fuel pins in three rings located within graphite sleeves. Eight fuel elements, end to end, form a fuel stringer assembly about thirty feet long. In contrast to GCR's, the plutonium produced in AGR's is likely to be recycled as a supplement to the uranium–235. Large scale plutonium recycle in these reactors can probably be expected to start before 1980. A small number of AGR's are under construction or planned outside the United Kingdom.

HWR's, which have been developed primarily in Canada, use natural uranium for fuel and heavy water for both moderator and coolant. The fuel is in the form of uranium oxide pellets in metal tubes about 0.5 inch in diameter and typically about eighteen feet long. A typical fuel assembly consists of thirty-six of these fuel rods arranged in three concentric circles. As in the case of other reactors that use natural uranium fuel, it is not planned to recycle plutonium through the HWR.

All fast breeder reactors now in operation or planned through 1980 use mixed oxides of plutonium and uranium as fuel, and liquid sodium as a coolant. Some use uranium at enrichments ranging from about 20 percent to nearly 95 percent to supplement the plutonium as fuel. Fuel element characteristics vary rather widely among several reactor types, but these differences do not appear to be particularly significant from the point of view of safeguards. Several countries (notably the United Kingdom, France, the Soviet Union, and the Federal Republic of Germany) have either started operation of prototype FBR's or expect to do so within the next three or four years.

As for research and test reactors, the MTR type and the TRIGA account for most of those in operation in foreign countries. There are, however, perhaps several dozen additional different types, many of which are especially designed facilities for rather specific purposes. They all typically have core loadings of only a few kilograms of high-enriched uranium. There are several hundred research or test reactors now operating in several dozen countries.

Characteristics of foreign power reactors, not included in Chapter 3, are summarized in Table B–1.