Uranium

Uranium:

Atomic Number: 92
Uranium Atomic Symbol: U
Atomic Weight: 238.0

Word Origin: Named after the planet Uranus

 

History:

(Planet Uranus) Yellow-colored glass, containing more than 1% uranium oxide and dating back to 79 A.D., has been found near Naples, Italy. Klaproth recognized an unknown element in pitchblende and attempted to isolate the metal in 1789. The metal apparently was first isolated in 1841 by Peligot, who reduced the anhydrous chloride with potassium. Uranium is a slightly radioactive metal that occurs throughout the Earth. Pitchblende was thought to be a ore with zinc, iron and tungsten. However, in 1789, the German chemist M. S. Klaproth discovered a new element in pitchblende ores which he named uranium in honor of the planet Uranus, which had been discovered just eight years before. The French scientist Henri Becquerel discovered the radioactive property of uranium in 1896.
Enrico Fermi and his co-workers observed in 1934 that the bombardment of uranium by neutrons produced beta radioactivity, although the full significance of this observation was not understood at the time. In 1938, Otto Hahn and Fritz Strassmann showed that when uranium was bombarded by thermal neutrons it fissioned into radioactive isotopes of lighter elements, such as krypton and barium, and that part of the binding energy holding the protons and neutrons together in the heavy uranium nucleus was released. In 1939, at a conference in the United States, Fermi suggested that when uranium nuclei are split under neutron bombardment other neutrons might also be released in sufficient number to cause a continuous self-sustaining fission reaction. The existence of these fission neutrons was confirmed in 1939 in studies by F. Joliot, Leo Szilard, H.L. Anderson and their coworkers.
The first self-sustaining nuclear chain reaction was achieved by Fermi and a team of scientists in a pile of 400 tons of graphite, six tons of uranium metal and 58 tons of uranium oxide, at the University of Chicago, on December 2, 1942. The first test of a nuclear explosive device occurred on Alamogordo, New Mexico, on July 16, 1945 and the first nuclear weapon was used in warfare August 6, 1945, at Hiroshima.

It is about 500 times more abundant than gold and about as common as tin. It is present in most rocks and soils as well as in many rivers and in sea water. It is, for example, found in concentrations of about four parts per million (ppm) in granite, which makes up 60% of the Earth's crust. In fertilisers, uranium concentration can be as high as 400 ppm (0.04%), and some coal deposits contain uranium at concentrations greater than 100 ppm (0.01%). Most of the radioactivity associated with uranium in nature is in fact due to other minerals derived from it by radioactive decay processes, and which are left behind in mining and milling. There are a number of areas around the world where the concentration of uranium in the ground is sufficiently high that extraction of it for use as nuclear fuel is economically feasible. Such concentrations are called ore.

Uranium in the form of the mineral pitchblende (Uranium Oxide) often turned up in the Middle Ages in Silver Mines of Joachimsthal (now part of the Czech Republic, but then the Kingdom of Bohemia) and was thought to contain zinc or iron. Its name pitchblende was derived from pech, meaning pitch (or ill/bad luck), and blende, meaning deceiver.

Then, in 1789, Martin Heinrich Klaproth, a pharmacist who had his own experimental laboratory in Berlin, Germany, investigated pitchblende and found that it dissolved in nitric acid and precipitated a yellow compound when the solution was neutralized with sodium hydroxide (184). He was convinced that that it was the oxide of an unknown element and when he heated the precipitate with charcoal and obtained a black powder, he had produced the metal itself. He therefore based its name on the newly discoved planet Uranus and gave it the name "uran," which later becameuranium.

Later tests showed that Klaproth's metal was in fact one of the oxides of uranium, and it fell to Eugene Peligot, who was professor of Analytical Chemistry at the Central School of Arts and Manufactures, in Paris, to isolate the first sample of uranium metal, which he did in 1841 by heating uranium tetrachloride with potassium. For the better part of the nineteenth century, uranium was not regarded as particularly dangerous and commercial andpractical uses were found for it.

The discovery that uranium was radioactive came only in 1896 by accident when Henri Becquerel in Paris found that a sample of uranium left in a drawer on top of an unexposed piece of photographic plate caused the plate to become "fogged," as if it had been partly exposed to light. From that he deduced that uranium was emitting invisible rays.










Practical Uses 





commercial uses were found for it. In 1855, a factory in Austria In the 19th century, uranium was not considered a dangerous element and manufactured uranium pigments for coloring pottery and glass. Glass to which uranium, or uranium oxide was added had a flourescent yellow-green color.

When uranium's radioactive properties were revealed, the military began to use uranium for an entirely different purpose. Atomic bombs and nuclear weapons in general have enough uranium in them to start a chain reaction with all the naturally occuring uranium in the earth. On the 6th of August, 1945 an atomic bomb code named "Little Boy" was dropped on the Japanese city of Hiroshima at 8:16 am. The bomb had the isotope uranium-235. It was the equivalant of 12,500 tonnes of TNT, destroyed 50,000 buildings, and killed about 75,000 people. Those who didn't die instantly died later of radiation burns.

However, there are other uses for radioactive uranium's other than pottery and military weapons, much of the world relies on nuclear power plants in order to generate electricity. The Uranium for these reactors is enriched with uranium-235 and these are clad in zirconium metal. As the fuel is consumed, the dissociation products accumulate and may absorb the neutrons necessary to sustain the reactor, so after 5 years a rod has to be replaced. The spent (used up) fuel rod is then sent for reprocessing, but only after being allowed to decay some of the intense radiation for a year.
The discovery that uranium was radioactive came only in 1896 by accident when Henri Becquerel in Paris found that a sample of uranium left in a drawer on top of an unexposed piece of photographic plate caused the plate to become "fogged," as if it had been partly exposed to light. From that he deduced that uranium was emitting invisible rays

Uranium Properties: 

Uranium generally has a valence of 6 or 4. Uranium is a heavy, lustrous, silvery-white metal, capable of taking a high polish. It exhibits three crystallographic modifications: alpha, beta, and gamma. It is a bit softer than steel; not hard enough to scratch glass. It is malleable, ductile, and slightly paramagnetic. Uranium is a hard, dense, malleable, ductile, silver-white, radioactive metal. Uranium metal has very high density. When finely divided, it can react with cold water. In air it is coated by uranium oxide, tarnishing rapidly. It is attacked by steam and acids. Uranium can form solids solutions and intermetallic compounds with many of the metals. When exposed to air, uranium metal becomes coated with a layer of oxide. Acids will dissolve the metal, but it is not affected by alkalis. Finely divided uranium metal is attached by cold water and is pyrophoric. Crystals of uranium nitrate are triboluminescent. Uranium and its (uranyl) compounds are highly toxic, both chemically and radiologically.

Physical & Chemical Properties of Uranium:

General properties
Name, symbol,number	uranium, U, 92
Element category	actinide
Group, period,block	n/a, 7, f
Standard atomic weight	238.02891(3)
Electron configuration	[Rn] 5f3 6d1 7s2 2, 8, 18, 32, 21, 9, 2
Physical properties
Phase	solid
Density (near r.t.)	19.1 g·cm−3
Liquid density atm.p.	17.3 g·cm−3
Melting point	1405.3 K2070 °F 1132.2 °C, ,
Boiling point	7468 °F 4131 °C, 4404 K,
Heat of fusion	9.14 kJ·mol−1
Heat of vaporization	417.1 kJ·mol−1
Molar heat capacity	27.665 J·mol−1·K−1
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 2325 2564 2859 3234 3727 4402
Atomic properties
Oxidation states	6, 5, 4, 3[1], 2 (weakly basic oxide)
Electronegativity	1.38 (Pauling scale)
Ionization energies	1st: 597.6 kJ·mol−1
	2nd: 1420 kJ·mol−1
Atomic radius	156 pm
Covalent radius	196±7 pm
Van der Waals radius	186 pm
Miscellanea
Crystal structure	orthorhombic
Magnetic ordering	paramagnetic
Electrical resistivity	(0 °C) 0.280 µΩ·m
Thermal conductivity	27.5 W·m−1·K−1
Thermal expansion	(25 °C) 13.9 µm·m−1·K−1
Speed of sound(thin rod)	(20 °C) 3155 m·s−1
Young's modulus	208 GPa
Shear modulus	111 GPa
Bulk modulus	100 GPa
Poisson ratio	0.23
CAS registry number	7440-61-1

Isotopes and Radioactive Decay:

Isotopes: Uranium has sixteen isotopes. All of the isotopes are radioactive. Naturally-occurring uranium contains approximately 99.28305 by weight U-238, 0.7110% U-235, and 0.0054% U-234. The percentage weight of U-235 in natural uranium depends on its source and may vary by as much as 0.1%. Naturally occurring uranium is a mixture of three isotopes. The most abundant (greater than 99%) and most stable is uranium-238 (half-life 4.5×10⁹ years); also present are uranium-235 (half-life 7×10⁸ years) and uranium-234 (half-life 2.5×10⁵ years). There are 16 other known isotopes. Uranium-238 is the parent substance of the 18-member radioactive decay series known as the uranium series (see radioactivity). Some relatively long-lived members of this series include uranium-234, thorium-230, and radium-226; the final stable member of the series is lead-206. Uranium-235, also called actinouranium, is the parent substance of the so-called actinium series, a 15-member radioactive decay series ending in stable lead-207; protactinium-231 and actinium-227 are the relatively stable members of this series. Because the rate of decay in these series is constant, it is possible to estimate the age of uranium samples (e.g., minerals) from the relative amounts of parent substance and final product 

Resources and reserves:

Sources: Uranium occurs in minerals including pitchblende, carnotite, cleveite, autunite, uraninite, uranophane, and tobernite. It is also found in phosphate rock, lignite, and monazite sands. Radium is always associated with uranium ores. Uranium can be prepared by reducing uranium halides with alkali or alkaline earth metals or by reducing uranium oxides by calcium, carbon, or aluminum at elevated temperatures. The metal can be produced through electrolysis of KUF₅ or UF₄, dissolved in a molten mixture of CaCl₂ and NaCl. High-purity uranium can be prepared by the thermal decomposition of uranium halides on a hot filament.
It is estimated that 5.5 million tonnes of uranium exists in ore reserves that are economically viable at US$59 per lb of uranium, while 35 million tonnes are classed as mineral resources (reasonable prospects for eventual economic extraction). Prices went from about $10/lb in May 2003 to $138/lb in July 2007. This has caused a big increase in spending on exploration, with US$200 million being spent worldwide in 2005, a 54% increase on the previous year. This trend continued through 2006, when expenditure on exploration rocketed to over $774 million, an increase of over 250% compared to 2004. The OECD Nuclear Energy Agency said exploration figures for 2007 would likely match those for 2006.
Australia has 31% of the world's known uranium ore reserves and the world's largest single uranium deposit, located at the Olympic Dam Mine in South Australia. There is a significant reserve of uranium in Bakoumaa sub-prefecture in the prefecture of Mbomou in Central African Republic. Some nuclear fuel comes from nuclear weapons being dismantled, such as from the Megatons to Megawatts Program. An additional 4.6 billion tonnes of uranium are estimated to be in sea water (Japanese scientists in the 1980s showed that extraction of uranium from sea water using ion exchangers was technically feasible).There have been experiments to extract uranium from sea water, but the yield has been low due to the carbonate present in the water.
In 2012, ORNL researchers announced the successful development of a new absorbent material dubbed HiCap, which vastly outperforms previous best adsorbents, which perform surface retention of solid or gas molecules, atoms or ions. "We have shown that our adsorbents can extract five to seven times more uranium at uptake rates seven times faster than the world's best adsorbents," said Chris Janke, one of the inventors and a member of ORNL's Materials Science and Technology Division. HiCap also effectively removes toxic metals from water, according to results verified by researchers at Pacific Northwest National Laboratory

Size of the Uranium Resource

Uranium is a dense metal found at an abundance of 2.8 parts per million in the Earth's crust. It is a highly reactive metal that does not occur in a free state in nature, commonly occurring as an oxide U₃O₈. Prices for Uranium in the world market are quoted in $US per pound of U₃O₈. The amount of Uranium commercially recoverable depends upon the market price of the metal. The market price in mid 2010 is around US$100/kg, after peaking at over $300/kg in 2007. In the early 1990's the spot price of Uranium reached historical lows of less than US$22/kg [1]. The cost of mining Uranium is a very small factor in the cost of running a nuclear power station and so movements in the price have little effect on the price of the power produced.

The sources of uranium are: mining, commercial inventories (from earlier periods of oversupply), reprocessing of spent full rods from nuclear power plants and down blending (mixing of enriched uranium with natural ordepleted uranium) of highly enriched uranium from dismantled nuclear weapons. Consumption of uranium at the end of 1999 was 61600 tonnes of Uranium metal (tU) per annum [2] of which 56% is sourced from uranium mining. The majority of the balance comes from stockpiles and down blending in former Soviet countries as they reduce or eliminate their stock of nuclear weapons. The importance of this source and that of commercial inventories is expected to diminish over the next ten years.

Reasonably assured reserves (or proven reserves) refers to known commercial quantities of Uranium recoverable with current technology and for the specified price. As well there are estimates of additional and speculative reserves in extensions to well explored deposits or in new deposits that are thought to exist based on well defined geological data. These are necessarily subject  to a larger uncertainty, however, the historically low price of uranium over the past ten years has provided a disincentive to exploration. This is beginning to be rectified as the price recovers. Further exploration will reduce the uncertainty in the estimates of additional reserves. There are around 4000 million tU in sea water at a concentration of approximately 3 parts per billion. Extracting this Uranium is a significant challenge [3] but substantial progress has been demonstrated by Seko et al. These researchers recovered approximately 1 kg of Uranium in a 16 square meter cage submerged for 240 days off the coast of Japan. A patent related to these efforts has been granted. This technology has continued to be developed by Tamada. He estimates that the cost of his process is currently $220/kg [8].

As of the beginning of 2003 World Uranium reserves were

• Reasonable Assured Reserves recoverable at less than $US130/kgU (or $US50/lb U3O8) [4] = 3.10 - 3.28 million tU [2,5].
• Additional reserves recoverable at less than $US130/kgU (or $US50/lb U₃O₈) = 10.690 million tU [2].

As of the beginning of 2005 World Uranium reserves were

• Reasonable Assured Reserves recoverable at less than $US130/kgU (or $US50/lb U3O8) = 4.7 million tU [6].
• Additional recoverable Uranium is estimated to be 35 million tU [6].

As of the beginning of 2009 identified World Uranium reserves were

• Reasonable Assured Reserves recoverable at less than $US300/kg = 6.3 million tU [7]

The substantial increase (almost 100%) from 2003 shows the results of the world-wide renewed exploration effort spurred by the increase in Uranium prices which commenced in 2004. This increase in activity has continued through to 2010. Thus, the provable uranium reserves amount to over 100 years supply at the current level of consumption with current technology, with another 500 years of additional reserves. Around 24% of the proven reserves are in Australia.

With current technology, ²³⁵U is the only fuel for nuclear reactors. Uranium-235 represents 0.72% of natural uranium. Future technological developments could allow other elements to fuel nuclear reactors. Thorium-232 is a possible nuclear fuel and has a similar abundance to uranium, though there are as yet no commercial reactors operating or planned that would utilize thorium. Fast breeder reactors could utilize both ²³⁵U (Uranium-235) and ²³⁹Pu (Plutonium-239) as a fuel. Plutonium-239 is created when ²³⁸U (99.27% of naturally occurring uranium) is bombarded with neutrons. Plutonium-239 is a by product of nuclear power generation with the current mix of ²³⁵U and ²³⁸U. It is currently a waste product of concern due to its extreme toxicity and link to nuclear weapons. If reactors could be made to utilize ²³⁹Pu the potential of known reserves of uranium would be greatly extended since ²³⁸U could then be turned into a fuel. The Super Phoenix fast breeder reactor in France has demonstrated the technology. Currently electricity from such a plant would cost around three times the amount per kilowatt as that from conventional nuclear power plants. Fast breeder reactors have a higher risk profile due to the need to handle large quantities of Plutonium, and so present a different balance between utility and risk than the other types of reactors.

Pakistan 1,000 uranium reserves:

Pakistan Atomic Energy                                   Commission has claimed to haven discovered around 1,000 uranium favourable sites, which could provide the required fuel for its proposed nuclear power plants.     

Four of the 1000 sites were being mined and another nine with potential uranium reserves had been identified as very promising, Dawn quoted officials as saying.     

"The effort was rewarded with the discovery of a large number of sites, which have indicated their potential for hosting uranium reserves," it said, quoting a latest official document.

It said that uranium favourable rocks constituted 12 per cent of the total areas of Pakistan.

"More than 65 per cent of the favourable sites have been scanned through airborne gamma-spectrometric and foot radiometry surveys for its potential, while 35 per cent is yet to be checked," the document said.

The initial exploration will be carried out throughout Pakistan using airborne, car-borne, foot survey, geo-chemical and geo-physical techniques to delineate anomalous sites.

After delineation of anomalous sites, a detailed exploration will be carried out by means of exploratory drilling to establish uranium reserves.

The officials said the PAEC had finalised a plan to establish more than 6,000 tons of reasonably assured reserves of uranium by 2011 to fulfil the one-third requirement of fuel for producing 8,800mw of nuclear power.

They said the government was expected to make available Rs 4.5 billion to the PAEC to implement a five-year uranium exploration programme (2006-2011) in the four provinces.

The plan is expected to ensure indigenous supply of fuel for country's future needs. An increased nuclear power will facilitate the overall industrial as well as infrastructure development.

A separate provision will be required for mining projects discovered as a result of these investigations.

"It is estimated that 350 tons of yellow cake (U3O8) will be required annually to achieve the target of 8,800mw of nuclear power. Therefore, the initiation of effort to bridge the gap between demand and supply of nuclear fuel is the need of the time," the document said.

The exploration to establish additional uranium reserves will be carried out through the establishment of mineral sector of the PAEC, including the Atomic Energy Minerals Centre, Lahore, and Detailed Exploration for Uranium projects in Kohat and Dera Ghazi Khan.

At present there are two nuclear power plants, which produce 380mw of electricity -- 80mw KANUPP and 300mw CHASNUPP-1. For these, the PAEC mineral sector is partially fulfilling the requirement of uranium.

The document said that country's electricity supply and demand gap needed to be bridged with additional generation of electricity through various sources -- hydro, thermal, nuclear and solar.

The share of nuclear sector is presently very low for which the PAEC has embarked upon a programme for the installation of several nuclear power plants in the coming years.

Characteristics:

An induced nuclear fission event involving uranium-235

When refined, uranium is a silvery white, weakly radioactive metal, which is harder than most elements. It is malleable, ductile, slightly paramagnetic, strongly electropositive and is a poor electrical conductor. Uranium metal has very high density, being approximately 70% denser than lead, but slightly less dense than gold.
Uranium metal reacts with almost all nonmetallic elements and their compounds, with reactivity increasing with temperature. Hydrochloric and nitric acids dissolve uranium, but non oxidizing acids attack the element very slowly. When finely divided, it can react with cold water; in air, uranium metal becomes coated with a dark layer of uranium oxide. Uranium in ores is extracted chemically and converted into uranium dioxide or other chemical forms usable in industry.
Uranium-235 was the first isotope that was found to be fissile. Other naturally occurring isotopes are fissionable, but not fissile. Upon bombardment with slow neutrons, its uranium-235 isotope will most of the time divide into two smaller nuclei, releasing nuclear binding energy and more neutrons. If too many of these neutrons are absorbed by other uranium-235 nuclei, a nuclear chain reaction occurs that results in a burst of heat or (in special circumstances) an explosion. In a nuclear reactor, such a chain reaction is slowed and controlled by a neutron poison, absorbing some of the free neutrons. Such neutron absorbent materials are often part of reactor control rods (see nuclear reactor physics for a description of this process of reactor control).
As little as 15 lb (7 kg) of uranium-235 can be used to make an atomic bomb. The first nuclear bomb used in war, Little Boy, relied on uranium fission, while the very first nuclear explosive (The gadget) and the bomb that destroyed Nagasaki (Fat Man) were plutonium bombs.
Uranium metal has three allotropic forms:

• α (orthorhombic) stable up to 660 °C
• β (tetragonal) stable from 660 °C to 760 °C
• γ (body-centered cubic) from 760 °C to melting point—this is the most malleable and ductile state.

Applications and Uses:

Uranium Uses: Uranium is of great importance as a nuclear fuel. Nuclear fuels are used to generate electrical power, to make isotopes, and to make weapons. Much of the internal heat of the earth is thought to be due to the presence of uranium and thorium. Uranuim-238, with a half-life of 4.51 x 10⁹ years, is used to estimate the age of igneous rocks. Uranium may be used to harden and strengthen steel. Uranium is used in inertial guidance devices, in gyro compasses, as counterweights for aircraft control surfaces, as ballast for missile reentry vehicles, for shielding, and for x-ray targets. The nitrate may be used as a photographic toner. The acetate is used in analytical chemistry. The natural presence of uranium in soils may be indicative of the presence of radon and its daughters. Uranium salts have been used for producing yellow 'vaseline' glass and ceramic glazes.
Uranium gained importance with the development of practical uses of nuclear energy. Depleted uranium is used as shelding to protect tanks, and also in bullets and missiles. The first atomic bomb used in warfare was an uranium bomb. This bomb contained enough of the uramium-235 isotope to start a runaway chain reaction which in a fraction of a second caused a large number of the uranium atoms to undergo fission, there by releasing a fireball of energy.

The main use of uranium in the civilian sector is to fuel commercial nuclear power plants. This require uranium to be enriched with the uranium-235 isotope and the chain reaction to be controlled so that the energy is released in a more manageable way.

The isotope uranium 238 is used to estimate the age of the earliest igneous rocks and for other types of radiometric dating.

Phosphate fertilizers are made from material typically high in uranium, so they usually contain high amounts of it.

Natural Occurrence and Processing:

Availability of Usable Uranium

Uranium is present at an abundance 2 - 3 parts per million in the Earth's crust which is about 600 times greater than gold and about the same as tin. The amount of Uranium that is available is mostly a measure of the price that we're willing to pay for it. At present the cost of Natural Uranium ($165 per kg) is a small component in the price of electricity generated by Nuclear Power. At a price of $US110 per kg the known reserves amount to about 85 years supply at the current level of consumption with an expected further 500 years supply in additional or speculative reserves. The price of Uranium would have to increase by over a factor of 3 before it would have an impact of the cost of electricity generated from Nuclear Power. Such a price rise would stimulate a substantial increase in exploration activities with a consequent increase in the size of the resource (as has been the case with every other mineral of value). The price of Uranium rose to a peak of over 300/kg in 2007 but has since declined to around $100 by mid 2010. Identified reserves of Uranium have increased by around 100% since the end of 2003.

However advanced technologies are being developed which are far more efficient in their use of Uranium or which utilize Thorium which is 3 times more abundant than Uranium. If perfected these technologies can make use of both the spent fuel from current nuclear reactors and the depleted Uranium stocks used for enrichment. Taken together these provide enough fuel for many thousands of years of energy production. This will mitigate the demand for newly mined Uranium. Uranium is widely distributed in its ores but is not 

found uncombined in nature. It is a fairly abundant element in the earth's crust, being about 40 time as abundant as silver. Several hundred uranium containing minerals have been found but only a few are commercially significant. The most important is pitchblende, mined in the Congo River basin and NW Canada. Coffinite (a uranium silicate) and carnotite (a potassium uranate-vanadate) are important minerals found in Colorado and Utah. Ores with as little as 0.1% uranium are mined and processed. Most ores are processed by chemical methods including leaching and solvent extraction. The

uranium is obtained as pure uranyl nitrate, UO₂(NO₃)₂·6H₂O, which is typically decomposed to the trioxide, UO₃, by heating and reduced to the dioxide, UO₂, with hydrogen. The dioxide is chemically and physically stable at high temperatures, and is the form most often used as nuclear reactor fuel. The dioxide may be converted to the tetrafluoride, UF₄, by treatment with hydrogen fluoride gas, HF. The pure metal is obtained by electrolysis or chemical reduction of the tetrafluoride, or by chemical reduction of the dioxide

 

 

URANIUM MINES:

Most uranium ore is mined in open pit or underground mines. The uranium content of the ore is often between only 0.1% and 0.2%. Therefore, large amounts of ore have to be mined to get at the uranium. In the early years up until the 1960's uranium was predominantly mined in open pit mines from ore deposits located near the surface. Later, mining was continued in underground mines.
After the decrease of uranium prices since the 1980's on the world market, underground mines became too expensive for most deposits; therefore, many mines were shut down.
New uranium deposits discovered in Canada have uranium grades of several percent.
To keep groundwater out of the mine during operation, large amounts of contaminated water are pumped out and released to rivers and lakes. When the pumps are shut down after closure of the mine, there is a risk of groundwater contamination from the rising water level.

 

WASTE ROCK

Waste rock is produced during open pit mining when overburden is removed, and during underground mining when driving tunnels through non-ore zones. Piles of so-called waste rock often contain elevated concentrations of radioisotopes compared to normal rock. Other waste piles consist of ore with too low a grade for processing. The transition between waste rock and ore depends on technical and economic feasibility.

All these piles threaten people and the environment after shut down of the mine due to their release of radon gas and seepage water containing radioactive and toxic material image. The former waste rock "pyramids" of Ronneburg, Germany, 1990)
Waste rock was often processed into gravel or cement and used for road and railroad construction. VEB Hartsteinwerke Oelsnitz in Saxony has processed 200,000 tonnes of material per year into gravel containing 50 g/t uranium. Thus, gravel containing elevated levels of radioactivity were dispersed over large areas.

URANIUM MILL TAILINGS DEPOSITS

Characteristics of uranium mill tailings

Uranium mill tailings are normally dumped as a sludge in special ponds or piles, where they are abandoned.. The largest such piles in the US and Canada contain up to 30 million tonnes of solid material. In Saxony, Germany the Helmsdorf pile near Zwickau contains 50 million tonnes, and in Thuringia the Culmitzsch pile near Seelingstädt 86 million tonnes of solids. The amount of sludge produced is nearly the same as that of the ore milled. At a grade of 0.1% uranium, 99.9% of the material is left over.
Apart from the portion of the uranium removed, the sludge contains all the constituents of the ore. As long lived decay products such as thorium-230 and radium-226 are not removed, the sludge contains 85% of the initial radioactivity of the ore. Due to technical limitations, all of the uranium present in the ore can not be extracted. Therefore, the sludge also contains 5% to 10% of the uranium initially present in the ore.
In addition, the sludge contains heavy metals and other contaminants such as arsenic, as well as chemical reagents used during the milling process.
Mining and milling removes hazardous constituents in the ore from their relatively safe underground location and converts them to a fine sand, then sludge, whereby the hazardous materials become more susceptible to dispersion in the environment. Moreover, the constituents inside the tailings pile are in a geochemical disequilibrium that results in various reactions causing additional hazards to the environment. For example, in dry areas, salts containing contaminants can migrate to the surface of the pile, where they are subject to erosion. If the ore contains the mineral pyrite (FeS₂), then sulfuric acid forms inside the deposit when accessed by precipitation and oxygen. This acid causes a continuous automatic leaching of contaminants.
Radon-222 gas emanates from tailings piles and has a half life of 3.8 days. This may seem short, but due to the continuous production of radon from the

decay of radium-226, which has a half life of 1600 years, radon presents a longterm hazard. Further, because the parent product of radium-226, thorium-230 (with a half life of 80,000 years) is also present, there is continuous production of radium-226.
After about 1 million years, the radioactivity of the tailings and thus its radon emanation will have decreased so that it is only limited by the residual uranium contents, which continuously produces new thorium-230. If, for example, 90% of the uranium contained in an ore with 0.1% grade was extracted during the milling process, the radiation of the tailings stabilizes after 1 million years at a level 33 times that of uncontaminated material. Due to the 4.5 billion year half-life of uranium-238, there is only a minuscule further decrease.

Compounds:

Oxidation states and oxides

Oxides:

Triuranium octaoxide (diagram pictured) and uranium dioxide are the two most common uranium oxides.

Calcined uranium yellowcake as produced in many large mills contains a distribution of uranium oxidation species in various forms ranging from most

oxidized to least oxidized. Particles with short residence times in a calciner will generally be less oxidized than those with long retention times or particles recovered in the stack scrubber. Uranium content is usually referenced to U₃O₈, which dates to the days of the Manhattan project whenU₃O₈ was used as an analytical chemistry reporting standard.
Phase relationships in the uranium-oxygen system are complex. The most important oxidation states of uranium are uranium(IV) and uranium(VI), and their two corresponding oxides are, respectively, uranium dioxide (UO₂) and uranium trioxide (UO₃). Other uranium oxides such as uranium monoxide (UO), diuranium pentoxide (U₂O₅), and uranium peroxide (UO₄·2H₂O) also exist.
The most common forms of uranium oxide are triuranium octaoxide (U₃O₈) and UO₂. Both oxide forms are solids that have low solubility in water and are relatively stable over a wide range of environmental conditions. Triuranium octaoxide is (depending on conditions) the most stable compound of uranium and is the form most commonly found in nature. Uranium dioxide is the form in which uranium is most commonly used as a nuclear reactor fuel. At ambient temperatures, UO₂ will gradually convert to U₃O₈. Because of their stability, uranium oxides are generally considered the preferred chemical form for storage or disposal.

Aqueous chemistry

Uranium in its oxidation states III, IV, V, VI

Salts of all four oxidation states of uranium are water-soluble and may be studied in aqueous solutions. The oxidation states are U³⁺ (brown-red), U⁴⁺ (green), UO+
2 (unstable), and UO2+
2 (yellow). A few solid and semi-metallic compounds such as UO and US exist for the formal oxidation state uranium(II), but no simple ions are known to exist

in solution for that state. Ions of U³⁺ liberate hydrogen from water and are therefore considered to be highly unstable. The UO2+
2 ion represents the uranium(VI) state and is known to form compounds such as uranyl carbonate, uranyl chloride and uranyl sulfate. UO2+
2 also forms complexes with various organicchelating agents, the most commonly encountered of which is uranyl acetate.

Carbonates

The interactions of carbonate anions with uranium(VI) cause the Pourbaix diagram to change greatly when the medium is changed from water to a carbonate containing solution. While the vast majority of carbonates are insoluble in water (students are often taught that all carbonates other than those of alkali metals are insoluble in water), uranium carbonates are often soluble in water. This is because a U(VI) cation is able to bind two terminal oxides and three or more carbonates to form anionic complexes.

Effects of pH

The uranium fraction diagrams in the presence of carbonate illustrate this further: when the pH of a uranium(VI) solution increases, the uranium is converted to a hydrated uranium oxide hydroxide and at high pHs it becomes an anionic hydroxide complex.
When carbonate is added, uranium is converted to a series of carbonate complexes if the pH is increased. One effect of these reactions is increased solubility of uranium in the pH range 6 to 8, a fact which has a direct bearing on the long term stability of spent uranium dioxide nuclear fuels.

Hydrides, carbides and nitrides

Uranium metal heated to 250 to 300 °C (482 to 572 °F) reacts with hydrogen to form uranium hydride. Even higher temperatures will reversibly remove the hydrogen. This property makes uranium hydrides convenient starting materials to create reactive uranium powder along with various uranium carbide, nitride, and halide compounds. Two crystal modifications of uranium hydride exist: an α form that is obtained at low

temperatures and a β form that is created when the formation temperature is above 250 °C.
Uranium carbides and uranium nitrides are both relatively inert semimetallic compounds that are minimally soluble in acids, react with water, and can ignite in air to form U₃O₈. Carbides of uranium include uranium monocarbide (UC), uranium dicarbide (UC₂), and diuranium tricarbide (U₂C₃). Both UC and UC₂ are formed by adding carbon to molten uranium or by exposing the metal to carbon monoxide at high temperatures. Stable below 1800 °C, U₂C₃ is prepared by subjecting a heated mixture of UC and UC₂ to mechanical stress. Uranium nitrides obtained by direct exposure of the metal to nitrogen include uranium mononitride (UN), uranium dinitride (UN₂), and diuranium trinitride (U₂N₃).

Halides

Uranium hexafluoride is the feedstock used to separateuranium-235 from natural uranium.

All uranium fluorides are created using uranium tetrafluoride (UF₄); UF₄ itself is prepared by hydrofluorination of uranium dioxide. Reduction of UF₄ with hydrogen at 1000 °C produces uranium trifluoride (UF₃). Under the right conditions of temperature and pressure, the reaction of solid UF₄ with gaseous uranium hexafluoride (UF₆) can form the intermediate fluorides of U₂F₉, U₄F₁₇, and UF₅.
At room temperatures, UF₆ has a high vapor pressure, making it useful in the gaseous diffusion process to separate uranium-235 from the common uranium-238 isotope. This compound can be prepared from uranium dioxide and uranium hydride by the following process:

UO₂ + 4 HF → UF₄ + 2 H₂O (500 °C, endothermic)

UF₄ + F₂ → UF₆ (350 °C, endothermic)

The resulting UF₆, a white solid, is highly reactive (by fluorination), easily sublimes (emitting a nearly perfect gas vapor), and is the most volatile compound of uranium known to exist.
One method of preparing uranium tetrachloride (UCl₄) is to directly combine chlorine with either uranium metal or uranium hydride. The reduction of UCl₄ by hydrogen produces uranium trichloride (UCl₃) while the higher chlorides of uranium are prepared by reaction with additional chlorine. All uranium chlorides react with water and air.
Bromides and iodides of uranium are formed by direct reaction of, respectively, bromine and iodine with uranium or by adding UH₃ to those element's acids. Known examples include: UBr₃, UBr₄, UI₃, and UI₄. Uranium oxyhalides are water-soluble and include UO₂F₂, UOCl₂, UO₂Cl₂, and UO₂Br₂. Stability of the oxyhalides decrease as the atomic weight of the component halide increases.
Nuclear Energy Is Energy in the Core of an Atom:
Atoms are tiny particles that make up every object in the universe. Nuclear energy is energy in the nucleus (core) of an atom. There is enormous energy in the bonds that hold the nucleus together. Breaking those bonds releases that energy.
Nuclear energy can be used to make electricity. But first the energy must be released. It can be released from atoms in two ways: nuclear fusion and nuclear fission.
In nuclear fission, atoms are split apart to form smaller atoms, releasing energy. Nuclear power plants use this energy to produce electricity.
In nuclear fusion, energy is released when atoms are combined or fused together to form a larger atom. This is how the sun produces energy. Fusion is the subject of ongoing research, but it is not yet clear that it will ever be a commercially viable technology for electricity generation.
Nuclear Fuel — Uranium:
The fuel most widely used by nuclear plants for nuclear fission is uranium. Uranium is nonrenewable, though it is a common metal found in rocks all over the world. Nuclear plants use a certain kind of uranium, referred to as U-235. This kind of uranium is used as fuel because its atoms are easily split apart. Though uranium is quite common, about 100 times more common than silver, U-235 is relatively rare.
Most U.S. uranium is mined in the Western United States.  Once uranium is mined, the U-235 must be extracted and processed before it can be used as a fuel.
During nuclear fission, a small particle called a neutron hits the uranium atom and splits it, releasing a great amount of energy as heat and radiation. More neutrons are also released. These neutrons go on to bombard other uranium atoms, and the process repeats itself over and over again. This is called a chain reaction.

Nuclear Power Plants

Nuclear Power Plants Generate About One-Fifth of U.S. Electricity
The United States has 65 nuclear power plants with 104 nuclear reactors. Thirty-six of the plants have two or more reactors. Nuclear power plants are located in 31 different states but most are located east of the Mississippi. Nuclear power has generated about one-fifth of U.S.electricity each year since 1991. Nuclear power provides about as much electricity as they use in California, Texas, and New York, the three states with the most people.
Nuclear reactors look like large concrete domes from the outside. Not all nuclear power plants have cooling towers.

Source: Stock photography (copyrighted)
The last new reactor to enter commercial service in the United States was the Tennessee Valley Authority’s Watts Bar 1 in Tennessee in 1996.
In 2008, TVA resumed construction on Watts Bar 2, which was partially complete when its construction was stopped in 1988. It is now expected to be completed in 2013. More new nuclear reactors are expected to be constructed in the future

Nuclear Power Comes from Fission
Most power plants, including nuclear plants, use heat to produce electricity. They rely on steam from heated water to spin large turbines, which generate electricity. Instead of burning fossil fuels to produce the steam, nuclear plants use heat given off during fission.
In nuclear fission, atoms are split apart to form smaller atoms, releasing energy. Fission takes place inside the reactor of a nuclear power plant. At the center of the reactor is the core, which contains the uranium fuel.
The uranium fuel is formed into ceramic pellets. The pellets are about the size of your fingertip, but each one produces roughly the same amount of energy as 150 gallons of oil. These energy-rich pellets are stacked end-to-end in 12-foot metal fuel rods. A bundle of fuel rods, sometimes hundreds, is called a fuel assembly. A reactor core contains many fuel assemblies.
The heat given off during fission in the reactor core is used to boil water into steam, which turns the turbine blades. As they turn, they drive generators that make electricity. Afterward, the steam is cooled back into water in a separate structure at the power plant called a cooling tower. The water can be used again and again.

Types of Fuel Cycle

The nuclear fuel cycle is the progression of steps in the utilization of fissile materials, from the initial mining of the uranium (or thorium) through the final disposition of the material removed from the reactor. It is called a cycle because in the general case, some of the material taken from a reactor may be used again, or “recycled.”

Fuel cycles differ in the nature of the fuel used, the fuel’s history in the reactor, and the manner of handling the fuel that is removed from the reactor at the end of the fuel’s useful life (known as the spent fuel). For uranium-fueled reactors—which means virtually all commercial reactors—a key difference is in the disposition of the plutonium and other actinides that are produced in a chain of neutron captures and beta decays that starts with neutron capture in 238U to produce 239Pu . The actinides are important because some, especially 239Pu, are fissile and can be used as nuclear fuel in other reactors or in bombs, and (2) many of the actinides have long half-lives, complicating the problems of nuclear waste disposal. The three broad fuel cycle categories are as follows

◆ Once-through fuel cycle. This is sometimes called an open fuel cycle or a

“throw-away” cycle. It is not really a cycle, in that the spent fuel is treated

as waste when it is removed from the reactor and is not used further. The n239Pu and other actinides are part of these wastes.

◆ Reprocessing fuel cycle. In the present standard reprocessing fuel cycle, plutonium and uranium are chemically extracted from the spent fuel. The

plutonium is used to make additional fuel, often by mixing it with uranium oxides to produce mixed-oxide fuel (MOX) for use in thermal reactors.

This provides additional energy and changes the nature of the wastes. In potential variants of the reprocessing fuel cycle, the minor actinides would

also be extracted, and they and the plutonium would be incorporated in fresh fuel for fast reactors

◆ Breeding cycle. For this cycle, the reactor is designed so that there is more fissile material (mostly 239Pu) in the spent fuel than there was in the fuel put into the reactor. As in the reprocessing fuel cycle, the plutonium can be removed and be used in another reactor. With a sequence of such steps, fission energy is in effect extracted from a substantial fraction of the 238U in uranium, not just from the small 235U component, increasing the energy output from a given amount of uranium by a factor that could, in principle, approach 100.

It may be noted that uranium accounts for most of the mass of the nuclear wastes in the once-through cycle. It is separated out in the reprocessing and

breeding cycles for possible reuse in reactor fuel.

At present, all U.S. commercial reactors and the majority of reactors worldwide are operating with a once-through fuel cycle, although some countries,

particularly France, have large-scale reprocessing programs with use of plutonium in the form of MOX fuel. It should be noted, of course, that even in the once-through fuel cycle, the potential for eventually using the fuel in a reprocessing cycle remains until the fuel is disposed of irretrievably. No country is employing a breeder cycle at this time, although France appeared on the verge of attempting such a program with its Phenix and Superphenix reactors—but this effort has been abandoned, at least for the time being.

Although virtually all entire world’s commercial reactors have used uranium fuel, there is continuing interest in the use of thorium fuel.2 In a thorium

fuel cycle, the thorium (all 232Th in nature) serves as the fertile fuel. Neutron capture and beta decay result in the production of 233U, which has favourable properties as a fissile fuel. To start the thorium cycle, a fissile material such as

235U or 239Pu is needed, but once begun, it can be sustained if enough 233U is produced to at least replace the initial fissile material. It is often argued

that a thorium cycle is preferable to a uranium cycle. The Fort St. Vrain high-temperature, gas-cooled, graphite-moderated reactor in Colorado, which was shut down in 1989, is one of several exceptions to the exclusive use of uranium, having used thorium for part of its fuel. Front End of the Fuel Cycle 195 tracted from the spent fuel, it can be “denatured” by mixing it with natural uranium to make a fuel that cannot be used in a bomb. Bomb material could be obtained only after the isotopic separation of 233U. In contrast, bomb material can be obtained from a uranium-fueled reactor by chemical separation of the plutonium. Isotopic separation is technically more difficult than chemical separation; thus, a thorium fuel cycle could be more

proliferation resistant than a uranium fuel cycle unless, in the latter case, the plutonium is well protected from diversion or theft.

Steps in the Nuclear Fuel Cycle

A schematic picture of the fuel cycle ,indicates

alternative paths, with and without reprocessing. The steps in the fuel cycle that precede the introduction of the fuel into the reactor are referred to as the front end of the fuel cycle. Those that follow the removal of the fuel from the reactor comprise the back end of the fuel cycle. At present, there is only a truncated back end to the fuel cycle in the United States, as virtually all commercial spent fuel is accumulating in cooling pools or storage casks at the reactor sites.

 Implementation of a spent fuel disposal plan, or of a reprocessing and waste disposal plan, would represent the “closing” of the fuel cycle. This closing is viewed by many to be an essential condition for the increased use of nuclear power in the United States—and perhaps even for its continued use beyond the next several decades

·         The nuclear fuel cycle is the series of industrial processes which involve the production of electricity from uranium in nuclear power reactors. 

·         Uranium is a relatively common element that is found throughout the world. It is mined in a number of countries and must be processed before it can be used as fuel for a nuclear reactor. 

·         Fuel removed from a reactor, after it has reached the end of its useful life, can be reprocessed to produce new fuel. 

The various activities associated with the production of electricity from nuclear reactions are referred to collectively as the nuclear fuel cycle. The nuclear fuel cycle starts with the mining of uranium and ends with the disposal of nuclear waste. With the reprocessing of used fuel as an option for nuclear energy, the stages form a true cycle.

Uranium Mining:

HEAP LEACHING

In some cases uranium has been removed from low-grade ore by heap leaching. This may be done if the uranium contents is too low for the ore to be economically processed in a uranium mill. The leaching liquid (often sulfuric acid) is introduced on the top of the pile and percolates down until it reaches a liner below the pile, where it is caught and pumped to a processing plant.
During leaching, piles present a hazard because of release of dust, radon gas and leaching liquid.
After completion of the leaching process, a longterm problem may result from naturally induced leaching if the ore contains the mineral pyrite (FeS₂), as with the uranium deposits in Thuringia, Germany) or Ontario, Canada. Then, acces of water and air may cause continuous bacterially induced production of sulfuric acid inside the pile, which results in the leaching of uranium and other contaminants for centuries and possibly permanent contamination of ground water.

 

IN SITU LEACHING

With the in situ leaching technology, a leaching liquid (e.g. ammonium-carbonate or sulfuric acid) is pumped through drill- holes into underground uranium deposits, and the uranium bearing liquid is pumped out from below. This technology can only be used for uranium deposits located in an aquifer in permeable rock, confined in non-permeable rock.

In situ leaching gains importance with a decrease in price of uranium. In the USA, in situ leaching is often used. In 1990, in Texas alone in situ leaching facilities for uranium were operated at 32 sites. In Saxony, Germany, an underground mine converted to an underground in situ leaching mine was operated until end of 1990 at Königstein near Dresden. In the Czech Republic, the in situ leaching technology was used at a large scale at Stráz pod Ralskem in Northern Bohemia.
The advantages of this technology are:

• The reduced risk for the employees from accidents and radiation;
• the lower cost; and
• no need for large tailings piles.

The disadvantages are:

• The risk of leaching liquid excursions beyond the uranium deposit and subsequent contamination of ground water;

• the unpredictable effects of the leaching liquid on the host rock of the deposit;
• the production of some amounts of waste sludge and waste water when recovering the leaching liquid; and
• the impossibility of restoring natural conditions in the leaching zone after finishing the leaching operation.

After finishing the in situ leaching, the waste sludge must be dumped in a final deposit and the ore zone aquifer must be restored to pre-leaching conditions. Ground water restoration is a very protracted and troublesome process, which is not yet completely understood. It is still impossible to establish pre- leach levels for all parameters.

MILLING OF THE ORE

Ore mined in open pit or underground mines is crushed and leached in a uranium mill. A uranium mill is a chemical plant designed to extract uranium from ore. It is usually located near the mines to limit transportation. In the most cases, sulfuric acid is used as the leaching agent, but alkaline leaching is also used. As the leaching agent not only extracts uranium from the ore, but also several other constituents like molybdenum, vanadium, selenium, iron, lead and arsenic, the uranium must be separated out of the leaching solution. The final product produced from the mill, commonly referred to as "yellow cake" (U₃O₈ with impurities), is packed and shipped in casks.
When closing down a uranium mill, large amounts of radioactively contaminated scrap are produced, which have to be disposed in a safe manner. In the case of Wismut's Crossen uranium mill, to reduce cost some of the scrap is intended to be disposed in the Helmsdorf tailings, but there it can produce gases and thus threaten the safe final disposal of the sludge.

Conversion and enrichment

The uranium oxide product of a uranium mill is not directly usable as a fuel for a nuclear reactor and additional processing is required. Only 0.7% of natural uranium is 'fissile', or capable of undergoing fission, the process by which energy is produced in a nuclear reactor. The form, or isotope, of uranium which is fissile is the uranium-235 (U-235) isotope. The remainder is uranium-

238 (U-238). For most kinds of reactor, the concentration of the fissile uranium-235 isotope needs to be increased – typically to between 3.5% and 5% U-235. Isotope separation is a physical process to concentrate (‘enrich’) one isotope relative to others. The enrichment process requires the uranium to be in a gaseous form. The uranium oxide concentrate is therefore first converted to uranium hexafluoride, which is a gas at relatively low temperatures.

At a conversion facility, the uranium oxide is first refined to uranium dioxide, which can be used as the fuel for those types of reactors that do not require enriched uranium. Most is then converted into uranium hexafluoride, ready for the enrichment plant. The main hazard of this stage of the fuel cycle is the use of hydrogen fluoride. The uranium hexafluoride is then drained into 14-tonne cylinders where it solidifies. These strong metal containers are shipped to the enrichment plant.

The enrichment process separates gaseous uranium hexafluoride into two streams, one being enriched to the required level and known as low-enriched uranium; the other stream is progressively depleted in U-235 and is called 'tails', or simply depleted uranium.

There are two enrichment processes which have been in large-scale commercial use, each of which uses uranium hexafluoride gas as feed: diffusion and centrifuge. These processes both use the physical properties of molecules, specifically the 1% mass difference between the two uranium isotopes, to separate them. The last diffusion enrichment plants are likely to be phased out by 2013.

The product of this stage of the nuclear fuel cycle is enriched uranium hexafluoride, which is reconverted to produce enriched uranium oxide. Up to this point the fuel material can be considered fungible (though enrichment levels vary), but fuel fabrication involves very specific designs.

Fuel fabrication

Reactor fuel is generally in the form of ceramic pellets. These are formed from pressed uranium oxide (UO2) which is sintered (baked) at a high temperature (over 1400°C)^a. The pellets are then encased in metal tubes to form fuel rods, which are arranged into a fuel assembly ready for introduction into a reactor. The dimensions of the fuel pellets and other components of the fuel assembly are precisely controlled to ensure consistency in the characteristics of the fuel.

In a fuel fabrication plant great care is taken with the size and shape of processing vessels to avoid criticality (a limited chain reaction releasing radiation). With low-enriched fuel criticality is most unlikely, but in plants handling special fuels for research reactors this is a vital consideration.

Power generation and burn-up

Inside a nuclear reactor the nuclei of U-235 atoms split (fission) and, in the process, release energy. This energy is used to heat water and turn it into steam. The steam is used to drive a turbine connected to a generator which produces electricity. Some of the U-238 in the fuel is turned into plutonium in the reactor core. The main plutonium isotope is also fissile and this yields about one third of the energy in a typical nuclear reactor. The fissioning of uranium (and the plutonium generated in situ) is used as a source of heat in a nuclear power station in the same way that the burning of coal, gas or oil is used as a source of heat in a fossil fuel power plant.

Typically, some 44 million kilowatt-hours of electricity are produced from one tonne of natural uranium. The production of this amount of electrical power from fossil fuels would require the burning of over 20,000 tonnes of black coal or 8.5 million cubic metres of gas.

An issue in operating reactors and hence specifying the fuel for them is fuel burn-up. This is measured in gigawatt-days per tonne and its potential is proportional to the level of enrichment. Hitherto a limiting factor has been the physical robustness of fuel assemblies, and hence burn-up levels of about 40 GWd/t have required only around 4% enrichment. But with better equipment and fuel assemblies, 55 GWd/t is possible (with 5% enrichment), and 70 GWd/t is in sight, though this would require 6% enrichment. The benefit of this is that operation cycles can be longer – around 24 months – and the number of fuel assemblies discharged as used fuel can be reduced by one third. Associated fuel cycle cost is expected to be reduced by about 20%.

As with as a coal-fired power station about two thirds of the heat is dumped, either to a large volume of water (from the sea or large river, heating it a few degrees) or to a relatively smaller volume of water in cooling towers, using evaporative cooling (latent heat of vapourisation).

Nuclear Energy Production
http://www.uic.com.au/uran.htm

Depleted uranium is also used for ship's ballast, as counterwieghts for aircraft and for coloring on ceramic glass. Depleted uranium is preferred over denser materials because it is easily cast and machined. It is also used as armor on tanks of various countries, though not of the U.S.

Used fuel

With time, the concentration of fission fragments and heavy elements formed in the same way as plutonium in the fuel will increase to the point where it is

no longer practical to continue to use the fuel. So after 18-36 months the used fuel is removed from the reactor. The amount of energy that is produced from a fuel assembly varies with the type of reactor and the policy of the reactor operator.

When removed from a reactor, the fuel will be emitting both radiation, principally from the fission fragments, and heat. Used fuel is unloaded into a storage pond immediately adjacent to the reactor to allow the radiation levels to decrease. In the ponds the water shields the radiation and absorbs the heat, which is removed by circulating the water to external heat exchangers. Used fuel is held in such pools for several months to several years. It may be transferred to naturally-ventilated dry storage on site after about five years.

Depending on policies in particular countries, some used fuel may be transferred to central storage facilities. Ultimately, used fuel must either be reprocessed or prepared for permanent disposal.

Reprocessing

Used fuel is about 94% U-238 but it also contains almost 1% U-235 that has not fissioned, almost 1% plutonium and 4% fission products, which are highly radioactive, with other transuranic elements formed in the reactor. In a reprocessing facility the used fuel is separated into its three components: uranium, plutonium and waste, which contains fission products. Reprocessing enables recycling of the uranium and plutonium into fresh fuel, and produces a significantly reduced amount of waste (compared with treating all used fuel as waste).

According to Areva, about eight fuel assemblies reprocessed can yield one MOX fuel assembly, two-thirds of an enriched uranium fuel assembly, and about three tonnes of depleted uranium (enrichment tails) plus about 150 kg of wastes. It avoids the need to purchase about 12 tonnes of natural uranium from a mine.

Wastes

Wastes from the nuclear fuel cycle are categorised as high-, medium- or low-level wastes by the amount of radiation that they emit. These wastes come from a number of sources and include:

·         low-level waste produced at all stages of the fuel cycle;

·         intermediate-level waste produced during reactor operation and by reprocessing;

·         high-level waste, which is waste containing fission products from reprocessing, and in many countries, the used fuel itself.

The enrichment process leads to the production of much 'depleted' uranium, in which the concentration of U-235 is significantly less than the 0.7% found in nature. Small quantities of this material, which is primarily U-238, are used in applications where high density material is required, including radiation shielding and some is used in the production of MOX fuel. While U-238 is not fissile it is a low specific activity radioactive material and some precautions must, therefore, be taken in its storage or disposal.

Material balance in the nuclear fuel cycle

The following figures may be regarded as typical for the annual operation of a 1000 MWe nuclear power reactor such as many operating today:

Mining	Anything from 20,000 to 400,000 tonnes of uranium ore
Milling	230 tonnes of uranium oxide concentrate (which contains 195 tonnes of uranium)
Conversion	288 tonnes uranium hexafluoride, UF6 (with 195 tU)
Enrichment	35 tonnes enriched UF6 (containing 24 t enriched U) – balance is 'tails'
Fuel fabrication	27 tonnes UO2 (with 24 t enriched U)
Reactor operation	8760 million kWh (8.76 TWh) of electricity at full output, hence 22.3 tonnes of natural U per TWh
Used fuel	27 tonnes containing 240 kg transuranics (mainly plutonium), 23 t uranium (0.8% U-235), 1100 kg fission products.

The following figures assume the annual operation of 1000 MWe of nuclear power reactor capacity such as in the new EPR, with 5% enriched fuel and higher (65 GWd/t) burn-up:

Mining	Anything from 20,000 to 400,000 tonnes of uranium ore
Milling	171 tonnes of uranium oxide concentrate (which contains 145 tonnes of uranium)
Conversion	214 tonnes uranium hexafluoride, UF6 (with 145 tU)
Enrichment	23 tonnes enriched UF6 (containing 15.6 t enriched U) – balance is 'tails' (0.20%)
Fuel fabrication	17.5 tonnes UO2 (with 15.6 t enriched U)
Reactor operation	8760 million kWh (8.76 TWh) of electricity at full output, hence 16.5 tonnes of natural U per TWh
Used fuel	17.5 tonnes containing 14.5 t uranium (0.8% U-235).

Prices of Uranium in Market:

11 countries are responsible for 97 % of the global uranium extraction in 2007.

The uranium market, like all commodity markets, has a history of volatility, moving not only with the standard forces of supply and demand, but also to whims of geopolitics. It has also evolved particularities of its own in response to the unique nature and use of this material.

The only significant commercial use for uranium is to fuel nuclear reactors for the generation of electricity. There are 440 reactors operating worldwide, and a total of 60 new reactors that are under construction, with over 150 power reactors (with a total net capacity of some 172,000 MWe) planned and over 340 more proposed (as of August 2011).^[1]

Before uranium is ready for use as nuclear fuel in reactors, it must undergo a number of intermediary processing steps which are identified as the front end of the nuclear fuel cycle: mining it (either underground or in open pit mines), milling it into yellowcake, enriching it and finally fuel fabrication to produce fuel assemblies or bundles. This technologically complicated and challenging process is simple in comparison to the complexity of the market that has evolved to provide these three services.

The Estimate of Available Uranium depends on what resources are included in the estimate. The squares represent relative sizes of different estimates, whereas the numbers at the lower edge show how long the given resource would last at present consumption.
██ Reserves in current mines
██ Known economic reserves
██ Conventional undiscovered resource
██ Total ore resources at 2004 prices
██ Unconventional resources (at least 4 billion tons, could last for million)

The world's present measured resources of uranium, economically recoverable at a price of US$130/kg, are enough to last for some 80 years at current consumption.

In 1983, physicist Bernard Cohen proposed that the world supply of uranium is effectively inexhaustible, and could therefore be considered a form of renewable energy He claims that fast breeder reactors, fueled by naturally-replenished uranium extracted from seawater, could supply energy at least as long as the sun's expected remaining lifespan of five billion years. These reactors use uranium-238, which is more common than the uranium-235 required by conventional reactors.

 Market operations

Unlike other metals such as copper or nickel, uranium is not traded on an organized commodity exchange such as the London Metal Exchange. Instead it is traded in most cases through contracts negotiated directly between a buyer and a seller. Recently, however, the New York Mercantile Exchange announced a 10-year agreement to provide for the trade of on and off exchange uranium futures contracts.

The structure of uranium supply contracts varies widely. Pricing can be as simple as a single fixed price, or based on various reference prices with economic corrections built in. Contracts traditionally specify a base price, such as the uranium spot price, and rules for escalation. In base-escalated contracts, the buyer and seller agree on a base price that escalates over time on the basis of an agreed-upon formula, which may take economic indices, such as GDP or inflation factors, into consideration.

A spot market contract usually consists of just one delivery and is typically priced at or near the published spot market price at the time of purchase. However 85% of all uranium has been sold under long-term, multi-year contracts with deliveries starting one to three years after the contract is made. Long-term contract terms range from two to 10 years, but typically run three to five years, with the first delivery occurring within 24 months of contract award. They may also include a clause that allows the buyer to vary the size of each delivery within prescribed limits. For example, delivery quantities may vary from the prescribed annual volume by plus or minus 15%.

One of the peculiarities of the nuclear fuel cycle is the way in which utilities with nuclear power plants buy their fuel. Instead of buying fuel bundles from the fabricator, the usual approach is to purchase uranium in all of these intermediate forms. Typically, a fuel buyer from power utilities will contract separately with suppliers at each step of the process. Sometimes, the fuel buyer may purchase enriched uranium product, the end product of the first three stages, and contract separately for fabrication, the fourth step to eventually obtain the fuel in a form that can be loaded into the reactor. The utilities believe – rightly or wrongly – that these options offers them the best price and service. They will typically retain two or three suppliers for each stage of the fuel cycle, who compete for their business by tender. Sellers consist of suppliers in each of the four stages as well as brokers and traders. There are fewer than 100 companies that buy and sell uranium in the western world.

In addition to being sold in different forms, uranium markets are differentiated by geography. The global trading of uranium has evolved into two distinct marketplaces shaped by historical and political forces. The first, the western world marketplace comprises the Americas, Western Europe and Australia. A separate marketplace comprises countries within the former Soviet Union, or the Commonwealth of Independent States (CIS), Eastern Europe and China. Most of the fuel requirements for nuclear power plants in the CIS are supplied from the CIS's own stockpiles. Often producers within the CIS also supply uranium and fuel products to the western world, increasing competition.

The separative work unit:

Separative Work Unit (SWU) is a complex unit which is a function of the amount of uranium processed and the degree to which it is enriched, i.e. the extent of increase in the concentration of the ²³⁵U isotope relative to the remainder. Separative work is expressed in SWUs, kg SW, or kg UTA (from the German Urantrennarbeit )

The unit is strictly: Kilogram Separative Work Unit, and it measures the quantity of separative work (indicative of energy used in enrichment) when feed, tails and product quantities are expressed in kilograms.

The number of Separative Work Units provided by an enrichment facility is directly related to the amount of energy that the facility consumes. Modern gaseous diffusion plants typically require 2,400 to 2,500 kilowatt-hours of electricity per SWU while gas centrifuge plants require just 50 to 60 kilowatt-hours of electricity per SWU.

Example:

A large nuclear power station with a net electrical capacity of 1,300 MW requires about 25,000 kg of enriched uranium annually with a ²³⁵U concentration of 3.75%. This quantity is produced from about 210,000 kg of raw uranium using about 120,000 SWU. An enrichment plant with a capacity of 1,000 kSWU/year is, therefore, able to enrich the uranium needed to fuel about eight large nuclear power stations

Cost Issues

In addition to the Separative Work Units provided by an enrichment facility, the other important parameter that must be considered is the mass of raw uranium that is needed in to order to yield a desired mass of enriched uranium. As with the number of SWUs, the amount of feed material required will also depend on the level of enrichment desired and upon the amount of ²³⁵U that ends up in the depleted uranium. However, unlike the number of SWUs required during enrichment which increases with decreasing levels of ²³⁵U in the depleted stream, the amount of raw uranium needed will decrease with decreasing levels of ²³⁵U that end up in the tails.

Example:

In the production of enriched uranium for use in a light water reactor it is typical for the enriched stream to contain 3.6% ²³⁵U (as compared to 0.7% in raw uranium) while the depleted stream contains 0.2% to 0.3% ²³⁵U. In order

to produce one kilogram of this enriched uranium it would require approximately 8 kilograms of raw uranium and 4.5 SWU if the tails stream was allowed to have 0.3% ²³⁵U. On the other hand, if the depleted stream had only 0.2% ²³⁵U, then it would require just 6.7 kilograms of raw uranium, but nearly 5.7 SWU of enrichment. Because the amount of raw uranium required and the number of SWUs required during enrichment change in opposite directions, if raw uranium is cheap and enrichment services are more expensive, then the operators will typically choose to allow more ²³⁵U to be left in the tails stream whereas if raw uranium is more expensive and enrichment is less so, then they would choose the opposite.

 Companies for Production of  Uranium:

Ever wonder who the top uranium miners are? Here are top 10 uranium-producing countries by tonnes U, and the top 5 uranium miners by market capitalization. You’ll notice some interesting relationships in the country data, and may recognize a name or two in the market cap section. These are just some ideas to get you thinking about possible uranium investments. It’s not too late to make some money off the uranium surge.

Top 10 Largest Uranium Miners by country :

1. Canada
2. Australia
3. Kazakhstan
4. Russia
5. Namibia
6. Niger
7. Uzbekistan
8. USA
9. Ukraine
10. China

Canada and Australia combined produce 51% of the world’s uranium from uranium mines. Notice that China is far down on the list at position #10. The growing demand from China for uranium in order to power their nuclear plants will provide growth opportunities for Australian and Canadian uranium miners. Don’t forget about the US as well. Clocking in at position #8, the United States must take similar actions as did the Chinese to support their growing nuclear demand.

Top 5 Largest Uranium Miners by Market Capitalization

Minimum Criteria:

  Must trade on a US Stock Exchange. I plan to calculate the market caps in terms of US dollars for foreign traded stocks in my next uranium post.

  Must actively operate in uranium production/mining industry.

1. BHP Billiton LTD (BHP) - $135 billion
2. Rio Tinto plc (RTP) - $72 billion
3. Cameco Corp. (CCJ) - $13 billion
4. USEC Inc. (USU) - $1.26 billion
5. Fronteer Development Group Inc. (FRG) - $800 million

There are two ways to go about uranium investing: either invest in pure uranium miners or diversified industrial miners. Small cap uranium stocks may offer a larger upside, but your risk is much greater. Diversified miners can take advantage of economies of scale, plus they own more capital, helping to preserve and operate existing uranium mines. A safer investment would be in a diversified industrial metals and materials miner that’s highly levered towards uranium.

World's 10 Largest producing uranium mines

The world's 10 largest producing uranium mines accounted for 29,337 tonnes of uranium (tU), or 55% of global production in 2010. Statistics provided by the World Nuclear Association.

1. McArthur River (Canada) - Areva/Cameco

MacArthur River is the world's largest high-grade uranium mine, producing 7654 tonnes of uranium (tU), or 14% of global production, in 2010. Ore grades at the underground mine average more than 10% uranium content, making them one hundred times the global average for uranium mines. Cameco operates the mine and controls 70% ownership, while Areva owns 30%.

2. Ranger (Australia) - Energy Resources of Australia Ltd.

Energy Resources of Australia Ltd. (ERA) has operated the Ranger mine, situated 260 kilometers east of Darwin, Australia, since 1980. The open-pit mine produced 3216tU, approximately 6% of the world total, in 2010. ERA is operated and 68% owned by Rio Tinto.

3. Rossing (Namibia) - Rio Tinto

Started in 1976, the Rossing mine in Namibia's Namib Desert is the world's longest running open-pit uranium mine. Rio Tinto owns 69% of the mine, which extracted 3077tU in 2010.

4. Kraznokamensk (Russia) - ARMZ

The town of Kraznokamensk was founded around the Priargunsky uranium mine over 40 years ago. Cumulative uranium production from the underground mine since that time has exceeded 117 000 tonnes. In 2010, production was 2920tU. Further development of new areas and capital modernization programs are currently being put in place at the mine to keep production volumes up despite declining ore quality.

 

5. Arlit (Niger) - Somair:

The Somair open-pit mine is situated 7 kilometers northwest of Arlit in Niger. Uranium is extracted from the sedimentary deposit at depths of 50 to 70 meters and heap leached on site, at the open-pit mine. Production at the mine, which is a wholly-owned subsidiary of AREVA, is expected to reach 3,000tU by 2012 and, at current production rates, has an expected life of 13 years.

6. Tortkuduk (Kazakhstan) - Kazatomprom/Areva

Operated by KATCO JV, Site No. 2 at the Tortkuduk uranium mine produced 2439tU using in-situ leaching techniques in 2010. Katco JV was set-up in 1996 between France's Areva, who controls 51%, and the national atomic company of Kazakhstan, Kazatomprom, who controls the remaining 49%.

 

7. Olympic Dam (Australia) - BHP Billiton

Olympic dame is Australia's largest mine and is characterized by a multi-mineral ore body that produces uranium as a well as copper, gold and silver. The underground operations resulted in 2330tU, or about 4% of the world's total uranium production, in 2010.

8. Budenovskoye 2 (Kazakhstan) - Kazatomprom

Karatau LLP was established in 2005 as a subsidiary of Kazatomprom to develop Site No. 2 of the Bedenovskoye uranium deposit in south Kazakhstan. Using in-situ leaching, the mine produced 1708tU in 2010 and has a design capacity to reach 3,000tU by 2015.

9. South Inkai (Kazakhstan) - Kazatomprom/Uranium One

Operating in the Suzak region of Kazakhstan, the South Inkai uranium deposit is an in-situ leaching operation that is operated by the Betpak-Dala joint venture of which Uranium One controls a 70% interest and Kazatomprom controls the balance. 1701tU were produced at the mine in 2010, while the design capacity of South Inkai is 2000tU per year. This rate of production is expected to be realized in 2011.

10. Inkai (Kazakhstan) - Kazatomprom/Cameco

Joint Venture Inkai (JVI) operates the Inkai uranium deposit in Kazakhstan. Cameco holds 60% interest in JVI and Kazatomprom holds the remaining 40%. Mine production began in 2009 using in-situ recovery technology and, in 2010, 1642tU were produced at blocks 1 and 2. Cameco is currently seeking approval to produce upwards of 2.3tU per year.