The COLEX process (or COLEX separation) is a chemical method of isotopic separation of lithium-6 and lithium-7, based on the use of mercury. COLEX stands for column exchange.
Since the beginning of the atomic era, a variety of lithium enrichments methods have been developed (such as chemical exchange, electromagnetic, laser, centrifugal [1] ) and the COLEX process has been the most extensively implemented method so far.
In the US, several chemical exchange methods for lithium isotope separation have been under investigation in the 1930s and 1940s to develop a process for lithium-6 production, so that tritium could be obtained for thermonuclear weapons research.
The system finally selected was the COLEX process, with aqueous lithium hydroxide (LiOH) contacted with lithium-mercury amalgam. This process was initially used in the US between 1955 and 1963 in the Y12 plant in Oak Ridge, Tennessee. The COLEX plants in Oak Ridge had a very rough start in 1955 with major problems in this entirely new, complicated, and potentially hazardous technology. [2] Stockpiles of lithium-6 and lithium-7 from that period have been available until recently to meet the relatively small domestic and world demand [3]
Since then, due to environmental concerns, the US has stopped lithium enrichments operations in 1963. [1]
South Africa also built a pilot plant using the COLEX method to make lithium-6 for its nuclear weapons program in the 1970s.
Natural lithium contains about 7.5% lithium-6 ( 6
3Li ), with the rest being lithium-7 ( 7
3Li ).
Naturally occurring lithium has many non nuclear industrial uses, ranging from Li-ion batteries, ceramics, lubricants, to glass.
In the beginning of the 21st century, the steady increase of lithium world production is mainly stimulated by the demand of Li-ion batteries for electric vehicles.
The nuclear applications of lithium requires relatively small annual quantities of lithium, in the form of enriched lithium-6 and lithium-7.
Lithium-6 is valuable as the source material for the production of tritium and as an absorber of neutrons in nuclear fusion reactions.
Enriched lithium-6 is used as a neutron booster in thermonuclear bombs, and will be a key component in the tritium breeding modules (required enrichment from 7.5% to 30%-90%) of the future fusion reactors based on plasma confinement. [1]
The separation of lithium-6 has by now ceased in the large thermonuclear powers (notably USA, Russia, China), but stockpiles of it remain in these countries.
Highly enriched lithium-7 (more than 99%) is used as a coolant in molten salt reactors (MSRs) and pH stabilizer in pressurized water reactors (PWRs). [4] [5]
Lithium-6 has a greater affinity than lithium-7 for the element mercury.[ citation needed ] When an amalgam of lithium and mercury is added to aqueous lithium hydroxide, the lithium-6 becomes more concentrated in the amalgam and the lithium-7 more in the hydroxide solution.
The COLEX separation method makes use of this by passing a counter-flow of lithium-mercury amalgam flowing down and aqueous lithium hydroxide flowing up through a cascade of stages. The fraction of lithium-6 is preferentially drained by the mercury, but the lithium-7 flows mostly with the hydroxide. At the bottom of the column, the lithium (enriched with lithium-6) is separated from the amalgam, and the mercury is recovered to be reused in the process. At the top, the lithium hydroxide solution is electrolyzed to liberate the lithium-7 fraction.
The enrichment obtained with this method varies with the column length, the flow speed, and the operating temperature. [6]
From a technical and economical point of view, the COLEX separation has been so far the only method that enables industrial scale production of enriched lithium at minimal costs. The technology is mature, and has changed little since its development in the 1950s and 1960s. [7]
The method is not without a number of drawbacks, the main of which are:
The technology has potentially disastrous environmental implications. A significant amount of mercury is required (24 million pounds were used in the U.S. between 1955 and 1963) and many opportunities for leaks into the environment exist. Cleanup remains extremely difficult and expensive. [7]
In spite of the health and environmental concerns associated with processes based on mercury, some research is still being done on the COLEX separation along with cleaner lithium enrichment methods. [3]
Nowadays, it seems that China is the only country in the world which officially employs the COLEX process to enrich lithium. [7] Due to environmental concerns and relatively low demand for enriched lithium, further use of the COLEX process is officially banned in the USA since 1963, which strengthens China's near unanimous hold over the market of enriched lithium, followed by Russia. [7]
Russian enrichment capacities focus on lithium-7 production by electrolysis of an aqueous lithium chloride solution using a mercury cathode, which is thus different from the COLEX process. [9]
Although US nuclear industry relies heavily on Chinese and Russian enriched lithium, ecological concerns over the process may impede its future domestic use at industrial scale.
However, with the upswing in research in the general area of fusion reactor technology (ITER, DEMO) there has been renewed interest during the last decade in better processes for 6Li-7Li separation, especially in Japan and the US. [3]
North Korea is assessed to have procured the means to build a lithium-6 enrichment plant based on the COLEX separation. [10]
No industrial-scale facilities exist today that could meet the future requirements of commercial fusion power plants. [1]
Heavy water is a form of water in which hydrogen atoms are all deuterium rather than the common hydrogen-1 isotope that makes up most of the hydrogen in normal water. The presence of the heavier isotope gives the water different nuclear properties, and the increase in mass gives it slightly different physical and chemical properties when compared to normal water.
Lithium is a chemical element; it has symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid element. Like all alkali metals, lithium is highly reactive and flammable, and must be stored in vacuum, inert atmosphere, or inert liquid such as purified kerosene or mineral oil. It exhibits a metallic luster. It corrodes quickly in air to a dull silvery gray, then black tarnish. It does not occur freely in nature, but occurs mainly as pegmatitic minerals, which were once the main source of lithium. Due to its solubility as an ion, it is present in ocean water and is commonly obtained from brines. Lithium metal is isolated electrolytically from a mixture of lithium chloride and potassium chloride.
Nuclear fusion is a reaction in which two or more atomic nuclei, usually deuterium and tritium, combine to form one or more different atomic nuclei and subatomic particles. The difference in mass between the reactants and products is manifested as either the release or absorption of energy. This difference in mass arises due to the difference in nuclear binding energy between the atomic nuclei before and after the reaction. Nuclear fusion is the process that powers active or main-sequence stars and other high-magnitude stars, where large amounts of energy are released.
Tritium or hydrogen-3 is a rare and radioactive isotope of hydrogen with half-life ~12.3 years. The tritium nucleus contains one proton and two neutrons, whereas the nucleus of the common isotope hydrogen-1 (protium) contains one proton and no neutrons, and that of non-radioactive hydrogen-2 (deuterium) contains one proton and one neutron. Tritium is the heaviest particle-bound isotope of hydrogen. It is one of the few nuclides with a distinct name. The use of the name hydrogen-3, though more systematic, is much less common.
Isotope separation is the process of concentrating specific isotopes of a chemical element by removing other isotopes. The use of the nuclides produced is varied. The largest variety is used in research. By tonnage, separating natural uranium into enriched uranium and depleted uranium is the largest application. In the following text, mainly uranium enrichment is considered. This process is crucial in the manufacture of uranium fuel for nuclear power plants and is also required for the creation of uranium-based nuclear weapons. Plutonium-based weapons use plutonium produced in a nuclear reactor, which must be operated in such a way as to produce plutonium already of suitable isotopic mix or grade.
Enriched uranium is a type of uranium in which the percent composition of uranium-235 has been increased through the process of isotope separation. Naturally occurring uranium is composed of three major isotopes: uranium-238, uranium-235, and uranium-234. 235U is the only nuclide existing in nature that is fissile with thermal neutrons.
Nuclear Weapons Design are physical, chemical, and engineering arrangements that cause the physics package of a nuclear weapon to detonate. There are three existing basic design types:
Operation Castle was a United States series of high-yield (high-energy) nuclear tests by Joint Task Force 7 (JTF-7) at Bikini Atoll beginning in March 1954. It followed Operation Upshot–Knothole and preceded Operation Teapot.
Castle Bravo was the first in a series of high-yield thermonuclear weapon design tests conducted by the United States at Bikini Atoll, Marshall Islands, as part of Operation Castle. Detonated on March 1, 1954, the device remains the most powerful nuclear device ever detonated by the United States and the first lithium deuteride-fueled thermonuclear weapon tested using the Teller-Ulam design. Castle Bravo's yield was 15 megatons of TNT [Mt] (63 PJ), 2.5 times the predicted 6 Mt (25 PJ), due to unforeseen additional reactions involving lithium-7, which led to radioactive contamination in the surrounding area.
A boosted fission weapon usually refers to a type of nuclear bomb that uses a small amount of fusion fuel to increase the rate, and thus yield, of a fission reaction. The neutrons released by the fusion reactions add to the neutrons released due to fission, allowing for more neutron-induced fission reactions to take place. The rate of fission is thereby greatly increased such that much more of the fissile material is able to undergo fission before the core explosively disassembles. The fusion process itself adds only a small amount of energy to the process, perhaps 1%.
Neutron activation is the process in which neutron radiation induces radioactivity in materials, and occurs when atomic nuclei capture free neutrons, becoming heavier and entering excited states. The excited nucleus decays immediately by emitting gamma rays, or particles such as beta particles, alpha particles, fission products, and neutrons. Thus, the process of neutron capture, even after any intermediate decay, often results in the formation of an unstable activation product. Such radioactive nuclei can exhibit half-lives ranging from small fractions of a second to many years.
Lithium hydride is an inorganic compound with the formula LiH. This alkali metal hydride is a colorless solid, although commercial samples are grey. Characteristic of a salt-like (ionic) hydride, it has a high melting point, and it is not soluble but reactive with all protic organic solvents. It is soluble and nonreactive with certain molten salts such as lithium fluoride, lithium borohydride, and sodium hydride. With a molar mass of 7.95 g/mol, it is the lightest ionic compound.
Naturally occurring lithium (3Li) is composed of two stable isotopes, lithium-6 (6Li) and lithium-7 (7Li), with the latter being far more abundant on Earth. Both of the natural isotopes have an unexpectedly low nuclear binding energy per nucleon when compared with the adjacent lighter and heavier elements, helium and beryllium. The longest-lived radioisotope of lithium is 8Li, which has a half-life of just 838.7(3) milliseconds. 9Li has a half-life of 178.2(4) ms, and 11Li has a half-life of 8.75(6) ms. All of the remaining isotopes of lithium have half-lives that are shorter than 10 nanoseconds. The shortest-lived known isotope of lithium is 4Li, which decays by proton emission with a half-life of about 91(9) yoctoseconds, although the half-life of 3Li is yet to be determined, and is likely to be much shorter, like 2He which undergoes proton emission within 10−9 s.
Lithium fluoride is an inorganic compound with the chemical formula LiF. It is a colorless solid that transitions to white with decreasing crystal size. Its structure is analogous to that of sodium chloride, but it is much less soluble in water. It is mainly used as a component of molten salts. Partly because Li and F are both light elements, and partly because F2 is highly reactive, formation of LiF from the elements releases one of the highest energies per mass of reactants, second only to that of BeO.
In applications such as nuclear reactors, a neutron poison is a substance with a large neutron absorption cross-section. In such applications, absorbing neutrons is normally an undesirable effect. However, neutron-absorbing materials, also called poisons, are intentionally inserted into some types of reactors in order to lower the high reactivity of their initial fresh fuel load. Some of these poisons deplete as they absorb neutrons during reactor operation, while others remain relatively constant.
Lithium titanates are chemical compounds of lithium, titanium and oxygen. They are mixed oxides and belong to the titanates. The most important lithium titanates are:
Hybrid nuclear fusion–fission is a proposed means of generating power by use of a combination of nuclear fusion and fission processes.
A pressurized heavy-water reactor (PHWR) is a nuclear reactor that uses heavy water (deuterium oxide D2O) as its coolant and neutron moderator. PHWRs frequently use natural uranium as fuel, but sometimes also use very low enriched uranium. The heavy water coolant is kept under pressure to avoid boiling, allowing it to reach higher temperature (mostly) without forming steam bubbles, exactly as for a pressurized water reactor (PWR). While heavy water is very expensive to isolate from ordinary water (often referred to as light water in contrast to heavy water), its low absorption of neutrons greatly increases the neutron economy of the reactor, avoiding the need for enriched fuel. The high cost of the heavy water is offset by the lowered cost of using natural uranium and/or alternative fuel cycles. As of the beginning of 2001, 31 PHWRs were in operation, having a total capacity of 16.5 GW(e), representing roughly 7.76% by number and 4.7% by generating capacity of all current operating reactors. CANDU and IPHWR are the most common type of reactors in the PHWR family.
In nuclear fusion power research, the plasma-facing material (PFM) is any material used to construct the plasma-facing components (PFC), those components exposed to the plasma within which nuclear fusion occurs, and particularly the material used for the lining the first wall or divertor region of the reactor vessel.
LIFE, short for Laser Inertial Fusion Energy, was a fusion energy effort run at Lawrence Livermore National Laboratory between 2008 and 2013. LIFE aimed to develop the technologies necessary to convert the laser-driven inertial confinement fusion concept being developed in the National Ignition Facility (NIF) into a practical commercial power plant, a concept known generally as inertial fusion energy (IFE). LIFE used the same basic concepts as NIF, but aimed to lower costs using mass-produced fuel elements, simplified maintenance, and diode lasers with higher electrical efficiency.