REACTOR TYPES

Light-water reactors will account for most of the nuclear power capacity expected to be installed in foreign countries by 1980. Several other reactor types, however, will account for significant amounts of the total nuclear power capacity in various countries. These are: the gas-cooled natural-uranium reactor (GCR); the gas-cooled enriched uranium reactor (AGR); heavy-water moderated and cooled, natural-uranium reactor (HWR); fast-breeder reactor (FBR); and high-temperature gas-cooled, high-enriched uranium reactor (HTGR).

The GCR, which has been developed primarily by the United Kingdom, uses natural uranium for fuel, graphite as a moderator, and carbon dioxide as a coolant. The fuel consists of natural uranium metal alloyed with about 1 percent molybdenum. This is contained in hollow rods 1.7 inches in diameter and about two feet long, clad with magnesium-zirconium alloy. The rods are inserted into graphite sleeves. Typically, about fifteen of these elements are stacked end to end to form fuel assemblies thirty feet long. These are inserted into hexagonal prisms of graphite that constitute the moderator. The plutonium produced in the GCR's is not expected to be recycled through these reactors, but rather is to be used for other purposes. Although most of these types of power plants have been built in the United Kingdom, several are in operation in other countries.

The AGR is the next generation of the United Kingdom's gas-cooled reactors and is fueled with low-enriched uranium (1.5 to 1.8 percent uranium–235 initially and two to 2.5 percent uranium–235 in equilibrium), graphite moderated, and cooled by carbon dioxide. The fuel consists of uranium oxide pellets in stainless steel tubes about 0.6 inch in diameter and about three feet long. A typical fuel element consists of a cluster of about thirty-six of these