This makes reactor-grade plutonium entirely unsuitable for use in a bomb see section on Plutonium and weapons below. This is also called 'civil plutonium'. Plutonium, Pu and Pu emit neutrons as a few of their nuclei spontaneously fission, albeit at a low rate. They and Pu also decay, emitting alpha particles and heat. A MWe light water reactor gives rise to about 25 tonnes of used fuel a year, containing up to kilograms of plutonium.
If the plutonium is extracted from used reactor fuel it can be used as a direct substitute for U in the usual fuel, the Pu being the main fissile part, but Pu also contributing. Plutonium can also be used in fast neutron reactors, where a much higher proportion of Pu fissions and in fact all the plutonium isotopes fission, and so function as a fuel.
As with uranium, the energy potential of plutonium is more fully realized in a fast reactor. Four of the six 'Generation IV' reactor designs currently under development are fast neutron reactors and will thus utilize plutonium in some way see page on Generation IV Nuclear Reactors.
In these, plutonium production will take place in the core, where burn-up is high and the proportion of plutonium isotopes other than Pu will remain high. In pure form plutonium exists in six allotropic forms or crystal structure — more than any other element. As temperature changes, it switches forms — each has significantly different mechanical and electrical properties. One is nearly twice the density of lead The alpha phase is hard and brittle, like cast iron, and if finely divided it spontaneously ignites in air to form PuO 2.
Beta, gamma and delta phases are all less dense. Alloyed with gallium, plutonium becomes more workable. Russia has maintained a positive policy of civil plutonium utilization. Apart from its formation in today's nuclear reactors, plutonium was formed by the operation of naturally-occurring nuclear reactors in uranium deposits at Oklo in what is now west Africa, some two billion years ago. Civil plutonium stored over several years becomes contaminated with the Pu decay product americium see page on The Many Uses of Nuclear Technology , which interferes with normal fuel fabrication procedures.
After long storage, Am must be removed before the plutonium can be used in a MOX fuel fabrication plant because it emits intense gamma radiation in the course of its alpha decay to Np The European Space Agency is paying NNL to produce Am for watt e radioisotope thermoelectric generators RTGs using very pure Am recovered from old civil plutonium, as the isotope is much less expensive than Pu now scarce.
Of some 2, types of radioisotopes known to humankind, only 22 are capable of powering a deep-space probe, according to a study by the US National Academy of Sciences. Of these, all but Pu are problematical due to being too expensive, emitting too much radiation to work with, or lacking enough heat output however, note European use of Am in above section on Plutonium and americium.
The decay heat of Pu 0. These spacecraft have operated for over 35 years and are expected to send back signals powered by their RTGs through to The Cassini spacecraft carried three generators with 33 kg of plutonium oxide providing watts power as it orbited around Saturn, having taken seven years to get there. See also information page on Nuclear Reactors and Radioisotopes for Space.
Plutonium is made by irradiating neptunium, recovered from research reactor fuel or special targets, in research reactors. Np is formed and quickly decays to Pu Pu was then recovered by further reprocessing at the H Canyon plant there.
This was essentially Cold War-origin material. Currently, supplies of high-purity Pu are scarce. Since the early s after production ceased at Savannah River in , the USA was buying all its supply for spacecraft from Russia — some INL supplies the neptunium and does some of the irradiation.
It uses the High Flux Isotope Reactor, irradiating neptunium targets for 72 days. Here, a computerenhanced image shows the mushroom-clouded aftermath of the dropping of the atomic bomb over Nagasaki, Japan, on August 9, Plutonium has been used to make nuclear weapons such as "atomic bombs" and in nuclear power plants to produce electricity. Plutonium has also been used as a portable energy supply in space probes and other space vehicles.
In , American physicists Edwin McMillan and Philip Abelson discovered the first transuranium element, neptunium atomic number The neptunium they produced was radioactive. They predicted it would break down to form a new element, atomic number But McMillan and Abelson were called away to do research on the atomic bomb.
They suggested to a colleague, Glenn Seaborg , that he continue their research on neptunium. Seaborg and his associates picked up where McMillan and Abelson had left off. They eventually proved that element 94 did exist. The proof came in an experiment they conducted in a particle accelerator at UCB. A particle accelerator is sometimes called an "atom smasher. The particles then collide with targets, such as gold, copper, or tin. When struck by the particles, the targets break apart, forming new elements and other particles.
Seaborg's team suggested the name plutonium for the new element, in honor of the planet Pluto. The two elements just before plutonium in the periodic table had also been named for planets: uranium for Uranus and neptunium for Neptune.
Glenn Seaborg later went on to find a number of other elements. One of those elements, atomic number , has been named seaborgium in his honor. See transfermium elements in this volume.
Plutonium is a silvery-white metal with a melting point of Glowing pellet of plutonium. Scientists now know that very small amounts of plutonium occur in the Earth's crust. It is formed in ores of uranium.
When uranium breaks down, it sometimes forms plutonium in very small quantities. Scientists believe that the abundance of plutonium in the earth is about one quintillionth parts per million.
About 15 isotopes of plutonium are known to exist. All of these isotopes are radioactive. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number.
The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope. The most stable isotopes of plutonium are plutonium and plutonium Nuclear weapons and as a fast reactor fuel.
Also, frequently used in chemical research where production-grade material of mixed isotopic content is suitable. Principally in flux monitors for fast reactors. The parent from which high-assay americium can be isolated for industrial purposes.
For study of the physical properties of plutonium; also as a mass spectroscopy tracer and standard. Department of Energy.
Of the 15 plutonium isotopes, the two that have proven most useful are masses and Plutonium is fissile, i. Chemical reactions can release a few electron volts of energy per atom; however, when a plutonium nucleus splits, it releases about MeV of energy and two or three neutrons. This release of energy makes plutonium useful for nuclear weapons and reactor fuel.
Once plutonium circulates through the body, it concentrates in the bones, liver, and spleen, exposing these organs to alpha particles. Plutonium that is ingested from contaminated food or water does not pose a serious threat to humans because the stomach does not absorb plutonium easily and so it passes out of the body in the feces.
Skip directly to site content Skip directly to page options Skip directly to A-Z link. Radiation Emergencies. Section Navigation. Facebook Twitter LinkedIn Syndicate. Radioisotope Brief: Plutonium. Minus Related Pages. What is it used for?
0コメント