The relative amounts of uranium and lead in rocks can be used in radioactive dating techniques. When neutrons are fired at uranium, the extremely unstable uranium isotope is produced, which quickly splits into two smaller nuclei such as barium and krypton , releasing some of the nuclear binding energy and more neutrons.
This process is known as nuclear fission. These neutrons can collide with other uranium isotopes, causing them to split and release energy and even more neutrons in a chain reaction.
Moderators such as beryllium, graphite, water, or heavy water D 2 O slow down the neutrons that are released in fission reactions, producing "thermal neutrons" that can be captured by uranium atoms, rather than simply bouncing off.
In "light water" reactors, the moderator is ordinary water — i. In "heavy water" reactors, the moderator is D 2 O — i. The rate of the nuclear reactions are controlled with control rods, which contain elements that are capable of absorbing neutrons without undergoing fission, such as silver, indium, cadmium, boron, cobalt, hafnium, gadolinium, and europium. Raising the control rods out of the reactor allows the reaction to speed up, while lowering them into the reactor slows the reaction down and prevents a runaway chain reaction from occurring.
In atomic bombs, the reaction goes out of control, causing a tremendous explosion which releases tremendous amounts of energy and radiation. The "Little Boy" atomic bomb that was exploded in Hiroshima, Japan on August 6, was a uranium bomb which had the destructive potential of 12, tons of TNT, and killed over 75, people. In this bomb, two pieces of sub-critical uranium were brought together quickly by explosives, making a critical mass of uranium in which a runaway chain reaction could occur.
One technique for enriching uranium with the fissionable uranium isotope is by converting it into the form of volatile uranium hexafluoride, UF 6 , which sublimes into the gas phase at The gas is then diffused through a series of permeable membranes: since UF 6 is 3 atomic mass units lighter than UF 6 , it diffuses 1.
Uranium hexafluoride is extremely corrosive: during the Manhattan Project to build the first atomic bomb, Teflon was used to make gastight fittings for the valves and seals used in the gas diffusion equipment. Enriched uranium can also be prepared in a high-speed gas centrifuge, or by using a laser to dissociate the U—F bonds in UF 6 , causing uranium to deposit out. Uranium does not undergo fission, but when bombarded with neutrons, uranium absorbs neutrons to produce plutonium Absorption of neutrons by uranium produce plutonium Uranium half-life of , years can be produced by neutron bombardment of thorium This uranium isotope also undergoes nuclear fission, and has the potential to be used in nuclear fusion plants.
Depleted uranium consists of uranium taken from spent fuel rods and alloyed with small percentages of other elements. It contains mostly U, and less than 0.
It is extremely dense, and is used to make armor-piercing ammunition, and ballast for ships and airplanes. Uranium glass is a yellow or yellow-green glass which is colored by uranium oxide. Under ultraviolet light, uranium glass fluoresces with a bright green color. By including other minerals, an opaque, yellow or white ceramic called "vaseline glass" can be produced so called because its appearance is similar to petroleum jelly.
Small amounts of uranium is also found in the red-colored pieces in a line of dinnerware called Fiestaware; the so-called "Red Fiesta" coloring contains uranium oxide in the glaze, which produces a vivid reddish-orange color see here for an example. Uranium entering the body becomes concentrated in the bones because uranium forms complexes with phosphate ions.
Neptunium is a silver, radioactive, artificially produced element. It is named for the planet Neptune, since Neptune follows Uranus in the solar system. It is found in uranium ores at very low concentrations, but the commercial source for neptunium is from spent uranium fuel rods from nuclear reactors.
The two longest-lived isotopes of neptunium are neptunium, which has a half-life of 2,, years, and neptunium, with a half-life of , years. All of the other isotopes have half-lives that range from a few minutes to a little over a year.
Neptunium is the first of the transuranium elements , which have higher atomic numbers than uranium. With very few exceptions, the transuranium elements are too rare, and too dangerous, to find much commercial use. Neptunium was first prepared in by Edwin M. McMillan and Philip H. Abelson at the University of California in Berkeley, California by bombarding uranium with neutrons, producing uranium, which underwent beta decay to produce neptunium Uranium can also be converted to neptunium by neutron bombardment, absorbing two neutrons to produce uranium, which then undergoes beta decay to produce neptunium Uranium can also absorb one neutron, emit two more neutrons and become uranium, which then undergoes beta decay to produce neptunium Plutonium is a silver, radioactive, artificially produced element.
It is named for the planet well, ex-planet of Pluto, since Pluto follows Neptune usually in the solar system. Its discoverer, Glenn T. Seaborg chose the symbol "Pu" for the element, rather than "Pl" "partly to avoid confusion with platinum, Pt, but also 'facetiously,' he says, 'to create attention' — P.
Plutonium was first synthesized by Glenn T. Seaborg, Arthur C. Wahl, and Joseph W. Kennedy at the University of California in Berkeley, California in , although its existence was not reported publicly until because of the security restrictions surrounding nuclear research and the Manhattan Project to build the first atomic bombs.
Uranium was bombarded with neutrons to produce uranium, which then underwent beta decay to produce neptunium, which also underwent beta decay to produce plutonium The longest-lived isotope of plutonium is plutonium, which has a half-life of 82,, years; plutonium and also have fairly long half-lives, of , years and 24, years.
The most commonly used isotopes are plutonium half-life of Plutonium is not fissionable, and emits alpha particles without also emitting gamma rays, making it a great deal safer to handle. It is used primarily as a long-lived power source in pacemakers, spacecraft and satellites, and deep-sea diving suits. Plutonium is fissionable, and is used in atomic weapons.
The critical mass for plutonium is about 16 kg, but this can be reduced by surrounding the plutonium with a shell of beryllium, which reflects neutrons back towards the plutonium, accelerating the fusion process. It is found in small amounts in most rocks and soils, where it is about three times more abundant than uranium.
Soil contains an average of around 6 parts per million ppm of thorium. Thorium is very insoluble, which is why it is plentiful in sands but not in seawater, in contrast to uranium. Thorium exists in nature in a single isotopic form — Th — which decays very slowly its half-life is about three times the age of the Earth. The decay chains of natural thorium and uranium give rise to minute traces of Th, Th and Th, but the presence of these in mass terms is negligible.
It decays eventually to lead When pure, thorium is a silvery white metal that retains its lustre for several months. However, when it is contaminated with the oxide, thorium slowly tarnishes in air, becoming grey and eventually black. When heated in air, thorium metal ignites and burns brilliantly with a white light.
Glass containing thorium oxide has both a high refractive index and wavelength dispersion, and is used in high quality lenses for cameras and scientific instruments. Thorium oxide ThO 2 is relatively inert and does not oxidise further, unlike UO 2. It has higher thermal conductivity and lower thermal expansion than UO 2 , as well as a much higher melting point. In nuclear fuel, fission gas release is much lower than in UO 2. Monazite is found in igneous and other rocks but the richest concentrations are in placer deposits, concentrated by wave and current action with other heavy minerals.
World monazite resources are estimated to be about 16 million tonnes, 12 Mt of which are in heavy mineral sands deposits on the south and east coasts of India.
There are substantial deposits in several other countries see Table below. Thorite ThSiO 4 is another common thorium mineral. A large vein deposit of thorium and rare earth metals is in Idaho. Some of the figures are based on assumptions and surrogate data for mineral sands monazite x assumed Th content , not direct geological data in the same way as most mineral resources.
Estimated world thorium resources 1. There is no international or standard classification for thorium resources and identified thorium resources do not have the same meaning in terms of classification as identified uranium resources. Thorium is not a primary exploration target and resources are estimated in relation to uranium and rare earths resources.
Chinese production is unknown. Thorium Th is not itself fissile and so is not directly usable in a thermal neutron reactor. In this regard it is similar to uranium which transmutes to plutonium All thorium fuel concepts therefore require that Th is first irradiated in a reactor to provide the necessary neutron dosing to produce protactinium The only fissile driver options are U, U or Pu None of these is easy to supply.
It is possible — but quite difficult — to design thorium fuels that produce more U in thermal reactors than the fissile material they consume this is referred to as having a fissile conversion ratio of more than 1.
Thermal breeding with thorium requires that the neutron economy in the reactor has to be very good ie, there must be low neutron loss through escape or parasitic absorption. The possibility to breed fissile material in slow neutron systems is a unique feature for thorium-based fuels and is not possible with uranium fuels.
Mixed thorium-plutonium oxide Th-Pu MOX fuel is an analog of current uranium-MOX fuel, but no new plutonium is produced from the thorium component, unlike for uranium fuels in U-Pu MOX fuel, and so the level of net consumption of plutonium is high.
Production of all actinides is lower than with conventional fuel, and negative reactivity coefficient is enhanced compared with U-Pu MOX fuel. In fresh thorium fuel, all of the fissions thus power and neutrons derive from the driver component.
As the fuel operates the U content gradually increases and it contributes more and more to the power output of the fuel. The ultimate energy output from U and hence indirectly thorium depends on numerous fuel design parameters, including: fuel burn-up attained, fuel arrangement, neutron energy spectrum and neutron flux affecting the intermediate product protactinium, which is a neutron absorber.
The fission of a U nucleus releases about the same amount of energy MeV as that of U An important principle in the design of thorium fuel systems is that of heterogeneous fuel arrangement in which a high fissile and therefore higher power fuel zone called the seed region is physically separated from the fertile low or zero power thorium part of the fuel — often called the blanket.
Such an arrangement is far better for supplying surplus neutrons to thorium nuclei so they can convert to fissile U, in fact all thermal breeding fuel designs are heterogeneous. This principle applies to all the thorium-capable reactor systems. Th is fissionable with fast neutrons of over 1 MeV energy. It could therefore be used in fast molten salt and other Gen IV reactors with uranium or plutonium fuel to initiate fission.
However, Th fast fissions only one tenth as well as U, so there is no particular reason for using thorium in fast reactors, given the huge amount of depleted uranium awaiting use. In Norway, Thor Energy is developing and testing a thorium-bearing fuel for use in existing nuclear power plants.
Fuel rods containing thorium additive Th-Add and also thorium MOX with Pu fuel rods were tested in a five-year irradiation trial that started in April at the Halden test reactor. The company is working towards obtaining regulatory approval for the commercial production and use of Th-Add fuel. This fuel is promoted as a means to improve power profiles within commercial reactors. There are seven types of reactor into which thorium can be introduced as a nuclear fuel. The first five of these have all entered into operational service at some point.
The last two are still conceptual:. Heavy Water Reactors PHWRs : These are well suited for thorium fuels due to their combination of: i excellent neutron economy their low parasitic neutron absorption means more neutrons can be absorbed by thorium to produce useful U , ii slightly faster average neutron energy which favours conversion to U, iii flexible on-line refueling capability.
Furthermore, heavy water reactors especially CANDU are well established and widely-deployed commercial technology for which there is extensive licensing experience. Fleets of PHWRs with near-self-sufficient equilibrium thorium fuel cycles could be supported by a few fast breeder reactors to provide plutonium.
The fuel particles are embedded in a graphite matrix that is very stable at high temperatures. Such fuels can be irradiated for very long periods and thus deeply burn their original fissile charge. Boiling Light Water Reactors BWRs : BWR fuel assemblies can be flexibly designed in terms of rods with varying compositions fissile content , and structural features enabling the fuel to experience more or less moderation eg, half-length fuel rods.
This design flexibility is very good for being able to come up with suitable heterogeneous arrangements and create well-optimised thorium fuels. And importantly, BWRs are a well-understood and licensed reactor type. Fuel needs to be in heterogeneous arrangements in order to achieve satisfactory fuel burn-up. It is not possible to design viable thorium-based PWR fuels that convert significant amounts of U Even though PWRs are not the perfect reactor in which to use thorium, they are the industry workhorse and there is a lot of PWR licensing experience.
They are a viable early-entry thorium platform. Fast Neutron Reactors FNRs : Thorium can serve as a fuel component for reactors operating with a fast neutron spectrum — in which a wider range of heavy nuclides are fissionable and may potentially drive a thorium fuel.
There is, however, no relative advantage in using thorium instead of depleted uranium DU as a fertile fuel matrix in these reactor systems due to a higher fast-fission rate for U and the fission contribution from residual U in this material. Also, there is a huge amount of surplus DU available for use when more FNRs are commercially available, so thorium has little or no competitive edge in these systems.
Molten Salt Reactors MSRs : These reactors are still at the design stage but are likely to be very well suited for using thorium as a fuel. The level of moderation is given by the amount of graphite built into the core. Certain MSR designs c will be designed specifically for thorium fuels to produce useful amounts of U Spallation neutrons are produced d when high-energy protons from an accelerator strike a heavy target like lead.
These neutrons are directed at a region containing a thorium fuel, eg, Th-plutonium which reacts to produce heat as in a conventional reactor. He even built a crude "neutron gun" to irradiate his thorium and get the chain reaction going. Perhaps fortunately, the Eagle Scout didn't understand chemistry very well and managed to irradiate only the contents of the potting shed including himself.
When law enforcement officials finally raided the place months later, their Geiger counters went wild. He even joined the Navy later, though the military didn't let him anywhere near a nuclear sub.
As with all technologies, thorium power has its shortcomings. Building any nuclear plant is still very expensive, and our nuclear-power infrastructure has focused on uranium for 50 years, meaning a switch to breeder reactors would cost even more.
Plus, thorium reactors would require new and largely untested safety controls. Even thorium's efficiency could cause problems: Because thorium can sustain a reaction on its own for so long, engineers would have to design reactors to withstand extreme conditions over long periods of time. All things considered, though, thorium does seem like a smart, abundant, and carbon-free energy option for the next century.
Correction, July 26, This article originally stated that no new power plants have come online since Actually, plants already in construction by have come online in the last 30 odd years, but no new construction projects have begun or been approved.
Return to the corrected sentence. Like Slate on Facebook. Follow us on Twitter. Antimatter and the Anti-Periodic Table By:. By: Sam Kean. Tungsten: There's No W in Tungsten.
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