Nuclear Energy and the Environment

Current Role of Nuclear Power Plants Worldwide Worldwide 436 power plants 436 power plants 17% of electricity 17% of electricity 4.8% of total energy 4.8% of total energy In US In US 104 power plants 104 power plants 20% of electricity 20% of electricity 8% of total energy 8% of total energy

Nuclear Energy FISSION + energy FUSION neutrons

Fission of U-235 Neutron strikes the U-235 nucleus, producing fission fragments, free neutrons and heat.Neutron strikes the U-235 nucleus, producing fission fragments, free neutrons and heat. Released neutrons may strike another U-235, releasing more neutrons, fission fragments, and energy.Released neutrons may strike another U-235, releasing more neutrons, fission fragments, and energy. Chain reaction develops.Chain reaction develops.

Conventional Nuclear Reactors Split U-235 by neutron bombardment Split U-235 by neutron bombardment Produces neutrons, fission fragments, heat Produces neutrons, fission fragments, heat Starts a chain reaction Starts a chain reaction Create steam that turns a turbine that generates electricity Create steam that turns a turbine that generates electricity Similar to coal or oil burning power plants Similar to coal or oil burning power plants

Coal or Oil Power Plant

Nuclear Power Plant

Control rods absorb neutrons to slow the chain reaction. Made from boron or cadmium

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13 WASTE GENERATED FROM NUCLEAR FISSION: Low Level High Level

Issues with Nuclear Power Uranium mines and mills produce radioactive waste material that can pollute the environment Uranium mines and mills produce radioactive waste material that can pollute the environment U-235 enrichment and fabrication of fuel assemblies also produces waste materials U-235 enrichment and fabrication of fuel assemblies also produces waste materials Site selection and construction is controversial Site selection and construction is controversial Power plant itself is the visible representation of past accidents or partial meltdowns Power plant itself is the visible representation of past accidents or partial meltdowns

Problems with Nuclear Power Handling and disposal of waste Handling and disposal of waste Nuclear power plants have a limited lifetime Nuclear power plants have a limited lifetime Decommissioning is expensive and uncertain Decommissioning is expensive and uncertain Terrorists could collect plutonium for dirty bomb Terrorists could collect plutonium for dirty bomb

How Radioactive Isotopes Reach People

Sources and Doses of Radiation

Radiation Doses and Health When does an exposure become a health hazard? When does an exposure become a health hazard? 5,000 mSv is considered lethal in 50% of people (LD-50) 5,000 mSv is considered lethal in 50% of people (LD-50) 1,000-2,000 mSv sufficient to cause health problems 1,000-2,000 mSv sufficient to cause health problems 50 mSv maximum allowed dose for workers in the industry (30 times average natural background) 50 mSv maximum allowed dose for workers in the industry (30 times average natural background)

Three Mile Island March 28, 1979 near Harrisburg, PA March 28, 1979 near Harrisburg, PA Malfunction of a valve resulted in partial core meltdown Malfunction of a valve resulted in partial core meltdown Intense radiation released to interior of containment structure Intense radiation released to interior of containment structure Small amount of radiation released into environment Small amount of radiation released into environment

Chernobyl April 26, 1986 in Cherbobyl, Soviet Union April 26, 1986 in Cherbobyl, Soviet Union Worst accident in nuclear power generation Worst accident in nuclear power generation Failure in cooling waters Failure in cooling waters Reactor overheated melting the uranium fuel Reactor overheated melting the uranium fuel Explosions removed top of building Explosions removed top of building Fires produced a cloud of radioactive particles Fires produced a cloud of radioactive particles 4,000 death were directly attributed to accident 4,000 death were directly attributed to accident Ultimately responsible for ~16,000-39,000 deaths Ultimately responsible for ~16,000-39,000 deaths

Transuranic Waste Highly radioactive Transported and stored in Carlsbad, NM salt beds Transported and stored in Carlsbad, NM salt beds Salt is 225 million years old and geologically stable Salt is 225 million years old and geologically stable No flowing groundwater and salt is easy to excavate No flowing groundwater and salt is easy to excavate Rock salt flows slowly into mined openings, naturally sealing the waste in 75 to 200 years Rock salt flows slowly into mined openings, naturally sealing the waste in 75 to 200 years

Yucca Mountain Nuclear Waste Depository Nuclear Waste Policy Act of 1982 Nuclear Waste Policy Act of 1982 Initiated high-level waste disposal program Initiated high-level waste disposal program Department of Energy investigated sites Department of Energy investigated sites To be disposed of underground in deep geologic waste repository To be disposed of underground in deep geologic waste repository Yucca Mountain site is no longer considered Yucca Mountain site is no longer considered

27 Nuclear Power Plants Nuclear power plants use water as a cooling agent. After the water is used, it is put back into a water supply at 9-20 o C warmer This 1988 thermal image of the Hudson River highlights temperature changes caused by discharge of 2.5 billion gallons of water each day from the Indian Point power plant. The plant sits in the upper right of the photo — hot water in the discharge canal is visible in yellow and red, spreading and cooling across the entire width of the river. Two additional outflows from the Lovett coal-fired power plant are also clearly visible against the natural temperature of the water, in green and blue.

28 Suffocated fish Low dissolved oxygen Decreased fish population Altered food web Thermal Pollution

Radon Gas – naturally occurring Source? decay of uranium in rocks cracks in the foundation groundwater How to remediate? ventilate a crawlspace 29

Why Nuclear Energy? Not produce potential global warming through release of carbon dioxide Not produce potential global warming through release of carbon dioxide Not cause acid rain Not cause acid rain If breeder reactors are developed (to recycle fuel), the amount of fuel will be greatly increased If breeder reactors are developed (to recycle fuel), the amount of fuel will be greatly increased Argument against Nuclear Energy Based on political and economic consideration Based on political and economic consideration Based on uncertainty of safety issues Based on uncertainty of safety issues Known reserves would be used up quickly Known reserves would be used up quickly May be a path to nuclear weapons May be a path to nuclear weapons

Key Topics for Discussion Half life of radioactive isotopes Disposal of highly radioactive vs low level radioactive waste Enrichment (U-238 to U-235) (naturally, 99.3% and 0.7% abundance) 31

Fusion Reactors Involves combining the nuclei of light elements to form heavier ones Involves combining the nuclei of light elements to form heavier ones Heat energy is released Heat energy is released Source of energy in sun and stars Source of energy in sun and stars In a hypothetical fusion reactor In a hypothetical fusion reactor Two isotopes of hydrogen injected into reactor chamber Two isotopes of hydrogen injected into reactor chamber Products include helium and neutrons Products include helium and neutrons Need T = 100 million degrees Need T = 100 million degrees