TABLE 5–2 Ratios of Uranium Feed and Separative Work Units to a Kilogram of Enriched Reactor Fuel, 3 Percent 235U, for Selected Tails Assays


Tails Assay (percent 235U)




Natural uranium, kg




Separative work units




Source: la Garza, “An Overview of U.S. Enriching Resources,” report to the Supply and Delivery Panel, Committee on Nuclear and Alternative Energy Systems, National Research Council, Washington, D.C., 1976.

Figure 5–6 illustrates production expected from enrichment plants over the next decade and contract commitments for separative work. The apparent gap between commitments and production from 1981 to 1988 could be closed if operation at high tails assay—about 0.36 percent—were possible. But this inordinately high tails assay would require more feed at a time when uranium supplies may become scarce. Conversely, since enrichment plants are being added in Europe, and since the Soviet Union apparently has spare enrichment capacity, some relief might be available from these sources.

A recent report points out that utilities holding long-term fixed-commitment contracts are required to provide uranium feed to the enrichment complex in amounts that may not agree with their fuel requirements, and it suggests that most of the apparent gap between production capacity and commitments could be eliminated through case-by-case adjustments.27 The substitution of fuel “enriched” by the addition of plutonium from reprocessed old fuel could also help prevent an “enrichment gap.”28

Whether additional enrichment capacity will be needed beyond 1990, and if so when, depends on the number and type of reactors built and their particular fuel needs. Existing and planned enrichment capacity, for example, can supply the fuel for 215 GWe generated by today’s light water reactors using a once-through cycle. Domestic capacity might approach this figure in the early 1990s, and in addition, it would be proper for the United States to supply its share of the enrichment needs of countries that must buy this service. The introduction of new reactors in the form of advanced converters would also affect projected demands for enrichment. Heavy water reactors using natural uranium, or uranium enriched to 1.2 percent 235U, have no enrichment requirements in the first case, and

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