concentrations of plutonium—although a Th-U cycle could also be used. The cycle with plutonium and uranium is designated the U-Pu cycle; as with the Th-U cycle, recycle is always assumed.
Table 5–4 presents fuel cycle characteristics of the reactors in Table 5–3. Some caution is needed in interpreting Table 5–4. There are continuous possibilities for varying enrichments, fuel concentrations, lattice spacings, and other reactor fueling parameters. How designers choose to operate a fuel cycle depends on finding a minimum fueling cost within broad technical limits, and only those parameters that seem interesting now are presented. Table 5–4 is schematic and highly simplified. In some cases, particularly those involving future developments, relatively crude estimates have been used.
Virtually all the nuclear power in the United States today, and all planned expansion of nuclear power, is in the form of light water reactors. As can be seen in Table 5–4, these reactors make large demands on supplies of natural uranium at economical prices. Such supplies (as pointed out under “Availability of Uranium”) are limited; therefore, this type of reactor has a limited term of service. How long this term might be depends, of course, on the demand for nuclear power as well as on the supply of uranium. A very long-lasting nuclear industry could only persist by the use of some form of breeder reactor, whose ultimate source of fuel, the fertile isotopes, could probably be supplied at economical prices for hundreds of millennia.
All U-Pu recycle schemes and all Th-U schemes that do not use denatured uranium present the problem that pure fissile material could be chemically isolated during the recycle steps. In particular, breeder reactors are intrinsically fuel-recycle systems. As such, they present the possibility that nuclear materials usable in weapons could be diverted, or that the fuel cycle could be used in national proliferation of nuclear arsenals. On these grounds, the United States has deferred civilian nuclear fuel reprocessing and is attempting to persuade other countries to do the same. On the same grounds, the Administration has opposed proceeding with the latest demonstration breeder reactor project in the United States, the Clinch River breeder reactor (CRBR), a subject discussed later in this chapter.
Nevertheless, a vigorous and durable nuclear power industry could be a very important part of our future energy supply system. Therefore, in what follows, we explore the various reactor systems that might be used, even though many interesting systems rely on recycle of nuclear fuel.
It has already been noted (Table 5–4) that the current generation of power reactors in the United States, consisting of light water reactors, is not very