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Tuesday April 8, 2014

Learn about nuclear fission, nuclear reactors, and the pros and cons associated with them. Discover how nuclear reactions differ from chemical reactions and the potential for induced nuclear reactions.

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Tuesday April 8, 2014

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  1. Tuesday April 8, 2014 (c) McGraw Hill Ryerson 2007

  2. Science Journal (10 minutes) • Initial Response • What is nuclear fission? • In what countries in the world would you find a nuclear reactor? • Can you list one pro and one con of nuclear reactors? • Why is it easier to crash a neutron into a nucleus than a positive proton into a nucleus to release energy? (c) McGraw Hill Ryerson 2007

  3. 7.3 Nuclear Reactions • Nuclear fission and fusion are processes that involve extremely large amounts of energy. • Fission = the splitting of nuclei • 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 = the joining of nuclei • 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. See page 312 (c) McGraw Hill Ryerson 2007

  4. Nuclear Reactions • Nuclear power plants can generate large amounts of electricity. • Ontario, Quebec and New Brunswick currently generate nuclear power. • Canadian-made nuclear reactors are called CANDU reactors. • CANDU reactors are considered safe and effective and are sold throughout the world • We will discuss this in more detail later The Bruce Nuclear Generating Station on the shore of Lake Huron, in Ontario (c) McGraw Hill Ryerson 2007

  5. Nuclear Fission • Nuclear energy used to produce power comes from fission. • Nuclear fission is the splitting of one heavy nucleus into two or more smaller nuclei, some sub-atomic particles, and energy. • A heavy nucleus is usually unstable, due to many positive protons pushing apart. • To increase their stability, atoms with heavy nuclei may split into atoms with lighter nuclei. • When fission occurs: • Energy is produced. • This energy is used to generate power to support our lifestyle. • Neutrons are released. • Video clip 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

  6. Pro and cons associated with Nuclear Reactors • Nuclear reactors reduce the need for burning fossil fuels (coal and natural gas). • Nuclear reactors produce wastes that need to be stored safely for hundreds of thousands of years. • The physical deterioration of nuclear power plants is a problem in Ontario. • Concern that the nuclear material could be used to make nuclear weapons. (c) McGraw Hill Ryerson 2007

  7. (c) McGraw Hill Ryerson 2007

  8. Nuclear Reactions • Nuclear reactions are different than chemical reactions. • In chemical reactions, mass is conserved, and energy changes are relatively small. • There are no changes to the nuclei in chemical reactions. • In nuclear reactions, the actual nucleus of atoms changes. • Protons, neutrons, electrons, and/or gamma rays can be lost or gained. • Small changes of mass = huge changes in energy (c) McGraw Hill Ryerson 2007

  9. Comparing chemical reactions with nuclear reactions Chemical Reactions Nuclear Reactions Atoms are changed from one isotope into another, producing different elements. Electrons, protons, neutrons, and other subatomic particles may be involved. Electrons may be produced in the nucleus. Nuclear reactions are accompanied by absorption or release of huge amounts of energy. • Atoms are rearranged by breaking chemical bonds and forming new bonds. • Only electrons are involved in bond formation and breaking. • Chemical reactions are accompanied by the release or absorption of relatively small amounts of energy. • Mass is conserved. (c) McGraw Hill Ryerson 2007

  10. Nuclear Equations for Induced Nuclear Reactions • Are there other kinds of nuclear reactions besides the natural radioactive decay (alpha, beta, and gamma) reactions that we have seen so far? • YES! (c) McGraw Hill Ryerson 2007

  11. Nuclear Equations for Induced Nuclear Reactions • Natural radioactive decay consists of the release of alpha, beta and gamma radiation. • Scientists can also create nuclear reactions immediately by smashing nuclei with alpha, beta and gamma radiation. This process is called an induced, or forced, nuclear reaction. • Figure 7.19 When a nitrogen-14 nucleus is bombarded by an alpha particle, a flourine-18 nucleus is produced, which decays into oxygen-17 and a proton. See pages 314 - 315 (c) McGraw Hill Ryerson 2007

  12. Nuclear Equation The above figure can be written in several possible ways. For example: (c) McGraw Hill Ryerson 2007

  13. Subatomic Particle Symbols • Remember Alpha is represented as: • A hydrogen-1 nucleus can be represented either as or as a proton, because a proton and a hydrogen-1 nucleus are the same thing. Mass # Atomic number • The proton notation shows that a proton has an atomic number of 1(1 proton) and a mass number of 1(1proton + 0 neutrons). (c) McGraw Hill Ryerson 2007

  14. Subatomic Particle Symbols • A neutron is symbolized meaning that it has an atomic number (charge) of 0 (0 protons) and a mass number of 1 (0 protons + 1 neutron). (c) McGraw Hill Ryerson 2007

  15. Rules for writing Nuclear Equations • The rules for writing these equations (induced nuclear reactions) are the same as earlier nuclear equations ( radioactive decay). • Mass numbers must equal on both sides of the equation • Charges (represented by atomic numbers) must equal on both sides of the equation Mass#: 1 + 235 = 236 92 + 141 + (3 x 1) = 236 Charges/atomic#: 0 + 92 = 92 36 + 56 + (3 x 0) = 92 (c) McGraw Hill Ryerson 2007

  16. Nuclear Fission of Uranium-235 • It is much easier to crash a neutron into a nucleus than a positive proton into a nucleus to release energy. • Why? • Because it takes a tremendous amount of energy for an alpha particle (with a charge of 2+) to collide with a nitrogen-14 nucleus (with a charge of 7+). The repulsion between the positive charges is very great. • Whereas, a neutron (0 negative charge) colliding with a nucleus takes much lower energy and has 0 positive charge to repel it. See pages 316 - 317 (c) McGraw Hill Ryerson 2007

  17. Neutron colliding with a nucleus • Most nuclear fission reactors and weapons use this principle. • A neutron, , crashes into an atom of stable uranium-235, the nucleus absorbs the neutron. • The mass number of the nucleus increases by one (ie. 235 to 236) creating unstable uranium-236 (number of protons has not changed, this is still an atom of uranium-it is just a different isotope). • which then undergoes radioactive decay. (c) McGraw Hill Ryerson 2007

  18. The newly formed and very high-energy uranium-236 is highly unstable and immediately splits apart into • atoms of krypton and barium • three neutrons • huge quantities of energy. The induced nuclear fission of uranium-235. This nuclear reaction is the origin of nuclear power and nuclear bombs. (c) McGraw Hill Ryerson 2007

  19. (c) McGraw Hill Ryerson 2007

  20. Lise Meitner- (1878-1968) • 1939, Austrian physicist Lise Meitner was the first to explain how nuclear fission occurs. • Meitner was Jewish, and this was not a good thing to be in 1930s Germany! When World War Two began in 1938, Meitner fled just in time to escape Hitler's death camps. She travelled to Sweden and continued her research although she had little equipment or resources. • Meitner realized that the total mass of the particles produced when the uranium nucleus split was less than that of the original nucleus. She soon realised it had the potential to unleash unimaginable amounts of energy. (c) McGraw Hill Ryerson 2007

  21. Lise Meitner • Albert Einstein had also been following Meitner's work and in 1939 he wrote a letter to the American president, Franklin D. Roosevelt, explaining what it meant. • Einstein feared that Germany would make an atomic bomb before the allies. • This led directly to the setting up of the 'Manhattan' project that developed the first atomic bomb only six years later. • Meitner always regretted her part in the creation of the atomic bomb, also called the 'destroyer of worlds'. • She refused to work on the project. • When she heard about Hiroshima she was devastated. • She was passed over for the nobel prize-her colleague Otto Hahn received it. • 1992 - the element 109, meitnerium was named in her honour (c) McGraw Hill Ryerson 2007

  22. Summary (c) McGraw Hill Ryerson 2007

  23. Practice problem • Which nuclear symbol correctly completes the following nuclear reaction? (c) McGraw Hill Ryerson 2007

  24. Questions • What is the indicated daughter nucleus? (c) McGraw Hill Ryerson 2007

  25. Science Journal (10 minutes) • Considered Response • What is nuclear fission? • In what countries in the world would you find a nuclear reactor? • Can you list one pro and one con of nuclear reactors? • Why is it easier to crash a neutron into a nucleus than a positive proton into a nucleus to release energy? (c) McGraw Hill Ryerson 2007

  26. Wednesday April 9, 2014 (c) McGraw Hill Ryerson 2007

  27. Science Journal (10 minutes) • Initial Response • What does CANDU stand for? • What is nuclear fusion? • How do you control a nuclear fission reaction so that it will not go out of control? • Where does fusion occur and under what conditions? (c) McGraw Hill Ryerson 2007

  28. Chain Reactions • Once the nuclear fission reaction has started, it can keep going. • The neutrons released in the induced reaction can then trigger more reactions on other uranium-235 atoms. • If one fission reaction produces 3 neutrons, these 3 neutrons can cause 3 additional fissions. • If those 3 fissions release 9 neutrons, those 9 neutrons could then produce nine more fissions and so on. Nuclear Chain Reaction. The number of fissions and the amount of energy released can increase rapidly and lead to a violent nuclear explosion. See page 318 (c) McGraw Hill Ryerson 2007

  29. How do you control the Chain reaction so that it will not get out of control? • This chain reaction can quickly get out of control. • Italian physicist Enrico Fermi, working with colleagues in the United States, realized that materials that could absorb some neutrons could help to control the chain reaction. • An uncontrolled chain reaction can result in a violent nuclear explosion. • Nuclear bombs are created using this concept. • Nuclear reactors have complex systems to ensure the chain reaction stays at safe levels. • Keeping the chain reaction going, while preventing it from getting out of control, requires precise monitoring and continual adjusting. (c) McGraw Hill Ryerson 2007

  30. Fukushima • Much of the concern about nuclear power plants focuses on the risk of losing control of the nuclear reactor, which could result in ----- • The accidental release of harmful levels of radiation. • A violent nuclear explosion • For example, the Japanese Fukushima Diichi nuclear disaster. 3min • video (c) McGraw Hill Ryerson 2007

  31. Other examples • Three Mile Island in the USA • Video • 4:30 • Chernobyl (Ukraine) • Video • 4:30 (c) McGraw Hill Ryerson 2007

  32. CANDU Reactors andHazardous Wastes • Canada’s nuclear research into the safe use of nuclear reactions has resulted in the creation of CANDU reactors. • CANDU –” Canadian deuterium uranium” reactor • Deuterium (symbol D or 2H, also known as heavy hydrogen/heavy water) is one of two stable isotopes of hydrogen. • It has a natural abundance in Earth's oceans of about one atom in 6,420 of hydrogen • Deuterium is an isotope of hydrogen-1 that is twice as heavy as it has both a proton and a neutron in its nucleus. • They use heavy water as both moderator and coolant See pages 319 - 320 (c) McGraw Hill Ryerson 2007

  33. CANDU Reactors andHazardous Wastes • CANDU reactors are found in various countries around the world. • Canada, South Korea, China, India, Argentina, Romania and Pakistan • The design of the CANDU reactor is among the safest in the world • The reactors are easy to shut down in an emergency. Inside a CANDU reactor. The reactor core produces heat as a result of reactions like the following: (c) McGraw Hill Ryerson 2007

  34. Nuclear power plants and fossil –fuel burning power plants are similar in that both produce a lot of heat. • The heat is used to boil water and generate steam, which then drives the turbines that produce electricity. • A turbine is a large rotating device that can be forced to turn when steam is applied to it. (A turbine drives a generator that produces electricity). • You tube clip • Heat energy produced turns electricity-generating turbines. (c) McGraw Hill Ryerson 2007

  35. Hazardous Wastes • The fuel used to produce heat in a CANDU reactor is in the form of bundles of rods containing uranium pellets. • Hazardous wastes produced by nuclear reactions are problematic. • Some waste products, like fuel rods, can be re-used. • Some countries reprocess used nuclear fuel to recover material to use in new reactor fuel. • Each CANDU fuel bundle is about 50cm in length and 10cm in diameter and generates about 1 million kW/h of electricity during its time in the reactor – about 15 months. (c) McGraw Hill Ryerson 2007

  36. Hazardous Wastes • Some products are very radioactive, however, and must be stored away from living things. • Most of this waste is buried underground or stored in concrete. • For example, at the Pickering Ontario, nuclear power plant they have containers that hold nuclear waste. • About 40 new containers are added each year and each container is designed to last 50 years while a long term storage solution is sought. • Most countries, including Canada, are planning to put used nuclear fuel in metal containers that would be placed deep underground in stable rock formations. (c) McGraw Hill Ryerson 2007

  37. Hazardous Wastes • The radioactivity of the used fuel bundles decreases significantly with time. However, • It will take 20 half-lives (thousands of years) before the material is safe. It must be isolated from the natural living environment. (c) McGraw Hill Ryerson 2007

  38. Nuclear Fusion • Nuclear fusion = joining of two light nuclei into one heavier nucleus. • 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. • The nuclear equation for fusion in the sun and in fusion reaction experiments is: The fusion of hydrogen nuclei In the sun, a fusion reaction occurs between hydrogen-2 and hydrogen-3. When these combine a huge about of energy is released. See pages 320 - 321 (c) McGraw Hill Ryerson 2007

  39. Nuclear Fusion • Researchers have worked for over half a century to find technology that will allow us to extract energy from fusion reactions. • One of the difficulties is achieving the high temperatures and pressures needed. • Another is simply finding a way to contain a reaction that is so hot that no vessel can hold it without being destroyed. • Scientists cannot yet find a safe, manageable method to harness the energy of nuclear fusion. • So-called “cold fusion” would occur at temperatures and pressures that could be controlled. (c) McGraw Hill Ryerson 2007

  40. Nuclear Fusion-Update • What’s happening today? Video • National Ignition Facility at Lawrence Livermore National Laboratory in California A cutaway view of a gold cylinder known as a hohlraum, with a spherical fusion fuel capsule gleaming inside. The hohlraum measures about half an inch (1 centimeter) in height, and the capsule is about a tenth of an inch (2mm) in diameter. Beams of light from 192 lasers are directed at the capsule to cause an implosion. (c) McGraw Hill Ryerson 2007

  41. Comparison of Fission and Fusion Reactions Take the Section 7.3 Quiz (c) McGraw Hill Ryerson 2007

  42. Science Journal (10 minutes) • Considered response • What does CANDU stand for? • What is nuclear fusion? • How do you control a nuclear fission reaction so that it will not go out of control? • Where does fusion occur and under what conditions? (c) McGraw Hill Ryerson 2007

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