Energy nuclear power plants

A technique called probabiUstic safety assessment (PSA) has been developed to analy2e complex systems and to aid in assuring safe nuclear power plant operation. PSA, which had its origin in a project sponsored by the U.S. Atomic Energy Commission, is a formali2ed identification of potential events and consequences lea ding to an estimate of risk of accident. Discovery of weaknesses in the plant allows for corrective action. 

Strategic Plan for Building New Nuclear Power Plants, Nuclear Energy Institute Executive Committee, Washiagton, D.C., 1994 (armual update). 

Nucleai energy is a principal contributor to the production of the world s electricity. As shown in Table 1, many countries are strongly dependent on nuclear energy. For some countries, more than half of the electricity is generated by nuclear means (1,3). There were 424 nuclear power plants operating worldwide as of 1995. Over 100 of these plants contributed over 20% of the electricity in the United States (see also Power generation). 

If possible comparisons are focused on energy systems, nuclear power safety is also estimated to be superior to all electricity generation methods except for natural gas (30). Figure 3 is a plot of that comparison in terms of estimated total deaths to workers and the pubHc and includes deaths associated with secondary processes in the entire fuel cycle. The poorer safety record of the alternatives to nuclear power can be attributed to fataUties in transportation, where comparatively enormous amounts of fossil fuel transport are involved. Continuous or daily refueling of fossil fuel plants is required as compared to refueling a nuclear plant from a few tmckloads only once over a period of one to two years. This disadvantage appHes to solar and wind as well because of the necessary assumption that their backup power in periods of no or Httie wind or sun is from fossil-fuel generation. Now death or serious injury has resulted from radiation exposure from commercial nuclear power plants in the United States (31). 

Taking into account the possibility of highly directional blast effects, Eichler and Napadensky (1977) recommend the use of a safe and conservative value for TNT equivalency, namely, between 20% and 40%, for the determination of safe standoff distances between transportation routes and nuclear power plants. This value is based on energy it should be applied to the total amount of hydrocarbon in the largest single, pressurized storage tank being transported. 

The nucleus of an atom consists of protons and neutrons that are bound together by a nuclear force. Neutrons and protons are rearranged in a nuclear reaction in a manner somewhat akin to rearrang ing atoms in a chemical reaction. The nuclear reaction liberating energy in a nuclear power plant is called nuclear fission. The word fission is derived from fissure, which means a crack or a separation. A nucleus is separated (fissioned) into two major parts by bombardment with a neutron. 

The fear of accidents like Chernobyl, and the high cost of nuclear waste disposal, halted nuclear power plant construction in the United States m the 1980s, and in most ol the rest ol the world by the 1990s. Because nuclear fusion does not present the waste disposal problem of fission reactors, there is hope that fusion will be the primary energy source late in the twenty-first centuiy as the supplies of natural gas and petroleum dwindle. 

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. 

Uranium is used as the primai-y source of nuclear energy in a nuclear reactor, although one-third to one-half of the power will be produced from plutonium before the power plant is refueled. Plutonium is created during the uranium fission cycle, and after being created will also fission, contributing heat to make steam in the nuclear power plant. These two nuclear fuels are discussed separately in order to explore their similarities and differences. Mixed oxide fuel, a combination of uranium and recovered plutonium, also has limited application in nuclear fuel, and will be briefly discussed. 

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. 

Excise taxes placed on specific energy sources tend to reduce the demand for these energy sources in both the short and the long run. The federal government imposes excise taxes on almost all petroleum products and coal (see Table I). The federal government also imposes excise taxes on many transportation uses of methanol, ethanol, natural gas, and propane and imposes a fee on electricity produced from nuclear power plants. 

Schematic view of a nuclear power plant. The energy source is the core, in which a fission reaction occurs. The rest of the plant is designed to transfer the energy released during fission and convert it into electricity.

The turbine and generator components of a nuclear power plant have exact counterparts in power plants fueled by fossil fuels. The uniqueness of the nuclear power plant lies in its core. The core is a nuclear reactor where fission takes place under conditions that keep the reactor operating just below the critical level. The core contains three parts fuel rods, moderators, and control rods. These components act on the flow of neutrons within the core, as shown in Figure 22-13. The fate of neutrons must be controlled carefully. Fission must be sustained at a steady rate that produces sufficient energy to mn a generator, but the rate must not be allowed to increase and destroy the reactor. 

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