Nuclear fission electricity generation

The radioactive wastes associated with nuclear reactors fall into two categories (1) commercial wastes — the result of operating nuclear-powered electric generating facilities and (2) military wastes—the result of reactor operations associated with weapons manufacture, Because the fuel in plutonium production reactors, as required by weapons, is irradiated less than the fuel in commercial power reactors, the military wastes contain fewer fission products and thus are not as active radiologically or thermally. They are nevertheless hazardous and require careful disposal. 

The concept of a nuclear fuel cycle is an old one, almost dating back to the concept of controlled nuclear fission to generate electricity. At the time of the development of the first nuclear power plants, it was generally taken for granted that fuel from power reactors would be reprocessed and that the recovered uranium and plutonium would be recycled. 

In many ways, the design of a nuclear power plant and that of a fossil fuel burning power plant are very similar. In both cases heat from a reaction is used to generate steam. The steam is then used to drive turbines that produce electricity. In a typical fossil fuel power plant, the chemical combustion of coal, oil, or gas generates the heat, whereas in a nuclear power plant, a nuclear fission reaction generates the heat. Because of the hazardous radioactive fuels and fission products present at nuclear power plants, a dense concrete structure is usually built to enclose... 

Nuclear reactor A system in which controlled nuclear fission reactions generate heat energy on a large scale. The heat energy is subsequently converted into electrical energy. 

Similarly, a nuclear-powered electricity generation plant can produce a lot of electricity from a small amount of fuel. Such plants exploit the heat created by fission, using it to boil water and make steam, which then turns the turbine on a generator to produce electricity (Figure 19.11 ). The fission reaction occurs in the nuclear core of the power plant. The core consists of uranium fuel rods—enriched to about 3.5% U-235— interspersed between retractable neutron-absorbing control rods. When the control rods... 

The fast reactor has characteristics which make it likely that most of the uranium atoms in natural uranium can be consumed by the process known as breeding. Consequently, if this type of system can be developed a nuclear energy electricity generating system should operate with a much smaller supply of fuel than in the case of natural uranium or slightly enriched uranium thermal fission reactors. The advantages of the fast reactor are therefore bound up with the cost and availability of uranium ores. 

The energy from nuclear fission is released mainly as kinetic energy of the new, smaller nuclei and neutrons that are produced. This kinetic energy is essentially heat, which is used to boil water to generate steam that turns turbines to drive electrical generators. In a nuclear power plant, the electrical generation area is essentially the same as in a plant that burns fossil fuels to boil the water. 

See also Electric Power, Generation of Environmental Problems and Energy Use Explosives and Propellants Meitner, Lise Military Energy Use, Historical Aspects of Molecular Energy Nuclear Energy Nuclear Energy, Historical Evolution of the Use of Nuclear Fission Fuel Nuclear Fusion Nuclear Waste. 

A nuclear power plant generates electricity in a manner similar to a fossil fuel plant. The fundamental difference is the source of heat to create the steam that turns the turbine-generator. A fossil plant relies on the combustion of natural resources (coal, oil) to create steam. A nuclear reactor creates steam with the heat produced from a controlled chain reaction of nuclear fission (the splitting of atoms). 

Plutonium-239 is a fissile element, and vvill split into fragments when struck by a neutron in the nuclear reactor. This makes Pu-239 similar to U-235, able to produce heat and sustain a controlled nuclear reaction inside the nuclear reactor. Nuclear power plants derive over one-third of their power output from the fission of Pu-239. Most of the uranium inside nuclear fuel is U-238. Only a small fraction is the fissile U-235. Over the life cycle of the nuclear fuel, the U-238 changes into Pu-239, which continues to provide nuclear energy to generate electricity. 

Nuclear reactor development began during the 1940s, following the demonstration of nuclear fission by Fermi in 1942. Since the 1950s, nuclear boilers have been used increasingly for the generation of electrical power. 

Nuclear fission accounted for 13 percent of the electricity generated in the United States in 1985. Plants under construction in 1985 will probably raise the proportion to 20 percent by 1993. However, overexpansion of electrical generating capacity in this country, actual and imagined hazards of nuclear power plants, and negative perceptions of nuclear power by the public have combined to halt commitments to build new plants. New constmction is not expected to resume before the 1990s. 

Nuclear power plants generate electricity in much the same way fossil fuel power plants do. Water is heated to create steam that can be used to turn electricity-generating fur bines. The fundamental difference between these two types of power pi ants i s th e fuel used to h eat th e water. A fossil fuel plant burns fossil fuel, such as coal or petroleum, but a nuclear plant, such as the one shown in this chapter s opening photograph, uses the heat created by nuclear fission to heat the water. 

Diagram of a nuclear fission power plant. Note that the water in contact with the fuel rods is completely contained and radioactive materials are not involved directly in the generation of electricity. The details of the production of electricity are covered in Chapter 19. 

Percentage of electricity generated from nuclear fission reactors in selected countries. 

---