Water injected with oxygen or an alkali, acid or other oxidizing solution is circulated through the uranium ore, extracting the uranium. The uranium solution is then pumped to the surface. The vast majority of nuclear power reactors use the isotope uranium as fuel; however, it only makes up 0. This increases the uranium concentration from 0.
A small number of reactors, most notably the CANDU reactors from Canada, are fuelled with natural uranium, which does not have to be enriched. The enrichment process requires the uranium to be in a gaseous form. This is achieved through a process called conversion, where uranium oxide is converted to a different compound uranium hexafluoride which is a gas at relatively low temperatures. Some companies apply a temperature profile across the centrifuges to help the process.
Banks of centrifuges are used to enrich the uranium. A new and improved type of centrifuge is gaining market use called a Zippe Centrifuge. The difference in the Zippe Centrifuge is that the U that moves toward the center wall moves up and out and U moves out and downward; therefore, they exit at opposite ends and produces a countercurrent.
Centrifuges are also much more energy efficient than gaseous diffusion plants. Any mention or link regarding a product, organization, company, or trade name is for information only and does not imply endorsement by the Bureau, NMT, or the State of New Mexico see more.
GLE will now decide in the light of commercial considerations on whether to proceed with a full-scale enrichment facility at Wilmington. There is about , tonnes of these at Paducah and Portsmouth among a total of , t tails. In November the DOE announced that it would proceed with contract negotiations to this end.
GLE expects licensing to take years. Negotiations with the DOE continued into , and in November an agreement was signed with the DOE for it to supply about , tonnes of high-assay tails, justifying construction by GLE of the plant in the early s. PLEF would become a commercial uranium enrichment production facility under a US NRC licence, producing about , tonnes of natural-grade uranium over 40 years or more. The DOE would dispose of the reduced-assay balance. The estimated plant size is 0.
Applications to silicon and zirconium stable isotopes are also being developed by Silex Systems near Sydney. CRISLA is another molecular laser isotope separation process which is the early stages of development. In this a gas is irradiated with a laser at a particular wavelength that would excite only the U isotope.
The entire gas is subjected to low temperatures sufficient to cause condensation on a cold surface or coagulation in the un-ionised gas. The excited molecules in the gas are not as likely to condense as the unexcited molecules. Hence in cold-wall condensation, gas drawn out of the system is enriched in the U isotope that was laser-excited. NeuTrek, the development company, is aiming to build a pilot plant in USA. The energy-intensive gaseous diffusion process of uranium enrichment is no longer used in the nuclear industry.
It involves forcing uranium hexafluoride gas under pressure through a series of porous membranes or diaphragms. As U molecules are lighter than the U molecules they move faster and have a slightly better chance of passing through the pores in the membrane.
The UF 6 which diffuses through the membrane is thus slightly enriched, while the gas which did not pass through is depleted in U This process is repeated many times in a series of diffusion stages called a cascade. Each stage consists of a compressor, a diffuser and a heat exchanger to remove the heat of compression. The enriched UF 6 product is withdrawn from one end of the cascade and the depleted UF 6 is removed at the other end. Diffusion plants typically have a small amount of separation through one stage hence the large number of stages but are capable of handling large volumes of gas.
Russia phased out the process in and the last diffusion plant was USEC's Paducah facility, which shut down in mid It was used to enrich some high-assay tails before being finally shut down after 60 years' operation. At Tricastin, in southern France, a more modern diffusion plant with a capacity of This Georges Besse I plant could produce enough 3. It was shut down in mid, after 33 years' continuous operation.
Its replacement GB II, a centrifuge plant — see above has commenced operation. However, though they have proved durable and reliable, gaseous diffusion plants reached the end of their design life and the much more energy-efficient centrifuge enrichment technology has replaced them. The large Georges Besse I enrichment plant at Tricastin in France beyond cooling towers was shut down in Most of the output from the nuclear power plant 4xMWe net was used to power the enrichment facility.
A very early endeavour was the electromagnetic isotope separation EMIS process using calutrons. This was developed in the early s in the Manhattan Project to make the highly enriched uranium used in the Hiroshima bomb, but was abandoned soon afterwards. However, it reappeared as the main thrust of Iraq's clandestine uranium enrichment program for weapons discovered in EMIS uses the same principles as a mass spectrometer albeit on a much larger scale.
Ions of uranium and uranium are separated because they describe arcs of different radii when they move through a magnetic field. The process is very energy-intensive — about ten times that of diffusion.
Two aerodynamic processes were brought to demonstration stage around the s. One is the jet nozzle process, with demonstration plant built in Brazil, and the other the Helikon vortex tube process developed in South Africa. They depend on a high-speed gas stream bearing the UF6 being made to turn through a very small radius, causing a pressure gradient similar to that in a centrifuge.
The light fraction can be extracted towards the centre and the heavy fraction on the outside. Thousands of stages are required to produce enriched product for a reactor. It is based on Helikon but pending regulatory authorisation it has not yet been tested on UF6 - only light isotopes such as silicon. However, extrapolating from results there it is expected to have an enrichment factor in each unit of 1.
One chemical process has been demonstrated to pilot plant stage but not used. In some countries used fuel is reprocessed to recover its uranium and plutonium, and to reduce the final volume of high-level wastes.
The plutonium is normally recycled promptly into mixed-oxide MOX fuel, by mixing it with depleted uranium. Where uranium recovered from reprocessing used nuclear fuel RepU is to be re-used, it needs to be converted and re-enriched. This is complicated by the presence of impurities and two new isotopes in particular: U and U, which are formed by or following neutron capture in the reactor, and increase with higher burn-up levels.
U is largely a decay product of Pu, and increases with storage time in used fuel, peaking at about ten years. Both decay much more rapidly than U and U, and one of the daughter products of U emits very strong gamma radiation, which means that shielding is necessary in any plant handling material with more than very small traces of it. U is a neutron absorber which impedes the chain reaction, and means that a higher level of U enrichment is required in the product to compensate.
For the Dutch Borssele reactor which normally uses 4. Centrifuge technology is at the heart of the enrichment process, and the line between its uses for civilian and military purposes is hard to distinguish. Once a country has mastered this technology, the centrifuges can be reconfigured into cascades to either produce fuel for an electricity-generating nuclear reactor or the 25 kilograms of weapon-grade uranium that is sufficient for a nuclear weapon.
The process is fairly simple for both. The uranium found in nature contains only 0. Centrifuges spin at enormous speeds and the heavier isotope, U, moves to the outside and is then removed, leaving a higher concentration of U behind, which can be further enriched.
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