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The discovery of the uranium and its wide use in nuclear energy production today

How Does it Work? Uranium occurs in seawater, and can be recovered from the oceans. It was named after the planet Uranus, which had been discovered eight years earlier. 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. 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: 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.

  • 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;
  • This increase in the proportion of the U-235 isotope became known as 'enrichment';
  • 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takes place in the core of a nuclear reactor is controlled by rods which absorb neutrons and which can be inserted or withdrawn to set the reactor at the required power level;
  • 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.

U-235 decays slightly faster. 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.

The heat is used to make steam to produce electricity. 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 reactors. Because of the kind of fuel used ie the concentration of U-235, see belowif 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.

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 fuelthese 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 the discovery of the uranium and its wide use in nuclear energy production today by in situ leaching ISLwhere 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.

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 UF6which enables it to be enriched.

Enrichment increases the proportion of the uranium-235 isotope from its natural level of 0. This enables greater technical efficiency in reactor design and operation, particularly in larger reactors, and allows the use of ordinary water as a moderator.

These fuel pellets are placed inside thin metal tubes, then 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. Who uses nuclear power? This amounts to over 2500 billion kWh each year, as much as from all sources of electricity worldwide in 1960. It comes from over 440 nuclear reactors with a total output capacity of about 390,000 megawatts MWe operating in 31 countries.

Over 60 more reactors are under construction and another 160 are planned. France gets three quarters 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 17,000 reactor-years of operational experience.

  1. Work at Arzamas-16 was influenced by foreign intelligence gathering and the first device was based closely on the Nagasaki bomb a plutonium device. The predicted critical size for a sphere of U-235 metal was about 8kg, which might be reduced by use of an appropriate material for reflecting neutrons.
  2. The first atomic bomb, which contained U-235, was dropped on Hiroshima on 6 August 1945. The latter point was confirmed by Szilard and Fermi, who proposed using a 'moderator' to slow down the emitted neutrons.
  3. Using relatively small special-purpose nuclear reactors it is possible to make a wide range of radioactive materials radioisotopes at low cost. According to the World Nuclear Association, these geological storage sites include natural and man-made barriers to keep waste from reaching the surface, even when earthquakes occur.

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.

Australia's known resources are over 1. Several countries have significant uranium resources. Apart from the top four, they are in order: Other countries have smaller deposits which could be mined if needed. Kazakhstan is the world's top uranium producer, followed by Canada and then Australia as the main suppliers of uranium to world markets - now over 60,000 tU per year.

Exploring the nature of the atom

Uranium is sold only to countries which are signatories of the Nuclear Non-Proliferation Treaty NPTand which allow international inspection to verify that it is used only for peaceful purposes. Other uses of nuclear energy 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 over 240 "research" reactors in 56 countries producing them. These are essentially neutron factories rather than sources of heat.

Radioisotopes 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. 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.

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. 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.

  • The reports also led to high level reviews in the USA, particularly by a Committee of the National Academy of Sciences, initially concentrating on the nuclear power aspect;
  • Thereafter, Churchill sought information on the cost of building a diffusion plant, a heavy water plant and an atomic reactor in Britain;
  • 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;
  • Natural uranium as found in the Earth's crust is a mixture largely of two isotopes;
  • It was claimed that the work of the committee had put the British in the lead and that "in its fifteen months' existence it had proved itself one of the most effective scientific committees that ever existed";
  • Then in 1896 Henri Becquerel found that pitchblende an ore containing radium and uranium caused a photographic plate to darken.

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. 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. 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 and Russia, 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.

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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. Since the 1990s, due to disarmament, a lot of military uranium has become available for electricity production. The military uranium is diluted about 25: Over two decades to 2013 one tenth of US electricity was made from Russian weapons uranium.

Military plutonium is starting to be used similarly, mixed with depleted uranium.