat However, high speed neutrons are released during fission. The reactor’s graphite core slows down the released neutrons so the chain reaction can keep going. control rod fuel rod Control rods made of boron absorb excess neutrons to prevent chain reactions getting out of control. graphite core
Why must chain reactions be controlled? Chain reactions can generate a lot of heat and can be extremely dangerous if they are not properly controlled. This is what happened in 1983 in the world’s worst nuclear power accident at Chernobyl, Ukraine. Most of the control rods had been removed from a reactor during a test. The chain reactions were uncontrolled and generated too much heat. The reactor overheated and caused a steam explosion, which blew the building apart and released a lot of radiation into the environment.
This 4 tonne uranium bomb was similar to one used during the second world war in Hiroshima, Japan. It has the same power as 20,000 tonnes of high explosive. How do nuclear weapons work? Nuclear bombs use uncontrolled chain reactions. For such a chain reaction to occur, there must be a certain amount of uranium atoms. This is called the critical mass. A nuclear weapon works by forcing together two masses of uranium-235 to create a critical mass. This results in uncontrolled chain reactions releasing huge amounts of energy.
What is nuclear fusion? Nuclear fusion is the process which powers the Sun and other stars. In this process, small nuclei join together to form larger nuclei and energy is released. In the Sun’s core, at temperatures of 15 million°C, hydrogen nuclei fuse to form helium nuclei and release vast amounts of energy. A worldwide research programme is being carried out to find ways in which nuclear fusion could be harnessed on Earth as a clean and plentiful source of energy.
+ + + + deuterium tritium fusion helium neutron What are the conditions for nuclear fusion? In nuclear fusion, small nuclei fuse together to form larger nuclei and energy is released. Nuclear fusion happens all the time in stars at very highpressuresand temperatures. These conditions overcome repulsive forces between the nuclei and force them together. Scientists have found it difficult to create the extreme conditions needed to carry out nuclear fusion on Earth. Various fusion reactors are being tested around the world.
How can nuclear fusion be used in the future? Could nuclear fusion help solve energy problems on Earth?
What does a fusion reactor look like? The largest nuclear fusion experimental reactor is JET (Joint European Torus) in Culham, Oxfordshire. Fusion on Earth requires temperatures about six times hotter than the Sun’s core. This vessel uses a magnetic field to trap super-hot hydrogen, which has changed from a gas into a high-energy plasma. The reactor is most efficient as a doughnut shape.
How will a fusion power station work? In a fusion power station, the hydrogen plasma will be ‘squeezed’ to produce helium and high energy neutrons. The energy of the neutrons will then be transferred by a water cooling loop to a heat exchanger to make steam. turbines heat exchanger plasma generator Then, like fossil fuel and fission power stations, the steam will drive turbines to produce electricity. It is hoped that the first fusion power station will be ready and working in about 30 years time.
Why use nuclear fusion? There are many advantages of using fusion energy: • Abundant fuels – Deuterium can be extracted from water and tritium is made from lithium, which is readily available. • Small amounts of fuel– 10 grams of deuterium and 15 grams of tritium could produce enough energy for the lifetime of an average person in an industrialized country. • Clean – No greenhouse or other polluting gases are made. • Safe – No need to keep chain reactions under control. • Less radioactive waste – The products of nuclear fusion are not radioactive, although the reactor walls will absorb neutrons and become radioactive. • No weapons material produced – The products are not suitable for making nuclear weapons.
Glossary • chain reaction – A self-sustaining series of reactions in which the neutrons produced in one fission cause more fission reactions to occur. • control rods – Tubes of material that absorb neutrons and are used to control chain reactions in a fission reactor. • daughter nuclei – The smaller nuclei formed by the fission of a larger nucleus. • fuel rods – Enriched uranium rods that are used to fuel nuclear fission reactors. • nuclear fission – The splitting of a large nucleus, which creates two smaller nuclei and releases a lot of energy. • nuclear fusion – The joining of two smaller nuclei, which makes a larger nucleus and releases a lot of energy.
