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

How are Nuclear Reactions different from Chemical Reactions? no changes to the nuclei   mass is conserved energy changes are relatively small nucleus of atoms changes by gaining or releasing particles or energy protons, neutrons, electrons, and/or gamma rays can be lost or gained Small changes of mass = huge changes in energy Eg nuclear fission of 1 g of uranium -235 releases the same amount of energy as obtained from burning about 2 tonnes of coal. (c) McGraw Hill Ryerson 2007

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

What is Nuclear Fission? Nuclear fission is the splitting of one heavy nucleus into: two or more smaller nuclei, some sub-atomic particles, and energy. Heavy nuclei tend to be unstable due to repulsive forces between the many protons. In order to increase their stability, atoms with heavy nuclei may split into atoms with lighter nuclei. (c) McGraw Hill Ryerson 2007

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

Why would an atom split apart? 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 increase their stability, atoms with heavy nuclei may split into atoms with lighter nuclei. (c) McGraw Hill Ryerson 2007

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

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

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. Scientist make nuc unstable by smashing it with a, B or gamma The difference is that the alpha particle is now a reactant, nt a product. The diagram can be written as a nuclear reaction See pages 314 - 315 (c) McGraw Hill Ryerson 2007

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 Scientist make nuc unstable by smashing it with a, B or gamma The difference is that the alpha particle is now a reactant, nt a product. The diagram can be written as a nuclear reaction See pages 314 - 315 (c) McGraw Hill Ryerson 2007

Subatomic Particle Symbols A hydrogen-1 nucleus can be written as 11H or as a proton, 11p because a proton and an hydrogen-1 nucleus are the same thing. Proton notationshows that a proton has an satomic number of 1 (1 proton)and a mass number of 1 (1proton + O neutrons) (c) McGraw Hill Ryerson 2007

Induced Nuclear Reactions The main reaction in fission nuclear weapon 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. Scientist make nuc unstable by smashing it with a, B or gamma The difference is that the alpha particle is now a reactant, nt a product. The diagram can be written as a nuclear reaction See pages 314 - 315 (c) McGraw Hill Ryerson 2007

Nuclear Fission of Uranium-235 It is much easier to crash a neutral neutron than a positive proton into a nucleus to release energy. When a nucleus of Uranium-235 is struck by a neutron, the nucleus absorbs the neutron. As a result, the mass number of the nucleaus increase by one. Because the number of protons has not changed, this is still an atom of uranium, just a different isotope. But the new Uranium-236 is very unstable andimmdediatey splits apart into two smaller nucl, relaseing serveral neutrons and a lot of energy. The released neutrons trigger more fission reacions. 369….chain reaction 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

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. When a nucleus of Uranium-235 is struckby a neutron, the nucleus absorbs the neutron. As a result, the mass number of the nucleaus increase by one. Because the number of protons has not changed, this is still an atomof uranium, just a different isotope. But the new Uranium-236 is very unstable andimmdediatey splits apart into two smaller nucl, relaseing serveral neutrons and a lot of energy. The released neutrons trigger more fission reacions. 369….chain reaction See pages 316 - 317 (c) McGraw Hill Ryerson 2007

Nuclear Fission of Uranium-235 But the new Uranium-236 is very unstable and immediately splits apart into two smaller nuclei, releasing several neutrons and a lot of energy. After several steps, atoms of krypton and barium are formed, along with the release of three neutrons and huge quantities of energy. (c) McGraw Hill Ryerson 2007

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

Once the nuclear fission reaction has started, it can keep going. Chain Reactions Once the nuclear fission reaction has started, it can keep going. The neutrons released can then trigger more reactions on other uranium-235 atoms. This process where one reaction starts the next is called a chain reaction. This chain reaction can quickly get out of control. This danger is managed using materials that absorb neutrons. Nuclear reactors have complex systems to ensure the chain reaction stays at safe levels. An uncontrolled chain reaction can result in a violent nuclear explosion. Nuclear bombs are created using this concept. Nuclear Chain Reaction. Once a nuclear fission reaction begins, it can initiate the next reaction, creating a chain reaction. The number of fissions and energy being released can increase rapidly and lead to a violent nuclear explosion.. How to keep the chain reaction from getting out of hand? Enrico Fermi received Nobel Prize I physics in 1938 for his work on induced radioactivity. He realized that materials that absorb neurtons could be used to control the chain reaction. See page 318 (c) McGraw Hill Ryerson 2007

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

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

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) moderator and its use of (originally, natural) uranium fuel. CANDU reactors are considered safe and effective and are sold throughout the world. Deuterium is an isotope of Hydrogen-1 that is twice as heavy asit has both a proton and a neutron. (c) McGraw Hill Ryerson 2007

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

CANDU reactors fuel is bundles of rods with uranium pellets How does it work? CANDU reactors fuel is bundles of rods with uranium pellets Each used for 15 months Used ones are very radioactive They must be stored in water pools for 10years Then transferred to shielded storage containers (c) McGraw Hill Ryerson 2007

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

CANDU Reactors and Hazardous Wastes 5. The CANDU reactors are known to be safe and easy to shut down in an emergency. Inside a CANDU reactor. Canada, South Korea, China, India, Argentina, Romania and Pakistan Produce a lot of heat. Heat used to make steam used to power turbines that drive generators that produce electricity See pages 319 - 320 (c) McGraw Hill Ryerson 2007

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. Sun uses fusion. Nuc Reaction use fission. (c) McGraw Hill Ryerson 2007

Hazardous wastes produced by nuclear reactions are problematic. 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. Canada, South Korea, China, India, Argentina, Romania and Pakistan Produce a lot of heat. Heat used to make steam used to power turbines that drive generators that produce electricity 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

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

The fusion of hydrogen nuclei 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 In the sun, fusion occurs between Hydo=rogen-2 and hydrogen-3  huge energyradiation to us as light and heat. High Temperature and pressure needed. Container would melt. See pages 320 - 321 Take the Section 7.3 Quiz (c) McGraw Hill Ryerson 2007

Check your understanding What is the standard atomic notation for a proton? What is the majory 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

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