—Uranium-235, found in certain rock formations, is mined for use as the fissile material in slow-reaction nuclear power generation. Rare in its natural state, uranium-235 is a nonrenewable resource, although small quantities go a long way. For example, the fission of one pound of uranium releases more energy than burning three million pounds of coal.
Nuclear fission reactors split atoms to release the energy from the nucleus of enriched uranium. In this process, the fuel is placed in rods in the reactor core, and a chain reaction is started by bombarding the fuel with slow neutrons. Heat from the chain reaction is absorbed by the water in the reactor. The water then turns into steam, which, in turn, drives a turbine and a generator to produce electricity. Control rods—made of cadmium or boron—are introduced to slow down or stop the chain reaction.
In fast-reaction nuclear power generation (breeder reactors), high-velocity neutrons cause the fissions, using plutonium or uranium-233. Breeder reactors produce more fuel (enriched uranium and plutonium) than they consume. Thus, fast-reaction nuclear power fuel is considered renewable and sustainable. Nuclear power plants do not release carbon dioxide (a contributor to global climate change) or sulfur dioxide (a contributor to acid rain).
One obstacle to nuclear fission power is that radioactive nuclear waste is generated. High-level radioactive waste—the fission products in the used fuel rods—will be dangerous for the next 100 to 1,000 years. There is no known way to speed the removal of radioactivity from waste. Spent fuel rods are first cooled in large tanks, then encapsulated in ceramic or glass containers. These containers are then placed in stainless steel containers and stored. Very little high-level waste is made by a reactor in a year—enough to occupy a volume of about half a cubic yard.
—including coal, oil, and natural gas—are sources of energy that humans have taken advantage of over thousands of years. About 90 percent of the world’s energy consumption comes from fossil fuels. These were created by the decomposition of primitive organisms, buried in sand and mud, and compressed under the weight of accumulating layers. Over millions of years, temperatures and pressures changed the organic matter into coal, oil, and gas. Deposits of these resources are now found below ground in many areas of the world.
Combusting fossil fuels with oxygen releases water, carbon dioxide, and other substances into the environment. In the case of coal, these substances include sulfur dioxide and nitrogen oxides, which have been shown to be responsible for acid rain. To control these emissions, today’s coal-fired power plants are equipped with scrubbers, filters, collectors, electrostatic precipitators, and other devices. Natural-gas-fired power plants release virtually no sulfur dioxide, but require controls to limit their nitrogen oxide emissions.
Smog is created by a photochemical reaction of sunlight with hydrocarbons, carbon monoxide, and other molecules emitted in car exhaust. To control smog, oil companies have reformulated gasoline, and automakers have designed cars that burn gasoline more cleanly and efficiently, with better filtering mechanisms. The results: tailpipe emissions from the average new car contain 95 percent less hydrocarbons than they did in the 1960s.
Global climate change is another environmental issue linked to fossil fuel use. As a greenhouse gas, the carbon dioxide released in the combustion of fossil fuels traps infrared radiation from the earth that would otherwise radiate out to space. This effect is believed to cause some increase in the temperature of the earth’s atmosphere. Planting more trees is one way to remove more carbon dioxide from the atmosphere, since trees need carbon dioxide as part of photosynthesis. Carbon dioxide and some other greenhouse gases—like methane —come from animals and industry practices.
Oil spills in the oceans can damage coastal and marine plants and wildlife. Double-hulled tankers and rigorous safety practices are highly effective in preventing spills and limiting damage. Since 1990, more than 99.999 percent of oil delivered by tankers to the U.S. reached its destination without incident.