The Gas-Cooled Graphite-Moderated Reactor

Another possible transient is that due to a loss of power to all the gas blowers, causing complete loss of forced circulation. In this case, natural convection should be adequate to remove the decay heat. Heat removal is aided by the large thermal capacity of the graphite, which acts as a heat sink for the fuel. In the event of a loss of circulation coupled with a depressurization accident, the heat removal capacity of the low-pressure gas is no longer adequate to remove heat by natural convection, and in this case the forced circulation must be restored. The slow depressurization rate of the PCPV allows a reasonable time margin for the institution of emergency cooling. 

The above analysis is based on the assumption that the reactor has been shut down as a result of the depressurization, so that only the decay heat has to be removed. If the shutdown system were to fail in an AGR, the negative temperature coefficient of the reactor would not be large enough to prevent melting of some of the stainless steel fuel cladding. The loss of the neutron absorption associated with the steel could initiate a reactivity transient which would result in a large-scale core melt. This event, however, is extremely unlikely on account of the extensive protective instrumentation and reliable shutdown system of the AGR. 

Apart from the clad melt mentioned above, it is difficult to find plausible mechanisms for significant reactivity transients in a gas-cooled thermal reactor. The number of control rods tends to be large, so that the maximum reactivity worth of a single rod is usually of the order of 0.1 %, in comparison with the 2% or so possible in a light water reactor. Consequently, rapid 

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General Characteristics of the Gas-Cooled Graphite-Moderated Reactor... 

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. 

D. R. Poulter, ed.. The Design of Gas-Cooled Graphite-Moderated Reactors, Oxford University Press, London, 1963. 

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... 

Gas-cooled, graphite moderated reactors have several significant advantages over other reactor designs by virtue of their inherent passive safety characteristics. These are the result of the large thermal mass of the graphite core, the high... 

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

In contrast with AGR-reactors, the high temperature reactors (HTR) currently in development, which are also gas-cooled graphite-moderated reactors, helium is the cooling gas, thereby avoiding the troublesome corrosion of graphite by carbon dioxide, according to the equation ... 

Uranium enrichment and fuel fabrication For light-water-moderated and light-water-cooled reactors (LWRs) and for advanced gas-cooled graphite moderated reactors (AGRs), the uranium processed at the mills needs to be enriched in the hssile isotope Enrichments of 2-5% are required. Before the enrichment, the uranium oxide (UsOg) must be converted to uranium tetra-fluoride (UF4) and then to uranium hexa-fluoride (UFg). 

For graphite reactors, the main carbon 14 production route is through irradiation of the moderator and, out of the 50 curies per year produced by a 200 to 250 MWe gas-cooled graphite-moderated reactor, 60 % is produced by interaction with the nitrogen impurities in the graphite and 40 % by interaction with the carbon 13 contained in the graphite pile. 

The power station is located some 40 miles south of Rome and was designed and constructed by TNPG in collaboration with refinements in the reactor design. It is a single refined gas-cooled graphite-moderated reactor which supplies steam to 3No.70 MW turbo alternator. 

It was becoming obvious that a gas-cooled graphite-moderated reactor would not be a very feasible option for a submarine. There was a further problem in that Diamond, who had been leading the work on behalf of the Admiralty, left Harwell in 1952 to become professor of engineering at Manchester University. This effectively brought the current work to an end, and it was clear that a fresh approach would be needed. 

In support of the development of graphite moderated reactors, an enormous amount of research has been conducted on the effects of neutron irradiation and radiolytic oxidation on the structure and properties of graphites. The essential mechanisms of these phenomena are understood and the years of research have translated into engineering codes and design practices for the safe design, construction and operation of gas-cooled reactors. 

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