Electrical Energy from Nuclear Fission

Uraniuin-235 is capable of sustaining a chain reaction, but it makes up only 0.7% of all naturally occurring uranium. Therefore, it is not a very satisfactory source of nuclear fuel (Fig. 20.16). An alternative is the plutonium isotope, Pu, produced from the most abundant uranium isotope (Equations 20.4 to 20.6). Pu has a long half-life (24,360 years) and is fissionable. It has been used in the production of atomic bombs and is also used in some nuclear power plants to generate electrical energy. It is made in a breeder reactor, the name given to a device whose purpose is to produce fissionable fuel from nonfissionable isotopes. 

How do the products of a fission reaction compare with the reactants  

Except what is produced by hydroelectric plants located on major rivers, most electrical energy comes from generators driven by steam. Traditionally, the steam comes from boilers fueled by oil, gas, or coal. The fast-dwindling supplies of these fossil fuels, and the uncertainties surrounding the availability and cost of petroleum from the countries where it is abundant, have turned attention to nuclear fission as an alternative energy source. 

Liquid water under high pressure (carries heat to steam generator) 

Condenser (steam from turbine is condensed by river water) 

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Deriving electrical energy from nuclear fission produces almost no atmospheric pollutants, such as carbon dioxide, sulfur oxides, nitrogen oxides, heavy metals, and airborne particulates. Although not discussed in the text, there is also an abundant supply of fuel for nuclear fission reactors in the form of plutonium-239, which can be manufactured from uranium-238. Use the keyword Breeder Reactor on your Internet search engine to learn about how this is so. 

Section 20.11 Electrical Energy from Nuclear Fission... 

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. 

Hafnium has only a few applications. Probably its most important use is in nuclear power plants. A nuclear power plant is a facility where energy released from nuclear fission reactions is used to generate electricity. 

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 fission energy for the commercial production of electricity has been with us since the 1950s. In the United States, about 20 percent of all electrical energy now originates from 103 nuclear fission reactors situated throughout the country. Other countries also depend on nuclear fission energy, as is shown in Figure 19.13. Worldwide, there are about 442 nuclear reactors in operation and 29 currently under construction. 

A nuclear reactor is a device in which nuclear chain reactions are initiated, controlled, and sustained at a steady rate. Nuclear reactors are used for many purposes, but the most significant current uses are for the generation of electrical power and for the production of plutonium for use in nuclear weapons. Currently, all commercial nuclear reactors are based on nuclear fission. The amount of energy released by one kg 235U is equal to the energy from the combustion of 3000 tons of coal or the energy from an explosion of 20,000 tons of TNT (Trinitrotoluene, called commonly dynamite). 

The third fact is that spent nuclear fuel is not waste. Spent nuclear fuel contains 2% to 3% waste, but is about 97% recoverable uranium and plutonium. Each bundle has the potential electric energy equivalent of more than 10 million barrels of oil. High-level nuclear wastes consist of fission products and actinides that are extracted from spent fuel, but not saved for commercial use or research. Spent fuel may be temporarily stored until it is reprocessed to separate the waste from the valuable plutonium and uranium. The remaining glassified waste will then be permanently entombed. 

Although, at the end of the twentieth century, the accident at Chernobyl has made the use of fission reactors (eventually breeders) politically unacceptable, it must be recalled that our society can be run on electricity from nuclear reactors, with hydrogen as the storage medium and fuel for transportation. Fail-safe reactor schemes have been described in the literature. The eventual choice between nuclear energy and renewables will be one of cost. 

Nuclear fission is a process in which the nucleus of an atom splits, usually into two pieces. This reaction was discovered when a target of uranium was bombarded by neutrons. Eission fragments were shown to fly apart with a large release of energy. The fission reaction was the basis of the atomic bomb, which was developed by the United States during World War II. After the war, controlled energy release from fission was applied to the development of nuclear reactors. Reactors are utilized for production of electricity at nuclear power plants, for propulsion of ships and submarines, and for the creation of radioactive isotopes used in medicine and industry. 

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