Chapter 20 Nuclear Energy and the Environment

Nuclear Energy –The energy of the atomic nucleus Nuclear Fission –The splitting of the atomic nuclei Nuclear Fusion –The fusing of atomic nuclei Nuclear Reactors –Devises that produce controlled nuclear fission

History Enrico Fermi (Italian Physicist) –Demonstrated the 1 st human controlled nuclear fission in –Led to the development of nuclear energy to produce electricity Nuclear reactors supply power for –Electricity for homes & industry –Submarines, aircraft carriers and icebreaker ships

Uranium Isotopes Three types of uranium isotopes occur in nature –U % –U % –U % U-235 & U-238 are two radioactive isotopes of uranium. U-235 is the only naturally occurring fissionable material – essential for production of nuclear energy

Fission Reactors Split U-235 by neutron bombardment. Produces: neutrons, fission fragments and heat. The released neutrons strike other U-235, releasing more neutrons, fragments and heat. Neutrons are fast moving, water is used as a “MODERATOR” to slow them down

Fission Reactors As fission occurs, energy is released (HEAT) Major components of a fission reactor: Core, control rods, coolant, reactor vessel Burner Reactors: 1% of uranium is used, 99% end up as waste. The heat produced is used to create steam to run turbine generators that produce electricity. (The reactor has the same function as a boiler in a coal or oil-burning plant)

Fission Reactor Reactor Core – made up of fuel pins – enriched uranium pellets. A minimum fuel concentration is necessary to keep the reactor “CRITICAL” – able to achieve a self-sustaining chain reaction. To control the number of neutrons that cause fission. A control rod is used. It is suspended fully into the core to STOP the fission reaction. B-10B-11Ag-105Ag-107Cd-113 †In-115Hf-174 Hf-176 High neutron absorption rate.

Reactor and Core

Fission Reactor Coolant is cycled through the reactor to remove heat. The rate of generation of heat – MUST EQUAL – the rate at which the heat is carried away. Major nuclear accidents occur when this balance is NOT maintained. Meltdown: a nuclear accident in which the nuclear fuel forms a molten mass that breaches the containment of the reactor, contaminating the outside environment with radioactivity

Sustainability and Nuclear Power Nuclear Radiation occurs when a radioisotope spontaneously undergoes radioactive decay and changes into another isotope 3 types of nuclear radiation: Alpha, Beta, Gamma

Breeder Reactor Uses nuclear fission Designed to produce new nuclear fuel a type of nuclear reactor that utilizes between 40-70% of its nuclear fuel and converts low level nuclear waste into fisible nuclear fuel. Highly radioactive, extremely high heat production.

Fusion Reactor Combining the nuclei of light elements (hydrogen) to form heavier ones (helium) Two isotopes of hydrogen – deuterium and tritium – are used in the fusion reaction to produce helium –Helium 20% of energy released –Neutrons 80% of energy released Temp must be approx. 100 million degrees celcius. Density of the fuel elements must be high One gram of DT fuel = 45 barrels of oil

Nuclear Energy and the Environment Nuclear Fuel Cycle: –the process involved in producing nuclear power from the mining and processing of uranium to controlled fission, the reprocessing of spent nuclear fuel, the decommissioning of power plants and the disposal of radioactive waste –Each part of the cycle is associated with different potential environmental problems

Problems with Nuclear Power Uranium mines & mills produce radioactive waste material. U-235 enrichment produces radioactive waste Environmental review process for the building of nuclear power plants is very cumbersome. The site on which a plant will be built is concerning to neighbors (NIMBY) The US does NOT reprocess spent fuel – disposal is a problem Nuclear waste disposal facilities are extremely controversal (NIMBY) Decommissioning of power plants is relatively new. The lifetime of a plant is several decades. Terrorist Activity

Effects of Radioisotopes Effect Environment in 2 Ways –Emitting radiation –Entering ecological food chains Biomagnification Ex. Ce-137 and reindeer moss (Read pg 420 and outline)

Nuclear Power Plant Accidents Three Mile Island, Pa (1979) Chernobyl (1986)

Three Mile Island March 28, 1979 Harrisburg, Pa Malfunction of a valve, along with human error Radiation released was contained by the “containment structure” – as designed. Small amounts of radiation released into environment On day 3 – at the site – radiation measured 12 mSv/hour. Comparison – Avg. American recieves 2 mSv/yr from natural radiation –mSv = millisievert

Chernobly April 26, 1986 The world found out about the accident two days later, when in Sweden, a nuclear power plant was measuring elevated radiation levels Cooling system failed, due to human error 3 billion people in the Northern Hemisphere received varying amts of radiation Acutely effects the 30-km zone surrounding the site

Chernobyl Major long term affect – Thyroid Cancer Most cancers associated with radiation exposure have an onset 10 – 25 yrs later (this is year 25) Radiation still contaminates soil, vegetation, surface & groundwaters.

Radioactive Waste Management Low-Level Radioactive Waste –Waste materials that contain sufficiently low concentrations or quantities of radioactivity so as not to present a significant environment hazard if properly handled –Solutions from chemical processing, sludges, acids, tools, plastics, glass, etc. –US started with 6 sites – 3 have been closed due to leaks – 1 closed due to finances –2 sites remain open in Washington and S. Carolina

Radioactive Waste Management Transuranic Waste –Radioactive waste consisting of human-made radioactive elements heavier than uranium –Contaminated clothing rags, tools, etc. –Generated from production of nuclear weapons and Cleanup of nuclear weapon facilities –Contain plutonium – ½ life of 250,000 yrs. –Carlsbad, N.Mexico –Isolated at 655m deep in salt beds, geologically stable

Radioactive Waste Management High-Level Radioactive Waste –Extremely toxic nuclear waste, such as spent fuel elements from commercial reactors. –Extremely toxic –Temporary solution –Stored at more than 100 sites in 40 states –Nuclear Waste Policy Act of 1982, 1987,1992,2002 –Yucca Mountain, Nevada – only site evaluation specified in the 1987 Act.