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 –Devices that produce controlled nuclear fission

Fission Reactors As fission occurs, energy is released. Major components of a fission reactor: Core, control rods, coolant, reactor vessel Burner Reactors: a type of nuclear reactor that consumes more fissionable material than it produces 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.

Radioactive Decay Radiation is a natural process Radioisotope: an isotope of a chemical element that spontaneously undergoes radioactive decay Radioactive decay: radioisotope changes from one isotope to another and emits one or more forms of radiation (radioactive decay chain) –alpha particles; beta particles; gamma rays –each radioisotope has its own characteristic emissions Half-life

Sustainability and Nuclear Power Nuclear Radiation occurs naturally (Alpha, Beta, Gamma) Breeder Reactor: –transforms waste or lower-grade uranium into fissionable material more expensive to build and run produces ingredients necessary for construction of nuclear weapons current technology does not make economical

Deuterium-tritium fusion reaction Hypothetical Conditions needed: –high temperature (100 million ˚C) for plasma state –very dense fuel element –plasma must be contained for a sufficient time to ensure more energy released than supplied to maintain plasma state

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 Waste production –Uranium mines and mills –U-235 enrichment and fabrication of fuel assemblies –handling and disposing of Site selection and construction of nuclear plants are controversial (NIMBY) Limited lifetime Terrorist activity

Exposure to Radiation Natural exposures: –sun –uranium in rocks (granite) –radioisotopes in atmosphere (radon, C-14) Effects of radioisotopes: –Effect environment in two ways Emitting radiation (explosions, bombs, fallout) Entering ecological food chains –radiation absorbed dose –biomagnification

Nuclear Power Plant Accidents Three Mile Island March 28, 1979 Malfunction of a valve and human error Partial core meltdown; radiation released to interior of containment structure PA not prepared

Nuclear Power Plant Accidents Chernobyl April 26, 1986 Cooling system failure (human error) Temp in reactor core melted uranium fuel Cloud of radioactive particles Long-term effects

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 Transuranic Waste –Radioactive waste consisting of human-made radioactive elements heavier than uranium (plutonium) –Contaminated clothing rags, tools, etc. High-Level Radioactive Waste –Extremely toxic nuclear waste, such as spent fuel elements from commercial reactors. –How do we dispose of this waste material?

Nuclear Reactors - U.S. Political sentiment and uncertainty –Three-Mile Island –Chernobyl Nuclear material and weapons (world) Cost

Waste Isolation Pilot Plant Storage of transuranic waste (sealed 2038) Geologically stable Salt easily mined Salt is impermeable and has little or no groundwater flow Salt experiences ductile flow, sealing voids or fissures Future cultures and languages (warnings)

Yucca Mountains May be operating into 24 th Century Communication with future societies –simple message –universal –“what is here is dangerous” –do not want to make others curious