Uranium resource estimates

Every two years, the International Atomic Energy Agency (IAEA) and the Nuclear Energy Agency of the Organization for Economic Co-operation and Development jointly publish global estimates of the uranium available in various categories of resources in the “Red Book”⁴ (Table I), based on mining-company estimates. In 2009, ∼4000 kt of uranium was classified as being in reasonably assured resources (RAR), for which there is direct geological evidence. Knowledge of existing deposits leads with high confidence to the location and size of an additional 2300 kt in inferred resources (IR). Together, these two classes constitute identified resources, and their distribution is shown in Figure 1. The world’s largest known deposit, Olympic Dam in South Australia, is estimated to have 1447 kt of uranium in RAR and 625 kt in IR (2010).⁶ Other deposits are much smaller, some having IR of 100–300 kt of uranium and many more with less than 100 kt.

Figure 1.

Worldwide distribution of reasonably assured resources (RAR) and inferred resources (IR) in 12 countries in 2009. These countries together have 90% of worldwide identified resources and produced ∼98% of the world uranium production of 51 kt of uranium in 2009.^{4, 5} Whereas Canada and Australia have most of the present resources and active mines, Russia and Kazakhstan have the greatest potential for increased production. This map does not include information on either price or undiscovered resources.

Table I.

Classification and estimates of uranium resources.

Note:

Data from the International Atomic Energy Agency (IAEA) “Red Book.”⁶ As of June 2011, yellowcake (U₃O₈) was priced at US$56/lb.

Beyond these identified resources, the Red Book estimates an additional 10,400 kt of uranium in undiscovered resources. Extrapolations concerning the existence of these deposits are based on evidence in known uranium provinces where there is either some direct evidence (prognosticated) or similarities in geologic occurrence (speculative).

In addition, there are unconventional sources of uranium, such as the tailings left behind at gold or uranium mines. Elevated uranium concentrations also occur in phosphate deposits and black shales. Uranium resources in phosphates are estimated to be more extensive than conventional uranium deposits. Extracting uranium as a byproduct of the production of phosphate-based fertilizers could yield up to roughly 10 kt per year, depending on the average ore concentration and world fertilizer demand. Finally, uranium could be extracted from seawater, where it constitutes about 3 ppb by weight, but technological advances are still required to make large-scale extraction economical.Reference MacFarlane and Miller⁷

A key issue in estimating the size of a resource is the interplay between the ore grade and the costs of exploration and extraction. The market price of uranium and the exploration activity are strongly correlated (Figure 2). Because increasing price (or more efficient extraction technology) makes it economical to mine lower concentrations, a higher price makes more resources economically attractive, as shown in Table I. The past 40 years of reported uranium resources are summarized in Figure 2. The resource estimates for identified and prognosticated resources have remained constant or increased despite the total cumulative production of 2500 kt.

Figure 2.

World uranium spot prices and exploration expenditures, as reported in the “Red Book” of the International Atomic Energy Agency (IAEA).⁴ Uranium prices and expenditures are inflation-adjusted and reported in 2010 U.S. dollars. Reported undiscovered resources fluctuated substantially, partly because of the failure of some countries to report. ^{4, 8–11}

Uranium production and secondary sources of uranium

During the past 20 years, the amount of uranium mined globally has been less than the global demand for nuclear reactors (Figure 3). Up to 50% of the demand has been satisfied from stockpiles built up in the 1970s and from secondary sources. The latter include highly enriched uranium (HEU) from nuclear weapons that have been dismantled and blended down for use in reactor fuels as part of the U.S.–Russian Megatons-to-Megawatts collaboration.Reference Timbie¹² By the end of 2013, this program will have blended down a total of 500 t of HEU (>90% ²³⁵U) from Russian nuclear weapons to low-enriched reactor-grade fuel. The low-enriched uranium has been used in civilian reactors since 1993, displacing 5–7 kt of natural uranium per year.

Figure 3.

Historical annual uranium production and demand. Because early uranium mining was mainly for military purposes, peak production occurred in the 1970s because of high uranium prices and military needs.¹⁰

Excess plutonium from weapons and separated plutonium from civilian power-production reactors can also be used to fabricate a fuel that is a mixed oxide of uranium and plutonium (MOX). As a rule, roughly 1 t of HEU or separated plutonium will support the operation of a 1 GW_e reactor for one year. The global HEU stockpile of ∼1700 t and stocks of separated plutonium of ∼500 t can provide nuclear fuel for 5–6 years of global demand, assuming the present consumption level.¹³

Another secondary source of uranium is the waste streams from enrichment plants. Depleted uranium, usually regarded as waste, still contains 0.2–0.4% ²³⁵U. The world stockpile of 1900 kt of depleted uranium could provide the equivalent of about 500 kt of natural uranium, 7–8 years of today’s global demand.

Because of the scheduled end of the Megatons-to-Megawatts program in 2013 and some technical, political, and financial difficulties in mine openings and operations, there have been predictions in the past several years that the strategic gap between supply and demand could increase after 2013. Despite a substantial increase in uranium production between 2003 and 2010 from 35 kt to 53 kt, current production is still short of the global demand. Nevertheless, the mining industry has already reacted, and more mining projects or extensions are scheduled to begin operation within the next 5–10 years.⁴ Most current projections now show a probable overproduction of uranium during the next 15 years.⁴ However, a tight supply situation might develop if some of the new projects do not develop as expected, leading to increased uranium prices but also to opportunities for uranium producers with new projects.

Scenarios for demand and consumption

Most studies that envision increasing nuclear power to reduce greenhouse gas emissions project a two- to tenfold expansion during the 21st century, although increases by a factor of two or three are the most that can reasonably be expected by 2050.¹⁴ As an example, the BLUE Map scenario from the International Energy Agency (IEA) aims to decrease CO₂ emissions to 50% of the 2005 level by 2050. In this scenario, nuclear power would more than triple, to 1200 GW_e, by 2050.¹⁵ Such an effort could increase the global nuclear share of electricity production to ∼24% by 2050, contributing ∼6% to the total reduction in global CO₂ emissions. In addition to the necessary replacement of the current fleet of reactors, 362 of which will have surpassed a 60-year lifetime by 2050,¹ more than 1000 new reactors would have to be constructed worldwide, a very demanding task.

Based on the IEA BLUE Map scenario, a once-through open cycle would consume all present RAR by 2045 (Figure 4). IR would satisfy demand until 2055, when the annual uranium demand is projected to be about 210 kt/yr. Before this time, substantial uranium resources must be discovered to meet the demand for the rest of the century, even with the projected threefold increase.

Figure 4.

Estimated usage of uranium resources in different categories⁴ according to different scenarios. The solid (orange) line shows the demand for uranium from the International Energy Agency (IEA) BLUE Map scenario.¹⁵ The dashed (red) line shows the demand for continued use of nuclear power at the current level (375 GW_e) throughout the 21st century. For comparison, the dotted (black) line shows the IAEA low-demand scenario until 2035.⁴ This plot extends the BLUE Map and the low-demand scenarios to 2100 assuming constant total power generation.

Although such projections of future energy utilization are highly speculative, they show that current identified resources by themselves cannot sustain a threefold increase in nuclear power from LWRs. Rather, to satisfy an extrapolated constant demand until 2100 (obtained by extending the BLUE Map scenario beyond 2050), all of today’s prognosticated and speculative uranium resources that are projected to cost less than US$130/kg must be discovered and brought into production, and lower-grade ores must be more efficiently extracted. Changes in the fuel cycle to extend uranium supply can help meet these requirements, but the advantages and disadvantages of each approach must be weighed carefully.

Higher-efficiency nuclear fuel cycles

To extend uranium resources, fissile nuclides can be reclaimed from spent nuclear fuel (SNF). In addition to the residual ²³⁵U in SNF, neutron captures by ²³⁸U and subsequent β-decay create ²³⁹Pu. Even in present-day LWRs, ²³⁹Pu accounts for about one-third of the fission energy produced. Different fuel cycles reflect different strategies for utilizing ²³⁵U and ²³⁹Pu, with important implications for uranium demand.

The once-through open cycle treats SNF as a waste that is directly discarded in a geological repository (Figure 5). This is the present strategy in the United States, Germany, Canada, Finland, and Sweden.

Figure 5.

Fissile material flow in once-through and closed fuel cycles [mixed oxide of uranium and plutonium (MOX), fast breeder]. The figure shows generic fuel cycles; actual numbers and paths will vary by reactor type. Some paths, such as seed materials for some fast reactor designs, are not included.

In contrast, France, Japan, and Russia consider the plutonium (∼1 atom %) and residual uranium in SNF as a recyclable resource. A closed fuel cycle with reprocessing retrieves approximately 99% of the fissile nuclides. Reusing reprocessed uranium in fresh fuel reduces an LWR’s demand for natural uranium by up to 10%. The separated plutonium can be combined with natural uranium to make MOX, reducing uranium demand by another 15%.Reference Kazimi, Moniz, Forsberg, Ansolabehere, Deutch, Driscoll, Golay, Kadak, Parsons, Regalbuto, Apostolakis, Hejzlar and Shwageraus¹⁶

A detailed analysisReference Bunn, Fetter, Holdren and van der Zwaan¹⁷ of the cost of reprocessing suggests that an open fuel cycle using LWRs will prevail as long as the price of new uranium fuel is lower than the cost of reprocessing and MOX fuel fabrication. However, several countries (e.g., France, United Kingdom, and Japan) reprocess used civilian fuel. Today, about 30 LWRs in Europe and several in Japan use MOX fuel, accounting for 2% of the total fuel used per year.¹⁸

Plutonium can also be used in MOX fuel in fully closed fuel cycles with fast reactors (Figure 5), which use higher-energy (fast) neutrons. A fast “breeder” reactor can be designed that actually produces more fissile material in the SNF than in the original fuel, which allows multiple cycles of reprocessing.

A scarcity of uranium resources would argue for reprocessing to reclaim fissile material. A closed fuel cycle can significantly reduce demand for fresh ore. In the long term, when the new breeder fuel cycle reaches steady state, it could even become almost fissile self-sufficient.Reference Cochran, Feiveson, Patterson, Pshakin, Ramana, Schneider, Suzuki and von Hippel¹⁹ In the near term, uranium savings in a closed fuel cycle depend on the scale and speed of fast reactor deployment and on the number of fissile atoms produced per destruction of a fissile atom (the breeding ratio). According to a recent study performed at the Massachusetts Institute of Technology (MIT),Reference Kazimi, Moniz, Forsberg, Ansolabehere, Deutch, Driscoll, Golay, Kadak, Parsons, Regalbuto, Apostolakis, Hejzlar and Shwageraus¹⁶ natural uranium usage could be reduced by 13% by 2050 and by up to 45% by 2100 through large-scale deployment of breeder reactors, but such deployment is not expected before 2040. Indeed, no fast breeder reactor has yet been operated commercially.²⁰

For both the open and closed fuel cycles, uranium- and thorium-based fuels can be used in other new reactor types, such as advanced heavy-water reactors (AHWRs), supercritical water-cooled reactors (SCWRs), high-temperature gas-cooled reactors (HTGRs) [also called very high-temperature reactors (VHTRs)], and molten salt reactors (MSRs).Reference Cochran, Feiveson, Patterson, Pshakin, Ramana, Schneider, Suzuki and von Hippel¹⁹ However, new fuels, new reactors, and advanced fuel cycles will require considerable resources and experience prior to deployment, so none of these reactors is likely to play a major role in energy production during the next 40 years.

Another method to extend uranium resources is using higher enrichments to more efficiently utilize the fissile ²³⁵U. The efficiency of fuel use is usually expressed as the “burnup,” in gigawatt days per ton of heavy metal (GWd/tHM). Raising the burnup above the 40–50 GWd/tHM that is typical for LWRs could reduce uranium requirements by 4–5%.Reference Kim and Taiwo²¹ To take advantage of even higher burnup, however, new fuel-assembly materials must be developed to withstand the higher cumulative irradiation.Reference Ewing, Runde and Albrecht-Schmitt²²

Another candidate design using high burnup is the travelling wave reactor (TWR), a type of fast reactor. After starting the reactor with a fissile material, fresh natural or even depleted uranium fuel assemblies are inserted and periodically shuffled to breed and burn plutonium in situ. Such a reactor could run for decades without reprocessing or refueling with fissile material.

Environmental impacts of different nuclear fuel cycles

The selection of a fuel cycle is complicated and depends on each country’s environmental, proliferation, economic, and energy policies.Reference Abdelouas²³ For all fuel cycles, the local environmental impacts of mining directly scale with the uranium consumption. The major issue is the voluminous mine and mill tailings from open pits or underground workings that contain radioactive uranium and thorium decay products, such as ²²²Rn, as well as toxic metals, such as arsenic. Mining techniques used from the 1950s through the early 1970s led to contamination of near-surface water and soil.²⁴ More recently, in situ leaching has been used to dissolve and extract uranium. Mildly oxidizing carbonated water (1 g/l NH₄HCO₃) or more aggressive concentrations of sulfuric acid (2–5 g/l H₂SO₄)Reference Ansolabehere, Deutch, Driscoll, Gray, Holdren, Joskow, Lester, Moniz, Todreas and Beckjord²⁵ is circulated through porous, uranium-bearing rock confined between impermeable layers of clay or shale. The fluids are treated at the surface to remove uranium. This technique economically recovers lower concentrations of uranium, and the radioactive decay products remain underground. An important concern, however, is the impact of these circulating fluids on local aquifers.Reference Ansolabehere, Deutch, Driscoll, Gray, Holdren, Joskow, Lester, Moniz, Todreas and Beckjord²⁵

With regard to nuclear weapons proliferation and nuclear waste disposal, two recent MIT studies compared generic fuel cycles for a two- or threefold global-growth scenarioReference Kazimi, Moniz, Forsberg, Ansolabehere, Deutch, Driscoll, Golay, Kadak, Parsons, Regalbuto, Apostolakis, Hejzlar and Shwageraus^{16, 26} and came to the following conclusions: The once-through cycle followed by direct geological disposal generates the largest volumes of SNF that contains substantial quantities of plutonium. The short-term proliferation risks are reduced because the plutonium is not separated from the SNF and is protected from diversion by the strong radiation generated by fission products.Reference Sutcliffe, Condit, Mansfield, Myers, Layton and Murphy²⁷ A closed fuel cycle (MOX with one recycle) generates lower SNF volumes but has similar repository requirements because the vitrified waste releases more heat. Plutonium, which can be viewed as either a source of energy or an environmental hazard, causes acute and long-term health effects upon ingestion or inhalation,Reference Bathke, Wallace, Ireland, Johnson, Bradley, Ebbinghaus, Manini, Smith and Prichard²⁸ which is an important public health concern.

Any closed fuel cycle will result in the separation of hundreds of tonnes of plutonium, exacerbating existing proliferation concerns. Since plutonium was first isolated in microgram quantities in 1941, more than 2000 t has been created in civilian reactors around the world, generally left in SNF. However, roughly 250 t has been separated from commercially generated SNF. In addition, approximately 70–80 t of new plutonium is added to the global inventory each year, and 10–20 t is separated. Depending on the sophistication of the design, almost all isotopic compositions of separated plutonium are potential weapons material.Reference Mark²⁹ A nuclear device can be made with less than 5 kg (0.005 t) of ²³⁹Pu.Reference Boczar, Gagnon, Chan, Ellis, Verrall and Dastur³⁰

The use of fast reactors without breeding can significantly reduce the inventories of plutonium and minor actinides in the final waste stream, transmuting the actinides to shorter-lived radionuclides. In this scheme, actinides produced in thermal reactors would be recycled and incorporated into MOX fuels for fast reactors. The amount of plutonium can be further reduced by burning the actinides in inert-matrix fuels (IMFs) that do not contain fertile ²³⁸U, for example, zirconia (ZrO₂).Reference Oversby, McPheeters, Degueldre and Paratte^31, Reference Oversby, McPheeters, Degueldre and Paratte³² Reactors would probably use a mixture of MOX and IMF, and irradiation would substantially reduce the plutonium and minor actinide contents of the IMF.Reference Gong, Lutze and Ewing³³ ZrO₂ is recognized as a durable, radiation-resistant waste form for direct disposal.³⁴

Thorium resource estimates

Figure 6 shows the distribution of identified thorium resources by country and type of deposit. In all countries, for a cost below US$80/kg, there are 829 kt of RAR and 1400 kt of IR, with another 1387 kt in prognosticated resources. Information on thorium reserves is limited (just one of the Red Book’s 457 pages),⁴ and some of the data are more than 20 years old,¹⁰ so estimates are much less certain than for uranium. Nevertheless, Australia, Brazil, India, the United States, and Venezuela have significant identified resources of thorium, of between 300 and 450 kt.⁴

Figure 6.

Distribution of thorium resources by the type of deposit and country, specified as either reasonably assured resources (RAR) or inferred resources (IR). The deposits include all identified resources, whereas the country data include only thorium recoverable for less than $US80/kg. The RAR or IR data were not available for countries that indicate only IR or RAR, respectively.^4, Reference Hedrick³⁵

Because the current market for thorium is modest, it is produced only as a byproduct of rare-earth (RE) recovery, largely from monazite (CePO₄). This mineral contains an average of 8–10 wt% thorium, so its processing theoretically recovers 500–740 t of thorium metal per year worldwide.Reference Hedrick³⁶ Some countries, such as India, stockpile this excess inventory for future nuclear fuel applications, whereas others dispose of it. For example, the United States disposed of 3220 t of thorium nitrate as low-level radioactive waste at the Nevada Test Site in 2005.Reference Jaffe, Price, Ceder, Eggert, Graedel, Gschneidner, Hitzman, Houle, Hurd, Kelley, King, Milliron, Skinner and Slakey³⁷ Thorium disposal costs are partially responsible for the decrease in the production of REs in the United States. If the thorium were instead used in a nuclear fuel cycle, it would limit the need for expensive disposal.Reference Hedrick^36, Reference Galperin, Shwageraus and Todosow³⁸

Because of the modest market for thorium, there has been little incentive to explore for new deposits or to survey known deposits. Most resources have been discovered and evaluated during exploration for uranium and REs. If thorium were exploited for commercial nuclear fuel applications, the minerals bastnaesite [(Ce,Th,La,Y,Ca)CO₃F] and thorite (ThSiO₄), which have higher thorium contents, would likely be exploited.Reference Hedrick³⁵

Thorium fuel cycle

Any thorium fuel cycle will need a neutron source, such as fission of ²³⁹Pu or ²³⁵U to breed fissile ²³³U from ²³²Th. Reactors and fuel cycles using thorium have been investigated since the 1950s. From the mid-1950s to the mid-1970s, several experimental and prototype reactors were operated. However, thorium fuels and fuel cycles have not received the attention required for their development because uranium reserves have thus far been judged to be adequate for the uranium/plutonium fuel cycle. A fuel cycle that reduces uranium demand is most important to countries with extensive thorium resources. India and China are actively developing the thorium fuel-cycle technology.

Like uranium, thorium can be used in either an open once-through cycle or a closed fuel cycle with reprocessing to reclaim the fissile ²³³U. In an open fuel cycle using LWRs, ²³⁵U or ²³⁹Pu can be used as a neutron source to generate ²³³U from ²³²Th. Because the nuclear reactions build up ²³³U, less ²³⁵U is needed during burnup. One simple fuel is a homogeneous 3:1 mixture of thorium and enriched uranium (20% ²³⁵U).Reference Kazimi, Moniz, Forsberg, Ansolabehere, Deutch, Driscoll, Golay, Kadak, Parsons, Regalbuto, Apostolakis, Hejzlar and Shwageraus^16, Reference Galperin, Reichert and Radkowsky³⁹ A more efficient approach involves the use of a heterogeneous fuel, in which either the core of a fuel assembly or even each fuel pin is a uranium “seed” of 20% enriched ²³⁵U surrounded by a (Th,U)O₂ “blanket.”

A preliminary reference design using heterogeneous thorium fuel assemblies is the Radkowsky Thorium Reactor (RTR), proposed for the Russian VVER-1000 pressurized water reactor (PWR). This design would consume 20% less natural uranium than using standard uranium fuel and was shown to be economically feasible.Reference Cordier⁴⁰ The RTR is more proliferation-resistant than an LWR, because it produces 80% less plutonium with an isotopic mixture that is less usable for weapons.

For the initial neutron investment of thorium-based fuels to break even with those of uranium-based fuels, a burnup of more than 100 GWd/tHM, more than double that typical for LWRs, will be required.Reference Kazimi, Moniz, Forsberg, Ansolabehere, Deutch, Driscoll, Golay, Kadak, Parsons, Regalbuto, Apostolakis, Hejzlar and Shwageraus¹⁶ A major challenge for thorium-based fuels is that new materials would have to be developed to withstand long irradiation times, just as for high-burnup uranium/plutonium fuel cycles.

One early study of thorium-recycling options in a closed fuel cycle compared resource utilization of various reactor fuel cycles in the Canadian heavy-water (CANDU) reactors. The thorium cycles considered only homogeneous fuel whose initial fissile material was either ²³⁵U or Pu and assumed that ²³³U and remaining fissile materials were recycled from the SNF whereas new fissile material was added to maintain burnup. At steady state, the analysis found a savings of up to 90% in natural-uranium usage compared with a once-through fueling with natural uranium.Reference Hedrick³⁵

India has greater thorium than uranium resources, which has led to a unique nuclear strategy employing (1) uranium-fueled pressurized heavy-water reactors (PHWRs) that produce plutonium, (2) plutonium-fueled fast breeder reactors (FBRs) that breed ²³⁹Pu and ²³³U, and (3) AHWRs that will enable a self-sustained ²³²Th-/²³³U-based fuel cycle and obtain 65% of their power from thorium.Reference Kakodkar⁴¹ Full commercialization of the AHWRs is not expected before 2030.Reference Kang and von Hippel⁴²

Although a thorium-based fuel cycle produces no plutonium, fissile ²³³U bred from ²³²Th is still very attractive for weapons purposes. However, accumulation of other radioactive isotopes, notably ²¹²Bi, which is a daughter product of ²³²U, and gamma-emitting ²⁰⁸Tl, which accumulates during irradiation of ²³²Th, increase proliferation resistance.Reference Forsberg, Wade, Bement, Boardman, Boullis, Crawford, Fukada, Glatz, Greneche, Halsey, Herring, Leroy, Lewis, Noda, Peterson, van den Durpel, Yang, Caponiti, Garrick, Khalil, Moisseysev and Ryskamp⁴³