Uranium, the critical raw material required for the production of nuclear energy, is very much in the news in India these days. First, India has taken a major initiative to expand nuclear power generation capacity, using uranium. Second, India commanding only over percent of the global uranium resources, is in dire need of this material. In order to carry forward its nuclear power programme, India has signed deals with countries endowed with uranium for its supply.
According to the World Nuclear Association,
Uranium is a relatively common metal, found in rocks and seawater. Economic concentrations of it are not uncommon.
Its availability to supply world energy needs is great, both geologically and because of the technology for its use.
Quantities of mineral resources are greater than commonly perceived.
The world’s known uranium resources increased 15 percent in two years to 2007 due to increased mineral exploration.
Uranium is ubiquitous on the Earth. It is a metal approximately as common as tin or zinc, and it is a constituent of most rocks and even of the sea. Some typical concentrations are: (ppm = parts per million).
An orebody is, by definition, an occurrence of mineralisation from which the metal is economically recoverable. It is therefore relative to both costs of extraction and market prices. At present neither the oceans nor any granites are orebodies, but conceivably either could become so if prices were to rise sufficiently.
Measured resources of uranium, the amount known to be economically recoverable from orebodies, are thus also relative to costs and prices. They are also dependent on the intensity of past exploration effort, and are basically a statement about what is known rather than what is there in the Earth’s crust.
Changes in costs or prices, or further exploration, may alter measured resource figures markedly. At ten times the current price, seawater might become a potential source of vast amounts of uranium. Thus, any predictions of the future availability of any mineral, including uranium, which are based on current cost and price data and current geological knowledge are likely to be extremely conservative.
From time to time concerns are raised that the known resources might be insufficient when judged as a multiple of present rate of use. But this is the Limits to Growth fallacy, a major intellectual blunder recycled from the 1970s, which takes no account of the very limited nature of the knowledge we have at any time of what is actually in the Earth’s crust. Our knowledge of geology is such that we can be confident that identified resources of metal minerals are a small fraction of what is there.
With those major qualifications the following Table gives some idea of our present knowledge of uranium resources. It can be seen that Australia has a substantial part (about 23 percent) of the world’s low-cost uranium, Kazakhstan 15 percent, and Canada 8.0 percent.
Current usage is about 65,000 tU/yr. Thus the world’s present measured resources of uranium (5.5 Mt) in the cost category somewhat below present spot prices and used only in conventional reactors, are enough to last for over 80 years. This represents a higher level of assured resources than is normal for most minerals. Further exploration and higher prices will certainly, on the basis of present geological knowledge, yield further resources as present ones are used up.
An initial uranium exploration cycle was military-driven, over 1945 to 1958. The second cycle was about 1974 to 1983, driven by civil nuclear power. There was relatively little uranium exploration between 1985 and 2003, so the significant increase in exploration effort that we are now seeing could readily double the known economic resources. In the two years 2005-06 the world’s known uranium resources tabulated above increased by 15 percent (17 percent in the cost category to $80/kgU). World uranium exploration expenditure in 2006 was US$ 774 million, and the 2007 level was much the same. In the third uranium exploration cycle from 2003 to the end of 2009 about US$ 3.4 billion will have been spent on uranium exploration and deposit delineation on over 600 projects. In this period over 400 new junior companies were formed or changed their orientation to raise over US$ 2 billion for uranium exploration. About 60 percent of this was spent on previously-known deposits. All this was in response to increased uranium price in the market.
The price of a mineral commodity also directly determines the amount of known resources which are economically extractable. On the basis of analogies with other metal minerals, a doubling of price from present levels could be expected to create about a tenfold increase in measured economic resources, over time, due both to increased exploration and the reclassification of resources regarding what is economically recoverable.
This is in fact suggested in the IAEA-NEA figures if those covering estimates of all conventional resources are considered – 10.5 million tonnes (beyond the 5.5 Mt known economic resources), which takes us to over 200 years’ supply at today’s rate of consumption. This still ignores the technological factor mentioned below. It also omits unconventional resources such as phosphate/ phosphorite deposits (22 Mt U recoverable as by-product) and seawater (up to 4000 Mt), which would be uneconomic to extract in the foreseeable future.
It is clear from this figure that known uranium resources have increased threefold since 1975, in line with expenditure on uranium exploration. (The decrease in the decade 1983-93 is due to some countries tightening their criteria for reporting. If this were carried back two decades, the lines would fit even more closely.) Increased exploration expenditure in the future is likely to result in a corresponding increase in known resources.
About 20 percent of US uranium came from central Florida’s phosphate deposits to the mid 1990s, as a by-product, but it then became uneconomic. With higher uranium prices today the resource is being examined again, as is another lower-grade one in Morocco. Plans for Florida extend only to 400 tU/yr at this stage.
Coal ash is another easily-accessible though minor uranium resource in many parts of the world. In central Yunnan province in China the coal uranium content varies up to 315 ppm and averages about 65 ppm. The ash averages about 210 ppm U (0.021%U) – above the cut-off level for some uranium mines. The Xiaolongtang power station ash heap contains over 1000 tU, with annual arisings of 190 tU. Recovery of this by acid leaching is about 70 percent.
Widespread use of the fast breeder reactor could increase the utilisation of uranium 50-fold or more. This type of reactor can be started up on plutonium derived from conventional reactors and operated in closed circuit with its reprocessing plant. Such a reactor, supplied with natural or depleted uranium for its “fertile blanket”, can be operated so that each tonne of ore yields 60 times more energy than in a conventional reactor.
Reactor Fuel Requirements
The world’s power reactors, with combined capacity of some 370 GWe, require about 65,000 tonnes of uranium from mines or elsewhere each year. While this capacity is being run more productively, with higher capacity factors and reactor power levels, the uranium fuel requirement is increasing, but not necessarily at the same rate. The factors increasing fuel demand are offset by a trend for higher burn-up of fuel and other efficiencies, so demand is steady. (Over the years 1980 to 2008 the electricity generated by nuclear power increased 3.6-fold while uranium used increased by a factor of only 2.5.)
Reducing the tails assay in enrichment reduces the amount of natural uranium required for a given amount of fuel. Reprocessing of spent fuel from conventional light water reactors also utilizes present resources more efficiently, by a factor of about 1.3 overall.
Today’s reactor fuel requirements are met from primary supply (direct mine output) and secondary sources: commercial stockpiles, nuclear weapons stockpiles, recycled plutonium and uranium from reprocessing used fuel, and some from re-enrichment of depleted uranium tails (left over from original enrichment). These various secondary sources make uranium unique among energy minerals.
Nuclear Weapons as a Source of Fuel
An important source of nuclear fuel is the world’s nuclear weapons stockpiles. Since 1987 the United States and countries of the former Soviet Union have signed a series of disarmament treaties to reduce the nuclear arsenals of the signatory countries by approximately 80 percent.
The weapons contain a great deal of uranium enriched to over 90 percent U-235 (ie up to 25 times the proportion in reactor fuel). Some weapons have plutonium-239, which can be used in mixed-oxide (MOX) fuel for civil reactors. From 2000 the dilution of 30 tonnes of military high-enriched uranium has been displacing about 10,600 tonnes of uranium oxide per year from mines, which represents about 13 percent of the world’s reactor requirements.
Other Secondary Sources of Uranium
The most obvious source is civil stockpiles held by utilities and governments. The amount held here is difficult to quantify, due to commercial confidentiality. As at January 2007 some 55,000 tU was known on the basis of partial data (Red Book) and 120,000 tU estimated just for utilities (WNA Market Report). These reserves are expected not to be drawn down, but to increase steadily to provide energy security for utilities and governments.
Recycled uranium and plutonium is another source, and currently saves 1500-2000 tU per year of primary supply, depending on whether just the plutonium or also the uranium is considered. In fact, plutonium is quickly recycled as MOX fuel, whereas the reprocessed uranium (RepU) is mostly stockpiled.
Re-enrichment of depleted uranium (DU) is another secondary source. There is about 1.5 million tonnes of depleted uranium available, from both military and civil enrichment activity since the 1940s, most at tails assay of 0.25 – 0.35 percent U-235. Non-nuclear uses of DU are very minor relative to annual arisings of over 35,000 tU per year. This leaves most DU available for mixing with recycled plutonium on MOX fuel or as a future fuel resource for fast neutron reactors. However, some that has relatively high assay can be fed through under-utilised enrichment plants to produce natural uranium equivalent, or even enriched uranium ready for fuel fabrication. Russian enrichment plants have treated 10-15,000 tonnes per year of DU assaying over 0.3percent U-235, stripping it down to 0.1 percent and producing a few thousand tonnes per year of natural uranium equivalent. This Russian program is due to wind down, however, but a new US one is expected to start, treating about 140,000 tonnes of old DU assaying 0.4percent U-235.
Thorium as Nuclear Fuel
Today uranium is the only fuel supplied for nuclear reactors. However, thorium can also be utilized as a fuel for CANDU reactors or in reactors specially designed for this purpose. Neutron efficient reactors, such as CANDU, are capable of operating on a thorium fuel cycle, once they are started using a fissile material such as U-235 or Pu-239. Then the thorium (Th-232) atom captures a neutron in the reactor to become fissile uranium (U-233), which continues the reaction. Some advanced reactor designs are likely to be able to make use of thorium on a substantial scale.
The thorium fuel cycle has some attractive features, though it is not yet in commercial use. Thorium is reported to be about three times as abundant in the earth’s crust as uranium. The 2007 IAEA-NEA “Red Book” gives a figure of 4.4 million tonnes of known and estimated resources, but points out that this excludes data from much of the world.