Nuclear Reactors and Power Production *

Abstract

This lecture deals with the design and construction of nuclear reactors, and particularly of types suitable for the generation of power. To introduce this a detailed description is given of the British Experimental Pile (BEPO) at Harwell. This is a typical ‘thermal’ reactor on a small scale, using natural uranium as fuel and graphite as moderator; it is air-cooled and the shielding and control arrangements illustrate general practice. There follows an account of some of the engineering and construction problems met in the erection of the Windscale piles, and the solutions achieved.

The problems involved in designing power-producing reactors are discussed. The choice of materials in the reacting core is restricted by nuclear physical considerations; large absorbers of neutrons cannot be used. There is a conflict between the demand for high temperatures to give satisfactory thermal efficiency and the limitations imposed by the metallurgical properties of the fuel elements and by the coolants employable. The safety aspect of design is considered and the influence of the coolant described; certain types of reactor can be designed to be inherently safe even in the event of a coolant failure but with others there is the risk of reaching a supercritical condition, and the effect of this is discussed.

The possible reactors may be divided into two groups: those which use ‘thermal’ neutrons and are similar in principle to BEPO, and those which use ‘intermediate’ or ‘fast’ neutrons and have a much smaller core size. Within each group are alternatives provided by differences in fuel, moderator, and coolant. A number of these are reviewed with general indications of their size, and some of the more detailed problems associated with their design are considered. The large reduction in core size resulting from the use of ‘fast’ neutrons leads to acute problems of heat transfer and, though the fuel investment is much less, the fissile material content of the fuel used must be much higher. One or two possibilities for the more distant future are briefly mentioned.

Prospects for the large-scale development of nuclear power are discussed, and it is argued that the replacement of coal-fired boilers by nuclear reactors as the heat source at power stations should, before many years have passed, be economically sound and is further justifiable as it would help to reduce the recurrent shortage of coal. A possible national scheme is outlined in which thermal reactors would be built in the first stage; these would produce supplies of fissile material as well as power, and this material would later be used in ‘breeder’ or ‘converter’ reactors in the second stage; these reactors should be self-sustaining in fuel after the initial charge.

An Appendix is included which gives a simple explanation of the underlying theory of atomic energy and of the terms used in the lecture.