cost of fuel for fossil-fired steam plants was 1.56 cents per kilowatthour (Fig.

Transcription

1 Uranium resources The context Nuclear energy in the late 1990s and early 2000s enjoyed a bit of a renaissance. In 1999, the average cost of uranium fuel was 0.52 cents per kilowatthour, while the comparable cost of fuel for fossil-fired steam plants was 1.56 cents per kilowatthour (Fig. E19.3.1). (17) The nuclear capacity factor was near 90% (Fig. 19.2). Utilities went looking for nuclear plants to buy as part of the consolidation of the energy industry spurred by the specter of deregulation (see Extension 8.2, Deregulation in the 21st century). (18-20) There were transatlantic purchases of nuclear facilities. (20) Fig. E Costs for fossil fuel are more expensive than those for nuclear plants. (Ref. 17, Fig. 8) The number of nuclear facilities in the U.S. may be stagnant, but there are indications that the international market is still strong. The countries having nuclear installations and their installations status are shown in Fig. E (see the listing in Table 19.1). China and India are going nuclear in a big way, as is apparent from Fig. E

2 Energy, Ch. 19 extension 3 Uranium resources 2 Fig. E The international outlook for nuclear energy. (Ref. 16, Fig. 2)

3 Energy, Ch. 19 extension 3 Uranium resources 3 In the last steps in making uranium fuel, gaseous uranium hexafluoride is changed into uranium dioxide (UO 2 ), a powder. The power is pressed into solid form, then sintered ( fired ) at high temperature to create hard ceramic pellets of enriched uranium. Where does the uranium used in reactor fuel come from? The resource Relatively large deposits of uranium are found in the United States, Australia, Canada, Gabon, South Africa, and the former Soviet Union. The uranium compound (U 3 O 8 ) produced from the ore is called yellowcake (1 kg of yellowcake contains 0.85 kg of uranium). The markets are worldwide, and growing, as we see in Fig. E Fig. E Projected cumulative uranium enrichment requirements for world nuclear power plants, Reference Case, (Ref. 16, Fig. 25) The history of uranium resources in the past 30 years resembles a ride on a roller coaster. In the early 1970s, many nuclear reactors were being built, here and elsewhere. In the

4 Energy, Ch. 19 extension 3 Uranium resources 4 growth atmosphere of that time, projections made by drawing straight lines on semilogarithmic paper (see Chapter 5) indicated a demand for yellowcake of 60 kt in the United States and 114 kt for the world by the year (21) Prices rose until the mid- 1970s, even to the extent of causing a major supplier to renege on its contracted price. (22) The price dropped disastrously in the 1980s. Since the Three Mile Island incident in 1979, few nuclear plants have been ordered, and many previously ordered have been canceled (due to cost overruns sometimes exceeding 1000%). (23) As a result, projected demand for enriched uranium dropped tenfold between 1975 and the mid-1980s, (24) and the price fell by a factor of 3. Furthermore, detailed studies during the 1980s of uranium ore deposits led to the conclusion that, for every decrease in ore grade of a factor of 10, there is a 300-fold increase in actual mass of recoverable uranium, (25) implying that supplies would be adequate far into the future. Hubbert (26) has pointed out that the Gassaway member of the Chattanooga shale outcrop is hundreds of square kilometers of 0.006% uranium 5 m thick. Similarly, the New Hampshire Conway Granite is 750 km 2 (330 mi 2 ) and a few km deep. It contains 56 grams of thorium per tonne of rock. The density of granite is about 3 tonnes per cubic meter; thus 1 m 3 of this rock contains about 150 grams of thorium. If breeder reactors (discussed later in this chapter and in Extension 19.5, New reactor types) are in use, this thorium is usable and equivalent to 1.5 x barrels of crude oil per cubic meter of rock. The exploitation of this resource would naturally cause large-scale visual pollution and ground water contamination, among its other consequences. At any rate, we may conclude that, with sufficiently large energy input, the resources could sustain the nuclear industry for quite a while.

5 Energy, Ch. 19 extension 3 Uranium resources 5 The cost of yellowcake has dropped substantially and risen substantially in recent times at least partly because so many reactors ordered in the mid-1970s were never built (Fig. E19.3.4). The average price fell in 1991 to $13.94/lb from $17.94/lb in In 1982, when the abandoned plants were still on order, the cost was $35.36/lb. (27) a. b. Fig. E a. Number of nuclear units ordered, licensed, and operating. b. A total of 124 of ordered units were never built. Of those built, 28 have been shut down permanently. (Ref. 13, Fig. 9.1) The price for yellowcake doubled in the late 1990s, then fell back, as shown in Fig. E It seems difficult to predict what will happen with yellowcake prices in the long term, but even with more expensive yellowcake, electricity costs from nuclear energy are much lower than from fossil fuels. (17)

6 Energy, Ch. 19 extension 3 Uranium resources 6 Fig. E Prices for yellowcake, which had fallen substantially in the 1980s, rose and fell again in the 1990s. (Ref. 16, Fig. 20) Energy in the supply of cheap yellowcake The reasonably assured supply of cheap yellowcake (less than $100/lb) is estimated at about 4.8 Mt, which corresponds to 4.1 Mt of available uranium. There is of course a much larger supply than was originally estimated if the acceptable grade of ore is reduced, (25) as was noted. Let us take 200 MeV to be the energy released in the average 235 U fission. At 100% use, the possible energy release from the 4.8 Mt of easily available U.S. uranium ore (remember that 235 U makes up only 0.70% of natural uranium) is (proportion of 235 U found in nature) x (energy release per atom of 235 U) x (mass of easily available uranium) x (number of atoms per gram of 235 U) = (0.0070) x (200 MeV/atom) x (4.8 x g) x (6.02 x atoms/235 g) = (200 MeV) x (7.0 x 4.8 x 6.02/2.35) x 10 ( ) = 1.72 x MeV = (1.72 x ) x 10 6 x 1.6 x joules = 2.76 x joules = 7.65 x kwh t,

7 Energy, Ch. 19 extension 3 Uranium resources 7 while 2000 U.S. energy use was about 10.3 x joules, (13) or thirty times this amount. Thus, if we use that much energy each year into the future, the uranium would last 30 years (energy used/use rate = time energy will last). Of course, this is unrealistic because nuclear energy does not supply our total energy requirements, and because energy use generally increases from year to year. And, of course, the world outside America uses uranium fuel. And, as discussed above and in Ch. 11, the supply increases as the grade accepted decreases. If the weapons to fuel uranium were simply dumped on the market, there is so much available (as we have seen, many tonnes, that the price would collapse. There is certainly a supply of relatively cheap uranium available that can last for centuries.