Nuclear Energy

NUCLEAR ENERGY In 2011, the 104 licensed nuclear power plants in the United States generated about ____% of the country's electricity. Isotopes of uranium and plutonium undergo controlled nuclear _____. 20 fission

Nuclear Fission

Mining Uranium Oxide 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. Uranium mine

Small amounts of radioactive gases Regulating Fission: Moderator: slows neutrons down (LightWaterReactor-water) Control rods: move in/out to absorb neutrons Fuel rods: contain fuel pellets Coolant: usually water, removes heat from core Uranium fuel input (reactor core) Control rods Containment shell Heat exchanger Steam Turbine Generator Electric power Waste heat Hot coolant Useful energy 25%–30% Hot water output Pump Pump Coolant Pump Pump Cool water input Waste heat Figure 16.16 Science: light-water–moderated and –cooled nuclear power plant with a pressurized water reactor. QUESTION: How does this plant differ from the coal-burning plant in Figure 16-13? Moderator Coolant passage Shielding Pressure vessel Water Condenser Periodic removal and storage of radioactive wastes and spent fuel assemblies Periodic removal and storage of radioactive liquid wastes Water source (river, lake, ocean) Fig. 16-16, p. 372

San Onofre nuclear power plant

NUCLEAR ENERGY Spent fuel rods are removed and stored in a deep pool of water contained in a steel-lined concrete container. After spent fuel rods are cooled considerably, they are sometimes moved to dry-storage containers made of steel or concrete.

Wastes have to be stored for at least 10,000 years! Decommissioning of reactor Fuel assemblies Reactor Enrichment of UF6 Fuel fabrication (conversion of enriched UF6 to UO2 and fabrication of fuel assemblies) Temporary storage of spent fuel assemblies underwater or in dry casks Conversion of U3O8 to UF6 Uranium-235 as UF6 Plutonium-239 as PuO2 Spent fuel reprocessing Low-level radiation with long half-life Figure 16.18 Science: the nuclear fuel cycle. QUESTION: Are any parts of the nuclear fuel cycle within 27 kilometers (17 miles) of where you live or go to school? Geologic disposal of moderate & high-level radioactive wastes Open fuel cycle today “Closed” end fuel cycle Wastes have to be stored for at least 10,000 years! Fig. 16-18, p. 373

What Happened to Nuclear Power? After more than 50 years of development and enormous government subsidies, why has nuclear power not lived up to its promise? Multi billion-dollar construction costs. Higher operation costs and more malfunctions than expected. Poor management. Public concerns about safety and strict government safety regulations.

Chernobyl Nuclear Power Plant Accident The world’s worst nuclear power plant accident occurred in 1986 in Ukraine. caused by poor reactor design and human error. (graphite moderator caught fire, reactor exploded) nuclear meltdown sent massive amounts of radiation into the atmosphere (more than the fallout from Hiroshima and Nagasaki) Radiation drifted westward toward Europe thousands of kids have been diagnosed with thyroid cancer, and an almost 20-mile area around the plant remains off-limits Reactor No. 4 has been sealed off in a large, concrete sarcophagus that is slowly deteriorating. 4,000 workers still report there for various assignments.

Three Mile Island Pennsylvania Partial melted down Known as one of a series of mechanical failures. a loss of reactor core coolant. operator errors unforeseen in safety studies Partial melted down Known as one of America's worst nuclear accidents No one died Facility is still in use It is often cited as the reason no new nuclear plant has been built in America in the past 30 years

Fukushima Daiichi Nuclear Power Plant worst accident since Chernobyl Partial meltdowns of the reactors, which released radioactivity in the atmosphere Winds continue to move the fallout to the northwest Evacuation of tens of thousands of nearby residents. Contaminated beef, water, veggies Eventually cover the plant with concrete Could take over a decade to clean up

NUCLEAR ENERGY What are some possible consequences to burying our radioactive waste?

The Future of NUCLEAR ENERGY At least 228 large commercial reactors worldwide (20 in the U.S.) are scheduled for retirement by 2012. Useful operating life of a nuclear power plant is 40 years. Many reactors are applying to extend their 40-year license to 60 years. Nuclear power plants wear out when: reactor's pressure vessels become brittle through neutron bombardment pipes and valves corrode. pressure and temperature changes weaken tubes.

Disposal of Nuclear Waste Scientists disagree about the best methods for long-term storage of high-level radioactive waste: Dismantle and bury it deep underground. Entomb it or physical barrier 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.

New and Safer Reactors? Pebble bed modular reactor (PBMR) smaller reactors that minimize the chances of runaway chain reactions. No need for backup cooling sys Uses Helium as coolant Take used pebbles out and refill with new ones. No need to shutdown to refuel. Breeder nuclear fission reactor Converts uranium-238 into plutonium-239. Then you can use the plutonium for another reactor The coolant employed in a breeder reactor is liquid sodium.