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How Nuclear Power Works

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How Nuclear Power Works A. The objective of nuclear power technology is to control nuclear reactions so that energy is released gradually as heat.

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How Nuclear Power Works B. In nuclear fission, a large atom of one element is split to produce two smaller atoms of different elements.

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Recall the Structure of an Atom Basic Structure of the Atom The atom is comprised of a nucleus, which contains protons and neutrons. Electrons orbit the nucleus held in place by electrostatic forces.

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Nuclear Energy Comes From Fission Neutrons Uranium atom Spit atoms

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Splitting Atoms Releases Neutrons, Creating Heat Heat Neutrons

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Nuclear Fission

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How Nuclear Power Works C. As with plants powered by fossil fuels, the heat energy produced by a nuclear plant is used to boil water and produce steam, which then drives conventional turbo generators.

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How Nuclear Power Works D. Nuclear power plants are always operating unless they are being refueled.

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Thursday (November 17, 2011) Todays Agenda: Journal Question: What is nuclear fission? (1) *Lecture III: Nuclear Fuel (2) Quiz tomorrow on Nuclear Power and Essay Prompt (3) Class Behavior/Norms (4) Homework: Get a textbook and bring it to class tomorrow.

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Nuclear Power Plant Turbines and Generators

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Nuclear Power Plant Turbines Spin to Generate Electricity SteamTurbines spin to generate electricity

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Heat Produces Steam, Generating Electricity Heat Steam produced Steam Turbine Generator Electricity

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Turbines High pressure, intermediate pressure and low pressure turbines required for pressure expansion to vacuum condenser conditions.

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Boiling Water Reactor

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Pressurized Water in the Reactor

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Controlling the Chain Reaction Withdraw control rods, reaction increases Insert control rods, reaction decreases Fuel Assemblies Control rods

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Types of Nuclear Reactors: A. Light-water reactors (LWRs) produce about 85% of the worlds nuclear-generated electricity. (1) 100% in the United States

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Electric Generation Pressurized Reactor

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Electric Generation Boiling Water Reactor

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BWR & PWR Comparison

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From Mass to Energy A. The release of nuclear energy is completely different from the burning of fuels or any other chemical reactions that occur with the use of fossil fuels.

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From Mass to Energy How fossil fuels are used to generate electricity:

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From Mass to Energy B. Nuclear energy involves changes at the atomic level through one of two basic processes: fission and fusion

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From Mass to Energy (Fusion) Basic nuclear fusion reaction: Tritium + Deuterium = Helium + free neutron

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Nuclear Fission versus Nuclear Fusion A. In fission, a large atom of one element is split to produce two smaller atoms of different elements.

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Nuclear Fission versus Nuclear Fusion B. In fusion, two small atoms combine to form a larger atom of a different element. (1) The sun produces helium by fusing hydrogen atoms together.

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Nuclear Fission versus Nuclear Fusion C. The amount of energy released in both nuclear fission and fusion is tremendous.

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Nuclear Power Plant Fuel A. All current nuclear power plants employ the fission (splitting) of uranium-235.

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Nuclear Power Plant Fuel B. The element uranium, which occurs naturally in various minerals in Earths crust, exists in two primary forms, or isotopes: Uranium-238 and Uranium-235.

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Nuclear Power Plant Fuel C. Isotopes of a given element contain different numbers of neutrons, but the same number of protons and electrons.

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Uranium Is Mined and Refined

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Uranium Is Encased in Solid Ceramic Pellets

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Energy Equivalent of One Fuel Pellet 1,780 Pounds of Coal 149 Gallons of Oil 157 Gallons of Regular Gasoline

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Nuclear Fuel and Assemblies 288 Fuel Pellets per Fuel Rod 64 Fuel Rods per Assembly (The number will vary depending on the output of the reactor.) 560 Fuel Assemblies per Reactor Core 10,321,920 Fuel Pellets

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Nuclear Fuel Enrichment A. To make nuclear fuel, uranium ore is mined, purified into uranium dioxide and enriched.

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Nuclear Fuel Enrichment B. Because 99.3% of all uranium found in nature is Uranium-238, enrichment involves separating uranium-235 from uranium-238 to produce a material containing a higher concentration of uranium-235.

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Nuclear Fuel Enrichment C. The technical difficulty of enrichment is the major hurdle that prevents less developed countries from advancing their own nuclear capabilities.

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Nuclear Fuel Enrichment D. Most of the 495 commercial nuclear power reactors operating or under construction in the world today require uranium enriched' in the U-235 isotope for their fuel.

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Enrichment Concentrates the Uranium Isotope

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Production of Plutonium (Pu) in Nuclear Reactors A. 239 Pu is produced in nuclear reactors. B. It also fissions by absorbing a thermal neutron, and on average produces 1/3 of the energy in a fuel cycle. C. 239 Pu is relatively stable, with a half life of 24 thousand years. D. It is used in nuclear weapons. E. It can be used for nuclear reactors.

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Nuclear Fission A. It takes a neutron hitting the nucleus at just the right speed to cause uranium-235 to undergo fission.

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Nuclear Fission B. The fission reaction gives off several more neutrons and releases a great deal of energy.

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Nuclear Fission C. As these neutrons continue to strike other neutrons, more energy is released, with the potential to repeat the process. -A domino effect, known as a chain reaction, may occur.

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Nuclear Bomb When uranium-235 is highly enriched, the spontaneous fission of an atom can trigger a chain reaction. B. In nuclear weapons, small masses of virtually pure uranium-235 or other fissionable materials are forced together so that two or three more atoms undergo fission; each of these in turn triggers two or three more fissions, and so on. C. The whole mass undergoes fission in a fraction of a second, releasing all the energy in one huge explosion.

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The Nuclear Reactor A. A nuclear reactor for a power plant is designed to sustain a continuous chain reaction, but not allow it to amplify into a nuclear explosion. B. Control is achieved by enriching the uranium to only 4% uranium-235 and 96% uranium 238 (more stable).

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The Nuclear Power Plant A. In a nuclear power plant, heat from the reactor is used to boil water to provide steam for driving conventional turbo generators. B. One way to boil water is to circulate it through the reactor. (Identify parts from diagram and understand their functions for your quiz)

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The Nuclear Power Plant

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Nuclear Power Plant Components A. Reactor Coolant: A coolant, usually water, circulates through the reactors core to remove heat (to keep fuels rods and other materials from melting) and to produce steam for generating electricity.

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The Heat Exchanger A. Heat is removed from the reactor vessel by water or another fluid that is pumped through the reactor. B. This fluid passes through a heat exchanger. C. The fluid boils water to produce steam, which runs the electrical generator. D. The steam is condensed again and pumped back to the heat exchanger.

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Heat Exchanger

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Monday (November 21, 2011) Todays Agenda: (1) Journal Question: What element is used to generate nuclear power? (2) What is the difference between nuclear fission and fusion? *Lecture IV: The components of a nuclear reactor. Storage of Nuclear Waste. Nuclear Accidents. Global Warming Revisited.

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This is how a nuclear reactor works:

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The Nuclear Reactor A. A nuclear reactor for a power plant is designed to sustain a continuous chain reaction, but not allow it to amplify into a nuclear explosion. B. Control is achieved by enriching the uranium to only 4% uranium-235 and 96% uranium 238 (more stable).

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The Nuclear Reactor C. The Core (1) Contains 35,000 40,000 long, thin fuel rods, each of which is packed with pellets of uranium oxide fuel. (2) Each pellet is about one-third the size of a cigarette.

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Nuclear Fuel Rods

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Nuclear Reactor in Japan

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The Nuclear Reactor (3) About 97% of the uranium in each fuel pellet is uranium-238, a non- fissionable isotope; the other 3% is uranium-235 which is fissionable. (4) The concentration of uranium-235 in the ore is increased (enriched) from.7% to 3% by removing some of the uranium-238 to create suitable fuel.

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The Nuclear Reactor D. Cadmium Control Rods are moved in and out of the reactor core to absorb neutrons and thus regulate the rate of fission and the amount of power the reactor produces. (metal cadmium absorbs neutrons)

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The Nuclear Reactor (1) As the cadmium control rods are removed, the fission reactions speed up. (2) If the reactor gets too hot, the control rods are moved back in place to slow down the chain reaction.

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The Nuclear Reactor: Depleted Fuel Rods a. After 3-4 years, the concentration of fissionable uranium-235 in a reactors fuel rod becomes too low to keep the chain reaction going or the rod becomes damaged from exposure to ionizing radiation. b. Each year about 1/3 of the spent fuel assemblies in a reactor are removed and placed in large, concrete-lined pools of water at the plant site.

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The Fate of Depleted Fuel Rods c. The water serves as a radiation shield and a coolant. d. After losing some of their radioactivity and cooling down, the spent fuel assemblies are supposed to be shipped to spent fuel- reprocessing plants or to permanent sites for long-term storage of high-level, long- lived radioactive waste.

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Low on Coolant The number 2 reactor at the Three Mile Island (TMI) nuclear plant near Harrisburg, Pennsylvania lost its coolant water because of a series of mechanical failures and human operation errors not anticipated in safety studies. (March 29, 1979)

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Three Mile Island

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A. The reactors core became partially uncovered and about 50% of it melted and fell to the bottom of the reactor. B. Unknown amounts of radioactive materials escaped into the atmosphere, 50,000 people were evacuated, and another 50,000 fled the area on their own.

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Three Mile Island C. Partial cleanup of the damaged reactor, lawsuits, and payment of damage claims has cost $1.2 billion so far, almost twice the reactors $700-million construction cost.

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Plants Around Three Mile Island A. Lack of chlorophyll. B. Deformed leaf patterns. C. Thick, flat, hollow stems. D. Missing reproductive parts. E. Abnormally large.

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Radioactive Waste

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Radioactive Plutonium Storage

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Nuclear Waste Storage Sites e. In the United States all spent fuel rods currently are being stored in concrete-lined pools of water at each of the countrys nuclear power plants until a permanent long-term underground storage facility is developed. f. Many of these plants are reaching their capacity for storing spent fuel.

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Sites of Nuclear Waste Storage

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Yucca Mountain Storage

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Long Term Storage

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Permanent Long Term Storage Sites

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Nuclear waste storage fun facts: 1. After 15-40 years of operation, a nuclear reactor becomes dangerously contaminated with radioactive materials. (It should be decommissioned or retired ) 2. The storage pools typically accommodate 10- 20 years of spent fuel. (Short Term) 3. Long term containment recommendations for storage: -The EPA recommends a 10,000 year minimum, and the National Research Council opted for 100,000 years, to provide protection from the long-lived isotopes from radioactive wastes.

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Problems with waste storage: The capacity of storage pools at U.S. nuclear plants reached 50% by 2004 and will be 100% by 2015.

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The Problem with Reprocessing Plants: A. Some highly radioactive materials can be released into the air, water, and soil. B. There can be diversion of bomb-grade materials by employees or terrorists. C. The U.S. has stopped the development of commercial fuel-reprocessing plants.

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The Nuclear Reactor E. The moderator slows down the neutrons emitted by the fission process so that the chain reaction can be kept going. (1) This is a material such as liquid water (75% of the worlds reactors, called pressurized water reactors), solid graphite (20% of reactors), or heavy water (D 2 0, 5% of reactors).

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The Nuclear Reactor Graphite-moderated reactors, including the ill-fated one at Chernobyl, can also produce fissionable plutonium-239 for nuclear weapons.

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The Life Expectancy of a Nuclear Reactor A. After 15-40 years of operation, a nuclear reactor becomes dangerously contaminated with radioactive materials B. The plant must be decommissioned or retired.

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The Problems with Retiring a Nuclear Power Plant: 1. Dismantling it and storing its large volume of highly radioactive materials in high-level nuclear waste storage facilities (which still do not exist). 2. Putting up a physical barrier and setting up full time security for 30-100 years before the plant is dismantled. 3. Enclosing the entire plant in a tomb that must last for several thousand years.

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The Nuclear Regulatory Commission A. Estimated that there is a 15-45% chance of a complete core meltdown at a U.S. reactor during the next 20 years. B. They also found that 39 U.S. reactors have an 80% chance of either containment failure from a meltdown or a tremendous explosion of gasses inside the containment structures.

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Nuclear Plant Future A. The countries of the world are each planning their own course of nuclear plant development or decline. B. Nuclear power is competitive with fossil fuels. C. It is non-polluting. D. Newer designs are being sought to make them more economical and safer. E. Nuclear fuel reprocessing makes disposal easier. F. Disposal of high level radioactive waste still being studied.

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Breeder Nuclear Fission a Feasible Alternative? A. Some nuclear power proponents urge the development of and widespread use of breeder nuclear fission reactors, which generate more nuclear fuel than they consume by converting non-fissionable uranium-238 into fissionable plutonium-239.

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Problems with Breeder Reactors A. If the safety system of a breeder reactor fails, the reactor could lose some of its liquid sodium coolant, which ignites when exposed to air and reacts explosively if it comes into contact with water. B. This could cause a runaway fission chain reaction and possible nuclear explosion

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Our Nuclear Fuel Demands We are buying highly enriched uranium (20% 235 U) from the former Soviet Union nuclear weapons for 20 years from 1993--2013 Converting it to low enriched uranium (3% 235 U) for reactor fuel. It will satisfy 9 years of US reactor fuel demand. It comes from 6,855 Soviet nuclear warheads so far.

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Radiation: A. A major concern regarding nuclear power is that a large number of the public may be exposed to low levels of radiation, thus elevating their risk of cancer and other disorders. B. Radioactive emissions can penetrate biological tissue.

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Types of Radiation

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Radiation C. The radioactive emissions leave no visible mark, nor are they felt, but they are capable of dislodging electrons from molecules or atoms that they strike.

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Radiation D. In high doses, radiation may cause enough damage to prevent cell division. E. In medical applications, radiation can be focused on a cancerous tumor to destroy it.

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Nuclear Power Plant Accidents A. April 26, 1986: Chernobyl Nuclear Power Plant in Ukraine (then a part of the Soviet Union), had a reactor meltdown. B. At least 50 tons of dust and debris bearing 100-200 million curies of radioactivity in the form of fission products were released in a plume that rained radioactive particles over thousands of square miles, one hundred times the radiation fallout from the bombs dropped on Hiroshima and Nagaski in 1945.

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Boiling Water Reactor: Turning Steam into Power

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A. Water is first circulated through the reactor core, where the water picks up heat while it passes through the fuel assembly. B. The water is eventually converted into steam.

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Boiling Water Reactor: Turning Steam into Power C. The steam then passes through the Main Steam Lines and right to the Turbine Generators. D. From the Turbine Generators the steam travels to a High Pressure Turbine.

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Boiling Water Reactor: Turning Steam into Power E. From the Turbine, the steam passes to moisture separators and onto a few (2 to 3) Low Pressure Turbines. F. All of the Turbines are connected by a drive shaft which is also connected to an electrical generator.

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Boiling Water Reactor: Turning Steam into Power G. After the steam has passed through the turbines it goes to a condenser which cools the steam. H. The water utilized comes from a large body of water like an ocean, lake, or river.

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Boiling Water Reactor: Turning Steam into Power I. The condensed steam is passed to a low pressure feed water heater and from there to feed water pumps to begin the cycle all over again.

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Too Much Heat in the Core A. 7% of the reactors heat comes from radioactive decay in the newly formed fission products. B. In time, the uncontrolled decay could release enough heat energy to melt the material in the core, a situation called a meltdown.

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Too Much Heat in the Core C. The molten material falling into the remaining water could cause a steam explosion. D. To guard against all of this, backup cooling systems keep the reactor immersed in water and the entire assembly is housed in a thick concrete containment building.

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Renewable Sources of Energy Hydroelectric: very useful At 30% 50% of maximum Effects of dams Variable with season and climate Wind power: Need high wind areas on cheap land Solar power: Good for heating Solar cell electricity more costly by a factor of 10 40 square miles equivalent to one nuclear reactor Biomass: Competes with farm use for food Insufficient for total power by a factor of 40 2,000 square miles equivalent of one nuclear reactor Burns to CO 2 Geothermal: Few sites, mostly in the west Produces sulfur and heavy element pollution

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Hydroelectric Power

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What do you think? In contrast to low-level radioactive waste, most high-level radioactive waste is currently (a) Put into steel drums and dumped into the ocean (b) Incinerated (c) Buried in government landfills (d) Recycled (e) Stored at reactor sites

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Correct Answer e. Stored at reactor sites.

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What do you think? Which of the following metals is considered an energy resource? (a) Uranium (b) Cobalt (c) Mercury (d) Copper (e) Palladium

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Correct Answer a) Uranium of course!

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What do you think? All of the following are considered toxic metal pollutants EXCEPT (a) Cadmium (b) Chromium (c) Lead (d) Mercury (e) Potassium

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Correct Answer e) Potassium

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Nuclear Power A. Nuclear power generation does not contribute to global warming. B. The burning of fossil fuels contributes to global warming. Next Slide: Indicators of Global Warming

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Burning of Fossil Fuels

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Signs of Global Warming 1. Carbon dioxide (CO 2 ) levels rise. 2. Mercury climbs (temperatures increase) 3. Oceans warm 4. Glaciers melt 5. Sea levels rise 6. Sea ice thins 7. Wildfires increase 8. Coral reefs disappear 9. Diseases spread 10. Coastlines erode Source -National Geographic

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From Alaska to the Andes A. The world is heating up right now, and fast. B. Globally, the temperature is up 1 degree Fahrenheit over the past century and some of the coldest, most remote spots on Earth have warmed much more. C. Ices is melting, rivers are running dry, and coastlines are eroding, threatening communities.

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Study for your quiz (45 Questions) Quiz will cover : 1. Nuclear Power 2. Green House Gases -There will be an essay question on Nuclear Power. (Make sure you know all of the parts of a nuclear reactor and how they operate from the beginning of the reaction to the production of electricity). -Know legislation and what do you think questions.