Reprocessing of spent nuclear fuel by the PUREX method, first developed in the 1940s to produce plutonium for nuclear weapons, was demonstrated commercially in Belgium to partially re-fuel a LWR in the 1960s. This aqueous chemical process continues to be used commercially to separate reactor grade plutonium (RGPu) for reuse as MOX fuel. It remains controversial, as plutonium can be used to make nuclear weapons.The most developed, though commercially unfielded, alternative reprocessing method, is Pyroprocessing, suggested as part of the depicted metallic-fueled, Integral fast reactor (IFR) a sodium fast reactor concept of the 1990s. After the spent fuel is dissolved in molten salt, all of the recyclable actinides, consisting largely of plutonium and uranium though with important minor constituents, are extracted using electrorefining/electrowinning. The resulting mixture keeps the plutonium at all times in an unseparated gamma and alpha emitting actinide form, that is also mildly self-protecting in theft scenarios.
The actinoid elements in this case consist primarily of the unconsumed remains of the original fuel (typically U-235, U-238, and/or Pu-239).
Chemical process
Structure of uranyl nitrate complex that is extracted in PUREX.
The fuel is first dissolved in nitric acid at a concentration around 7 M. Solids are removed by filtration to avoid the formation of emulsions, referred to as third phases in the solvent extraction community.
The organic solvent consists of 30% tributyl phosphate (TBP) in a hydrocarbon such as kerosene. Uranyl(VI) UO2+ 2 ions are extracted in the organic phase as UO2(NO3)2·2TBP complexes; plutonium is extracted as similar complexes. The heavier actinides, primarily americium and curium, and the fission products remain in the aqueous phase. The nature of uranyl nitrate complexes with trialkyl phosphates has been characterized.[10]
Plutonium is separated from uranium by treating the TBP-kerosene solution with reducing agents to convert the plutonium to its +3 oxidation state, which will pass into the aqueous phase. Typical reducing agents include N,N-diethyl-hydroxylamine, ferroussulphamate, and hydrazine. Uranium is then stripped from the kerosene solution by back-extraction into nitric acid at a concentration around 0.2 M.[11]
PUREX raffinate
The term PUREX raffinate describes the mixture of metals in nitric acid which are left behind when the uranium and plutonium have been removed by the PUREX process from a nuclear fuel dissolution liquor. This mixture is often known as high level nuclear waste.
Two PUREX raffinates exist. The most highly active raffinate from the first cycle is the one which is most commonly known as PUREX raffinate. The other is from the medium-active cycle in which the uranium and plutonium are refined by a second extraction with tributyl phosphate.
Deep blue is the bulk ions, light blue is the fission products (group I is Rb/Cs) (group II is Sr/Ba) (group III is Y and the lanthanides), orange is the corrosion products (from stainless steel pipework), green are the major actinides, violet are the minor actinides and magenta is the neutron poison)
The PUREX plant at the Hanford Site was responsible for producing 'copious volumes of liquid wastes', resulting in the radioactive contamination of groundwater.[12]
Greenpeace measurements in La Hague and Sellafield indicated that radioactive pollutants are steadily released into the sea, and the air. Therefore, people living near these processing plants are exposed to higher radiation levels than the naturally occurring background radiation. According to Greenpeace, this additional radiation is small but not negligible.[13]
↑ Paiva, A. P.; Malik, P. (2004). "Recent advances on the chemistry of solvent extraction applied to the reprocessing of spent nuclear fuels and radioactive wastes". Journal of Radioanalytical and Nuclear Chemistry. 261 (2): 485–496. doi:10.1023/B:JRNC.0000034890.23325.b5. S2CID94173845.
↑ Burns, J. H.; Brown, G. M.; Ryan, R. R. (1985). "Structure of dinitratodioxobis(triisobutyl phosphate)uranium(VI) at 139 K". Acta Crystallographica Section C Crystal Structure Communications. 41 (10): 1446–1448. Bibcode:1985AcCrC..41.1446B. doi:10.1107/S0108270185008125.
↑ J.H. Burns (1983). "Solvent-extraction complexes of the uranyl ion. 2. Crystal and molecular structures of catena-bis(.mu.-di-n-butyl phosphato-O,O')dioxouranium(VI) and bis(.mu.-di-n-butyl phosphato-O,O')bis[(nitrato)(tri-n-butylphosphine oxide)dioxouranium(VI)]". Inorganic Chemistry. 22 (8): 1174–1178. doi:10.1021/ic00150a006.
The actinide or actinoid series encompasses at least the 14 metallic chemical elements in the 5f series, with atomic numbers from 89 to 102, actinium through nobelium. The actinide series derives its name from the first element in the series, actinium. The informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide.
Radioactive waste is a type of hazardous waste that contains radioactive material. Radioactive waste is a result of many activities, including nuclear medicine, nuclear research, nuclear power generation, nuclear decommissioning, rare-earth mining, and nuclear weapons reprocessing. The storage and disposal of radioactive waste is regulated by government agencies in order to protect human health and the environment.
The nuclear fuel cycle, also called nuclear fuel chain, is the progression of nuclear fuel through a series of differing stages. It consists of steps in the front end, which are the preparation of the fuel, steps in the service period in which the fuel is used during reactor operation, and steps in the back end, which are necessary to safely manage, contain, and either reprocess or dispose of spent nuclear fuel. If spent fuel is not reprocessed, the fuel cycle is referred to as an open fuel cycle ; if the spent fuel is reprocessed, it is referred to as a closed fuel cycle.
Nuclear reprocessing is the chemical separation of fission products and actinides from spent nuclear fuel. Originally, reprocessing was used solely to extract plutonium for producing nuclear weapons. With commercialization of nuclear power, the reprocessed plutonium was recycled back into MOX nuclear fuel for thermal reactors. The reprocessed uranium, also known as the spent fuel material, can in principle also be re-used as fuel, but that is only economical when uranium supply is low and prices are high. Nuclear reprocessing may extend beyond fuel and include the reprocessing of other nuclear reactor material, such as Zircaloy cladding.
Mixed oxide fuel, commonly referred to as MOX fuel, is nuclear fuel that contains more than one oxide of fissile material, usually consisting of plutonium blended with natural uranium, reprocessed uranium, or depleted uranium. MOX fuel is an alternative to the low-enriched uranium fuel used in the light-water reactors that predominate nuclear power generation.
Nuclear chemistry is the sub-field of chemistry dealing with radioactivity, nuclear processes, and transformations in the nuclei of atoms, such as nuclear transmutation and nuclear properties.
The integral fast reactor (IFR), originally the advancedliquid-metal reactor (ALMR), is a design for a nuclear reactor using fast neutrons and no neutron moderator. IFRs can breed more fuel and are distinguished by a nuclear fuel cycle that uses reprocessing via electrorefining at the reactor site.
Tributyl phosphate, known commonly as TBP, is an organophosphorus compound with the chemical formula (CH3CH2CH2CH2O)3PO. This colourless, odorless liquid finds some applications as an extractant and a plasticizer. It is an ester of phosphoric acid with n-butanol.
The Thermal Oxide Reprocessing Plant, or THORP, is a nuclear fuel reprocessing plant at Sellafield in Cumbria, England. THORP is owned by the Nuclear Decommissioning Authority and operated by Sellafield Ltd.
Nuclear fuel is material used in nuclear power stations to produce heat to power turbines. Heat is created when nuclear fuel undergoes nuclear fission. Nuclear fuel has the highest energy density of all practical fuel sources. The processes involved in mining, refining, purifying, using, and disposing of nuclear fuel are collectively known as the nuclear fuel cycle.
Fluoride volatility is the tendency of highly fluorinated molecules to vaporize at comparatively low temperatures. Heptafluorides, hexafluorides and pentafluorides have much lower boiling points than the lower-valence fluorides. Most difluorides and trifluorides have high boiling points, while most tetrafluorides and monofluorides fall in between. The term "fluoride volatility" is jargon used particularly in the context of separation of radionuclides.
The Magnox Reprocessing Plant is a former nuclear reprocessing facility at Sellafield in northern England, which operated from 1964 to 2022. The plant used PUREX chemistry to extract plutonium and uranium from used nuclear fuel originating primarily from Magnox reactors. The plant was originally constructed and operated by the United Kingdom Atomic Energy Authority (UKAEA), but in 1971 control was transferred to British Nuclear Fuels Limited (BNFL). Since 2005 the plant has been operated by Sellafield Ltd.
This page discusses each of the main elements in the mixture of fission products produced by nuclear fission of the common nuclear fuels uranium and plutonium. The isotopes are listed by element, in order by atomic number.
This article compares the radioactivity release and decay from the Chernobyl disaster with various other events which involved a release of uncontrolled radioactivity.
The bismuth-phosphate process was used to extract plutonium from irradiated uranium taken from nuclear reactors. It was developed during World War II by Stanley G. Thompson, a chemist working for the Manhattan Project at the University of California, Berkeley. This process was used to produce plutonium at the Hanford Site. Plutonium was used in the atomic bomb that was used in the atomic bombing of Nagasaki in August 1945. The process was superseded in the 1950s by the REDOX and PUREX processes.
The bis-triazinyl bipyridines (BTBPs) are a class of chemical compounds which are tetradentate ligands similar in shape to quaterpyridine. The BTBPs are made by the reaction of hydrazine and a 1,2-diketone with 6,6'-dicyano-2,2'-bipyridine. The dicyanobipy can be made by reacting 2,2'-bipy with hydrogen peroxide in acetic acid, to form 2,2'-bipyridine-N,N-dioxide. The 2,2'-bipyridine-N,N-dioxide is then converted into the dicyano compound by treatment with potassium cyanide and benzoyl chloride in a mixture of water and THF.
The plutonyl ion is an oxycation of plutonium in the oxidation state +6, with the chemical formula PuO2+ 2. It is isostructural with the uranyl ion, compared to which it has a slightly shorter M–O bond. It is easily reduced to plutonium(III). The plutonyl ion forms many complexes, particularly with ligands that have oxygen donor atoms. Plutonyl salts are important in nuclear fuel reprocessing.
Actinide chemistry is one of the main branches of nuclear chemistry that investigates the processes and molecular systems of the actinides. The actinides derive their name from the group 3 element actinium. The informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide. All but one of the actinides are f-block elements, corresponding to the filling of the 5f electron shell; lawrencium, a d-block element, is also generally considered an actinide. In comparison with the lanthanides, also mostly f-block elements, the actinides show much more variable valence. The actinide series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.
Remix Fuel was developed in Russia to make use of mixed recycled uranium and plutonium from spent nuclear fuel to manufacture fresh fuel suitable for widespread use in Russian reactor designs.
The advanced reprocessing of spent nuclear fuel is a potential key to achieve a sustainable nuclear fuel cycle and to tackle the heavy burden of nuclear waste management. In particular, the development of such advanced reprocessing systems may save natural resources, reduce waste inventory and enhance the public acceptance of nuclear energy. This strategy relies on the recycling of major actinides and the transmutation of minor actinides in appropriate reactors. In order to fulfill this objective, selective extracting agents need to be designed and developed by investigating their complexation mechanism.
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