Nuclear graphite-moderated reactors

Carbides of the Actinides, Uranium, and Thorium. The carbides of uranium and thorium are used as nuclear fuels and breeder materials for gas-cooled, graphite-moderated reactors (see Nuclearreactors). The actinide carbides are prepared by the reaction of metal or metal hydride powders with carbon or preferably by the reduction of the oxides uranium dioxide [1344-57-6] UO2 tduranium octaoxide [1344-59-8], U Og, or thorium... 

The first self-sustaining nuclear reactor built by Fermi in Chicago, which came on stream in 1942, was a gas-cooled graphite-moderated reactor. 

Many see the commercial nuclear power station as a hazard to human life and the environment. Part of this is related to the atomic-weapon heritage of the nuclear reactor, and part is related to the reactor accidents that occurred at the Three Mile Island nuclear power station near Harrisburg, Pennsylvania, in 1979, and Chernobyl nuclear power station near Kiev in the Ukraine in 1986. The accident at Chernobyl involved Unit-4, a reactor that was a light water cooled, graphite moderated reactor built without a containment vessel. The accident resulted in 56 deaths that have been directly attributed to it, and the potential for increased cancer deaths from those exposed to the radioactive plume that emanated from the reactor site at the time of the accident. Since the accident, the remaining three reactors at the station have been shut down, the last one in 2000. The accident at Three Mile Island... 

Uranium is almost entirely used for energy production in nuclear power plants. The commercial nuclear era began with graphite-moderated reactors. The first plant for production of electricity (5 MW) was built at Obninsk near Moscow. In England, at Calder Hall, four reactors of this type, each with a power of 45 MW, were built in 1956. The Chernobyl reactors also were graphite-moderated. 

For physics reasons, uranium in the form of metal rods was extensively employed as fuel for the first generation of nuclear reactors. The requirement for metallic fuel for a natural uranium graphite-moderated reactor is based on the need for a high fuel density and a fuel rod of sufficiently large diameter to reduce the resonance capture to a level where criticality may be achieved. Only uranium in metalhc form has sufficiently high thermal conductivity to permit adequate heat removal from rods of the required diameter. 

Following a general survey of the basic types of nuclear power reactor, separate chapters are devoted to each of the principal designs—the gas-cooled graphite-moderated reactor, the light-water-moderated reactor, the heavy-water-moderated reactor, and the fast reactor. Each chapter includes a discussion of the evolution of the design and a detailed description of one or more typical power plants. 

As of January 2016, the vast majority of nuclear power reactors are not in operation. However, there are plans to put them into qpeiation in the nearest future, dumber of light-water graphite-moderated reactors. 

The neutron dose to graphite due to irradiation is commonly reported as a time integrated flux of neutrons per unit area (or fluence) referenced to a particular neutron energy. Neutron energies greater that 50 keV, 0.1 MeV, 0.18 MeV, and 1 MeV were adopted in the past and can be readily foimd in the literature. In the U.K., irradiation data are frequently reported in fluences referenced to a standard flux spectrum at a particular point in the DIDO reactor, for which the displacement rate was measured by the nickel activation [ Ni(np) t o] reaction [equivalent DIDO nickel (EDN)]. Early on, neutron irradiation doses to the graphite moderator were reported in terms of the bum-up (energy extracted) from imit mass of the adjacent nuclear fuel, i.e., MW days per adjacent tonne of fuel, or MWd/Ate. 

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