Uranium jawad(FROM NOTHING TO MEGATONS)

FROM NOTHING TO MEGATONS

URANIUM

A silvery-white metallic chemical element in the actinide series of the periodic table with atomic number 92. It is assigned the chemical symbol U. The uranium nucleus binds between 141 and 146 neutrons, establishing six isotopes, the most common of which are U-238 (146 neutrons) and U-235 (143 neutrons). All isotopes are unstable and uranium is weakly radioactive. Uranium has the second highest atomic weight of the naturally occurring elements, lighter only than plutonium-244. Its density is about 70% higher than that of lead, but not as dense as gold or tungsten. It occurs naturally in low concentrations in soil, rock and water, and is commercially extracted from uranium-bearing minerals such as uraninite.U-235 is fissile, fissile is a material that can sustain chain reaction.

THINGS TO KNOW INTERESTING FACTS

Uranium is 40 times more naturally abundant than silver

An artificial fissile isotope, uranium-233, can be produced from natural thorium and is also important in nuclear technology

In nature, uranium is found as uranium-238 (99.284%), uranium-235 (0.711%).

A gallon of milk weighs about 8 lbs. A chunk of uranium metal the size of a gallon milk jug weighs over 150 lbs

Finely divided uranium burns readily in air at 150 to 175 degrees Celsius (300 to 350 degrees Fahrenheit).

Uranium boils at about 3,818 degrees Celsius (about 6,904 degrees Fahrenheit)

ORIGIN OF URANIUM

Cosmo chemists have been concerned not only with patterns and secular trends of abundance of the elements in galaxies but also with the origins of abundance anomalies in particular stars and with theories on the synthesis of different nuclei to account for these observations. According to the theories developed, the Earth's uranium was produced in one or more supernovae (An explosive brightening of a star in which the energy radiated by it increases by a factor of ten billion, A supernova explosion occurs when a star has burned up all its available nuclear fuel and the core collapses catastrophically)

Sudden collapse in the centre of a massive star triggers the explosive ejection of much of the star into space, together with a flood of neutrons. Remnants of hundreds of supernovae have been found, and world witnessed one in the Magellanic Clouds in 1987.

we can calculate the abundances of U-235 and U-238 at the time the Earth was formed. Knowing further that the production ratio of U-235 to U-238 in a supernova is about 1.65, we can calculate that if all of the uranium now in the solar system were made in a single supernova, this event must have occurred some 6.5 billion years ago.

The present-day abundance of uranium in the 'depleted' mantle exposed on the ocean floor is about 0.004 ppm. The continental crust, on the other hand, is relatively enriched in uranium at some 1.4 ppm.


Since 2.5 billion years ago ore deposits of uranium have been formed primarily on earth where reduction of uranium-bearing fluids was achieved, for example by bacteria or through contact with graphitic shales

The half-life of uranium-238 is about 4.47 billion years and that of uranium-235 is 704 million years, making them useful in dating the age of the Earth

Cosmologists believed that multiple supernovae from over 6 billion to about 200 million years ago were responsible of today’s uranium on earth.

Theory that much of the uranium in the primordial planet sunk to the core and has formed a core there, some 8 km across, which has been fissioning ever since,called as Geo reactor theory

HISTORY OF URANIUM

Uranium was found in 1789 by the German chemist Martin Heinrich in his laboratory in Berlin. While he was working in his experimental laboratory in Berlin in 1789, Klaproth was able to precipitate a yellow compound (likely sodium diuranate) by dissolving pitchblende in nitric acid and neutralizing the solution with sodium hydroxide.

In 1841, Eugene-Melchior Peligot, Professor of Analytical Chemistry at the Conservatoire National des Arts et Métiers (Central School of Arts and Manufactures) in Paris, isolated the first sample of uranium metal by heating uranium tetrachloride with potassium

Antoine Henri Becquerel discovered radioactivity by using uranium in 1896.Becquerel made the discovery in Paris by leaving a sample of a uranium salt, K2UO2(SO4)2, on top of an unexposed photographic plate in a drawer and noting that the plate had become 'fogged. He determined that a form of invisible light or rays emitted by uranium had exposed the plate.

A team led by Enrico Fermi in 1934 observed that bombarding uranium with neutrons produces the emission of beta rays. The experiments leading to the discovery of uranium's ability to fission into lighter elements and release binding energy were conducted by Otto Hahn and Fritz Strassmann in Hahn's laboratory in Berlin.

On 2 December 1942, as part of the Manhattan Project, another team led by Enrico Fermi was able to initiate the first artificial self-sustained nuclear chain reaction, Chicago Pile-1. Working in a lab below the stands of Stagg Field at the University of Chicago, the team created the conditions needed for such a reaction by piling together 400 tons (360 tonnes) of graphite, 58 tons of uranium oxide, and six tons of uranium metal.

Martin Heinrich Klaproth Enrico and its team


Enrico was awarded the Nobel Prize in Physics in 1938 for his work on induced radioactivity.

First time world nuclear fusin was used by Lise Meitner and her nephew, physicist Otto Robert Frisch,as they published the physical explanation in February 1939 and named the process 'nuclear fission'

Klaproth mistakenly assumed the yellow substance was the oxide of a yet-undiscovered element and heated it with charcoal to obtain a black powder.

The fission products were at first mistaken for new elements of atomic numbers 93 and 94.

URANIUM DEPSOITS

http://xerius.jergym.hiedu.cz/~canovm/objevite/objev/objev.htm

Uranium ore deposits are economically recoverable concentrations of uranium within the Earth's crust. Uranium is one of the more common elements in the Earth’s crust, some 40 times more common than silver and 500 times more common than gold. It can be found almost everywhere in rock, soil, rivers, and oceans. The challenge is to find those areas where the concentrations are adequate to form an economically viable deposit.

Globally, the distribution of uranium ore deposits is widespread on all continents, with the largest deposits found in Australia, Kazakhstan, and Canada. To date, high-grade deposits are only found in the Athabasca Basin region of Canada.

Uranium deposits world-wide can be grouped into 14 major categories of deposit types based on the geological setting of the deposits. The IAEA classification of uranium ore deposits contains following types

1. Unconformity-related deposits 2. Sandstone deposits 3. Quartz-pebble conglomerate deposits 4. Breccia complex deposits 5. Vein deposits 6. Intrusive deposits (Alaskites)7. Phosphorite deposits 8. Collapse breccia pipe deposits 9. Volcanic deposits 10. Surficial deposits 11. Metasomatite deposits 12. Metamorphic deposits 13. Lignite 14. Black shale deposits

1. UNCONFIRMITY RELATED DEPOSITS

Unconformity-related deposits arise from geological changes occurring close to major unconformities. Below the unconformity, the meta sedimentary rocks which host the mineralization are usually faulted and brecciated. Minerals are uraninite and pitchblende. The main deposits occur in Canada and Australia

Unconformity-related deposits constitute a major proportion of Australia's total uranium resources, and much of Australia's total production since 1980

2. SANDSTONE RELATED DEPOSITS

Sandstone uranium deposits occur in medium to coarse-grained sandstones deposited in a continental fluvial or marginal marine sedimentary environment. Impermeable shale/mudstone units are interbedded in the sedimentary sequence and often occur immediately above and below the mineralised sandstone. Uranium is precipitated under reducing conditions caused by a variety of reducing agents within the sandstone. The main primary uranium minerals are uraninite and coffinite.

The USA has large resources in sandstone deposits in the Western Cordillera region, and most of its uranium production has been from these deposits, recently by in situ leach (ISL) mining.

3. QUARTZ PEBBLE CONGLOMERATE DEPOSITS

Detrital uranium occurs in some Archaean-early Palaeoproterozoic quartz-pebble conglomerates that unconformably overlie granitic and metamorphic basement. Quartz-pebble conglomerate uranium deposits occur in conglomerates deposited in the range 3070-2200 million years ago. Fluvial transport of detrital uraninite was possible at the time because of the prevailing anoxic atmosphere. Major examples are the Elliot Lake deposits in Canada and the Witwatersrand gold-uranium deposits in South Africa. The mining operations in the Elliot

4. BRECIA COMPLEX DEPSOITS

The deposit occurs in a hematite-rich granite breccia complex in Craton. It is overlain by approximately 300 metres of flat-lying sedimentary rocks. The Olympic Dam deposit is one of the world’s largest deposits of uranium, and accounts for the major part of Australia’s uranium resources. The deposit may contains iron, copper, uranium, gold, silver, rare earth element and fluorine.

5. VEIN DEPOSITS

Vein deposits of uranium are those in which uranium minerals fill cavities such as cracks, veins, fissures, pore spaces, breccias and stockworks. The dimensions of the openings have a wide range, from the massive veins of pitchblende. Examples are Schinkolobwe deposit (Democratic Republic of the Congo) and Port Radium deposit (Canada) to the narrow pitchblende-filled cracks, faults and fissures in some of the ore bodies in Europe, Canada and Australia.

6. VOLCANIC AND CALDERA RELATED DEPOSITS

Uranium deposits of this type occur in acid to intermediate volcanic rocks and are related to faults and shear zones within the volcanics. Uranium occurs in veins or disseminated and is commonly associated with molybdenum and fluorine. These deposits make up only a small proportion of the world's uranium resources. Significant resources of this type occur in China, Kazakhstan, Russian Federation and Mexico.

7. SURFICIAL DEPOSITS

Surficial uranium deposits are broadly defined as young (Tertiary to Recent) near-surface uranium concentrations in sediments or soils. These deposits usually have secondary cementing minerals including calcite, gypsum, dolomite, ferric oxide, and halite. Uranium deposits in calcrete are the largest of the surficial deposits. Uranium mineralisation is in fine-grained surficial sand and clay, cemented by calcium and magnesium carbonates.

8. METASOMATIC DEPOSITS

Metasomatite deposits consist of unevenly disseminated uranium in structurally deformed rocks that were affected by sodium metasomatism.- the introduction of sodium (or potassium or calcium) into these rocks. Major examples of this type include Espinharas deposit (Brazil) and the Zheltye Vody deposit (Ukraine).

9. COLLAPSE BRECCIA PIPE DEPOSIT

These occur in circular, vertical collapse structures filled with coarse fragments and a fine matrix of the penetrated sediments. The collapse pipes are 30-200 metres in diameter and up to 1000 metres deep. Uranium mineralization is mostly within permeable sandstone breccias within the pipe. The principal uranium mineral is pitchblende. The best-known examples of this type are deposits in the Arizona Strip in Arizona, USA. Several of these have been mined.

10. PHOSPHORITE DEPOSITS

Sedimentary phosphorites of marine origin contain low concentrations of uranium in fine-grained apatite. Uranium concentrations are 0.01-0.015% U3O8. Very large phosphorite deposits occur in the USA (Florida and Idaho), Morocco, Jordan and other Middle Eastern countries and these are mined for phosphate

11. LIGNITE DEPOSITS

Uranium mineralization occurs in lignite and in clay and sandstone immediately adjacent to the lignite, in the Serres Basin, Greece, in North and South Dakota, USA and at Mulga Rock, Western Australia. Uranium has been adsorbed on to carbonaceous matter and consequently no discrete uranium minerals have formed.

12. BLACK SHALE DEPOSITS

Black shale-related uranium mineralization consists of marine organic-rich shale or coal-rich pyritic shale, containing synsedimentary disseminated uranium adsorbed onto organic material. Examples include the uraniferous alum shale in Sweden, the Rudnoye and Zapadno-Kokpatasskaya deposits in Uzbekistan, the Chatanooga shale in the USA, deposits in the Guangxi Autonomous Region, China, and the Gera-Ronneburg deposit, Germany.

13. METAMORPHIC DEPOSITS

Metamorphic deposits those that occur in metasediments or metavolcanic rocks where there is no direct evidence for mineralization post-dating metamorphism. These deposits were formed during regional metamorphism of uranium bearing or mineralized sediments or volcanic precursors

14. INTRUSIVE DEPOSITSincluded in this type are those associated with intrusive rocks including alaskite, granite, pegmatite, and monzonites. . Major world deposits include Rossing (Namibia), Ilimaussaq (Greenland) and Palabora (South Africa).


Conventional mining/milling operations of sandstone deposits have been progressively replaced by cheaper in situ leach (ISL) mining methods.

Sandstone deposits are further divided into 3 further types. Roll front, Tabular and Tectonic.

Calcerete deposits are associated with suficial deposits, They formed where uranium-rich granites were deeply weathered in a semi-arid to arid climate.

There are three major subtypes of vein style uranium mineralization :intragranitic veins, veins in metasedimentary rocks in exocontacts of granites and mineralised fault and shear zones

Unconformity-related deposits constitute approximately 33% of the western world's uranium resources and they include some of the largest and richest deposits.

Sandstone deposits constitute about 18% of world uranium resources

Quartz pebble conglomerate deposits make up approximately 13% of the world's uranium resources.

Surficial deposits comprise about 4% of world uranium resources

The only volcanic hosted deposits currently being exploited are those of the Streltsovkoye district of eastern Siberia.

In some countries like Hungary and China trials are underway to extract uranium from fly ash

TOP 10 MINES OF THE WORLD

MINE COUNTRY OWNER MINE TYPE1 MCArthur River Canda Cameco Conventional

2 Ranger Australia ERA(Riotinto 68%) Conventional3 Rossing Namibia Rio Tinto(69%) Conventional4 Olympic Dam Australia BHP Billion ByProduct(Copper)5 Priargunsky Russia ARMZ Conventional6 Arlit Niger Areva Conventional7 Rabbit Lake Canada Cameco Conventional8 Akouta Niger Areva Conventional9 McClean lake Canda Areva Conventional10 Akdala Kazakhstan Uranium One ISL

Pie chart shows the totall uranium production in year 2008

THINGS TO KNOW INTERESTING FACTS In situ leach (ISL, or ISR) mining has

been steadily increasing its share of the total.

There are two ways to go about uranium investing: either invest in pure uranium miners or diversified industrial miners.

Canada and Australia combined produce 51% of the world’s uranium from uranium mines.

Kazakhstan produces the largest share of uranium from mines (27% of world supply from mines).

URANIUM RESERVES OF PAKISTAN

Uranium deposits and noteworthy occurrences are reported from the Dera Ghazi Khan District, Sulaiman Range, Bannu Basin, and Issa Khel, Mianwali District, in central Pakistan, and from the Kirthar Range in south Pakistan.

A number of radioactive localities associated with alkaline igneous rocks, pegmatites, and schists have been discovered in the mountainous northern part of Pakistan.

Pakistan’s former U production was essentially concentrated in the Dera Ghazi Khan District, estimates a cumulative production of 970 t U from 1971, First reports on the discovery of uranium mineralization date back to the year 1959. Uranium was found in Siwalik sandstone near Rakhi Munh in the Sulaiman Range. Subsequent exploration led to the discovery of about a dozen small U deposits in the Dera Ghazi Khan District in the early 1970s. Taunsa, discovered in 2000/2001 in this district, was the latest success.

Regional Distribution Of Uranium Producing Siwalik Group

This group, 4 600–5 500 m thick, was almost continuously deposited from Middle Miocene to Lower Pleistocene. The Siwalik System or its equivalents in time, respectively, extend continuously along the Himalayan foothills from Assam in the east to southern Kashmir, and across the Indus Valley in Pakistan through the Potwar Plateau and Balillu Plains where they turn southwesterly into the Bannu Basin and then south into the Sulaiman Range. From this point, they continue as a more marine facies to the Arabian Sea

Siwalik sediments have been spread differently in different regions i.e Siwalik System along the outer Himalayas, Manchhar System in Sind, Mekran Series in Baluchistan, Dihing Series in Assam, and Irrawady System in Burma.

Intermittent U mineralization in Siwalik sandstones, mainly in the Middle Siwalik Dhok Pathan Formation, is known for at least 1000 km along the sinuous outcrop of this group from 50 km south of Dera Ghazi Khan along the Sulaiman Range, to the Bannu Basin and other areas to the north in Pakistan, and further to the east within India

SULAIMAN RANGE,DERA GHAZI KHAN

The Dera Ghazi Khan District lies in the Sulaiman Range, a prominent morphological element in the Sulaiman physiographic province in central Pakistan. Numerous radioactive anomalies, some with visible U minerals, are spread over an outcrop length of more than 160 km along the foothills of this range. They include about a dozen small blanket sandstone-type U deposits confi ned to a single horizon near the base of the Middle Siwalik Member in a N-S strip to the west of the town of Dera Ghazi Khan. Reported deposits include Baghal Chur (or Baghal chor), Rakuchur, Rakhi Munh, Nangar Nai, Kaha Nalo, Rajanpur; and, located to the north of the district, Taunsa

Most resources of the early discovered deposits are exhausted. Some early mining of these deposits was by conventional open pit and underground methods to depths of 150–200 m and later by ISL techniques and produced an estimated total of some 800 t U. At a cutoff grade of 0.03% U, the ore had grades of 0.1% U as maximum.

Regional Geological Settings

The Middle Miocene to Lower Pleistocene Siwalik Group is exposed in the Sulaiman Range as a narrow north-south trending belt, some 300 km long and dipping to the east. This group has been divided into an Upper, Middle, and Lower division (Moghal 1974, based on Wadia 1961)

1. Upper Siwalik Division 2. Middle Siwalik Division 3. Lower Siwalik Division

Map shows the generalized map of Dera Ghazi khan, with location of Uranium deposits and occurrences

BAGHAL CHUR

The blanket sandstone-type Baghal Chur deposit lies about 40 km NNW of Dera Ghazi Khan. Original resources are not published but are assumed to have been on the order of a few hundreds tonnes U at grades of 0.05% U. Th e deposit was mined from 1971 to 1999 by conventional methods and is depleted.

Geological Setting

Baghal Chur is situated in the asymmetrical Baghal Chur syncline; its eastern (Zinda Pir) flank dips 30–50° W while the major portion of the western limb, that hosts all U lodes, shows gentle and uniform 5–10° easterly dips which, however, increase sharply near the western anticline. Host rocks are fluvial lacustrine sediments of the Dhok Pathan Formation, Middle Siwalik Division in which U mineralization is confined to an NE-SW-striking and 5–10° SE dipping arenite horizon, about 60–75 m thick, termed Baghal Chur Sand. Shale beds occur below (Bogo Shale) and locally above (Vidor Shale) the sands

The Baghal Chur Sand was deposited primarily as sheets by southerly flowing rivers. It is a light grey, poorly to well sorted, commonly medium- to fine grained, soft , and friable subarkose or subgreywacke. Major constituents are quartz, feldspars (10– 25% plagioclase, microcline, orthoclase), muscovite, and biotite. Lithic rock fragments of magmatic and metamorphic provenance are common and include chips of occasionally pyritiferous slate and carbonaceous schists. Some rock fragments may represent diagenetically altered volcanic tuff .

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Mineralization

Uranium(-vanadium) mineralization occurs above and below the groundwater table, respectively, in oxidized and non-oxidized greywacke in which schist fragments, biotite and feldspar predominate. In both environments, mineralization is out of equilibrium

Non-oxidized mineralization: Pitchblende and coffinite are the principal U minerals in the non-oxidized zone. In addition, uranium is adsorbed by goethite, hematite, martite, biotite, clay

minerals, and plant remains. An appreciable uranium content is also bound in zeolite (clinoptilolite, heulandite) that occurs as discrete diagenetic crystals in pore cavities.

Oxidized mineralization: Tyuyamunite is the principal U mineral but some carnotite occurs occasionally. These minerals, in the form of a greenish-yellow amorphous powder, coat grains, pebbles, and clay pellets, impregnate the interstices between clasts, and locally also associate with crossbeds of heavy minerals. In the latter case, bands of yellow U minerals about 1 cm thick follow above or below, or on both sides 5–10 mm thick black, primarily magnetite, heavy mineral bands and cross beds.

Shape and Dimension of Deposits

The deposit consists of a group of overlapping ore bodies distributed from surface to depths of 150–200 m. Ore bodies are of strata peneconcordant, elongated to amoeba shape.

BANU BASIN SURGHAR RANGE, NW PAKISTAN

The Bannu Basin is located in the North-West Frontier Province of Pakistan. It contains the small Qabul Khel, Eagle Hill, and Shanawah sandstone U deposits in the Surghar Range, an eastern marginal hill range of the basin. U showings hosted by Middle Siwalik molasse also occur intermittently over a strike length of 30 km between Kundal and Baggi Qammar in the Khisor Range, a continuation of the Surghar Range, south of the Kurram River.

QABUL KHEL

Qabul Khel (Kubul Khel), named aft er a small nearby village, is located in the southern Surghar Range.. Grades are about 0.05% U. A number of small ore bodies were explored in the early 1980s. An experimental underground mining operation was carried out initially but ISL mining was finally adopted and a semi-commercial scale ISL operation began in mid-1995 on one ore body. Conventional and ISL mining, respectively, are hampered by the shape of the ore body, high dip of strata, structural complications, poorly cemented rocks, poor solution confinement, influx of a high quantity of water, absence of bottom shale at places, high calcium content in water, and a water table cover of only 3 m.

Geological Setting

The Qabul Khel deposit is located in the plunging, southern part of the Surghar anticline at the eastern margin of the structural Bannu Basin. This basin consists of folded molasse of the Siwalik Group. Ore bodies are hosted by the Dhok Pathan Formation that forms the upper unit of the Middle Siwalik Division. The Dhok Pathan Formation is a cyclic alternating sand-shale sequence that is variably inclined, between 20 and 45° SW, in the Qabul Khel area.

At the deposit, the sandstone beds are 40–60 m and the intercalated shales 10–15 m thick. The sandstones are grey, soft and friable, and the shales dull brown and grey. Th e shales are silty and often contain variable amounts of volcanic material in the form of bentonite and bedded ash with glass shards. Brittle tectonism resulted in numerous strata discordant and some

intraformational faults, fractures, and joints in the Qabul Khel area that are filled with sand and are partly calcified but only above the water table

Mineralization

Coffinite and pitchblende are the principal U minerals in the unoxidized environment below the water table; they occur as pore fillings whereas pitchblende also occurs as micro fine globules. Uranophane is typical for the oxidized zone. The ore minerals are contained in an assemblage of predominant amphibole, calcite, quartz, mica, and clay minerals. The ore is poorly cemented, largely unconsolidated, and fragile

Shape and Dimensions of Deposits

The ore body is of irregular tape-like configuration; it has a NW-SE length of some 200 m, a thickness commonly from 2 to 15 m averaging 6.5 m, persists over a depth interval from 68 to 118 m below the surface, and averages 0.053% U. The ore follows, in NW-SE direction, the trace of the water table at the contact of the Qabul Khel Sandstone with underlying\ shale. Most of the ore is concentrated along the interface of the sandstone with the underlying shale,

but at places the ore forms another limb penetrating strata discordant into the sandstone for as much as 120 m, parallel to the present day water table.

OTHER URANIUM OCCURENCES IN PAKISTAN

Minor Uranium occurrences are reported from various parts of Pakistan including the following sites

Kirthar Range, Sind Province, south Pakistan: U mineralization occurs discontinuously over a strike length of 25 km in sandstone of the Lower Manchar Formation in the Karunuk-Sehwan, Rehman Dhora (Aamri), and Wahi Pandi areas. Uraniferous lenses range from 200 to 1 000 m in length. Samples yield from 0.02 to 4% U. Uranium minerals include carnotite, curite, phurcalite, and saleeite.

Shanawah near Karak, Northwest Frontier Province: U mineralization extends over a strike length of 2 km. The average thickness is as much as 17 m and averages 10 m. Grades average 0.04% U. Carnotite occurs in the oxidized zone above the water table whereas pitchblende prevails below the water table.

Kallar Kahar, Salt Range, central-north Pakistan: Uranium occurs in sandstone of the Middle-Late Miocene Kamlial Formation near Kallar Kahar in the Salt Range, some 120 km SSW of Islamabad. The formation consists of purple-grey and brick red sandstones interbedded with purple shales. Partly calcified and non-calcified sandstones that contain abundant organic matter and more or less devitrified volcanic material host the mineralization.

Maraghzar Area, north Pakistan: A vein system with U concentration cutting across the Swat granitic gneiss complex occurs in the high mountains at Maraghzar area in the Swat region, but depths and strike continuity remain to be established

THIINGS TO KNOW INTERESTING FACTS

The Siwalik System is a typical sequence of flood-plain sediments of major rivers that was deposited in the foredeep between the Indian Shield and the rising Himalayas.

Baghal Chur Ore bodies are from tens of meters to more than 100 m long, from 0.3 to more than 3 m thick

The Qabul Khel Sandstone rests

Uranium mining began in Pakistan at Baghal Chur in 1971

ISL operations began at Rakhi Munh in 1995 and were tested at Nangar Nai in 1997.

In Bannu basin Qabul Khel is the only deposit explored in more detail

Oxidized uranium mineralization has been found in the Manchar

upon the Qabul Khel Shale,5 m in average thickness.

Häggite is the major vanadium mineral in the non-oxidized ore bodies.

Formation (Kirthar Range) in Sindh recently.

Several radioactive carbonatites have been found in northern Pakistan including one near Sallai Patti village in Malakand Agency

NUCLEAR FUEL CYCLE

The nuclear fuel cycle, also called nuclear fuel chain, is the progression of nuclear fuel through a series of differing stages. It consists of steps in the front end, which are the preparation of the fuel, steps in the service period in which the fuel is used during reactor operation, and steps in the back end, which are necessary to safely manage, contain, and either reprocess or dispose of spent nuclear fuel. Following are the steps involoved in nuclear fuel cycle.

Exploration. Mining. Milling. Conversion. Enrichment. Fuel Fabrication. Fuel Storage Reprocessing. Vitrification Waste Disposal.

Here only brief introduction of these topics will be given, in coming units detail of some of these topics will be given in this assignment.

Nuclear Fuel Cycle

EXPLORATION

A deposit of uranium, such as uraninite, discovered by geophysical techniques, is evaluated and sampled to determine the amounts of uranium materials that are extractable at specified costs from the deposit. Uranium reserves are the amounts of ore that are estimated to be recoverable at stated costs. 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.

MINING

Uranium is usually mined by either surface (open cut) or underground mining techniques, depending on the depth at which the ore body is found. In general, Open pit mines require large holes on the surface, larger than the size of the ore deposit, since the walls of the pit must be sloped to prevent collapse. As a result, the quantity of material that must be removed in order to access the ore may be large. Underground mines have relatively small surface disturbance and the quantity of material that must be removed to access the ore is considerably less than in the case of an open pit mine. Special precautions, consisting primarily of increased ventilation, are required in underground mines to protect against airborne radiation exposure.

MILLING

Milling, which is generally carried out close to a uranium mine, extracts the uranium from the ore. Most mining facilities include a mill, although where mines are close together, one mill may process the ore from several mines. Milling produces a uranium oxide concentrate which is shipped from the mill. It is sometimes referred to as 'yellowcake'..

CONVERSION

Milled uranium oxide, U3O8, must be converted to uranium hexafluoride, UF6, which is the form required by most commercial uranium enrichment facilities currently in use. A solid at room temperature, uranium hexafluoride can be changed to a gaseous form at moderately higher temperature of 57 °C (134 °F). The uranium hexafluoride conversion product contains only natural, not enriched, uranium.

ENRICHMENT

The vast majority of all nuclear power reactors in operation and under construction require 'enriched' uranium fuel in which the proportion of the U-235 isotope has been raised from the natural level of 0.7% to about 3.5% or slightly more. The enrichment process removes about 85% of the U-238 by separating gaseous uranium hexafluoride into two streams: One stream is enriched to the required level and then passes to the next stage of the fuel cycle. The other stream is depleted in U-235 and is called 'tails'. It is mostly U-238.

FUEL FABRICATION

For use as nuclear fuel, enriched uranium hexafluoride is converted into uranium dioxide (UO2) powder that is then processed into pellet form. The pellets are then fired in a high temperature sintering furnace to create hard, ceramic pellets of enriched uranium. The cylindrical pellets then undergo a grinding process to achieve a uniform pellet size. The pellets are stacked, according to each nuclear reactor core's design specifications, into tubes of corrosion-resistant metal alloy. The tubes are sealed to contain the fuel pellets: these tubes are called fuel rods.

FUEL STORAGE

Used fuel assemblies taken from the reactor core are highly radioactive and give off a lot of heat. They are therefore stored in special ponds which are usually located at the reactor site, to allow both their heat and radioactivity to decrease. The water in the ponds serves the dual purpose of acting as a barrier against radiation and dispersing the heat from the spent fuel.

Spent fuel can be stored safely in these ponds for long periods. It can also be dry stored in engineered facilities, cooled by air. However, both kinds of storage are intended only as an interim step before the spent fuel is either reprocessed or sent to final disposal. The longer it is stored, the easier it is to handle, due to decay of radioactivity.

REPROCESSING

Spent fuel still contains approximately 96% of its original uranium, of which the fissionable U-235 content has been reduced to less than 1%.

Reprocessing separates uranium and plutonium from waste products (and from the fuel assembly cladding) by chopping up the fuel rods and dissolving them in acid to separate the various materials. Recovered uranium can be returned to the conversion plant for conversion to uranium hexafluoride and subsequent re-enrichment. The reactor-grade plutonium can be blended with enriched uranium to produce a mixed oxide (MOX) fuel, in a fuel fabrication plant

VITRIFICATION

After reprocessing the liquid high-level waste can be calcined (heated strongly) to produce a dry powder which is incorporated into borosilicate (Pyrex) glass to immobilise the waste. The glass is then poured into stainless steel canisters, each holding 400 kg of glass. A year's waste from a 1000 Mwe reactor is contained in 5 tonnes of such glass, or about 12 canisters 1.3 metres high and 0.4 metres in diameter. These can be readily transported and stored, with appropriate shielding.

This is as far as the nuclear fuel cycle goes at present. The final disposal of vitrified high-level wastes, or the final disposal of spent fuel which has not been reprocessed spent fuel, has not yet taken place.

NUCLEAR WASTE DISPOSAL

A current concern in the nuclear power field is the safe disposal and isolation of either spent fuel from reactors or, if the reprocessing option is used, wastes from reprocessing plants. These materials must be isolated from the biosphere until the radioactivity contained in them has diminished to a safe level. At the present time, there are no disposal facilities (as opposed to storage facilities) in operation in which used fuel, not destined for reprocessing, and the waste from reprocessing, can be placed.


If spent fuel is not reprocessed, the fuel cycle is referred to as an open fuel cycle, if the spent fuel is reprocessed, it is referred to as a closed fuel cycle.

Yellow cake contains more than 80% uranium.

Wastes from the nuclear fuel cycle are categorized as high-, medium- or low-level wastes by the amount of radiation that they emit.

MOX is an abbreviation of Mixed oxide fuel.

After enrichment, the bulk (96%) of the byproduct from enrichment is depleted uranium (DU), which can be used for armor, kinetic energy penetrators, radiation shielding and ballast.

An increasing proportion of the world's uranium now comes from in situ leach (ISL) mining

As of 2008, known uranium ore resources that can be mined at about current costs are estimated to be sufficient to produce fuel for about a century, based on current consumption rates.

URANIUM MINING AND METHODS USED

Uranium mining is the process of extraction of uranium ore from the ground. As uranium ore is mostly present at relatively low concentrations, most uranium mining is very volume-intensive, and thus tends to be undertaken as open-pit mining. It is also undertaken in only a small number of countries of the world, partly because sufficiently high uranium concentrations to motivate mining at current prices are rare.

METHODS OF URANIUM MINING

As with other types of hard rock mining there are several methods of extraction depending on the depth at which the ore body occurs. The main methods of mining are box cut mining, open ptt mining and in situ leaching (ISL)

1. Open pit 2. Underground Mining

3. ISL(In Situ Leaching)

4. Heap Leaching

Open Pit Method

In open pit mining, overburden is removed by drilling and blasting to expose the ore body, which is then mined by blasting and excavation using loaders and dump trucks. Workers spend much time in enclosed cabins thus limiting exposure to radiation. Water is extensively used to suppress airborne dust levels.

Under Ground Mining Method

If the uranium is too far below the surface for open pit mining, an underground mine might be used with tunnels and shafts dug to access and remove uranium ore. There is less waste material removed from underground mines than open pit mines, however this type of mining exposes underground workers to the highest levels of radon gas.

Once the ore body has been identified a shaft is sunk in the vicinity of the ore veins, and crosscuts are driven horizontally to the veins at various levels, usually every 100 to 150 metres. Similar tunnels, known as drifts, are driven along the ore veins from the crosscut. To extract the ore, the next step is to drive tunnels, known as raises when driven upwards and winzes when driven downwards through the deposit from level to level. Raises are subsequently used to develop the stopes where the ore is mined from the veins.

ISL(In Situ Leaching) Method

In-situ leaching (ISL), also known as solution mining, or in-situ recovery (ISR) in North America, involves leaving the ore where it is in the ground, and recovering the minerals from it by dissolving them and pumping the pregnant solution to the surface where the minerals can be recovered. Consequently there is little surface disturbance and no tailings or waste rock generated. However, the orebody needs to be permeable to the liquids used, and located so that they do not contaminate ground water away from the orebody.

Uranium ISL uses the native groundwater in the orebody which is fortified with a complexing agent and in most cases an oxidant. It is then pumped through the underground orebody to recover the minerals in it by leaching. Once the pregnant solution is returned to the surface, the uranium is recovered in much the same way as in any other uranium plant (mill).

Heap Leaching

Heap leaching is a process by which chemicals (usually sulfuric acid) are used to extract the economic element form the ore. Heap leaching is generally only economically feasible only for oxide ore deposits. Oxidation of sulphide deposits occur during the geological process called weatherization. Therefore oxide ore deposits are typically found close to the surface. If there are no other economic elements within the ore a mine might choose to extract the Uranium using a leaching agent, usually a low molar sulphuric acid

ISL(In situ eaching) Heap leaching


The stope, which is the workshop of the mine, is the excavation from which the ore is extracted

Another method, known as room and pillar, is used for thinner, flatter ore bodies

An increasing proportion of uranium, now 36%, is produced by in situ leaching

The worldwide production of uranium in 2008 amounted to 43,853 tones

Mining methods have been changing. In 1990, 55% of world production came from underground mines, but this shrunk dramatically to 1999, with 33% then

URANIUM MILLLING

Mined uranium ores normally are processed by grinding the ore materials to a uniform particle size and then treating the ore to extract the uranium by chemical leaching. The milling process commonly yields dry powder-form material consisting of natural uranium, "yellowcake," which is sold on the uranium market as U3O8.There are numerous steps involved in the uranium milling process

Steps involved in uranium milling are following

Crushing Grinding Leaching Slime Separation Thickening Ion Exchange Method Solvent Extraction Precipitation Filtration Drying and Roasting Shipment for Conversion

THINGS TO KNOW INTERESTING FACTS Uranium is finally recovered in a

chemical precipitate which is filtered and dried to produce a yellow powder known as yellowcake.

For ISL operations, uranium is recovered in a processing plant using either ion exchange or solvent extraction technologies.

Uranium milling process now a day is mostly carried out on the plants located nearby to extraction fields inorder to save transport and shipment cost.

Before world war 2 the uranium milling process involves only 5 steps know a days milling processes involves 10-15 steps.

URANIUM ENRICHMENT

Mined uranium ore comprises 0.7% of the U235 isotope, the rest being U238. U235 is much more unstable and undergoes fission more readily, and is a much better fuel for a reactor. Enrichment of uranium is undertaken to increase the amount of U235 to 3-5%, which is needed in most current reactor designs. For comparison, uranium used for nuclear weapons, for which enrichment technology was developed, would have to be enriched in plants specially designed to produce at least 90% U235

Because of the presence of small quantities of U-235, natural uranium can sustain a chain reaction under certain conditions, and therefore can be used as a fuel in certain kinds of nuclear reactors.For the most common reactor type in use around the world today, which uses ordinary water as a coolant and moderator, the percentage of U-235 in the fuel must be higher than the 0.7 percent found in natural uranium. The set of industrial processes that are used to increase the percentage of U-235 in a given quantity of uranium go under the general method of “uranium enrichment” with the term “enrichment” referring to the increase in the percentage of the fissile isotope U-235.

ENRICHMENT METHODS USED

Only four technologies have been used on a large scale for enriching uranium. Three of these, gaseous diffusion, gas centrifuges, and jet nozzle / aerodynamic separation, are based on converting uranium into uranium hexafluoride (UF6) gas. The fourth technique, electromagnetic separation, is based on using ionized uranium gas produced from solid uranium tetrachloride (UCl4).

There are currently two main commercial methods to enrich uranium: gaseousdiffusion and gas centrifugation. Both use uranium hexafluoride (UF6) as thefeed, which is converted to uranium dioxide after enriching

The enrichment process removes about 85% of the U238 by separating gaseous uranium hexafluoride into two streams, one stream is enriched to the required level, while the other stream is depleted in U235 and is known as 'tails'. The tails comprises roughly 99.75% U238 and is of no further use for energy.

1. Gaseous diffusion

In the gaseous diffusion process, U235 and U238 atoms are separated by feeding UF6 in gaseous form through a series of porous walls or membranes. Because the lighter U235 particles travel faster than U238 particles, more of them penetrate each membrane. This is repeated through hundreds of membranes until the correct enrichment level is reached. The high amount of energy required to force the UF6 through the membranes makes the gaseous diffusion process expensive.

2. Gas Centrifuges

In this process, the gaseous UF6 is placed in a centrifuge. The rapid spinning flings the heavier U238 atoms to the outside of the centrifuge, leaving the UF6 in the centre enriched with a higher proportion of U235 atoms. The enrichment level achieved by a single centrifuge is insufficient to obtain the desired concentration of U235. Therefore a number of centrifuges are connected together in an arrangement known as a cascade. The U235 concentration gradually

increases to 3 – 5% as it passes through the cascade. This method has a significant cost advantage over gaseous diffusion, as it requires about 2% of the energy needed to perform gaseous diffusion..

3. Electromagnetic Isotope Separation (EMIS)

EMIS uses the same principles as a mass spectrometer (albeit on a much larger scale). Ions of U238 and U235 are separated because they describe arcs of different radii when they move through a magnetic field. A major problem with this method is that less than half of the UCl4 feed is converted to the desired U ions, and less than half of the desired U ions are collected. Recovering unused material from the interior surfaces of the tanks is laborious, time-consuming process that reduces the effective output of an EMIS facility. EMIS is both energy intensive and labour intensive, and not economically competitive with other enrichment technologies.

4. Aerodynamic/Jet Nozzle: stationary wall centrifuge

Although not in common use, techniques using gas flow and pressure gradients have been developed (Roux and Grant,1975), including the separation nozzle process and the vortex tube separation process. These aerodynamic separation processes depend upon diffusion driven by pressure gradients, and can be thought-of as a non-rotating centrifuge. For both of these processes, the high proportion of carrier gas required in relation to UF6 process gas results in high specific-energy consumption and substantial requirements for removal of waste heat.

Gas Centrifuge Gaseous Diffusion

EMIS Aerodynamic jet nozzle method


After enrichment little U-235 remains in the tails (usually less than 0.25%).

The most challenging step in building a gas diffusion plant is to manufacture the permeable barriers required in the diffusers

The use of centrifuges also reduces the amount of waste heat generated in compressing the gaseous UF6.

The electromagnetic separations process is based on the fact that a charged particle moving in a magnetic field will follow a curved path with the radius of that path dependent on the mass of the particle

In the jet nozzle plants, uranium hexafluoride gas is pressurized with either helium or hydrogen gas in order to increase the velocity of the gas stream.

There are a number of other uranium enrichment technologies such as atomic vapor laser isotope separation (AVLIS), molecular

Gaseous diffusion first developed in the 1940s as part of the Manhattan Project and was used to enrich a portion of the uranium used in the bomb that was dropped on Hiroshima.

If converted to uranium metal, all of the uranium in the Nation's DUF6 inventory would cover a football field to a depth of about 15 feet. It would take water almost 290 feet high on the same field to weigh as much.

The centrifuge is a common technology used routinely in a variety of applications such as separating blood plasma from the heavier red blood cells.

Typical modern centrifuges can achieve approximately 2 to 4 SWU annually.

In order to achieve as much enrichment in each stage as possible, modern centrifuges can rotate at speeds approaching the speed of

laser isotope separation (MLIS) are developed recently.

sound.

Stacking 57,600 standard DUF6 cylinders end to end would make a tower 720,000 feet tall! That's over 136 miles high.

A.Q khan network supplies centrifuge technology to Libya,Iran,Iraq and N.Korea.

NUCLEAR REACTORS

A nuclear reactor is a device to initiate, control, and sustain a nuclear chain reaction. The most common use of nuclear reactors is for the generation of electrical power. This is usually accomplished by methods that involve using heat from the nuclear reaction to power steam turbines. The energy released from continuous fission of the atoms of the fuel is harnessed as heat in either a gas or water, and is used to produce steam. The steam is used to drive the turbines which produce electricity (as in most fossil fuel plants).

TYPES OF NUCLEAR REACTORS

There are various types of nuclear reactors now a days producing electricity, they are classified on the various schemes such as on bases of coolant,moderator and classification on bases of generation or technology.We will here discuss the nuclear reactors used commercially, follwing are the nuclear reactors used commercially.

Pressurised Water Reactor (PWR)

This is the most common type, with over 230 in use for power generation and several hundred more employed for naval propulsion. PWRs use ordinary water as both coolant and moderator. The design is distinguished by having a primary cooling circuit which flows through the core of the reactor under very high pressure, and a secondary circuit in which steam is generated to drive the turbine. Water in the reactor core reaches about 325°C, hence it must be kept under about 150 times atmospheric pressure to prevent it boiling. Pressure is maintained by steam in a pressuriser . In the primary cooling circuit the water is also the moderator, and if any of it turned to steam the fission reaction would slow down. This negative feedback effect is one of the safety features of the type. The secondary shutdown system involves adding boron to the primary circuit.

Boiling Water Reactor (BWR)

BWR design has many similarities to the PWR, except that there is only a single circuit in which the water is at lower pressure (about 75 times atmospheric pressure) so that it boils in the core at about 285°C. The reactor is designed to operate with 12-15% of the water in the top part of the core as steam, and hence with less moderating effect and thus efficiency there.The steam passes through drier plates (steam separators) above the core and then directly to the turbines, which are thus part of the reactor circuit. Since the water around the core of a reactor is always contaminated with traces of radionuclides, it means that the turbine must be shielded and radiological protection provided during maintenance.

Pressurised Heavy Water Reactor (PHWR or CANDU)

It uses natural uranium (0.7% U-235) oxide as fuel, hence needs a more efficient moderator, in this case heavy water (D20). The moderator is in a large tank called a calandria, penetrated by several hundred horizontal pressure tubes which form channels for the fuel, cooled by a flow of heavy water under high pressure in the primary cooling circuit, reaching 290°C. As in the PWR, the primary coolant generates steam in a secondary circuit to drive the turbines. The pressure tube design means that the reactor can be refuelled progressively without shutting down, by isolating individual pressure tubes from the cooling circuit.

Fast Breeder Reators

Under appropriate operating conditions, the neutrons given off by fission reactions can "breed" more fuel from otherwise non-fissionable isotopes. The most common breeding reaction is that of plutonium-239 from non-fissionable uranium-238. The term "fast breeder" refers to the types of configurations which can actually produce more fissionable fuel than they use, such as the LMFBR. This scenario is possible because the non-fissionable uranium-238 is 140 times more abundant than the fissionable U-235 and can be efficiently converted into Pu-239 by the neutrons from a fission chain reaction.

Boiling Water Reactors (BWR) Pressurized water Reactor(PWR)

CANDU Fast Breeder ReactorTHINGS TO KNOW INTERESTING FACTS

Light water reactors typically use 3 to 5 percent enriched uranium

A PWR has fuel assemblies of 200-300 rods each, arranged vertically in the core, and a large reactor would have about 150-250 fuel assemblies with 80-100 tonnes of uranium.

A CANDU fuel assembly consists of a bundle of 37 half metre long fuel rods (ceramic fuel pellets in zircaloy tubes) plus a support structure, with 12 bundles lying end to end in a fuel channel.

A BWR fuel assembly comprises 90-100 fuel rods, and there are up to 750 assemblies in a reactor core, holding up to 140 tonnes of uranium.

One ton of natural uranium can produce more than 40 million kilowatt-hours of electricity. This is equivalent to burning 16,000 tons of coal or 80,000 barrels of oil.

Worldwide, there are 441 nuclear power plants that supply about 16 percent of the world's electricity.

The PHWR reactor design has been developed since the 1950s in Canada as the CANDU.

The design of PWRs originated as a submarine power plant.

Nuclear power plants are also used for the power in some ships

HYBIRD FUSION

Hybrid nuclear fusion is the use of a combination of nuclear fusion and fission processes to generate power. This is in contrast to pure fusion which does not have any fissionable component. The goal is to use fuel pellets of deuterium and tritium surrounded by a fissionable

(or fertile) blanket to produce energy sufficiently greater than the input (laser) energy for electrical power generation. The principle involved is to induce inertial confinement fusion (ICF) in the fuel pellet which acts as a highly concentrated point source of neutrons which in turn converts and fissions the outer fissionable blanket. The fusion process alone currently does not achieve sufficient gain (power output over power input) to be viable as a power source. By using the excess neutrons from the fusion reaction to in turn cause a high-yield fission reaction (close to 100%) in the surrounding subcritical fissionable blanket, the net yield from the hybrid fusion-fission process can provide a targeted gain of 100 to 300 times the input energy.

The surrounding blanket can be a fissionable material (enriched uranium or plutonium) or a fertile material (capable of conversion to a fissionable material by neutron bombardment) such as depleted uranium or spent nuclear fuel. This offers currently the only means of active disposal (versus storage) of spent nuclear fuel without reprocessing. Fission by-products produced by the operation of commercial light water nuclear reactors LWRs are long-lived and highly radioactive, but they can be consumed using the excess neutrons in the fusion reaction along with the fissionable components in the blanket, essentially destroying them and producing a waste product which is far safer and less of a risk for nuclear proliferation.In contrast to current commercial fission reactors, hybrid reactors potentially demonstrate what is considered inherently safe behavior because they remain deeply subcritical under all conditions and decay heat removal is possible via passive mechanisms.


Unlike a conventional fission reactor, the fusion hybrid can consume almost all of the uranium fuel without enrichment or reprocessing.

There are three main components to the hybrid fusion fuel cycle: deuterium, tritium, and fissionable elements

There would be about 20 times less waste per unit of electricity produced in Hybird fusion.

The University of Texas at Austin is developing a system based on the tokamak fusion reactor, optimising for nuclear waste disposal versus power generation.

USE OF URANIUM IN MILITARY

The major application of uranium in the military sector is in high-density penetrators. This ammunition consists of depleted uranium (DU) alloyed with 1–2% other elements. At high impact speed, the density, hardness, and flammability of the projectile enable destruction of heavily armored targets. DU provides a substantial performance advantage, well above other competing materials. Depleted Uranium (DU) is a low cost material that is readily available. DU's high density and its high atomic number Z = 92.During the later stages of World War II, the entire Cold War, and to a lesser extent afterwards, uranium has been used as the fissile explosive material to produce nuclear weapons. Two

major types of fission bombs were built: a relatively simple device that uses uranium-235 and a more complicated mechanism that uses uranium-238-derived plutonium-239.

DU penetrators Typical design of Du penetrator

HEU plate used in nukes A-10 warthog with DU armored plate


Depleted uranium results from the enriching of natural uranium for use in

DU was extensively used by the

US forces during the Gulf War.

nuclear reactors

Control surfaces on wide body aircraft require heavy counterweights, yet have insufficient surface clearance for lighter materials. Tungsten (with density 19.3 g/cm3) or DU are ideal materials for this application

DU is hardened by reduction of the carbon content and by alloying with 0.75% by weight (3.7% by stoichiometry) of titanium.

DU can enter the body in the form of uranium metal from fragments and as uranium oxides from oxidized DU formed after impact on hard targets

Apparently thisis s the only conflict where large DU projectiles were fired from tanks.

A new radiation shielding material called DUCRETETM has been developed and patented by Idaho Technologies Co.

About 10,800 DU rounds (approximately 3 tons of DU) were fired during NATO air strikes in Bosnia–Herzegovina in 1994 and 1995.

Depleted uranium weapons have been acquired by 17 countries.

Depleted uranium is also used to reinforce the armor protection of M1 series tanks.

A-10 Warthog aircraft can pierce steel armor up to 9 cm (3.5 in.) thick using 30mm DU rounds.

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Uranium jawad(FROM NOTHING TO MEGATONS)