Graphite Moderated Power Producing Reactors

A variety of graphite moderated reactor concepts have evolved since the first aircooled reactors of the 1940s. Reactors with gas, water, and molten salt coolants have been constructed and a variety of fuels, and fissile/fertile fuel mixtures, have been used. The evolution and essential features of graphite moderated power producing reactors are described here, and details of their graphites cores are given. 

The Magnox reactor concept owes its origins to a design study conducted at Harwell, U.K., during the early 1950s. The reactor was designed with the dual role of plutonium and power production, and was known by the code word PIPPA 

By the end of 1952 it was certain that a PIPPA design had been produced which could and should be built. A summary report was prepared in January 1953, and soon after approval was granted for construction of the first two Magnox reactors at Calder Hall. Before the first reactor went critical in 1956 work had started on a further two reactors at Calder Hall, and all four were at power in 1959. Construction at Chapelcross, in the southwest of Scotland, began in 1955. The fist 

Location Commissioning Date Coolant Pressure (MPa) Reactor Vessel1 Rating1 [MW(c)] 

Parameters Units Hall Berkeley fynydd Wylfa 

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The MSR produces power by circulating a molten salt and fuel mixture through graphite core flow channels. The slowing down of neutrons by the graphite moderator in the core region provides the epithermal neutrons necessary to produce the fission power for sustained operation of the reactor. 

The rapid fission of a mass of or another heavy nucleus is the principle of the atomic bomb, the energy liberated being the destructive power. For useful energy the reaction has to be moderated this is done in a reactor where moderators such as water, heavy water, graphite, beryllium, etc., reduce the number of neutrons and slow those present to the most useful energies. The heat produced in a reactor is removed by normal heat-exchange methods. The neutrons in a reactor may be used for the formation of new isotopes, e.g. the transuranic elements, further fissile materials ( °Pu from or of the... 

When controlled carefully, fission can be used to produce electricity. In nuclear power plants, moderators are used to slow down the neutrons produced during nuclear fission. It is common to have moderators made from graphite or with heavy water, 2H20. Control rods are also placed in the nuclear reactor to absorb neutrons and slow down the rate at which the fission takes place. 

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