What is Uranium? How Does it Work (2023)

(Updated August 2022)

  • Uranium is a heavy metal which has been used as anabundant source of concentrated energy for over 60 years.
  • Uraniumoccurs in most rocksin concentrations of 2 to 4 parts per million and is as common in the Earth's crust as tin, tungsten and molybdenum. Uranium occurs in seawater, and can be recovered from the oceans.
  • Uranium wasdiscovered in 1789by Martin Klaproth, a German chemist, in the mineral called pitchblende. It was named after the planet Uranus, which had been discovered eight years earlier.
  • Uranium was apparentlyformed in supernovae about 6.6 billion years ago. While it is not common in the solar system, today its slow radioactive decay provides themain source of heat inside the Earth,causing convection and continental drift.
  • Thehigh densityof uranium means that it also finds uses in the keels of yachts and as counterweights for aircraft control surfaces, as well as for radiation shielding.
  • Uranium has a melting point of 1132°C. Thechemical symbolfor uranium is U.

The uranium atom

On a scale arranged according to the increasing mass of their nuclei, uranium is one of the heaviest of all the naturally-occurring elements (hydrogen is the lightest). Uranium is 18.7 times as dense as water.

Like other elements, uranium occurs in several slightly differing forms known as 'isotopes'. These isotopes differ from each other in the number of uncharged particles (neutrons) in the nucleus. Natural uranium as found in the Earth's crust is a mixture largely of two isotopes: uranium-238 (U-238), accounting for 99.3% and uranium-235 (U-235) about 0.7%.

The isotope U-235 is important because under certain conditions it can readily be split, yielding a lot of energy. It is therefore said to be 'fissile' and we use the expression 'nuclear fission'.

Meanwhile, like all radioactive isotopes, they decay. U-238 decays very slowly, its half-life being about the same as the age of the Earth (4500 million years). This means that it is barely radioactive, less so than many other isotopes in rocks and sand. Nevertheless it generates 0.1 watts/tonne as decay heat and this is enough to warm the Earth's core. U-235 decays slightly faster.

Energy from the uranium atom

The nucleus of the U-235 atom comprises 92 protons and 143 neutrons (92 + 143 = 235). When the nucleus of a U-235 atom captures a moving neutron it splits in two (fissions) and releases some energy in the form of heat, also two or three additional neutrons are thrown off. If enough of these expelled neutrons cause the nuclei of other U-235 atoms to split, releasing further neutrons, a fission 'chain reaction' can be achieved. When this happens over and over again, many millions of times, a very large amount of heat is produced from a relatively small amount of uranium.

It isthis process, in effect 'burning' uranium, which occurs in a nuclear reactor. The heat is used to make steam to produce electricity.

What is Uranium? How Does it Work (1)

Examples of nuclear fissioning of uranium-235

Inside the reactor

Nuclear power stations and fossil-fuelled power stations of similar capacity have many features in common. Both require heat to produce steam to drive turbines and generators. In a nuclear power station, however, the fissioning of uranium atoms replaces the burning of coal or gas. In a nuclear reactor the uranium fuel is assembled in such a way that a controlled fission chain reaction can be achieved. The heat created by splitting the U-235 atoms is then used to make steam which spins a turbine to drive a generator, producing electricity.

The chain reaction that takes place in the core of a nuclear reactor is controlled by rods which absorb neutrons and which can be inserted or withdrawn to set the reactor at the required power level.

The fuel elements are surrounded by a substance called a moderator to slow the speed of the emitted neutrons and thus enable the chain reaction to continue. Water, graphite and heavy water are used as moderators in different types of reactor.

Because of the kind of fuel used (i.e. the concentration of U-235, see below), if there is a major uncorrected malfunction in a reactor the fuel may overheat and melt, but it cannot explode like a bomb.

A typical 1000 megawatt (MWe) reactor can provide enough electricity for a modern city of up to one million people.

What is Uranium? How Does it Work (2)

(Video) How Uranium Becomes Nuclear Fuel

Uranium and plutonium

Whereas the U-235 nucleus is 'fissile', that of U-238 is said to be 'fertile'. This means that it can capture one of the neutrons which are flying about in the core of the reactor and become (indirectly) plutonium-239, which is fissile. Pu-239 is very much like U-235, in that it fissions when hit by a neutron and this yields a similar amount of energy.

Because there is so much U-238 in a reactor core (most of the fuel), these reactions occur frequently, and in fact about one-third of the fuel's energy yield comes from 'burning' Pu-239.

But sometimes a Pu-239 atom simply captures a neutron without splitting, and it becomes Pu-240. Because the Pu-239 is either progressively 'burned' or becomes Pu-240, the longer the fuel stays in the reactor the more Pu-240 is in it. (The significance of this is that when the spent fuel is removed after about three years, the plutonium in it is not suitable for making weapons but can be recycled as fuel.)

From uranium ore to reactor fuel

Uranium ore can be mined by underground or open-cut methods, depending on its depth. After mining, the ore is crushed and ground up. Then it is treated with acid to dissolve the uranium, which is recovered from solution.

Uranium may also be mined by in situ leaching (ISL), where it is dissolved from a porous underground ore body in situ and pumped to the surface.

The end product of the mining and milling stages, or of ISL, is uranium oxide concentrate (U3O8). This is the form in which uranium is sold.

Before it can be used in a reactor for electricity generation, however, it must undergo a series of processes to produce a useable fuel.

For most of the world's reactors, the next step in making the fuel is to convert the uranium oxide into a gas, uranium hexafluoride (UF6), which enables it to be enriched. Enrichment increases the proportion of the uranium-235 isotope from its natural level of 0.7% to 4-5%. This enables greater technical efficiency in reactor design and operation, particularly in larger reactors, and allows the use of ordinary water as a moderator.

After enrichment, the UF6gas is converted to uranium dioxide (UO2) which is formed into fuel pellets. These fuel pellets are placed inside thin metal tubes, known as fuel rods, which are assembled in bundles to become the fuel elements or assemblies for the core of the reactor.In a typical large power reactor there might be 51,000 fuel rods with over 18 million pellets.

What is Uranium? How Does it Work (3)

A worker holds up a newly made fuel pellet (KazAtomProm)

For reactors which use natural uranium as their fuel (and hence which require graphite or heavy water as a moderator) the U3O8concentrate simply needs to be refined and converted directly to uranium dioxide.

When the uranium fuel has been in the reactor for about three years, the used fuel is removed, stored, and then either reprocessed or disposed of underground (seeNuclear Fuel CycleorRadioactive Waste Management).

Who uses nuclear power?

About 10% of the world's electricity is generated from uranium in nuclear reactors. This amounts to over 2500 TWh each year, as much as from all sources of electricity worldwide in 1960.

It comes from about 440 nuclear reactors with a total output capacity of about 390,000 megawatts (MWe) operating in 32 countries. About 55 more reactors are under construction and about 100 are planned.


Belgium, Bulgaria, Czech Republic, Finland, France, Hungary, Slovakia, Slovenia, Sweden and Ukraine all get 30% or more of their electricity from nuclear reactors. The USA has about 90 reactors operating, supplying 20% of its electricity. France gets about 70% of its electricity from uranium.

Over the 60 years that the world has enjoyed the benefits of cleanly-generated electricity from nuclear power, there have been about 18,500 reactor-years of operational experience.

See also Nuclear Generation by Country.

Who has and who mines uranium?

Uranium is widespread in many rocks, and even in seawater. However, like other metals, it is seldom sufficiently concentrated to be economically recoverable. Where it is, we speak of an orebody. In defining what is ore, assumptions are made about the cost of mining and the market price of the metal. Uranium reserves are therefore calculated as tonnes recoverable up to a certain cost.

Uranium resources by country in 2019

tonnes Upercentage of world












South Africa






















World total


Identified resources recoverable (reasonably assured resources plus inferred resources), to $130/kg U, 1/1/19, from OECD NEA & IAEA,Uranium 2020: Resources, Production and Demand('Red Book'). The total recoverable identified resources to $260/kg U is 8.070 million tonnes U.

Production from mines (tonnes U)

(Video) What Is Uranium | How Does it Work

Uzbekistan (est.)2400240024002385332534003450350035003500
China (est.)1500150015001616161616921885188518851885
India (est.)385385385385385421423308400615
South Africa (est.)465531573393490308346346250385
Iran (est.)0003804071717171
Pakistan (est.)45454545454545454545
Czech Republic22821519315513800000
Total world58,49359,33156,04160,30463,20760,51454,15454,74247,73148,332
tonnes U3O868,97469,96666,08771,11374,35771,36163,86164,55456,28756,995
% of world demand94%91%85%98%96%93%80%81%74%77%

* Data from the World Nuclear Association. NB: the figures in this table are liable to change as new data becomes available. Totals may not sum exactly due to rounding.

Mining methods have been changing. In 1990, 55% of world production came from underground mines, but this shrunk dramatically to 1999, with 33% then. From 2000 the new Canadian mines increased it again. In situ leach (ISL, also called in situ recovery, ISR) mining has been steadily increasing its share of the total, mainly due to Kazakhstan, and in 2021 accounted for over 60% of production:

Methodtonnes U%
In situ leach (ISL)32,08866%
Underground & open pit (except Olympic Dam)13,93729%

Other uses of nuclear energy

Uranium is sold only to countries which are signatories of the Nuclear Non-Proliferation Treaty (NPT), and which allow international inspection to verify that it is used only for peaceful purposes.

Many people, when talking about nuclear energy, have only nuclear reactors (or perhaps nuclear weapons) in mind. Few people realise the extent to which the use of radioisotopes has changed our lives over the last few decades.

Using relatively small special-purpose nuclear reactors, it is possible to make a wide range of radioactive materials (radioisotopes) at low cost. For this reason the use of artificially-produced radioisotopes has become widespread since the early 1950s, and there are now about 220 'research' reactors in 56 countries producing them. These are essentially neutron factories rather than sources of heat.


In our daily life we need food, water and good health. Today, radioactive isotopes play an important part in the technologies that provide us with all three. They are produced by bombarding small amounts of particular elements with neutrons.

Inmedicine, radioisotopes are widely used for diagnosis and research. Radioactive chemical tracers emit gamma radiation which provides diagnostic information about a person's anatomy and the functioning of specific organs. Radiotherapy also employs radioisotopes in the treatment of some illnesses, such as cancer. About one person in two in the Western world is likely to experience the benefits of nuclear medicine in their lifetime. More powerful gamma sources are used to sterilise syringes, bandages and other medical utensils– gamma sterilisation of equipment is almost universal.

In thepreservation of food, radioisotopes are used to inhibit the sprouting of root crops after harvesting, to kill parasites and pests, and to control the ripening of stored fruit and vegetables. Irradiated foodstuffs are accepted by world and national health authorities for human consumption in an increasing number of countries. They include potatoes, onions, dried and fresh fruits, grain and grain products, poultry and some fish. Some prepacked foods can also be irradiated.

In the growing ofcropsand breedinglivestock, radioisotopes also play an important role. They are used to produce high yielding, disease-resistant and weather-resistant varieties of crops, to study how fertilisers and insecticides work, and to improve the productivity and health of domestic animals.

Industrially, and in mining, they are used to examine welds, to detect leaks, to study the rate of wear of metals, and for on-stream analysis of a wide range of minerals and fuels.

There are many other uses. A radioisotope derived from the plutonium formed in nuclear reactors is used in most householdsmoke detectors.

Radioisotopes are used to detect and analyse pollutants in the environment, and to study the movement of surface water in streams and also of groundwater.

See also The Many Uses of Nuclear Technology.

Other reactors

There are also other uses for nuclear reactors. About 200 small nuclear reactors power some 150 ships, mostly submarines, but ranging from icebreakers to aircraft carriers. These can stay at sea for long periods without having to make refuelling stops. In the Russian Arctic where operating conditions are beyond the capability of conventional icebreakers, very powerful nuclear-powered vessels operate year-round, where previously only two months allowed northern access each year.

The heat produced by nuclear reactors can also be used directly rather than for generating electricity. In Sweden, Russia and China, for example, surplus heat is used to heat buildings. Nuclear heat may also be used for a variety of industrial processes such as water desalination. Nuclear desalination is likely to be a major growth area in the next decade.

(Video) URANIUM Documentary: Mining, History and Future Outlook

High-temperature heat from nuclear reactors is likely to be employed in some industrial processes in future, especially for making hydrogen.

Military sources of fuel

Both uranium and plutonium were used to make bombs before they became important for making electricity and radioisotopes. The type of uranium and plutonium for bombs is different from that in a nuclear power plant. Bomb-grade uranium is highly-enriched (>90% U-235, instead of up to 5%); bomb-grade plutonium is fairly pure Pu-239(>90%, instead of about 60% in reactor-grade)and is made in special reactors.

Since the 1990s, due to disarmament, a lot of military uranium has become available for electricity production. The military uranium is diluted about 25:1 with depleted uranium (mostly U-238) from the enrichment process before being used in power generation. Over two decades to 2013 one-tenth of US electricity was made from Russian weapons uranium.


What is uranium and how does it work? ›

Uranium is a heavy metal which has been used as an abundant source of concentrated energy for over 60 years. Uranium occurs in most rocks in concentrations of 2 to 4 parts per million and is as common in the Earth's crust as tin, tungsten and molybdenum. Uranium occurs in seawater, and can be recovered from the oceans.

How does uranium energy work? ›

Nuclear Power

Nuclear energy originates from the splitting of uranium atoms – a process called fission. This generates heat to produce steam, which is used by a turbine generator to generate electricity. Because nuclear power plants do not burn fuel, they do not produce greenhouse gas emissions.

What is uranium simple explanation? ›

Uranium is a silvery-white metallic chemical element in the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium has the highest atomic weight of all naturally occurring elements.

How much uranium is enough? ›

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.

What uranium is used for? ›

What is it used for? Uranium “enriched” into U-235 concentrations can be used as fuel for nuclear power plants and the nuclear reactors that run naval ships and submarines. It also can be used in nuclear weapons.

Why is uranium used in bombs? ›

The isotopes uranium-235 and plutonium-239 were selected by the atomic scientists because they readily undergo fission. Fission occurs when a neutron strikes the nucleus of either isotope, splitting the nucleus into fragments and releasing a tremendous amount of energy.

Where do you find uranium? ›

Uranium is found in small amounts in most rocks, and even in seawater. Uranium mines operate in many countries, but more than 85% of uranium is produced in six countries: Kazakhstan, Canada, Australia, Namibia, Niger, and Russia.

How is uranium used as fuel? ›

Uranium is the most widely used fuel by nuclear power plants for nuclear fission. Nuclear power plants use a certain type of uranium—U-235—as fuel because its atoms are easily split apart. Although uranium is about 100 times more common than silver, U-235 is relatively rare at just over 0.7% of natural uranium.

Why is uranium a good energy source? ›

Nuclear is a zero-emission clean energy source. It generates power through fission, which is the process of splitting uranium atoms to produce energy. The heat released by fission is used to create steam that spins a turbine to generate electricity without the harmful byproducts emitted by fossil fuels.

What was uranium first used for? ›


The element was isolated in 1841 and added to the periodic table as element number 92. - Throughout the 1800s uranium was used mainly as it had been historically -- to tint glass and ceramics in shades ranging from yellow-green to orange and red.

What is uranium look like? ›

Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons.

What color is uranium? ›

Uranium, U, is a silver-gray metallic chemical element, that has the highest atomic weight of the naturally occurring elements. It's pretty low in radioactivity, and when refined, it has a silver-white color. Uranium, U, is a silvery gray metallic. It is about 70% more dense than lead but is weakly radioactive.

How long will uranium last? ›

The world's present measured resources of uranium (6.1 Mt) in the cost category less than three times present spot prices and used only in conventional reactors, are enough to last for about 90 years.

Who produces uranium? ›

Worldwide Uranium Production

In 2021, 20 countries produced 77%, 48,303 tons, of the world's uranium. Kazakhstan, Canada, and Australia alone produced three-fourths of the world's production from their mines. The following countries are the top producers of uranium, based on 2021 figures: Kazakhstan: 21,819 tonnes U.

Who uses the most uranium? ›

United States

What products are made from uranium? ›

Uranium is the icon of the nuclear age, It's the basis of nuclear power reactors and nuclear bombs (including those made with plutonium, which must be made from uranium in nuclear reactors). Surprisingly, even though there are no stable isotopes, it's also used as a metal for metal-like things.

What are some examples of uranium? ›

It is an important nuclear fuel. Uranium constitutes about two parts per million of Earth's crust. Some important uranium minerals are pitchblende (impure U3O8), uraninite (UO2), carnotite (a potassium uranium vanadate), autunite (a calcium uranium phosphate), and torbernite (a copper uranium phosphate).

Can you own uranium? ›

Yet, the truth is, you can buy uranium ore from places like Amazon or Ebay, and you won't have to produce any special authorization to get it. The purpose of buying Uranium-238, the most common isotope of the element, is purely for research.

Can you hold uranium? ›

In fact, since uranium is a heavy metal, its chemical toxicity is actually more of a danger than its radioactivity. If you touch it directly with your hands, you should wash your hands afterwards. You should not eat it. Apart from that, it is not dangerous.

Where does Russia get uranium? ›

This is possible because most of the uranium Russia exports is bought from Kazakhstan—a country that is landlocked and ships its uranium to Europe and the United States through Russia. Kazakhstan is the world's largest uranium producer with 19,500 tonnes in 2020.

What's the most radioactive thing on earth? ›

The radioactivity of radium then must be enormous. This substance is the most radioactive natural element, a million times more so than uranium.

Where do we get uranium from? ›

Uranium is found in small amounts in most rocks, and even in seawater. Uranium mines operate in many countries, but more than 85% of uranium is produced in six countries: Kazakhstan, Canada, Australia, Namibia, Niger, and Russia.

Why is uranium so radioactive? ›

Uranium is naturally radioactive: Its nucleus is unstable, so the element is in a constant state of decay, seeking a more stable arrangement. In fact, uranium was the element that made the discovery of radioactivity possible.

How much uranium is in a nuke? ›

Nuclear weapons typically use a concentration of more than 90 percent uranium-235. 15 kilograms: weight of a solid sphere of 100 percent uranium-235 just large enough to achieve a critical mass with a beryllium reflector.

Where is uranium found in the world? ›

Deposits of this type are found in China, Russia, Kazakhstan, Mexico, Namibia, Greenland, South Africa, United States, Canada and Australia. Vein deposits. Uranium ore is associated with veins or other lenses in igneous, metamorphic or sedimentary rocks.

How long will uranium last? ›

The world's present measured resources of uranium (6.1 Mt) in the cost category less than three times present spot prices and used only in conventional reactors, are enough to last for about 90 years.

What color is uranium? ›

Uranium, U, is a silver-gray metallic chemical element, that has the highest atomic weight of the naturally occurring elements. It's pretty low in radioactivity, and when refined, it has a silver-white color. Uranium, U, is a silvery gray metallic. It is about 70% more dense than lead but is weakly radioactive.

Who buys uranium? ›

Historically, uranium has been mined in countries willing to export, including Australia and Canada. However, countries now responsible for more than 50% of the world's uranium production include Kazakhstan, Namibia, Niger, and Uzbekistan. Uranium from mining is used almost entirely as fuel for nuclear power plants.

Is uranium magnetic yes or no? ›

These materials shouldn't be able to become magnets – but they actually can. Andrew Wray at New York University and his colleagues found that a compound of uranium and antimony can become a magnet, even though its particles are in singlet states.

Can you hold uranium in your hand? ›

If you hold it [in] your hand (and I've held tons of it my hand, a pound or two at a time), it's heavy, like lead. It's toxic, like lead or arsenic, but not much more so.

How poisonous is uranium? ›

Chemical Toxicity

Once in the bloodstream, the uranium compounds are filtered by the kidneys, where they can cause damage to the kidney cells. Very high uranium intakes (ranging from about 50 to 150 mg depending on the individual) can cause acute kidney failure and death.

How many nuclear bombs would it take to destroy the world? ›

As of 2019, there are 15,000 nuclear weapons on planet Earth. It would take just three nuclear warheads to destroy one of the 4,500 cities on Earth, meaning 13,500 bombs in total, which would leave 1,500 left.

How far can a nuclear bomb destroy? ›

The dangerous fallout zone can easily stretch 10 to 20 miles (15 to 30 kilometers) from the detonation depending on explosive yield and weather conditions.

How hot is a nuclear bomb? ›

From 0.2 to 3 seconds after detonation, the intense heat emitted from the fireball exerted powerful effects on the ground. Temperatures near the hypocenter reached 3,000 to 4,000 degrees Celsius. This heat burned human skin as far as 3.5 kilometers from the hypocenter.

How much uranium is in the earth? ›

According to the NEA, identified uranium resources total 5.5 million metric tons, and an additional 10.5 million metric tons remain undiscovered—a roughly 230-year supply at today's consumption rate in total.

Does the human body use uranium? ›

Natural uranium is in your normal diet, so there will always be some level of uranium in all parts of your body. If in addition you are exposed to depleted uranium, it adds to the total uranium level in your body. There are reliable medical tests that can detect whether uranium is in your body.

Who uses the most uranium? ›

United States


1. What is Uranium?
2. How Does Uranium Works | How does a nuclear reactor work?
3. What Does It Take to Enrich Uranium?
4. How Uranium Is Made Part 2
(How is it Made)
5. Nuclear Reactor - Understanding how it works | Physics Elearnin
6. How It's Made Uranium Part 1
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