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7.3 Nuclear Reactions (text p 312-325)

7.3 Nuclear Reactions (text p 312-325). You will learn: Fission is a nuclear reaction in which a large nucleus breaks apart, producing two or more smaller nuclei, subatomic particles, and energy.

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7.3 Nuclear Reactions (text p 312-325)

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  1. 7.3 Nuclear Reactions (text p 312-325) You will learn: • Fission is a nuclear reaction in which a large nucleus breaks apart, producing two or more smaller nuclei, subatomic particles, and energy. • Fission is the source of energy for all nuclear power generation used today. The daughter products are often radioactive and are a significant waste disposal problem. • Fusion is a nuclear reaction in which small nuclei combine to produce a larger nucleus. Other subatomic particles as well as energy are released in this process. • Fusion is the source of energy in the Sun. (c) McGraw Hill Ryerson 2007

  2. Nuclear Ractions • Reactions that involve a change in an atom’s nucleus are called nuclear reactions. • A nuclear reaction is a process in which an atoms’s nucleus changes by gaining or releasing particles of energy. • A nuclear reaction can release one, two, or all three types of subatomic particles (p,n,e) as well as gamma rays. • In nuclear reactions, a small change in mass results in a LARGE change in energy • Example: the nuclear fission of 1 g of Uranium-235 release the same amount of energy as obtained from burning about 2 tonnes of coal. (c) McGraw Hill Ryerson 2007

  3. How are Nuclear Reactions different from Chemical Reactions? (c) McGraw Hill Ryerson 2007

  4. Crash Course Video • https://www.youtube.com/watch?v=FU6y1XIADdg (c) McGraw Hill Ryerson 2007

  5. What is Nuclear Fission? • Nuclear fission is the splittingof one heavy nucleus into: • two or more smaller nuclei, • some sub-atomic particles, • and energy. (c) McGraw Hill Ryerson 2007

  6. Nuclear Fission • Why would an atom split apart? (c) McGraw Hill Ryerson 2007

  7. Nuclear Fission • Why would an atom split apart? • Heavy nuclei tend to be unstable due to repulsive forces between the many protons. • In order to gain stability, atoms with heavy nuclei may split into atoms with lighter nuclei. (c) McGraw Hill Ryerson 2007

  8. What good is Nuclear Fission? • Nuclear Fission generates a lot of power (c) McGraw Hill Ryerson 2007

  9. Nuclear Fission recap • A heavy nucleus is usually unstable, due to many positive protons pushing apart. • When fission occurs: • Energy is produced. • Neutrons are released. Albert Einstein’s famous equation E = mc2 illustrates the energy found in even small amounts of matter See pages 313 - 314 (c) McGraw Hill Ryerson 2007

  10. Induced Nuclear Reactions • Natural radioactive decay consists of the release of three types of radiation: alpha, beta and gamma radiation. Induced Nuclear Reactions: Scientists create nuclear reactions by smashing nuclei with alpha, beta and gamma radiation. See pages 314 - 315 (c) McGraw Hill Ryerson 2007

  11. Induced Nuclear Reactions • The rules for writing these equations are the same as earlier nuclear equations: • Mass numbers must equal on both sides of the equation • Charges must equal on both sides of the equation See pages 314 - 315 (c) McGraw Hill Ryerson 2007

  12. Subatomic Particle Symbols (c) McGraw Hill Ryerson 2007

  13. Induced Nuclear Reactions • The main reaction in fission nuclear weapons and in Canadian nuclear power plants: • The uranium-235 nucleus absorbs a neutron briefly becoming uranium-236 which is unstable so it decays into two smaller nuclei releasing 3 neutrons and energy. (c) McGraw Hill Ryerson 2007

  14. Nuclear Fission of Uranium-235 • It is much easier to bombard a nucleus with a neutral neutron than a positive proton to release energy. The induced nuclear fission of uranium-235. This nuclear reaction is the origin of nuclear power and nuclear bombs. See pages 316 - 317 (c) McGraw Hill Ryerson 2007

  15. Nuclear Fission of Uranium-235 • When a stable nucleus of Uranium-235 is struck by a neutron , the nucleus absorbs the neutron. • As a result, the mass number of the nucleus increases by one, creating unstable uranium-236, which then undergoes radioactive decay. • Because the number of protons has not changed, this is still an atom of uranium, just a different isotope. (c) McGraw Hill Ryerson 2007

  16. Nuclear Fission of Uranium-235 • But the new Uranium-236 is very unstable and immediately splits apart. into two smaller nuclei (krypton and barium), releasing threeneutrons and huge quantity of energy. (c) McGraw Hill Ryerson 2007

  17. Chain Reaction • The neutrons released in the induced reaction can then trigger more reactions on other uranium-235 atoms, causing a chain reaction. 369 (c) McGraw Hill Ryerson 2007

  18. Chain Reactions • Once the nuclear fission reaction has started, it can keep going. • This chain reaction can quickly get out of control. • An uncontrolled chain reaction can result in a violent nuclear explosion. Nuclear bombs are created using this concept.

  19. Control Rods • Control Rods are used in nuclear reactors to control the fission rate of uranium and plutonium by absorbing neutrons. • They are composed of chemical elements such as boron, silver, indium and cadmium that are capable of absorbing many neutrons without themselves fissioning. • Control rods can be stuck down into the fuel to absorb neutrons, to slow the reaction down, or withdraw to speed the reaction up. (c) McGraw Hill Ryerson 2007

  20. Chain Reactions • Enrico Fermi used cadmium rods to absorb neutrons in the first reactor and control the chain reaction (c) McGraw Hill Ryerson 2007

  21. Nuclear Energy • Nuclear Energy used to produce power comes from fission. See page 312 (c) McGraw Hill Ryerson 2007

  22. Nuclear Power Plants generate large amounts of electricity • Ontario, Quebec and New Brunswick currently generate nuclear power. • Eg CANDU (CANada Deuterium Uranium) • Deuterium is an isotope of hydrogen with a proton and neutron in its nucleus. • deuterium oxide (heavy water, D2O) is used to moderate fission reactors, to slow neutron absorption. • CANDU reactors are considered safe and effective and are sold throughout the world. (c) McGraw Hill Ryerson 2007

  23. The Bruce Nuclear Generating Station on the shore of Lake Huron, in Ontario (c) McGraw Hill Ryerson 2007

  24. How Nuclear Reactors Work • Fuel produces heat and heat is used to boil water and is turned into steam • Steam turns a turbine • Turbine turns a generator and the generator makes electricity • Electricity goes to the transformers to produce the correct voltage (c) McGraw Hill Ryerson 2007

  25. Nuclear Reactors • The only difference between fossil fuel and nuclear power stations is how the water is heated. Fossil fuel power stations burn their fuel while a nuclear power station uses the fission of uranium to generate heat. • Uranium is a non-renewable energy resource. (c) McGraw Hill Ryerson 2007

  26. Nuclear Waste • CANDU reactors fuel is bundles of rods with uranium pellets. • Each used for 15 months. • Used ones are very radioactive. (c) McGraw Hill Ryerson 2007

  27. Nuclear Waste • They must be stored in water pools for 10years. • Then transferred to shielded storage containers. (c) McGraw Hill Ryerson 2007

  28. Nuclear Energy: Advantages Advantages of using Nuclear Energy: • Nuclear Energy produces fewer greenhouse gas emissions during the production of electricity compared to traditional sources like coal power plants. • Used in medical imaging. • Produce a lot of heat. Heat used to make steam used to power turbines that drive generators that produce electricity. (c) McGraw Hill Ryerson 2007

  29. CANDU Reactors andHazardous Wastes 4. The CANDU reactors are known to be safe and easy to shut down in an emergency. Inside a CANDU reactor. See pages 319 - 320 (c) McGraw Hill Ryerson 2007

  30. Nuclear Power: Disadvantages Disadvantages of Nuclear Energy: • Like fossil fuels, nuclear fuels are non-renewable energy resources. • And if there is an accident, large amounts of radioactive material could be released into the environment. • Waste products of fission are radioactive and remains radioactive and is hazardous to health for thousands of years. (c) McGraw Hill Ryerson 2007

  31. Radioactive Waste Hazardous wastes produced by nuclear reactions are problematic. Used U-235 rods can be hazardous to get rid of as they continue to be radioactive for twenty half-lives (thousands of years). Some rods can be re-used, but others must be stored sealed inside concrete or metal containers underground. See pages 319 - 320 (c) McGraw Hill Ryerson 2007

  32. Nuclear Fusion Nuclear fusion is the joining of two light nuclei into one heavier nucleus. (c) McGraw Hill Ryerson 2007

  33. Nuclear Fusion In the core of the Sun, two hydrogen nuclei join under tremendous heat and pressure to form a helium nucleus. • When the helium atom is formed, huge amounts of energy are released. • Scientists cannot yet find a safe, manageable method to harness the energy of nuclear fusion. Need high pressure and temperature. • So-called “cold fusion” would occur at temperatures and pressures that could be controlled. The fusion of hydrogen nuclei See pages 320 - 321 Take the Section 7.3 Quiz (c) McGraw Hill Ryerson 2007

  34. Check your understanding • What is the standard atomic notation for a proton? • What is the major difference between a chemical and nuclear reaction? • What do you call a nuclear reaction caused by bombarding nucleus with subatomic articles? • What is a chain reaction? • What do CANDU reactors use as fuel? • What happens to used CANDU reactor fuel bundles? • Fission or Fusion: • Used for electrical power generation • Joining of two lighter nuclei • Occurs in our sun\often creates radioactive products (c) McGraw Hill Ryerson 2007

  35. 7.3 Nuclear Reactions (c) McGraw Hill Ryerson 2007

  36. (c) McGraw Hill Ryerson 2007

  37. Nuclear Weapons • Only two nuclear weapons have been deployed in combat—both by the United States against Japan in World War II. • The first event occurred on the morning of 6 August 1945, when the United States Army Air Forces dropped a uranium gun-type device, code-named "Little Boy", on the city of Hiroshima, with a blast yield of 15 kilotons, killing 70,000 people. • The second event occurred three days later when the United States Army Air Forces dropped plutonium implosion-type device, code-named "Fat Man", on the city of Nagasaki, with a blast yield of 21 kilotons, killing 39,000 people. (c) McGraw Hill Ryerson 2007

  38. (c) McGraw Hill Ryerson 2007

  39. Nuclear Meltdowns • On April 26, 1986, the number four reactor at the Chernobyl Nuclear Power Plant in the Ukraine exploded. • considered the worst power plant accident in history, and is one of only two classified as a level 7 event on the International Nuclear Event Scale (the other being the Fukushima, Daiichi disaster in 2011).  • a 30 square kilometer area surrounding the plant, remains relatively uninhabited.  (c) McGraw Hill Ryerson 2007

  40. Nuclear Disaster • The Fukushima Daiichi nuclear disaster was a series of equipment failures, nuclear meltdowns and releases of radioactive materials at the Fukushima, Nuclear Power Plant, following the Tohoku Tsunami on 11 March, 2011.   • It is the largest nuclear disaster since the Chernobyl disaster of 1986 and only the second disaster (along with Chernobyl) to measure Level 7 on the INES. • http://www.processindustryforum.com/hottopics/nucleardisasters (c) McGraw Hill Ryerson 2007

  41. Difference between H bombs and atomic bombs • Fission bombs work by splitting the nucleus of an atom. • When the neutrons or particles from the atom’s nucleus split, some hit the nuclei of nerar by atoms, splitting them too. • The result is a very explosive chain reaction. • Hydrogen bombs start with the same fission reaction that powers atomic bombs. But in atomic bombs, most of the uranium or plutonium goes unused. • Intense pressure causes hydrogen atoms, creating a chain reaction that release more neutrons and splits more atoms. This boosts the hydrogen bomb’s explosive power. • First test of US H-bomb in 1952 produced explosion of 10 kilitonnes • https://www.youtube.com/watch?v=glnHxnOa3t4 (c) McGraw Hill Ryerson 2007

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