Since it is naturally radioactive, uranium, usually in the form of uranium dioxide UO 2 , is most commonly used in the nuclear power industry to generate electricity.
Naturally occurring uranium consists of three isotopes : uranium, uranium and uranium Although all three isotopes are radioactive, only uranium is a fissionable material that can be used for nuclear power. When a fissionable material is struck by a neutron , its nucleus can release energy by splitting into smaller fragments. If some of the fragments are other neutrons, they can strike other atoms and cause them to split as well.
A fissionable material, such as uranium, is a material capable of producing enough free neutrons to sustain a nuclear chain reaction. Only 0. This is too low a concentration to sustain a nuclear chain reaction without the help of a material known as a moderator. A moderator is a material that can slow down a neutron without absorbing it. Slow neutrons are more likely to react with uranium and reactors using natural uranium can be made using graphite or heavy water as a moderator. Methods also exist for concentrating uranium Uranium, uranium's most common isotope, can be converted into plutonium , a fissionable material that can also be used as a fuel in nuclear reactors.
To produce plutonium, atoms of uranium are exposed to neutrons. Uranium forms when uranium absorbs a neutron. Uranium has a half-life of about 23 minutes and decays into neptunium through beta decay. 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 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 U , accounting for The isotope U 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 decays very slowly, its half-life being about the same as the age of the Earth million years. This means that it is barely radioactive, less so than many other isotopes in rocks and sand. Nevertheless it generates 0. U decays slightly faster. When the nucleus of a U 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 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 is this process , in effect 'burning' uranium, which occurs in a nuclear reactor. The heat is used to make steam to produce electricity. 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 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. A typical megawatt MWe reactor can provide enough electricity for a modern city of up to one million people. Whereas the U nucleus is 'fissile', that of U 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, which is fissile.
Pu is very much like U, in that it fissions when hit by a neutron and this yields a similar amount of energy. Because there is so much U 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 But sometimes a Pu atom simply captures a neutron without splitting, and it becomes Pu Because the Pu is either progressively 'burned' or becomes Pu, the longer the fuel stays in the reactor the more Pu 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. 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. This is the form in which uranium is sold. To understand uranium, it's important to understand radioactivity.
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.
In , French physicist Henri Becquerel left some uranium salts on a photographic plate as part of some research on how light influenced these salts. To his surprise, the plate fogged up, indicating some sort of emissions from the uranium salts. Martin Heinrich Klaproth, a German chemist, discovered uranium in , although it had been known about since at least A. Klaproth discovered the element in the mineral pitchblende, which at the time was thought to be a zinc and iron ore.
The mineral was dissolved in nitric acid, and then potash potassium salts was added to the remaining yellow precipitate. Klaproth concluded that he had discovered a new element when the reaction between the potash and precipitate didn't follow any reactions of known elements. His discovery turned out to be uranium oxide and not pure uranium as he had originally believed.
According to the Los Alamos National Laboratory , Klaproth named the new element after the recently discovered planet Uranus, which was named for the Greek god of the sky.
Uranium was found to be radioactive in by Antoine H. Becquerel, a French physicist. Becquerel had left a sample of uranium on top of an unexposed photographic plate, which became cloudy. He concluded it was giving off invisible rays, according to the Royal Society of Chemistry. This was the first instance that radioactivity had been studied and opened up a new field of science. Marie Curie, a Polish scientist, coined the term radioactivity shortly after Becquerel's discovery, and with Pierre Curie, a French scientist, continued the research to discover other radioactive elements, such as polonium and radium, and their properties.
The universe's uranium formed 6. It is all over the planet, and makes up about 2 to 4 parts per million of most rocks. It is 48th among the most abundant elements found in natural crustal rock, according to the U. Department of Energy , and is 40 times more abundant than silver. Though uranium is highly associated with radioactivity, its rate of decay is so low that this element is actually not one of the more radioactive ones out there.
Uranium has a half-life of an incredible 4. Uranium has a half-life of just over million years. Uranium has the shortest half-life of them all at , years, but it occurs only indirectly from the decay of U In comparison, the most radioactive element is polonium.
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