The Light-Water-Moderated Reactor

Abstract

Much of the early development work on power reactors concentrated, of necessity, on the use of natural uranium. This demanded the selection of high-grade moderator, of low-neutron cross section, either graphite, as in the United Kingdom magnox system, or heavy water, as in the Canadian CANDU reactor. The United States, on the other hand, had available from an early date adequate supplies of enriched uranium from the diffusion plants constructed for military purposes. The high specific fission cross section of the enriched fuel enabled an adequate thermal utilization to be achieved even when a relatively low-grade moderator of high absorption cross section, such as ordinary water, was used. Having chosen water as moderator on account of its excellent moderation properties and ready availability, it was natural to employ it also as the coolant, because of its good heat transfer properties. Reactor development in the United States over the past two decades has been largely devoted to the water-moderated, water-cooled type of reactor, and the last few years have seen an increasing installation of this type in other countries. As of 1980, the 142 light water reactors in operation were producing a total annual output of 109 GWe, out of a total world nuclear generating capacity of about 130 GWe.