Uranium in the environment is a global health concern, and comes from both natural and man-made sources. Mining, phosphates in agriculture, weapons manufacturing, and nuclear power are sources of uranium in the environment.
In the natural environment, radioactivity of uranium is generally low, but uranium is a toxic metal that can disrupt normal functioning of the kidney, brain, liver, heart, and numerous other systems. Chemical toxicity can cause public health issues when uranium is present in groundwater, especially if concentrations in food and water are increased by mining activity. The biological half-life (the average time it takes for the human body to eliminate half the amount in the body) for uranium is about 15 days.
Uranium's radioactivity can present health and environmental issues in the case of nuclear waste produced by nuclear power plants or weapons manufacturing.
Uranium is weakly radioactive and remains so because of its long physical half-life (4.468 billion years for uranium-238). The use of depleted uranium (DU) in munitions is controversial because of questions about potential long-term health effects.
Natural occurrence
Uranium ore
Uranium
is a naturally occurring element found in low levels within all rock,
soil, and water. This is the highest-numbered element to be found
naturally in significant quantities on earth. According to the United Nations Scientific Committee on the Effects of Atomic Radiation the normal concentration of uranium in soil is 300 μg/kg to 11.7 mg/kg.
It is considered to be more plentiful than antimony, beryllium, cadmium, gold, mercury, silver, or tungsten and is about as abundant as tin, arsenic or molybdenum. It is found in many minerals including uraninite (most common uranium ore), autunite, uranophane, torbernite, and coffinite. Significant concentrations of uranium occur in some substances such as phosphate rock deposits, and minerals such as lignite, and monazite sands in uranium-rich ores (it is recovered commercially from these sources). Coal fly ash
from uranium bearing coal is particularly rich in uranium and there
have been several proposals to "mine" this waste product for its uranium
content.
Due to the fact that part of the ash of a coal power plant escapes
through the smokestack, the radioactive contamination released by coal
power plants in regular operation is actually higher than that of
nuclear power plants.
Seawater contains about 3.3 parts per billion of uranium by weight, approximately (3.3 µg/kg) or, 3.3 micrograms per liter of seawater.
Mining is the largest source of uranium contamination in the environment. Uranium milling creates radioactive waste in the form of tailings,
which contain uranium, radium, and polonium. Consequently, uranium
mining results in "the unavoidable radioactive contamination of the
environment by solid, liquid and gaseous wastes".
Seventy percent of global uranium resources are on or adjacent to
traditional lands belonging to Indigenous people, and perceived
environmental risks associated with uranium mining have resulted in environmental conflicts involving multiple actors wherein local campaigns become national or international debates.
Some of these environmental conflicts have limited uranium exploration. Incidents at Ranger uranium mine in the Northern Territory of Australia and disputes over Indigenous land rights led to increased opposition to development of the nearby Jabiluka deposits and suspension of that project in the early 2000s. Similarly, environmental damage from Uranium mining on traditional Navajo lands in the southwestern United States resulted in restrictions on additional mining in Navajo lands in 2005.
Occupational hazards
The
radiation hazards of uranium mining and milling were not appreciated in
the early years, resulting in workers exposed to high levels of
radiation. Inhalation of radon gas caused sharp increases in lung cancers among underground uranium miners employed in the 1940s and 1950s.
DU penetrator from the PGU-14/B incendiary 30 mm round
Military activity is a source of uranium, especially at nuclear or munitions testing sites. Depleted uranium (DU) is a byproduct of uranium enrichment that is used for defensive armor plating and armor-piercingprojectiles.
Uranium contamination has been found at testing sites in the UK, in
Kazakhstan, and in several countries as a result of DU munitions used in
the Gulf War and the Yugoslav wars. During a three-week period of conflict in 2003 in Iraq, 1,000 to 2,000 tonnes of DU munitions were used.
Combustion and impact of DU munitions can produce aerosols that disperse
uranium metal into the air and water where it can be inhaled or
ingested by humans. A United Nations Environment Programme (UNEP) study has expressed concerns about groundwater contamination from these munitions. Studies of DU aerosol exposure suggest that uranium particles would quickly settle out of the air, and thus should not affect populations more than a few kilometres from target areas.
Sites in Kosovo and southern Central Serbia where NATO aviation used depleted uranium munitions during 1999 bombing
In 2020, there were over 250,000 metric tons of high-level radioactive waste being stored globally in temporary containers. This waste is produced by nuclear power plants
and weapons facilities, and is a serious human health and environmental
issue. There are plans to permanently dispose of high-level waste in deep geological repositories, but none of these are operational. Corrosion of aging temporary containers has caused some waste to leak into the environment.
Spent uranium dioxide fuel is very insoluble in water, it is likely to release uranium (and fission products) even more slowly than borosilicate glass when in contact with water.
Soluble uranium salts are toxic, though less so than those of other heavy metals such as lead or mercury. The organ which is most affected is the kidney. Soluble uranium salts are readily excreted in the urine, although some accumulation in the kidneys does occur in the case of chronic exposure. The World Health Organization
has established a daily "tolerated intake" of soluble uranium salts for
the general public of 0.5 μg/kg body weight (or 35 μg for a 70 kg
adult): exposure at this level is not thought to lead to any significant
kidney damage.
Tiron may be used to remove uranium from the human body, in a form of chelation therapy. Bicarbonate may also be used as uranium (VI) forms complexes with the carbonate ion.
Public health
Uranium mining produces toxic tailings that are radioactive and may contain other toxic elements such as radon.
Dust and water leaving tailing sites may carry long-lived radioactive
elements that enter water sources and the soil, increase background radiation,
and eventually be ingested by humans and animals. A 2013 analysis in a
medical journal found that, "The effects of all these sources of
contamination on human health will be subtle and widespread, and
therefore difficult to detect both clinically and epidemiologically." A 2019 analysis of the global uranium industry said that the industry was shifting mining activities toward the Global South
where environmental regulations are typically less stringent; and that
people in impacted communities would "surely experience adverse
environmental consequences" and public health
issues arising from mining activities carried out by powerful
multi-national corporations or mining companies based in foreign
countries.
Cancer
In 1950,
the US Public Health service began a comprehensive study of uranium
miners, leading to the first publication of a statistical correlation
between cancer and uranium mining, released in 1962. The federal government eventually regulated the standard amount of radon in mines, setting the level at 0.3 WL on January 1, 1969.
Out of 69 present and former uranium milling sites in 12 states, 24 have been abandoned, and are the responsibility of the US Department of Energy. Accidental releases from uranium mills include the 1979 Church Rock uranium mill spill in New Mexico, called the largest accident of nuclear-related waste in US history, and the 1986 Sequoyah Corporation Fuels Release in Oklahoma.
The use of depleted uranium (DU) in munitions is controversial because of questions about potential long-term health effects. Normal functioning of the kidney, brain, liver, heart, and numerous other systems can be affected by uranium exposure, because uranium is a toxic metal. Some people have raised concerns about the use of DU munitions because of its mutagenicity, teratogenicity in mice, neurotoxicity,
and its suspected carcinogenic potential. Additional concerns address
unexploded DU munitions leeching into groundwater over time.
The toxicity of DU is a point of medical controversy. Multiple
studies using cultured cells and laboratory rodents suggest the
possibility of leukemogenic, genetic, reproductive, and neurological effects from chronic exposure.
A 2005 epidemiology
review concluded: "In aggregate the human epidemiological evidence is
consistent with increased risk of birth defects in offspring of persons
exposed to DU." The World Health Organization states that no risk of reproductive, developmental, or carcinogenic effects have been reported in humans due to DU exposure. This report has been criticized by Dr. Keith Baverstock for not including possible long-term effects.
Birth defects
Most
scientific studies have found no link between uranium and birth
defects, but some claim statistical correlations between soldiers
exposed to DU, and those who were not, concerning reproductive
abnormalities.
One study found epidemiological evidence for increased risk of birth defects in the offspring of persons exposed to DU. Several sources have attributed an increased rate of birth defects in the children of Gulf War veterans and in Iraqis to inhalation of depleted uranium.
A 2001 study of 15,000 Gulf War combat veterans and 15,000 control
veterans found that the Gulf War veterans were 1.8 (fathers) to 2.8
(mothers) times more likely to have children with birth defects.
A study of Gulf War Veterans from the UK found a 50% increased risk of
malformed pregnancies reported by men over non-Gulf War veterans. The
study did not find correlations between Gulf war deployment and other
birth defects such as stillbirth, chromosomal malformations, or
congenital syndromes. The father's service in the Gulf War was
associated with increased rate of miscarriage, but the mother's service
was not.
In animals
Uranium causes reproductive defects and other health problems in rodents, frogs and other animals. Uranium was also shown to have cytotoxic, genotoxic and carcinogenic effects in animals.It has been shown in rodents and frogs that water-soluble forms of uranium are teratogenic.
It has been suggested that it is possible to form a reactive barrier by adding something to the soil which will cause the uranium to become fixed. One method of doing this is to use a mineral (apatite) while a second method is to add a food substance such as acetate to the soil. This will enable bacteria to reduce the uranium(VI) to uranium(IV), which is much less soluble. In peat-like soils, the uranium will tend to bind to the humic acids; this tends to fix the uranium in the soil.
Steroid hormones help control metabolism, inflammation, immune functions, salt and water balance, development of sexual characteristics, and the ability to withstand injury and illness. The term steroid
describes both hormones produced by the body and artificially produced
medications that duplicate the action for the naturally occurring
steroids.
The natural steroid hormones are generally synthesized from cholesterol in the gonads and adrenal glands. These forms of hormones are lipids. They can pass through the cell membrane as they are fat-soluble, and then bind to steroid hormone receptors
(which may be nuclear or cytosolic depending on the steroid hormone) to
bring about changes within the cell. Steroid hormones are generally
carried in the blood, bound to specific carrier proteins such as sex hormone-binding globulin or corticosteroid-binding globulin. Further conversions and catabolism occurs in the liver, in other "peripheral" tissues, and in the target tissues.
Synthetic steroids and sterols
A variety of synthetic steroids and sterols have also been contrived. Most are steroids, but some nonsteroidal
molecules can interact with the steroid receptors because of a
similarity of shape. Some synthetic steroids are weaker or stronger than
the natural steroids whose receptors they activate.
Steroid hormones are transported through the blood by being bound to
carrier proteins—serum proteins that bind them and increase the
hormones' solubility in water. Some examples are sex hormone-binding globulin (SHBG), corticosteroid-binding globulin, and albumin.
Most studies say that hormones can only affect cells when they are not
bound by serum proteins. In order to be active, steroid hormones must
free themselves from their blood-solubilizing proteins and either bind
to extracellular receptors, or passively cross the cell membrane and
bind to nuclear receptors. This idea is known as the free hormone hypothesis. This idea is shown in Figure 1 to the right.
This shows a possible pathway through which steroid hormones are endocytosed and proceed to affect cells via a genomic pathway.
One study has found that these steroid-carrier complexes are bound by megalin, a membrane receptor, and are then taken into cells via endocytosis.
One possible pathway is that once inside the cell these complexes are
taken to the lysosome, where the carrier protein is degraded and the
steroid hormone is released into the cytoplasm of the target cell. The
hormone then follows a genomic pathway of action. This process is shown
in Figure 2 to the right. The role of endocytosis in steroid hormone transport is not well understood and is under further investigation.
In order for steroid hormones to cross the lipid bilayer of cells, they must overcome energetic barriers that would prevent their entering or exiting the membrane. Gibbs free energy
is an important concept here. These hormones, which are all derived
from cholesterol, have hydrophilic functional groups at either end and
hydrophobic carbon backbones. When steroid hormones are entering
membranes free energy barriers exist when the functional groups are
entering the hydrophobic interior of membrane, but it is energetically
favorable for the hydrophobic core of these hormones to enter lipid
bilayers. These energy barriers and wells are reversed for hormones
exiting membranes. Steroid hormones easily enter and exit the membrane
at physiologic conditions. They have been shown experimentally to cross
membranes near a rate of 20 μm/s, depending on the hormone.
Though it is energetically more favorable for hormones to be in
the membrane than in the ECF or ICF, they do in fact leave the membrane
once they have entered it. This is an important consideration because
cholesterol—the precursor to all steroid hormones—does not leave the
membrane once it has embedded itself inside. The difference between
cholesterol and these hormones is that cholesterol is in a much larger
negative Gibb's free energy well once inside the membrane, as compared
to these hormones. This is because the aliphatic tail on cholesterol has
a very favorable interaction with the interior of lipid bilayers.
Mechanisms of action and effects
There
are many different mechanisms through which steroid hormones affect
their target cells. All of these different pathways can be classified as
having either a genomic effect or a non-genomic effect. Genomic
pathways are slow and result in altering transcription levels of certain
proteins in the cell; non-genomic pathways are much faster.
Flowchart showing the binding of a steroid hormone to a target cell
Genomic pathways
The first identified mechanisms of steroid hormone action were the genomic effects. In this pathway, the free hormones first pass through the cell membrane because they are fat soluble. In the cytoplasm, the steroid may or may not undergo an enzyme-mediated alteration such as reduction, hydroxylation, or aromatization. Then the steroid binds to a specific steroid hormone receptor, also known as a nuclear receptor, which is a large metalloprotein. Upon steroid binding, many kinds of steroid receptors dimerize: two receptor subunits join together to form one functional DNA-binding unit that can enter the cell nucleus. Once in the nucleus, the steroid-receptor ligand complex binds to specific DNA sequences and induces transcription of its target genes.
Non-genomic pathways
Because
non-genomic pathways include any mechanism that is not a genomic
effect, there are various non-genomic pathways. However, all of these
pathways are mediated by some type of steroid hormone receptor found at the plasma membrane. Ion channels, transporters, G-protein coupled receptors (GPCR), and membrane fluidity have all been shown to be affected by steroid hormones. Of these, GPCR linked proteins are the most common. For more information on these proteins and pathways, visit the steroid hormone receptor page.
2021 uranium mining by nationSchematic diagram of stages from uranium mining to energy production
Uranium mining is the process of extraction of uranium ore from the ground. Over 50 thousand tons of uranium were produced in 2019. Kazakhstan, Canada, and Australia
were the top three uranium producers, respectively, and together
account for 68% of world production. Other countries producing more than
1,000 tons per year included Namibia, Niger, Russia, Uzbekistan, the United States, and China. Nearly all of the world's mined uranium is used to power nuclear power plants. Historically uranium was also used in applications such as uranium glass or ferrouranium
but those applications have declined due to the radioactivity of
uranium and are nowadays mostly supplied with a plentiful cheap supply
of depleted uranium
which is also used in uranium ammunition. In addition to being cheaper,
depleted uranium is also less radioactive due to a lower content of
short-lived 234 U and 235 U than natural uranium.
Uranium is mined by in-situ leaching (57% of world production) or by conventional underground or open-pit mining
of ores (43% of production). During in-situ mining, a leaching solution
is pumped down drill holes into the uranium ore deposit where it
dissolves the ore minerals. The uranium-rich fluid is then pumped back
to the surface and processed to extract the uranium compounds from
solution. In conventional mining, ores are processed by grinding the ore
materials to a uniform particle size and then treating the ore to
extract the uranium by chemical leaching. The milling process commonly yields dry powder-form material consisting of natural uranium, "yellowcake," which is nowadays commonly sold on the uranium market as U3O8. While some nuclear power plants – most notably heavy water reactors like the CANDU – can operate with natural uranium (usually in the form of uranium dioxide), the vast majority of commercial nuclear power plants and many research reactors require uranium enrichment, which raises the content of 235 U from the natural 0.72% to 3–5% (for use in light water reactors) or even higher, depending on the application. Enrichment requires conversion of the yellowcake into uranium hexafluoride and production of the fuel (again usually uranium dioxide, but sometimes uranium carbide, uranium hydride or uranium nitride) from that feedstock.
History
Early uranium mining
Miners on North Star Mountain in Colorado, 1879Yellowcake and ore mined in Australia
Before 1789, when Martin Heinrich Klaproth discovered the element, uranium compounds produced included nitrate, sulfate, phosphate, acetate and potassium- and sodium-diuranate. Klaproth detected the element in pitchblende from the George Wagsfort mine, Ore Mountains, and established commercial use as glass coloring. Pitchblende from these mountains was mentioned as early as 1565, and 110 t of uranium was produced from 1825 until 1898. In 1852, the uranium mineral autunite from the Massif Central was identified.
Around 1850, uranium mining began in Joachimsthal, Bohemia, where more than 620 t
of uranium metal (tU) was produced from 1850 and 1898, with 10,000 tU
produced before closure in 1968. In 1871, uranium ore mining began in Central City, Colorado, where 50 t were mined before 1895. In 1873, the uranium mining began in the South Terras mine, St Stephen-in-Brannel, Cornwall, producing most of the 300 tU from that area in the 19th century. In 1898, carnotite was first mined in the Uravan Mineral Belt, yielding 10 tU annually.
In 1898, Pierre Curie and Marie Skłodowska-Curie took delivery of 1 t of pitchblende from St. Joachimsthal, from which Marie identified the element radium. Pierre advocated its usage as a cancer cure, which fostered a spa business for that town.
In 1922, Union Minière du Haut Katanga
started producing medicinal radium from the Shinkolobwe mine, but
closed down in the late 1930s as the radium market diminished. In May
1940, the Nazis invaded Belgium and seized Union Minière's uranium ore
stored there. On 18 September 1942, 1250 t of Shinkolobwe uranium ore
for the Manhattan Project was purchased from Union Minière's Edgar Sengier, who had stockpiled the ore in an Archer Daniels Midland warehouse near the Bayonne Bridge, Staten Island. In 1943, the Sengier reopened the Sinkolobwe mine with U.S. Army Corps of Engineers' resources, and a $13 million investment from the United States.
Sengier reported that uranium ore had been extracted from the mine
down to a depth of 79 meters, but that another 101 meters of ore was
available for extraction. This amounted to 10,000 tons of up to 60% triuranium octoxide. The project also acquired most of the production from the Eldorado Mine (Northwest Territories).
According to Richard Rhodes, referring to German uranium research, "Auer,
the thorium specialists ... delivered the first ton of pure uranium
oxide processed from Joachimsthal ores to the War Office in January
1940. In June 1940 ... Auer ordered sixty tons of refined uranium oxide
from the Union Miniére in occupied Belgium."hile the Soviet Republics of Kazakhstan and the RSFSR
would later become some of the leading uranium producers in the world,
immediately after the end of World War II the availability of large
uranium deposits in the USSR wasn't yet known and thus the Soviets
developed immense mining operations in their satellite states East Germany and Czechoslovakia which had known uranium deposits in the Ore Mountains. The deliberately opaquely named SDAG Wismut (the German term "Wismut" for Bismuth should give the illusion of prospection for a metal the Soviets definitely weren't after) became the biggest employer in the Saxon Ore Mountains and remote mining towns like Johanngeorgenstadt
swelled to ten times their population in a few years. The mining cost
immense amounts of money and miners were on the one hand subject to
heavier repression and surveillance but on the other hand allowed more
generous supply with consumer goods than other East Germans. While
production was never able to compete with global uranium market prices, the dual use nature of the mined material as well as the possibility to pay miners in soft currency but sell uranium for hard currency
or substitute imports which would have had to be paid for in hard
currency tipped the scales in favor of continuing mining operations
throughout the Cold War. After German reunification, mining was wound down and the arduous task of rehabilitating the land impacted by mining was begun.
The seventeen towns and mines under Wismut's control contributed
50 percent of the uranium used in the Soviet's first atomic bomb, Joe-1,
and 80 percent of the uranium used in the Soviet nuclear program. Of
the 150,000 laborers, 1281 were killed in accidents and 20,000 suffered
injuries. After Stalin's death in 1953, the Red Army turned over control
of production to SDAG, and prison laborers were released, reducing the
population of laborers to 45,000. At its peak in 1953, the St.
Joachimsthal mines had 16,100 inmates, half of whom were Soviet
political prisoners.
In 1990, 55% of world production came from underground mines, but
this shrank to 33% by 1999. From 2000, new Canadian mines again
increased the proportion of underground mining, and with Olympic Dam it is now 37%. In situ leach (ISL, or ISR) mining has been steadily increasing its share of the total, mainly due to Kazakhstan.
Many different types of uranium deposits have been discovered and
mined.
There are mainly three types of uranium deposits including
unconformity-type deposits, namely paleoplacer deposits and
sandstone-type, also known as roll front type deposits.
Uranium deposits are classified into 15 categories according to
their geological setting and the type of rock in which they are found.
This geological classification system is determined by the International Atomic Energy Agency (IAEA).
Uranium is also contained in seawater but at present prices on the uranium market, costs would have to be lowered by a factor of 3–6 to make its recovery economical.
Sedimentary
The Mi Vidauranium mine, near Moab, Utah. Note alternating red and white/green sandstone.
This type of uranium deposit is easier and cheaper to mine than the
other types because the uranium is found not far from the surface of the
crust.
Sandstone uranium deposits are generally of two types. Roll-front type deposits occur at the boundary between the up dip and oxidized part of a sandstone body and the deeper down dip reduced part of a sandstone body. Peneconcordant sandstone uranium deposits, also called Colorado Plateau–type
deposits, most often occur within generally oxidized sandstone bodies,
often in localized reduced zones, such as in association with carbonized
wood in the sandstone.
Precambrian quartz-pebble conglomerate-type uranium deposits
occur only in rocks older than two billion years old. The conglomerates
also contain pyrite. These deposits have been mined in the Blind River–Elliot Lake district of Ontario, Canada, and from the gold-bearing Witwatersrand conglomerates of South Africa.
Unconformity-type deposits make up about 33% of the World Outside Centrally Planned Economies Areas' (WOCA) uranium deposits.
Igneous or hydrothermal
Hydrothermal
uranium deposits encompass the vein-type uranium ores. Vein-type
hydrothermal uranium deposits represent epigenetic concentrations of
uranium minerals that typically fill breccias, fractures, and shear
zones.
Many studies have sought to identify the source of uranium with
hydrothermal vein-type deposits and the potential sources still remains a
mystery, but are thought to include preexisting rocks that have been
broken down by weathering and force that come from areas of long-term
sediment build up.
The South Chine Block is an example of a region that has been relying
on vein-type hydrothermal uranium deposit demand for the past half
century. Igneous deposits include nepheline syenite intrusives at Ilimaussaq, Greenland; the disseminated uranium deposit at Rossing, Namibia; uranium-bearing pegmatites, and the Aurora crater lake deposit of the McDermitt Caldera in Oregon. Disseminated deposits are also found in the states of Washington and Alaska in the US.
Breccia
Breccia
uranium deposits are found in rocks that have been broken due to
tectonic fracturing, or weathering. Breccia uranium deposits are most
common in India, Australia and the United States.
A large mass of breccia is called a breccia pipe or chimney and is
composed of the rock forming an irregular and almost cylinder-like
shape. The origin of breccia pipe is uncertain but it is thought that
they form on intersections and faults. When the formations are found
solid in ground host rock called rock flour, it usually is often a site
for copper or uranium mining. Copper Creek, Arizona, is home to
approximately 500 mineralized breccia pipes and Cripple Creek, Colorado,
also is a site that contains breccia pipe ore deposits that is
associated with a volcanic pipe.
Uranium
prospecting is similar to other forms of mineral exploration with the
exception of some specialized instruments for detecting the presence of
radioactive isotopes.
The Geiger counter
was the original radiation detector, recording the total count rate
from all energy levels of radiation. Ionization chambers and Geiger
counters were first adapted for field use in the 1930s. The first
transportable Geiger–Müller counter (weighing 25 kg) was constructed at
the University of British Columbia
in 1932. H.V. Ellsworth of the GSC built a lighter weight, more
practical unit in 1934. Subsequent models were the principal instruments
used for uranium prospecting for many years, until geiger counters were
replaced by scintillation counters.
The use of airborne detectors to prospect for radioactive
minerals was first proposed by G. C. Ridland, a geophysicist working at Port Radium in 1943. In 1947, the earliest recorded trial of airborne radiation detectors (ionization chambers and Geiger counters) was conducted by Eldorado Mining and Refining Limited. (a Canadian Crown Corporation since sold to become Cameco Corporation). The first patent for a portable gamma-rayspectrometer was filed by Professors Pringle, Roulston & Brownell of the University of Manitoba in 1949, the same year as they tested the first portable scintillation counter on the ground and in the air in northern Saskatchewan.
Airborne gamma-ray spectrometry is now the accepted leading
technique for uranium prospecting with worldwide applications for
geological mapping, mineral exploration & environmental monitoring.
Airborne gamma-ray spectrometry used specifically for uranium
measurement and prospecting must account for a number of factors like
the distance between the source and the detector and the scattering of
radiation through the minerals, surrounding earth and even in the air.
In Australia, a Weathering Intensity Index has been developed to help
prospectors based on the Shuttle Radar Topography Mission (SRTM)
elevation and airborne gamma-ray spectrometry images.
A deposit of uranium, discovered by geophysical techniques, is
evaluated and sampled to determine the amounts of uranium materials that
are extractable at specified costs from the deposit. Uranium reserves
are the amounts of ore that are estimated to be recoverable at stated
costs. As prices rise or technology allows for lower cost of recovery of
known, previously uneconomic, deposits, reserves increase. For uranium
this effect is particularly pronounced as the biggest currently
uneconomic reserve – uranium extraction from seawater – is bigger than all known land based resources of uranium combined.
Mining techniques
As with other types of hard rock mining there are several methods of extraction. In 2016, the percentage of the mined uranium produced by each mining method was: in-situ leach (49.7 percent), underground mining (30.8 percent), open pit (12.9 percent), heap leaching (0.4 percent), co-product/by-product (6.1%). The remaining 0,1% was derived as miscellaneous recovery.
In open pit mining, overburden
is removed by drilling and blasting to expose the ore body, which is
then mined by blasting and excavation using loaders and dump trucks.
Workers spend much time in enclosed cabins thus limiting exposure to
radiation. Water is extensively used to suppress airborne dust levels.
Groundwater is an issue in all types of mining, but in open pit mining,
the usual way of dealing with it – i.e. when the target mineral is found
below the natural water table – is to lower the water table by pumping
off the water. The ground may settle considerably when groundwater is
removed and may again move unpredictably when groundwater is allowed to
rise again after mining is concluded. Land reclamation after mining
takes different routes, depending on the amount of material removed. Due
to the high energy density of uranium, it is often sufficient to fill
in the former mine with the overburden, but in case of a mass deficit
exceeding the height difference between the previous surface level and
the natural water table, artificial lakes develop when groundwater
removal ceases. If sulfites, sulfides or sulfates are present in the
now-exposed rocks acid mine drainage
can be a concern for those newly developing bodies of water. Mining
companies are now required by law to establish a fund for future
reclamation while mining is ongoing and those funds are usually
deposited in such a way as to be unaffected by bankruptcy of the mining
company.
Underground
If
the uranium is too far below the surface for open pit mining, an
underground mine might be used with tunnels and shafts dug to access and
remove uranium ore.
Underground uranium mining is in principle no different from any other hard rock mining
and other ores are often mined in association (e.g., copper, gold,
silver). Once the ore body has been identified a shaft is sunk in the
vicinity of the ore veins, and crosscuts are driven horizontally to the
veins at various levels, usually every 100 to 150 metres. Similar
tunnels, known as drifts, are driven along the ore veins from the
crosscut. To extract the ore, the next step is to drive tunnels, known
as raises when driven upwards and winzes when driven downwards, through
the deposit from level to level. Raises are subsequently used to develop
the stopes where the ore is mined from the veins.
The stope, which is the workshop of the mine, is the excavation
from which the ore is extracted. Three methods of stope mining are
commonly used. In the "cut and fill" or "open stoping" method, the space
remaining following removal of ore after blasting is filled with waste
rock and cement. In the "shrinkage" method, only sufficient broken ore
is removed via the chutes below to allow miners working from the top of
the pile to drill and blast the next layer to be broken off, eventually
leaving a large hole. The method known as "room and pillar" is used for
thinner, flatter ore bodies. In this method the ore body is first
divided into blocks by intersecting drives, removing ore while so doing,
and then systematically removing the blocks, leaving enough ore for
roof support.
Historical method of underground uranium mining, Nucla, Colorado, 1972
The health effects discovered from radon exposure in unventilated uranium mining prompted the switch away from uranium mining via tunnel mining towards open cut and in-situ leaching
technology, a method of extraction that does not produce the same
occupational hazards, or mine tailings, as conventional mining.
With regulations in place to ensure the use of high volume
ventilation technology if any confined space uranium mining is
occurring, occupational exposure and mining deaths can be largely
eliminated. The Olympic Dam
and Canadian underground mines are ventilated with powerful fans with
radon levels being kept at a very low to practically "safe level" in
uranium mines. Naturally occurring radon in other, non-uranium mines,
also may need control by ventilation.
Heap leaching
Heap leaching is an extraction process by which chemicals (usually sulfuric acid)
are used to extract the economic element from ore which has been mined
and placed in piles on the surface. Heap leaching is generally
economically feasible only for oxide ore deposits. Oxidation of sulfide
deposits occurs during the geological process called weathering.
Therefore, oxide ore deposits are typically found close to the surface.
If there are no other economic elements within the ore a mine might
choose to extract the uranium using a leaching agent, usually a low
molar sulfuric acid.
If the economic and geological conditions are right, the mining
company will level large areas of land with a small gradient, layering
it with thick plastic (usually HDPE or LLDPE),
sometimes with clay, silt or sand beneath the plastic liner. The
extracted ore will typically be run through a crusher and placed in
heaps atop the plastic. The leaching agent will then be sprayed on the
ore for 30–90 days. As the leaching agent filters through the heap, the
uranium will break its bonds with the oxide rock and enter the solution.
The solution will then filter along the gradient into collecting pools
which will then be pumped to on-site plants for further processing. Only
some of the uranium (commonly about 70%) is actually extracted.
The uranium concentrations within the solution are very important
for the efficient separation of pure uranium from the acid. As
different heaps will yield different concentrations, the solution is
pumped to a mixing plant that is carefully monitored. The properly
balanced solution is then pumped into a processing plant where the
uranium is separated from the sulfuric acid.
Heap leach is significantly cheaper than traditional milling
processes. The low costs allow for lower grade ore to be economically
feasible (given that it is the right type of ore body). US environmental
law requires that the surrounding ground water is continually monitored
for possible contamination. The mine will also have to have continued
monitoring even after the shutdown of the mine. In the past mining
companies would sometimes go bankrupt, leaving the responsibility of mine reclamation
to the public. 21st century additions to US mining law require that
companies set aside the money for reclamation before the beginning of
the project. The money will be held by the public to insure adherence to
environmental standards if the company were to ever go bankrupt.
Trial well field for in-situ recovery at Honeymoon, South Australia
In-situ leaching (ISL), also known as solution mining, or in-situ
recovery (ISR) in North America, involves leaving the ore where it is in
the ground, and recovering the minerals from it by dissolving them and
pumping the pregnant solution to the surface where the minerals can be
recovered. Consequently, there is little surface disturbance and no
tailings or waste rock generated. However, the orebody needs to be
permeable to the liquids used, and located so that they do not
contaminate ground water away from the orebody.
Uranium ISL uses the native groundwater in the orebody which is
fortified with a complexing agent and in most cases an oxidant. It is
then pumped through the underground orebody to recover the minerals in
it by leaching. Once the pregnant solution is returned to the surface,
the uranium is recovered in much the same way as in any other uranium
plant (mill).
In Australian ISL mines (Beverley, Four Mile and Honeymoon Mine)
the oxidant used is hydrogen peroxide and the complexing agent sulfuric
acid. Kazakh ISL mines generally do not employ an oxidant but use much
higher acid concentrations in the circulating solutions. ISL mines in
the USA use an alkali leach due to the presence of significant
quantities of acid-consuming minerals such as gypsum and limestone in
the host aquifers. Any more than a few percent carbonate minerals means
that alkali leach must be used in preference to the more efficient acid
leach.
The Australian government has published a best practice guide for
in situ leach mining of uranium, which is being revised to take account
of international differences.
Seawater recovery
The uranium concentration in sea water is low, approximately 3.3 parts per billion or 3.3 micrograms per liter of seawater.
But the quantity of this resource is gigantic and some scientists
believe this resource is practically limitless with respect to
world-wide demand. That is to say, if even a portion of the uranium in
seawater could be used the entire world's nuclear power generation fuel
could be provided over a long time period. Some proponents claim this statistic is exaggerated.Although research and development for recovery of this low-concentration element by inorganic adsorbents such as titanium oxide
compounds has occurred since the 1960s in the United Kingdom, France,
Germany, and Japan, this research was halted due to low recovery
efficiency.
At the Takasaki Radiation Chemistry Research Establishment of the
Japan Atomic Energy Research Institute (JAERI Takasaki Research
Establishment), research and development has continued culminating in
the production of adsorbent by irradiation of polymer fiber. Adsorbents
have been synthesized that have a functional group (amidoxime group)
that selectively adsorbs heavy metals, and the performance of such
adsorbents has been improved. Uranium adsorption capacity of the polymer fiber adsorbent is high, approximately tenfold greater in comparison to the conventional titanium oxide adsorbent.
One method of extracting uranium from seawater is using a
uranium-specific nonwoven fabric as an adsorbent. The total amount of
uranium recovered from three collection boxes containing 350 kg of
fabric was >1 kg of yellowcake after 240 days of submersion in the ocean. The experiment by Seko et al.
was repeated by Tamada et al. in 2006. They found that the cost varied
from ¥15,000 to ¥88,000 depending on assumptions and "The lowest cost
attainable now is ¥25,000 with 4g-U/kg-adsorbent used in the sea area of
Okinawa, with 18 repetitionuses [sic]." With the May, 2008 exchange rate, this was about $240/kg-U.
In 2012, ORNL
researchers announced the successful development of a new adsorbent
material dubbed "HiCap", which vastly outperforms previous best
adsorbents, which perform surface retention of solid or gas molecules,
atoms or ions.
"We have shown that our adsorbents can extract five to seven times more
uranium at uptake rates seven times faster than the world's best
adsorbents," said Chris Janke, one of the inventors and a member of
ORNL's Materials Science and Technology Division. HiCap also effectively
removes toxic metals from water, according to results verified by
researchers at Pacific Northwest National Laboratory.
In 2012 it was estimated that this fuel source could be extracted at 10 times the current price of uranium.[40]
In 2014, with the advances made in the efficiency of seawater uranium
extraction, it was suggested that it would be economically competitive
to produce fuel for light water reactors from seawater if the process
was implemented at large scale.
Uranium extracted on an industrial scale from seawater would constantly
be replenished by both river erosion of rocks and the natural process
of uranium dissolved from the surface area of the ocean floor, both of which maintain the solubility equilibria of seawater concentration at a stable level. Some commentators have argued that this strengthens the case for nuclear power to be considered a renewable energy.
Co-product/by-product
Uranium
can be recovered as a by-product along with other co-products
such as molybdenum, vanadium, nickel, zinc and petroleum
products. Uranium is also often found in phosphate minerals, where it has to be removed because phosphate is mostly used for fertilizers. Phosphogypsum is a waste product from phosphate mining that can contain significant amounts of uranium and radium. Coal fly ash also contains significant amounts of uranium and has been suggested as a source for uranium extraction.
Resources
Uranium
occurs naturally in many rocks, and even in seawater. However, like
other metals, it is seldom sufficiently concentrated to be economically
recoverable.
Like any resource, uranium cannot be mined at any desired concentration.
No matter the technology, at some point it is too costly to mine lower
grade ores.
Mining companies usually consider concentrations greater than 0.075%
(750 ppm) as ore, or rock economical to mine at current uranium market
prices.
There are around 40 trillion tons of uranium in Earth's crust, but most is distributed at trace concentration over its 3×1019 ton mass.Estimates of the amount concentrated into ores affordable to extract for
under $130 per kg can be less than a millionth of that total.
Uranium grades
Source
Concentration
Very high-grade ore – 20% U
200,000 ppm U
High-grade ore – 2% U
20,000 ppm U
Low-grade ore – 0.1% U
1,000 ppm U
Very low-grade ore – 0.01% U
100 ppm U
Granite
4–5 ppm U
Sedimentary rock
2 ppm U
Earth's continental crust (av)
2.8 ppm U
Seawater
0.003 ppm U
Economically extractable reserves of uranium (0.01% ore or better)
Ore concentration
tonnes of uranium
Ore type
>1%
10000
vein deposits
0.2–1%
2 million
pegmatites, unconformity deposits
0.1–0.2%
80 million
fossil placers, sandstones
0.02–0.1%
100 million
lower grade fossil placers, sandstones
100–200 ppm
2 billion
volcanic deposits
The table assumes the fuel will be used in a LWR burner. Uranium becomes far more economical when used in a fast burner reactor such as the Integral Fast Reactor.
Uranium-235, the fissile isotope of uranium used in nuclear reactors,
makes up about 0.7% of uranium from ore. It is the only naturally
occurring isotope capable of directly generating nuclear power.
While uranium-235 can be "bred" from 234 U, a natural decay product of 238 U present at 55 ppm in all natural uranium samples, uranium-235 is ultimately a finite non-renewable resource.
Due to the currently low price of uranium, the majority of commercial light water reactors operate on a "once through fuel cycle" which leaves virtually all the energy contained in the original 238 U, which makes up over 99% of natural uranium, unused. Nuclear reprocessing can recover part of that energy by producing MOX fuel or Remix Fuel
for use in conventional power generating light water reactors. This
technology is currently used at industrial scale in France, Russia and
Japan. However, at current uranium prices, this is widely deemed
uneconomical if only the "input" side is considered.
Reserves are the most readily available resources.
About 96% of the global uranium reserves are found in these ten
countries: Australia, Canada, Kazakhstan, South Africa, Brazil, Namibia,
Uzbekistan, the United States, Niger, and Russia.
The known uranium resources represent 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. There
was very little uranium exploration between 1985 and 2005, so the
significant increase in exploration effort that we are now seeing could
readily double the known economic resources. On the basis of analogies
with other metal minerals, a doubling of price from price levels in 2007
could be expected to create about a tenfold increase in measured
resources, over time.
Known conventional resources
Known conventional resources are resources that are known to exist and easy to mine.
In 2006, there were about 4 million tons of conventional resources.
In 2011, this increased to 7 million tonnes.
Exploration for uranium has increased: from 1981 to 2007, annual
exploration expenditures grew modestly, from US$4 million to US$7
million. This increased to US$11 million in 2011.
The world's largest deposits of uranium are found in three
countries.
Australia has just over 30% of the world's reasonably assured resources
and inferred resources of uranium – about 1.673 megatonnes (3.69×109 lb).
Kazakhstan has about 12% of the world's reserves, or about 651 kilotonnes (1.4×109 lb).
Canada has 485 kilotonnes (1,100×106 lb) of uranium, representing about 9%.
Undiscovered conventional resources
Undiscovered conventional resources are resources that are thought to exist but have not been mined.
It will take a significant exploration and development effort to locate
the remaining deposits and begin mining them. However, since the entire
earth's geography has not been explored for uranium at this time, there
is still the potential to discover exploitable resources.
The OECD Redbook cites areas still open to exploration throughout the
world. Many countries are conducting complete aeromagnetic gradiometer
radiometric surveys to get an estimate the size of their undiscovered
mineral resources. Combined with a gamma-ray survey, these methods can
locate undiscovered uranium and thorium deposits.
The U.S. Department of Energy conducted the first and only national
uranium assessment in 1980 – the National Uranium Resource Evaluation
(NURE) program.
Secondary resources
Secondary
uranium resources are recovered from other sources such as nuclear
weapons, inventories, reprocessing and re-enrichment. Since secondary
resources have exceedingly low discovery costs and very low production
costs, they have displaced a significant portion of primary production.
In 2017, about 7% of uranium demand was met from secondary resources.
Due to reduction in nuclear weapons stockpiles, a large amount of
former weapons uranium was released for use in civilian nuclear
reactors. As a result, starting in 1990, a significant portion of
uranium nuclear power requirements were supplied by former weapons
uranium, rather than newly mined uranium. In 2002, mined uranium
supplied only 54 percent of nuclear power requirements.
But as the supply of former weapons uranium has been used up, mining
has increased, so that in 2012, mining provided 95 percent of reactor
requirements, and the OCED Nuclear Energy Agency and the International
Atomic Energy Agency projected that the gap in supply would be
completely erased in 2013.
Inventories
Inventories are kept by a variety of organizations – government, commercial and others.
The US DOE keeps inventories for security of supply in order to cover for emergencies where uranium is not available at any price.
Both the US and Russia have committed to recycle their nuclear
weapons into fuel for electricity production. This program is known as
the Megatons to Megawatts Program.
Down blending 500 tonnes (1,100×103 lb) of Russian weapons high enriched uranium (HEU) will result in about 15 kilotonnes (33,000×103 lb) of low enriched uranium (LEU) over 20 years. This is equivalent to about 152 kilotonnes (340×106 lb) of natural U, or just over twice annual world demand. Since 2000, 30 tonnes (66×103 lb) of military HEU is displacing about 10.6 kilotonnes (23×106 lb) of uranium oxide mine production per year which represents some 13% of world reactor requirements.
The Megatons to Megawatts program came to an end in 20
Plutonium recovered from nuclear weapons or other sources can be
blended with uranium fuel to produce a mixed-oxide fuel. In June 2000,
the US and Russia agreed to dispose of 34 kilotonnes (75×106 lb)
each of weapons-grade plutonium by 2014. The US undertook to pursue a
self-funded dual track program (immobilization and MOX). The G-7 nations
provided US$1 billion to set up Russia's program. The latter was
initially MOX specifically designed for VVER reactors, the Russian
version of the Pressurized Water Reactor (PWR), the high cost being
because this was not part of Russia's fuel cycle policy. This MOX fuel
for both countries is equivalent to about 12 kilotonnes (26×106 lb) of natural uranium.
The U.S. also has commitments to dispose of 151 tonnes (330×103 lb) of non-waste HEU.
Nuclear reprocessing (or recycling) can increase the supply of uranium by separating the uranium from spent nuclear fuel.
Spent nuclear fuel is primarily composed of uranium, with a typical concentration of around 96% by mass.
The composition of reprocessed uranium depends on the time the fuel has been in the reactor, but it is mostly uranium-238, with about 1% uranium-235, 1% uranium-236 and smaller amounts of other isotopes including uranium-232.
Currently, there are eleven reprocessing plants in the world. Of
these, two are large-scale commercially operated plants for the
reprocessing of spent fuel elements from light water reactors with
throughputs of more than 1 kilotonne (2.2×106 lb) of uranium per year. These are La Hague, France with a capacity of 1.6 kilotonnes (3.5×106 lb) per year and Sellafield, England at 1.2 kilotonnes (2.6×106 lb) uranium per year.
The rest are small experimental plants.he two large-scale commercial reprocessing plants together can reprocess 2,800 tonnes of uranium waste annually.he United States had reprocessing plants in the past but banned
reprocessing in the late 1970s due to the high costs and the risk of nuclear proliferation via plutonium.
The main problems with uranium reprocessing are the cost of mined uranium compared to the cost of reprocessing present, reprocessing and the use of plutonium as reactor fuel is far
more expensive than using uranium fuel and disposing of the spent fuel
directly – even if the fuel is only reprocessed once.
Reprocessing is most useful as part of a nuclear fuel cycle using fast-neutron reactors since reprocessed uranium and reactor-grade plutonium both have isotopic compositions not optimal for use in today's thermal-neutron reactors.
Unconventional resources
Unconventional
resources are occurrences that require novel technologies for their
exploitation and/or use. Often unconventional resources occur in
low-concentration. The exploitation of unconventional uranium requires
additional research and development efforts for which there is no
imminent economic need, given the large conventional resource base and
the option of reprocessing spent fuel.
Phosphates, seawater, uraniferous coal ash, and some type of oil shales are examples of unconventional uranium resources.
Phosphates
Uranium occurs at concentrations of 50 to 200 parts per million (ppm) in phosphate-laden earth or phosphate rock.
As uranium prices increase, there has been interest in extraction of
uranium from phosphate rock, which is normally used as the basis of
phosphate fertilizers.
There are 22 million tons of uranium in phosphate deposits. Recovery of uranium from phosphates is a mature technology;
it has been utilized in Belgium and the United States, but high
recovery costs limit the utilization of these resources, with estimated
production costs in the range of US$60–100/kgU including capital
investment, according to a 2003 OECD report for a new 100 tU/year
project.
Historical operating costs for the uranium recovery from phosphoric acid range from $48–$119/kg U3O8.
In 2011, the average price paid for U3O8 in the United States was $122.66/kg.
Worldwide, approximately 400 wet-process phosphoric acid
plants were in operation. Assuming an average recoverable content of
100 ppm of uranium, and that uranium prices do not increase so that the
main use of the phosphates are for fertilizers, this scenario would result in a maximum theoretical annual output of 3.7 kilotonnes (8.2×106 lb) U3O8.
Seawater
Unconventional uranium resources include up to 4,000 megatonnes (8,800×109 lb)
of uranium contained in sea water. Several technologies to extract
uranium from sea water have been demonstrated at the laboratory scale.
According to the OECD, uranium may be extracted from seawater for about
US$300/kgU.
In 2012, ORNL
researchers announced the successful development of a new absorbent
material dubbed HiCap, which vastly outperforms previous best
adsorbents, which perform surface retention of solid or gas molecules,
atoms or ions. "We have shown that our adsorbents can extract five to
seven times more uranium at uptake rates seven times faster than the
world's best adsorbents", said Chris Janke, one of the inventors and a
member of ORNL's Materials Science and Technology Division. HiCap also
effectively removes toxic metals from water, according to results
verified by researchers at Pacific Northwest National Laboratory.
Uraniferous coal ash
Annual release of "technologically enhanced"/concentrated Naturally occurring radioactive material, uranium and thoriumradioisotopes naturally found in coal and concentrated in heavy/bottom coal ash and airborne fly ash. As predicted by ORNL
to cumulatively amount to 2.9 million tons over the 1937–2040 period,
from the combustion of an estimated 637 billion tons of coal worldwide.
According to a study by Oak Ridge National Laboratory, the theoretical maximum energy potential (when used in breeder reactors) of trace uranium and thorium in coal actually exceeds the energy released by burning the coal itself. This is despite very low concentration of uranium in coal of only several parts per million average before combustion.
From 1965 to 1967 Union Carbide operated a mill in North Dakota, United States, burning uraniferous lignite and extracting uranium from the ash. The plant produced about 150 metric tons of U3O8 before shutting down.
An international consortium has set out to explore the commercial
extraction of uranium from uraniferous coal ash from coal power
stations located in Yunnan province, China. The first laboratory scale amount of yellowcake uranium recovered from uraniferous coal ash was announced in 2007.
The three coal power stations at Xiaolongtang, Dalongtang and Kaiyuan
have piled up their waste ash. Initial tests from the Xiaolongtang ash
pile indicate that the material contains (160–180 parts per million
uranium), suggesting a total of 2.085 kilotonnes (4.60×106 lb) U3O8 could be recovered from that ash pile alone.
Oil shales
Some oil shales contain uranium, which may be recovered as a byproduct. Between 1946 and 1952, a marine type of Dictyonema shale was used for uranium production in Sillamäe, Estonia, and between 1950 and 1989 alum shale was used in Sweden for the same purpose.
A breeder reactor produces more nuclear fuel than it consumes and
thus can extend the uranium supply. It typically turns the dominant
isotope in natural uranium, uranium-238, into fissile plutonium-239.
This results in a hundredfold increase in the amount of energy to be
produced per mass unit of uranium, because uranium-238, which comprises
99.3% of natural uranium, is not used in conventional reactors, which
instead use uranium-235 (comprising 0.7% of natural uranium). In 1983, physicist Bernard Cohen proposed that the world supply of uranium is effectively inexhaustible, and could therefore be considered a form of renewable energy.
He claims that fast breeder reactors,
fueled by naturally-replenished uranium-238 extracted from seawater,
could supply energy at least as long as the sun's expected remaining
lifespan of five billion years.
There are two types of breeders: fast breeders and thermal
breeders.
Efforts at commercializing breeder reactors have been largely
unsuccessful, due to higher costs and complexity compared to LWR, as
well as political opposition.
A few commercial breeder reactors exist. In 2016, the Russian BN-800 fast-neutron breeder reactor started producing commercially at full power (800 MWe), joining the previous BN-600. As of 2020, the Chinese CFR-600 is under construction after the success of the China Experimental Fast Reactor,
based on the BN-800. These reactors are currently generating mostly
electricity rather than new fuel because the abundance and low price of
mined and reprocessed uranium oxide makes breeding uneconomical, but
they can switch to breed new fuel and close the cycle as needed.
The CANDU reactor, which was designed to be fueled with natural uranium, is capable of using spent fuel from Light Water Reactors as fuel, since it contains more fissile material
than natural uranium. Research into "DUPIC" – direct use of PWR spent
fuel in CANDU type reactors – is ongoing and could increase the
usability of fuel without the need for reprocessing.
A fast breeder, in addition to consuming uranium-235, converts fertile uranium-238 into plutonium-239, a fissile
fuel. Fast breeder reactors are more expensive to build and operate,
including the reprocessing, and could only be justified economically if
uranium prices were to rise to pre-1980 values in real terms. In
addition to considerably extending the exploitable fuel supply, these
reactors have an advantage in that they produce less long-lived transuranic wastes, and can consume nuclear waste from current light water reactors, generating energy in the process.
Uranium turned out to be far more plentiful than anticipated, and
the price of uranium declined rapidly (with an upward blip in the
1970s). This is why the United States halted their use in 1977, and the UK abandoned the idea in 1994.
Significant technical and materials problems were encountered with FBRs,
and geological exploration showed that scarcity of uranium was not
going to be a concern for some time. By the 1980s, due to both factors,
it was clear that FBRs would not be commercially competitive with
existing light water reactors. The economics of FBRs still depend on the
value of the plutonium fuel which is bred, relative to the cost of
fresh uranium.
At higher uranium prices breeder reactors
may be economically justified. Many nations have ongoing breeder
research programs. China, India, and Japan plan large scale utilization
of breeder reactors during the coming decades. 300 reactor-years
experience has been gained in operating them.
Fissile uranium can be produced from thorium
in thermal breeder reactors. Thorium is three times more plentiful than
uranium. Thorium-232 is in itself not fissile, but it can be made into
fissile uranium-233 in a breeder reactor. In turn, the uranium-233 can be fissioned, with the advantage that smaller amounts of transuranics are produced by neutron capture, compared to uranium-235 and especially compared to plutonium-239.
Despite the thorium fuel cycle
having a number of attractive features, development on a large scale
can run into difficulties, mainly due to the complexity of fuel
separation and reprocessing.
Advocates for liquid core and molten salt reactors such as LFTR claim that these technologies negate the above-mentioned thorium's disadvantages present in solid-fueled reactors.
The first successful commercial reactor at the Indian Point Energy Center in Buchanan, New York, (Indian Point Unit 1) ran on thorium. The first core did not live up to expectations.
The 10 countries responsible for 94% of all uranium extraction.
The world's top uranium producers in 2017 were Kazakhstan (39% of world production), Canada (22%) and Australia (10%). Other major producers include Namibia (6.7%), Niger (6%), and Russia (5%).
Uranium production in 2017 was 59,462 tonnes, 93% of the demand.
The balance came from inventories held by utilities and other fuel
cycle companies, inventories held by governments, used reactor fuel that
has been reprocessed, recycled materials from military nuclear programs
and uranium in depleted uranium stockpiles.
Demand
World consumption of primary energy by energy type in terawatt-hours (TWh)
Uranium demand was 62.8 kilotonnes (138×106 lb) in 2017.
As some countries are not able to supply their own needs of
uranium economically, countries have resorted to importing uranium ore
from elsewhere. For example, owners of U.S. nuclear power reactors
bought 67 million pounds (30 kt) of natural uranium in 2006. Out of that
84%, or 56 million pounds (25 kt), were imported from foreign
suppliers, according to the Energy Department.
Because of the improvements in gas centrifuge technology in the 2000s, replacing former gaseous diffusion plants, cheaper separative work units have enabled the economic production of more enriched uranium from a given amount of natural uranium, by re-enriching tails ultimately leaving a depleted uranium tail of lower enrichment. This has somewhat lowered the demand for natural uranium.
Demand forecasts
According
to Cameco Corporation, the demand for uranium is directly linked to the
amount of electricity generated by nuclear power plants. Reactor
capacity is growing slowly, reactors are being run more productively,
with higher capacity factors, and reactor power levels. Improved reactor
performance translates into greater uranium consumption.
Nuclear power stations of 1000 megawatt electrical generation capacity require around 200 tonnes (440×103 lb)
of natural uranium per year. For example, the United States has 103
operating reactors with an average generation capacity of 950 MWe
demanded over 22 kilotonnes (49×106 lb) of natural uranium in 2005. As the number of nuclear power plants increases, so does the demand for uranium.
As nuclear power plants take a long time to build and refuelling
is undertaken at sporadic, predictable intervals, uranium demand is
rather predictable in the short term. It is also less dependent on
short-term economic boom–bust cycles as nuclear power has one of
strongest fixed costs to variable costs ratios (i.e. the marginal costs of running, rather than leaving idle an already constructed power plant are very low, compared to the capital costs
of construction) and it is thus nearly never advisable to leave a
nuclear power plant idle for economic reasons. However, nuclear policy
can lead to short term fluctuations in demand, as evidenced by the
German nuclear phaseout, which was decided upon by the government of Gerhard Schröder (1998–2005) reversed during the second Merkel cabinet (2009–2013) only for a reversal of that reversal to occur as a consequence of the Fukushima nuclear accident, which also led to the temporary shutdown of several German nuclear power plants.
Uranium prices can fluctuate widely, which has an effect on mining companies
Generally speaking, in the case of nuclear energy the cost of fuel
has the lowest share in total energy costs of all fuel consuming energy
forms (i.e. Fossil fuels, biomass and nuclear). Furthermore, given the
immense energy density of nuclear fuel (particularly in the form of
enriched uranium or high grade plutonium), it is easy to stockpile
amounts of fuel material to last several years at constant consumption.
Power plants that do not have online refuelling
capabilities, as is the case for the vast majority of commercial power
plants in operation, will refuel as seldom as possible to avoid costly
downtime and usually plan refuelling shutdowns long in advance so as to
allow maintenance and inspection to use the scheduled downtime as well.
As such power plant operators tend to have long-term contracts with fuel
suppliers that are – if at all – only minorly affected by the
fluctuations of uranium prices. The effect on electricity price for end
consumers is negligible even in countries like France, which derive a
majority of their electric energy from nuclear power. Nonetheless, short
term price developments like the 2007 uranium bubble,
can have drastic effects on mining companies, prospection and the
economic calculations as to whether a certain deposit is worthwhile for
commercial purposes.
Since 1981 uranium prices and quantities in the US are reported by the Department of Energy.
The import price dropped from 32.90 US$/lb-U3O8 in 1981 down to 12.55 in 1990 and to below 10 US$/lb-U3O8 in the year 2000. Prices paid for uranium during the 1970s were higher, 43 US$/lb-U3O8
is reported as the selling price for Australian uranium in 1978 by the
Nuclear Information Centre. Uranium prices reached an all-time low in
2001, costing US$7/lb, but in April 2007 the price of Uranium on the
spot market rose to US$113.00/lb, a high point of the uranium bubble of 2007. This was very close to the all time high (adjusted for inflation) in 1977.
Following the 2011 Fukushima nuclear disaster,
the global uranium sector remained depressed with the uranium price
falling more than 50%, declining share values, and reduced profitability
of uranium producers since March 2011 and into 2014. As a result,
uranium companies worldwide are reducing costs, and limiting operations. As an example, Westwater Resources
(previously Uranium Resources), has had to cease all uranium operations
due to unfavorable prices. Since then, Westwater has tried branching
out into other markets, namely lithium and graphite.
As of July 2014, the price of uranium concentrate remained near a
five-year low, the uranium price having fallen more than 50% from the
peak spot price in January 2011, reflecting the loss of Japanese demand
following the 2011 Fukushima nuclear disaster. As a result of continued low prices, in February 2014 mining company Cameco deferred plans to expand production from existing Canadian mines, although it continued work to open a new mine at Cigar Lake.
Also in February 2014, Paladin energy suspended operations at its mine
in Malawi, saying that the high-cost operation was losing money at
current prices.
Effect of price on mining and nuclear power plants
In
general short term fluctuations in the price of uranium are of more
concern to operators and owners of mines and potentially lucrative
deposits than to power plant operators. Due to its high energy density, uranium is easy to stockpile in the form of strategic reserves and thus a short term increase in prices can be compensated by accessing those reserves. Furthermore, many countries have de facto reserves in the form of reprocessed uranium or depleted uranium which still contain a share of fissile material that can make re-enrichment worthwhile if market conditions call for it. Nuclear reprocessing of spent fuel
is – as of the 2020s – done commercially primarily to use the fissile
material still contained in spent fuel. The commonly employed PUREX process recovers uranium and plutonium which can then be converted into MOX-fuel
for use in the same light water reactors that produced the spent fuel.
Whether reprocessing is economical is subject to much debate and depends
in part on assumptions as to the price of uranium and the cost of
disposal via deep geological repository or nuclear transmutation. Reactors that can run on natural uranium consume less mined uranium per unit of power produced but can have higher capital costs to build due to the need for heavy water as moderator. Furthermore they need to be capable of online refueling because the burnup
achievable with natural uranium is lower than that achievable with
enriched uranium – having to shut down the entire reactor for every
refueling would quickly make such a reactor uneconomic. Breeder reactors
also become more economical as uranium prices rise and it was among
other things a decline in uranium prices in the 1970s that led to a
decline in interest in breeder reactor technology. The thorium fuel cycle
is a further alternative if and when uranium prices remain at a
sustained high level and consequently interest in this alternative to
current "mainstream" light water reactor technology is dependent in no
small part on uranium prices.
Legality
Uranium
mining is illegal in a number of jurisdictions. As uranium is often
mined incidental to other minerals a ban in practice typically means
that uranium is buried again at the mine after initial extraction.
In March 1951, the United States Atomic Energy Commission (AEC) set a high price for uranium ore. The resultant uranium rush attracted many prospectors to the Southwest. Charles Steen made a significant discover near Moab, Utah, while Paddy Martinez made another near Grants, New Mexico.
However, by the 1960s, the United States, USSR, France and China were
reducing their acquisitions of uranium. The United States started
enriching only uranium mined within its country, but by 1965, production
had dropped by 40 percent. By 1971, in an attempt to stop further
reductions in prices, mining executives from UCAN, Nufcor, Rio Tinto,
and government representatives agreed to share the market with Canadians
getting 33.5 percent, South Africa 23.75 percent, France 21.75 percent,
Australia 17 percent, and Rio Tinto Zinc 4 percent. By 1974, this market share agreement ended as uranium prices rose in concert with energy prices due to OPEC boycotts, and the United States ending its trade ban of foreign uranium.
U.S. Delegates at the Fourth General Conference of the International Atomic Energy Agency in Vienna, Austria, 1960
In Europe a mixed situation exists. Considerable nuclear power
capacities have been developed, notably in Belgium, Finland, France,
Germany, Spain, Sweden, Switzerland, and the UK. In many countries
development of nuclear power has been stopped and phased out by legal actions. In Italy the use of nuclear power was barred by a referendum in 1987; this is now under revision. Ireland in 2008 also had no plans to change its non-nuclear stance.
The years 1976 and 1977 saw uranium mining become a major political issue in Australia, with the Ranger Inquiry (Fox) report opening up a public debate about uranium mining.
The Movement Against Uranium Mining group was formed in 1976, and many
protests and demonstrations against uranium mining were held. Concerns relate to the health risks and environmental damage from uranium mining. Notable Australian anti-uranium activists have included Kevin Buzzacott, Jacqui Katona, Yvonne Margarula, and Jillian Marsh.
The Kingdom of Saudi Arabia
with the help of China has built an extraction facility to obtain
uranium yellowcake from uranium ore. According to Western officials with
information regarding the extraction site, the process is conducted by
the oil-rich kingdom to champion nuclear technology. However, Saudi
Energy Minister denied having built a uranium ore facility and claimed
that the extraction of minerals is a fundamental part of the kingdom's
strategy to diversify its economy.
Despite sanctions on Russia some countries still buy its uranium in 2022, and some argue the EU should stop. As of 2022 S&P Global say non-Russian miners await more certainty before deciding whether to invest in new mines.
Health risks
Uranium ore emits radon gas. The health effects of high exposure to radon are a particular problem in the mining of uranium; significant excess lung cancer deaths have been identified in epidemiological studies of uranium miners employed in the 1940s and 1950s.
The first major studies with radon and health occurred in the context of uranium mining, first in the Joachimsthal region of Bohemia and then in the Southwestern United States during the early Cold War. Because radon is a product of the radioactive decay of uranium, underground uranium mines may have high concentrations of radon. Many uranium miners in the Four Corners region contracted lung cancer
and other pathologies as a result of high levels of exposure to radon
in the mid-1950s. The increased incidence of lung cancer was
particularly pronounced among Navajo and Mormon (who generally have low rates of lung cancer) miners. This is in part due to the religious prohibition on smoking in Mormonism.
Safety standards requiring expensive ventilation were not widely implemented or policed during this period. While radon exposure is the main source of lung cancer in non-smokers who aren't exposed to asbestos,
there is evidence that the combination of smoking and radon exposure
increases the risk above the combined risks of either harmful substance.
In studies of uranium miners, workers exposed to radon levels of 50 to 150 picocuries of radon per liter of air (2000–6000 Bq/m3) for about 10 years have shown an increased frequency of lung cancer. Statistically significant excesses in lung cancer deaths were present after cumulative exposures of less than 50 WLM. There is unexplained heterogeneity in these results (whose confidence intervals do not always overlap).
The size of the radon-related increase in lung cancer risk varied by
more than an order of magnitude between the different studies.
Since that time, ventilation and other measures have been used to
reduce radon levels in most affected mines that continue to operate. In
recent years, the average annual exposure of uranium miners has fallen
to levels similar to the concentrations inhaled in some homes. This has
reduced the risk of occupationally induced cancer from radon, although
it still remains an issue both for those who are currently employed in
affected mines and for those who have been employed in the past.
The power to detect any excess risks in miners nowadays is likely to be
small, exposures being much smaller than in the early years of mining. Coal mining
in addition to other health risks can also expose miners to radon as
uranium (and its decay product radon) are often found in and near coal
deposits and can accumulate underground as radon is denser than air.
In the USA, the Radiation Exposure Compensation Act provides compensation to sufferers of various health problems linked to radiation exposure,
or to their surviving relatives. Uranium miners, uranium mill workers
and uranium transport workers have been compensated under the scheme.
Despite efforts made in cleaning up uranium sites, significant
problems stemming from the legacy of uranium development still exist
today on the territory of the Navajo Nation
and in the states of Utah, Colorado, New Mexico, and Arizona. Hundreds
of abandoned mines have not been cleaned up and present environmental
and health risks in many communities.
At the request of the U.S. House Committee on Oversight and Government
Reform in October 2007, and in consultation with the Navajo Nation, the
Environmental Protection Agency (EPA), along with the Bureau of Indian
Affairs (BIA), the Nuclear Regulatory Commission (NRC), the Department
of Energy (DOE), and the Indian Health Service (IHS), developed a
coordinated Five-Year Plan to address uranium contamination.
Similar interagency coordination efforts are beginning in the State of
New Mexico as well.
In 1978, Congress passed the Uranium Mill Tailings Radiation Control Act
(UMTRCA), a measure designed to assist in the cleanup of 22 inactive
ore-processing sites throughout the southwest. This also included
constructing 19 disposal sites for the tailings, which contain a total
of 40 million cubic yards of low-level radioactive material.
The Environmental Protection Agency estimates that there are 4000 mines
with documented uranium production, and another 15,000 locations with
uranium occurrences in 14 western states, most found in the Four Corners area and Wyoming.
Peak uranium is the point in time that the maximum global uranium
production rate is reached. Predictions of peak uranium differ greatly.
Pessimistic predictions of future high-grade uranium production operate
on the thesis that either the peak has already occurred in the 1980s or that a second peak may occur sometime around 2035. Optimistic predictions claim that the supply is far more than demand and do not predict peak uranium.
As of 2017, identified uranium reserves recoverable at US$130/kg
were 6.14 million tons (compared to 5.72 million tons in 2015). At the
rate of consumption in 2017, these reserves are sufficient for slightly
over 130 years of supply. The identified reserves as of 2017 recoverable
at US$260/kg are 7.99 million tons (compared to 7.64 million tons in
2015).
The expected amount of usable uranium for nuclear power that is
recoverable depends greatly on how it is used. The main factor is the
nuclear technology: light-water reactors, which comprise the great
majority of reactors today, only consume about 0.5% of their uranium
fuel, leaving over 99% of it as spent fuel waste. Fast breeder reactors
instead consume closer to 99% of uranium fuel. Another factor is the
ability to extract uranium from seawater. About 4.5 billion tons of
uranium are available from seawater at about 10 times the current price
of uranium with current extraction technology, which is about a thousand
times the known uranium reserves.
The Earth's crust contains approximately 65 trillion tons of uranium,
of which about 32 thousand tons flow into oceans per year via rivers,
which are themselves fed via geological cycles of erosion, subduction
and uplift. The ability to extract uranium from seawater economically would therefore make uranium a renewable resource in practice.
Uranium can also be bred from thorium
(which is itself 3–4 times as abundant as uranium) in certain breeder
reactors, although there are currently no commercially practical thorium
reactors in the world and their development would require substantial
financial investment which is not justified given the current low prices
of natural uranium.
Thirteen countries have hit peak and exhausted their economically
recoverable uranium resources at current prices according to the Energy Watch Group.
In a similar manner to every other natural metal resource, for
every tenfold increase in the cost per kilogram of uranium, there is a
three-hundredfold increase in available lower quality ores that would
then become economical. The theory could be observed in practice during the Uranium bubble of 2007
when an unprecedented price hike led to investments in the development
of uranium mining of lower quality deposits which mostly became stranded assets after uranium prices returned to a lower level.
There is around 40 trillion tons of uranium in Earth's crust, but
most is distributed at low parts per million trace concentration over
its 3×1019 ton mass.
Estimates of the amount concentrated into ores affordable to extract
for under $130 per kg can be less than a millionth of that total.
One highly criticized life cycle study by Jan Willem Storm van Leeuwen
suggested that below 0.01–0.02% (100–200 ppm) in ore, the energy
required to extract and process the ore to supply the fuel, operate
reactors and dispose properly comes close to the energy gained by using
the uranium as a fissible material in the reactor. Researchers at the Paul Scherrer Institute who analyzed the Jan Willem Storm van Leeuwen
paper, however, have detailed the number of incorrect assumptions of
Jan Willem Storm van Leeuwen that led them to this evaluation, including
their assumption that all the energy used in the mining of Olympic Dam
is energy used in the mining of uranium, when that mine is
predominantly a copper mine and uranium is produced only as a
co-product, along with gold and other metals. The report by Jan Willem Storm van Leeuwen also assumes that all enrichment is done in the older and more energy intensive gaseous diffusion technology, whereas the less energy intensive gas centrifuge technology has produced the majority of the world's enriched uranium now for a number of decades.
In the early days of the nuclear industry, uranium was thought to be very scarce, so a closed fuel cycle would be needed. Fast breeder
reactors would be needed to create nuclear fuel for other power
producing reactors. In the 1960s, new discoveries of reserves and new
uranium enrichment techniques allayed these concerns.
An appraisal of nuclear power by a team at MIT in 2003, and updated in 2009, stated that:
Most commentators conclude that a half century of unimpeded growth is
possible, especially since resources costing several hundred dollars per
kilogram (not estimated in the Red Book) would also be economically
usable ... We believe that the world-wide supply of uranium ore is
sufficient to fuel the deployment of 1000 reactors over the next half
century.
Production
According
to Robert Vance of the OECD's Nuclear Energy Agency, the world
production rate of uranium has already reached its peak in 1980,
amounting to 69,683 tonnes (150×106 lb) of U3O8
from 22 countries. However, this is not due to lack of production
capacity. Historically, uranium mines and mills around the world have
operated at about 76% of total production capacity, varying within a
range of 57% and 89%. The low production rates have been largely
attributable to excess capacity. Slower growth of nuclear power and
competition from secondary supply significantly reduced demand for
freshly mined uranium until very recently. Secondary supplies include
military and commercial inventories, enriched uranium tails, reprocessed
uranium and mixed oxide fuel.
According to data from the International Atomic Energy Agency,
world production of mined uranium has peaked twice in the past: once,
circa 1960 in response to stockpiling for military use, and again in
1980, in response to stockpiling for use in commercial nuclear power. Up
until about 1990, the mined uranium production was in excess of
consumption by power plants. But since 1990, consumption by power plants
has outstripped the uranium being mined; the deficit being made up by
liquidation of the military (through decommissioning of nuclear weapons)
and civilian stockpiles. Uranium mining has increased since the
mid-1990s, but is still less than the consumption by power plants.
Primary sources
Various agencies have tried to estimate how long uranium primary resources will last, assuming a once-through cycle.
The European Commission said in 2001 that at the current level of
uranium consumption, known uranium resources would last 42 years. When
added to military and secondary sources, the resources could be
stretched to 72 years. Yet this rate of usage assumes that nuclear power
continues to provide only a fraction of the world's energy supply. If
electric capacity were increased six-fold, then the 72-year supply would
last just 12 years.
The world's present measured resources of uranium, economically
recoverable at a price of US$130/kg according to the industry groups Organisation for Economic Co-operation and Development (OECD), Nuclear Energy Agency (NEA) and International Atomic Energy Agency (IAEA), are enough to last for "at least a century" at current consumption rates. According to the World Nuclear Association,
yet another industry group, assuming the world's current rate of
consumption at 66,500 tonnes of uranium per year and the world's present
measured resources of uranium (4.7–5.5 Mt) are enough to last for some 70–80 years.
Predictions
There have been numerous predictions of peak uranium in the past. In 1943, Alvin M. Weinberg et al. believed that there were serious limitations on nuclear energy if only U-235 were used as a nuclear power plant fuel. They concluded that breeding was required to usher in the age of nearly endless energy.
In 1956, M. King Hubbert
declared world fissionable reserves adequate for at least the next few
centuries, assuming breeding and reprocessing would be developed into
economical processes.
In 1975 the US Department of the Interior,
Geological Survey, distributed the press release "Known US Uranium
Reserves Won't Meet Demand". It was recommended that the US not depend
on foreign imports of uranium.
Pessimistic predictions
Panel from All-Atomic Comics (1976) citing pessimistic uranium supply predictions as an argument against nuclear power.
Many analysts predicted a uranium peak and exhaustion of uranium reserves in the past or the near future.
Edward Steidle, Dean of the School of Mineral Industries at Pennsylvania State College, predicted in 1952 that supplies of fissionable elements were too small to support commercial-scale energy production.
Michael Meacher,
the former environment minister of the UK 1997–2003, and UK Member of
Parliament, reports that peak uranium happened in 1981. He also predicts
a major shortage of uranium sooner than 2013 accompanied with hoarding
and its value pushed up to the levels of precious metals.
M. C. Day projected that uranium reserves could run out as soon as 1989, but, more optimistically, would be exhausted by 2015.
Jan Willem Storm van Leeuwen,
an independent analyst with Ceedata Consulting, contends that supplies
of the high-grade uranium ore required to fuel nuclear power generation
will, at current levels of consumption, last to about 2034. Afterwards,
he expects the cost of energy to extract the uranium will exceed the
price the electric power provided.
The Energy Watch Group
has calculated that, even with steep uranium prices, uranium production
will have reached its peak by 2035 and that it will only be possible to
satisfy the fuel demand of nuclear plants until then. Various agencies have tried to estimate how long these resources
will last.
The European Commission said in 2001 that at the current level of
uranium consumption, known uranium resources would last 42 years. When
added to military and secondary sources, the resources could be
stretched to 72 years. Yet this rate of usage assumes that nuclear power
continues to provide only a fraction of the world's energy supply. If
electric capacity were increased six-fold, then the 72-year supply would
last just 12 years.
According to the industry groups OECD, NEA and IAEA,
the world's present measured resources of uranium, economically
recoverable at a price of US$130/kg, are enough to last for 100 years at
current consumption. According to the Australian Uranium Association,
another industry group, assuming the world's current rate of
consumption at 66,500 tonnes of uranium per year and the world's present
measured resources of uranium (4.7 Mt) are enough to last for 70 years.
Optimistic predictions
All the following references claim that the supply is far more than demand. Therefore, they do not predict peak uranium.
In his 1956 paper, M. King Hubbert wrote that nuclear energy would last for the 'foreseeable future.'" Hubbert's study assumed that breeder reactors would replace light water reactors
and that uranium would be bred into plutonium (and possibly thorium
would be bred into uranium). He also assumed that economic means of
reprocessing would be discovered. For political, economic and nuclear
proliferation reasons, the plutonium economy never materialized. Without it, uranium is used up in a once-through process and will peak and run out much sooner.
However, at present, it is generally found to be cheaper to mine new
uranium out of the ground than to use reprocessed uranium, and therefore
the use of reprocessed uranium is limited to only a few nations.
The OECD estimates that with the world nuclear electricity
generating rates of 2002, with LWR, once-through fuel cycle, there are
enough conventional resources to last 85 years using known resources and
270 years using known and as yet undiscovered resources. With breeders,
this is extended to 8,500 years.
If one is willing to pay $300/kg for uranium, there is a vast quantity available in the ocean.
It is worth noting that since fuel cost only amounts to a small
fraction of nuclear energy total cost per kWh, and raw uranium price
also constitutes a small fraction of total fuel costs, such an increase
on uranium prices wouldn't involve a very significant increase in the
total cost per kWh produced.
In 1983, physicist Bernard Cohen proposed that uranium is effectively inexhaustible, and could therefore be considered a renewable source of energy. He claims that fast breeder reactors,
fueled by naturally replenished uranium extracted from seawater, could
supply energy at least as long as the sun's expected remaining lifespan
of five billion years.
While uranium is a finite mineral resource within the earth, the
hydrogen in the sun is finite too – thus, if the resource of nuclear
fuel can last over such time scales, as Cohen contends, then nuclear
energy is every bit as sustainable as solar power or any other source of
energy, in terms of sustainability over the time scale of life
surviving on this planet.
His paper assumes extraction of uranium from seawater at the rate of 16
kilotonnes (35×106 lb) per year of uranium. The current demand for uranium is near 70 kilotonnes (150×106 lb) per year; however, the use of breeder reactors means that uranium would be used at least 60 times more efficiently than today.
James Hopf, a nuclear engineer writing for American Energy
Independence in 2004, believes that there is several hundred years'
supply of recoverable uranium even for standard reactors. For breeder
reactors, "it is essentially infinite".
The IAEA
estimates that using only known reserves at the current rate of demand
and assuming a once-through nuclear cycle that there is enough uranium
for at least 100 years. However, if all primary known reserves,
secondary reserves, undiscovered and unconventional sources of uranium
are used, uranium will be depleted in 47,000 years.
Kenneth S. Deffeyes estimates that if one can accept ore one tenth as rich then the supply of available uranium increased 300 times.
His paper shows that uranium concentration in ores is log-normal
distributed. There is relatively little high-grade uranium and a large
supply of very low grade uranium.
Ernest Moniz, a professor at the Massachusetts Institute of Technology and the former United States Secretary of Energy,
testified in 2009 that an abundance of uranium had put into question
plans to reprocess spent nuclear fuel. The reprocessing plans dated from
decades previous, when uranium was thought to be scarce. But now,
"roughly speaking, we've got uranium coming out of our ears, for a long,
long time," Professor Moniz said.
Possible effects and consequences
As
uranium production declines, uranium prices would be expected to
increase. However, the price of uranium makes up only 9% of the cost of
running a nuclear power plant, much lower than the cost of coal in a
coal-fired power plant (77%), or the cost of natural gas in a gas-fired
power plant (93%).
Uranium is different from conventional energy resources, such as
oil and coal, in several key aspects. Those differences limit the
effects of short-term uranium shortages, but most have no bearing on the
eventual depletion. Some key features are:
The uranium market is diverse, and no country has a monopoly influence on its prices.
Thanks to the extremely high energy density of uranium, stockpiling of several years' worth of fuel is feasible.
Significant secondary supplies of already mined uranium exist,
including decommissioned nuclear weapons, depleted uranium tails
suitable for reenrichment, and existing stockpiles.
Vast amounts of uranium, roughly 800 times the known reserves of
mined uranium, are contained in extremely dilute concentrations in
seawater.
Introduction of fast neutron reactors would increase the uranium utilization efficiency by about 100 times.
Substitutes
An alternative to uranium is thorium
which is three times more common than uranium. Fast breeder reactors
are not needed. Compared to conventional uranium reactors, thorium
reactors using the thorium fuel cycle may produce about 40 times the amount of energy per unit of mass. However, creating the technology, infrastructure and know-how needed for a thorium-fuel economy is uneconomical at current and predicted uranium prices.
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