Nuclear Energy AP Environmental
NUCLEAR ENERGY • When isotopes of uranium and plutonium undergo controlled nuclear fission, the resulting heat produces steam that spins turbines to generate electricity. • The uranium oxide consists of about 97% nonfissionable uranium-238 and 3% fissionable uranium-235. • The concentration of uranium-235 is increased through an enrichment process.
NUCLEAR ENERGY • After three or four years in a reactor, spent fuel rods are removed and stored in a deep pool of water contained in a steel-lined concrete container. Figure 16-17
NUCLEAR ENERGY • After spent fuel rods are cooled considerably, they are sometimes moved to dry-storage containers made of steel or concrete. Figure 16-17
What Happened to Nuclear Power? • After more than 50 years of development and enormous government subsidies, nuclear power has not lived up to its promise because: • Multi billion-dollar construction costs. • Higher operation costs and more malfunctions than expected. • Poor management. • Public concerns about safety and stricter government safety regulations.
Case Study: The Chernobyl Nuclear Power Plant Accident • The world’s worst nuclear power plant accident occurred in 1986 in Ukraine. • The disaster was caused by poor reactor design and human error. • By 2005, 56 people had died from radiation released. • 4,000 more are expected from thyroid cancer and leukemia.
NUCLEAR ENERGY • In 1995, the World Bank said nuclear power is too costly and risky. • In 2006, it was found that several U.S. reactors were leaking radioactive tritium into groundwater. Figure 16-19
NUCLEAR ENERGY • A 1,000 megawatt nuclear plant is refueled once a year, whereas a coal plant requires 80 rail cars a day. Figure 16-20
NUCLEAR ENERGY • When a nuclear reactor reaches the end of its useful life, its highly radioactive materials must be kept from reaching the environment for thousands of years. • At least 228 large commercial reactors worldwide (20 in the U.S.) are scheduled for retirement by 2012. • Many reactors are applying to extent their 40-year license to 60 years. • Aging reactors are subject to embrittlement and corrosion.
Radioactive Wastes Low-level High-level Stored safely at least 10,000 – 240,000 years Most are spent fuel rods from nuclear power plants and wastes from plants which produce plutonium and tritium Usually encased in concrete • Stored safely 100-500 years • From commercial nuclear power plants, hospitals, universities, industries • Stored in steel drums
NUCLEAR ENERGY • Scientists disagree about the best methods for long-term storage of high-level radioactive waste: • Bury it deep underground. • Shoot it into space. • Bury it in the Antarctic ice sheet. • Bury it in the deep-ocean floor that is geologically stable. • Change it into harmless or less harmful isotopes.
Yucca Mountain Underground storage of high-level radioactive wastes
Why Yucca Mountain Yucca Mountain is about 100 miles northwest of Las Vegas, Nevada, on land owned by the federal government.No one lives on Yucca Mountain.The area has a very dry climate — receiving a combined average of about 7.5 inches of precipitation per year. Approximately 95% of this total either runs off, evaporates, or is taken up by the desert vegetation.Yucca Mountain has a very deep water table. If a repository is built at Yucca Mountain, it would be located about 1,000 feet below the surface and 1,000 feet above the water table. So any water that does not run off or evaporate at the surface would have to move down nearly 1,000 feet before reaching the repository and then another 1,000 feet before it reached the water table.The dry climate is an important feature because water is the primary way by which radioactive material could move from a repository
New and Safer Reactors • Pebble bed modular reactor (PBMR) are smaller reactors that minimize the chances of runaway chain reactions. Figure 16-21
New and Safer Reactors • Some oppose the pebble reactor due to : • A crack in the reactor could release radioactivity. • The design has been rejected by UK and Germany for safety reasons. • Lack of containment shell would make it easier for terrorists to blow it up or steal radioactive material. • Creates higher amount of nuclear waste and increases waste storage expenses.
NUCLEAR ENERGY • Nuclear fusion is a nuclear change in which two isotopes are forced together. • No risk of meltdown or radioactive releases. • May also be used to breakdown toxic material. • Still in laboratory stages. • There is a disagreement over whether to phase out nuclear power or keep this option open in case other alternatives do not pan out.