Marl is an earthy material rich in carbonate minerals , clays , and silt . When hardened into rock , this becomes marlstone . It is formed in marine or freshwater environments, often through the activities of algae .
104-526: Marl makes up the lower part of the cliffs of Dover , and the Channel Tunnel follows these marl layers between France and the United Kingdom. Marl is also a common sediment in post- glacial lakes , such as the marl ponds of the northeastern United States. Marl has been used as a soil conditioner and neutralizing agent for acid soil and in the manufacture of cement . Marl or marlstone is
208-541: A carbonate -rich mud or mudstone which contains variable amounts of clays and silt . The term was originally loosely applied to a variety of materials, most of which occur as loose, earthy deposits consisting chiefly of an intimate mixture of clay and calcium carbonate , formed under freshwater conditions. These typically contain 35–65% clay and 65–35% carbonate. The term is today often used to describe indurated marine deposits and lacustrine (lake) sediments which more accurately should be named 'marlstone'. Marlstone
312-508: A campaign for donations to buy 170 acres (0.7 km ) of land atop Dover's cliffs when it was feared that they might be sold to developers; the campaign met its target after only three weeks. The National Trust, which owns the surrounding areas, plans to return the land to a natural state of chalk grassland and preserve existing military structures from the Second World War. In June 2021, a wildflower meadow on White Cliffs of Dover
416-443: A classroom and exhibition area. Staff and volunteers are available to answer questions and provide information about the wildlife in the reserve. The building's design incorporates eco-construction criteria. The nature reserve is named after the edible plant rock samphire , which grows on the cliffs and used to be gathered by hanging ropes over the cliff's edge. Shakespeare mentions rock samphire in his play King Lear and includes
520-541: A currently uneconomic prospect. A summary of the amounts of radioactive waste and management approaches for most developed countries are presented and reviewed periodically as part of a joint convention of the International Atomic Energy Agency (IAEA). A quantity of radioactive waste typically consists of a number of radionuclides , which are unstable isotopes of elements that undergo decay and thereby emit ionizing radiation , which
624-517: A developing organism such as a fetus is irradiated, it is possible a birth defect may be induced, but it is unlikely this defect will be in a gamete or a gamete-forming cell . The incidence of radiation-induced mutations in humans is small, as in most mammals, because of natural cellular-repair mechanisms, many just now coming to light. These mechanisms range from DNA, mRNA and protein repair, to internal lysosomic digestion of defective proteins, and even induced cell suicide—apoptosis Depending on
728-568: A general rule, short-lived waste (mainly non-fuel materials from reactors) is buried in shallow repositories, while long-lived waste (from fuel and fuel reprocessing) is deposited in geological repository. Regulations in the United States do not define this category of waste; the term is used in Europe and elsewhere. ILW makes up 6% of all radioactive waste volume in the UK. High-level waste (HLW)
832-541: A great sea. The sea bottom was covered with white mud formed from fragments of coccoliths , the skeletons of tiny algae that floated in the surface waters and sank to the bottom and, together with the remains of bottom-living creatures, formed muddy sediments. It is thought that the sediments were deposited very slowly, probably half a millimetre a year, equivalent to about 180 coccoliths piled one on top of another. Up to 500 metres (1,600 ft) of sediments were deposited in some areas. The weight of overlying sediments caused
936-492: A half-life that can stretch to as long as 24,000 years. The amount of HLW worldwide is increasing by about 12,000 tonnes per year. A 1000- megawatt nuclear power plant produces about 27 tonnes of spent nuclear fuel (unreprocessed) every year. For comparison, the amount of ash produced by coal power plants in the United States is estimated at 130,000,000 t per year and fly ash is estimated to release 100 times more radiation than an equivalent nuclear power plant. In 2010, it
1040-444: A host plant. It has yellow, white, or blue snapdragon-like flowers and about 90 per cent of the UK's population is found on the cliffs. Viper's-bugloss , a showy plant in vivid shades of blue and purple with red stamens, also grows along the cliffs. The abundance of wildflowers provides homes for about thirty species of butterfly. The rare Adonis blue can be seen in spring and again in autumn. Males have vibrant blue wings lined with
1144-455: A pair at Dover which helped shipping navigate the port. It is likely the area around the surviving lighthouse was inhabited in the early medieval period as archaeologists have found a Saxon cemetery here, and the church of St Mary in Castro was built next to the lighthouse in the 10th or 11th century. It is thought that the name Albion , an ancient or poetic term referring to Great Britain ,
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#17327929575741248-438: A range of applications, such as oil well logging. Substances containing natural radioactivity are known as NORM (naturally occurring radioactive material). After human processing that exposes or concentrates this natural radioactivity (such as mining bringing coal to the surface or burning it to produce concentrated ash), it becomes technologically enhanced naturally occurring radioactive material (TENORM). Much of this waste
1352-447: A reactor. At that point, the fuel has to be replaced in the reactor with fresh fuel, even though there is still a substantial quantity of uranium-235 and plutonium present. In the United States, this used fuel is usually "stored", while in other countries such as Russia, the United Kingdom, France, Japan, and India, the fuel is reprocessed to remove the fission products, and the fuel can then be re-used. The fission products removed from
1456-400: A reference to this trade with the lines "Half-way down / Hangs one that gathers samphire; dreadful trade!" (Act IV, Scene VI Lines 14–15). This refers to the dangers involved in collecting rock samphire on sea cliffs. Shakespeare Cliff was named after the reference to this "dreadful trade". Fan Bay Deep Shelter is a series of tunnels constructed during World War II. The tunnels were opened to
1560-405: A result of the processing or consumption of coal, oil, and gas, and some minerals, as discussed below. Waste from the front end of the nuclear fuel cycle is usually alpha-emitting waste from the extraction of uranium. It often contains radium and its decay products. Uranium dioxide (UO 2 ) concentrate from mining is a thousand or so times as radioactive as the granite used in buildings. It
1664-554: A ridge that acted as a natural dam to hold back a large freshwater pro-glacial lake , now submerged under the North Sea . The land masses remained connected until between 450,000 and 180,000 years ago when at least two catastrophic glacial lake outburst floods breached the anticline and destroyed the ridge that connected Britain to Europe. A land connection across the southern North Sea existed intermittently at later times when periods of glaciation resulted in lower sea levels. At
1768-426: A similar way, the alpha emitting actinides and radium are considered very harmful as they tend to have long biological half-lives and their radiation has a high relative biological effectiveness , making it far more damaging to tissues per amount of energy deposited. Because of such differences, the rules determining biological injury differ widely according to the radioisotope, time of exposure, and sometimes also
1872-446: A stable state but rather to radioactive decay products within a decay chain before ultimately reaching a stable state. Exposure to radioactive waste may cause health impacts due to ionizing radiation exposure. In humans, a dose of 1 sievert carries a 5.5% risk of developing cancer, and regulatory agencies assume the risk is linearly proportional to dose even for low doses. Ionizing radiation can cause deletions in chromosomes. If
1976-505: A storage area, and the enrichment methods required have high capital costs. Pu-239 decays to U-235 which is suitable for weapons and which has a very long half-life (roughly 10 years). Thus plutonium may decay and leave uranium-235. However, modern reactors are only moderately enriched with U-235 relative to U-238, so the U-238 continues to serve as a denaturation agent for any U-235 produced by plutonium decay. One solution to this problem
2080-545: A sustainable National Trust visitor centre was built in the area. The Gateway building, designed by van Heyningen and Haward Architects , houses a restaurant, an information centre on the work of the National Trust, and details of local archaeology, history and landscape. During the Late Cretaceous , between 100 million and 66 million years ago, Great Britain and much of Europe were submerged under
2184-424: A very low permeability , they have been exploited for construction of the Channel Tunnel between England and France and are being investigated for the storage of nuclear waste . Marl is one of the oldest soil amendments used in agriculture. In addition to increasing available calcium, marl is valuable for improving soil structure and decreasing soil acidity and thereby making other nutrients more available. It
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#17327929575742288-466: A white margin, whereas the females are a rich chocolate brown. This species' sole larval food plant is the horseshoe vetch and it has a symbiotic relationship with red or black ants. The eggs are laid singly on very small foodplants growing in short turf. This provides a warm microclimate, suitable for larval development, which is also favoured by ants. The caterpillar has green and yellow stripes to provide camouflage while it feeds on vetch. The ants milk
2392-539: A year, and that the erosion is caused by the loss of beach underneath the cliffs exacerbated by stronger storms and human activity such as gravel extraction. Despite this, the cliffs are expected to survive for tens of thousands of years more. In 2001, a large chunk of the cliff edge, as large as a football pitch , fell into the Channel. Further large sections collapsed on 15 March 2012, 4 February 2020, and on 3 February 2021. The chalk grassland environment above
2496-505: Is alpha particle -emitting matter from the decay chains of uranium and thorium. The main source of radiation in the human body is potassium -40 ( K ), typically 17 milligrams in the body at a time and 0.4 milligrams/day intake. Most rocks, especially granite , have a low level of radioactivity due to the potassium-40, thorium and uranium contained. Usually ranging from 1 millisievert (mSv) to 13 mSv annually depending on location, average radiation exposure from natural radioisotopes
2600-434: Is reactor-grade plutonium . In addition to plutonium-239 , which is highly suitable for building nuclear weapons, it contains large amounts of undesirable contaminants: plutonium-240 , plutonium-241 , and plutonium-238 . These isotopes are extremely difficult to separate, and more cost-effective ways of obtaining fissile material exist (e.g., uranium enrichment or dedicated plutonium production reactors). High-level waste
2704-487: Is 2.0 mSv per person a year worldwide. This makes up the majority of typical total dosage (with mean annual exposure from other sources amounting to 0.6 mSv from medical tests averaged over the whole populace, 0.4 mSv from cosmic rays , 0.005 mSv from the legacy of past atmospheric nuclear testing, 0.005 mSv occupational exposure, 0.002 mSv from the Chernobyl disaster , and 0.0002 mSv from
2808-605: Is a 10-mile-long (16 km) sandbank at the southern end of the North Sea lying six miles (10 km) off the Deal coast. The area consists of a layer of fine sand approximately 82 ft (25 m) deep resting on a chalk platform belonging to the same geological feature that incorporates the White Cliffs of Dover. More than 2,000 ships are believed to have been wrecked on the Goodwin Sands because they lie close to
2912-503: Is a fertile material that can undergo a neutron capture reaction and two beta minus decays, resulting in the production of fissile U-233 . The SNF of a cycle with thorium will contain U-233. Its radioactive decay will strongly influence the long-term activity curve of the SNF for around a million years. A comparison of the activity associated to U-233 for three different SNF types can be seen in
3016-406: Is a fissile material used in nuclear bombs, plus some material with much higher specific activities, such as Pu-238 or Po. In the past the neutron trigger for an atomic bomb tended to be beryllium and a high activity alpha emitter such as polonium ; an alternative to polonium is Pu-238 . For reasons of national security, details of the design of modern nuclear bombs are normally not released to
3120-424: Is a gamma emitter (increasing external-exposure to workers) and is an alpha emitter which can cause the generation of heat . The plutonium could be separated from the americium by several different processes; these would include pyrochemical processes and aqueous/organic solvent extraction . A truncated PUREX type extraction process would be one possible method of making the separation. Naturally occurring uranium
3224-413: Is an indurated (resists crumbling or powdering) rock of about the same composition as marl. This is more correctly described as an earthy or impure argillaceous limestone . It has a blocky subconchoidal fracture, and is less fissile than shale . The dominant carbonate mineral in most marls is calcite , but other carbonate minerals such as aragonite or dolomite may be present. Glauconitic marl
Marl - Misplaced Pages Continue
3328-717: Is closest to continental Europe , on a clear day the cliffs are visible from France, approximately 20 miles (32 km) away. A celebrated UK landmark, the cliffs have featured on commemorative postage stamps issued by the Royal Mail , including in their British coastline series in 2002 and UK A-Z series in 2012. The cliffs are part of the coastline of Kent in England between approximately 51°06′N 1°14′E / 51.100°N 1.233°E / 51.100; 1.233 and 51°12′N 1°24′E / 51.200°N 1.400°E / 51.200; 1.400 , at
3432-422: Is easily recognizable in core samples and helped establish the right level for excavating the tunnel. Marl soil has poor engineering properties, particularly when alternately wetted and dried. The soils can be stabilized by adding pozzolan ( volcanic ash ) to the soil. Some marl beds have a very low permeability and are under consideration for use in the storage of nuclear waste . One such proposed storage site
3536-615: Is full of highly radioactive fission products , most of which are relatively short-lived. This is a concern since if the waste is stored, perhaps in deep geological storage, over many years the fission products decay, decreasing the radioactivity of the waste and making the plutonium easier to access. The undesirable contaminant Pu-240 decays faster than the Pu-239, and thus the quality of the bomb material increases with time (although its quantity decreases during that time as well). Thus, some have argued, as time passes, these deep storage areas have
3640-516: Is generated from hospitals and industry, as well as the nuclear fuel cycle . Low-level wastes include paper, rags, tools, clothing, filters, and other materials which contain small amounts of mostly short-lived radioactivity. Materials that originate from any region of an Active Area are commonly designated as LLW as a precautionary measure even if there is only a remote possibility of being contaminated with radioactive materials. Such LLW typically exhibits no higher radioactivity than one would expect from
3744-477: Is harmful to humans and the environment. Different isotopes emit different types and levels of radiation, which last for different periods of time. The radioactivity of all radioactive waste weakens with time. All radionuclides contained in the waste have a half-life —the time it takes for half of the atoms to decay into another nuclide . Eventually, all radioactive waste decays into non-radioactive elements (i.e., stable nuclides ). Since radioactive decay follows
3848-560: Is highly radioactive and hot due to decay heat, thus requiring cooling and shielding. In nuclear reprocessing plants, about 96% of spent nuclear fuel is recycled back into uranium-based and mixed-oxide (MOX) fuels . The residual 4% is minor actinides and fission products , the latter of which are a mixture of stable and quickly decaying (most likely already having decayed in the spent fuel pool ) elements, medium lived fission products such as strontium-90 and caesium-137 and finally seven long-lived fission products with half lives in
3952-429: Is important to distinguish the processing of uranium to make fuel from the reprocessing of used fuel. Used fuel contains the highly radioactive products of fission (see high-level waste below). Many of these are neutron absorbers, called neutron poisons in this context. These eventually build up to a level where they absorb so many neutrons that the chain reaction stops, even with the control rods completely removed from
4056-560: Is marl containing pellets of glauconite , a clay mineral that gives the marl a green color. Glauconite is characteristic of sediments deposited in marine conditions. The lower stratigraphic units of the chalk cliffs of Dover consist of a sequence of glauconitic marls followed by rhythmically banded limestone and marl layers. Such alternating cycles of chalk and marl are common in Cretaceous beds of northwestern Europe. The Channel Tunnel follows these marl layers between France and
4160-597: Is not fissile because it contains 99.3% of U-238 and only 0.7% of U-235. Due to historic activities typically related to the radium industry, uranium mining, and military programs, numerous sites contain or are contaminated with radioactivity. In the United States alone, the Department of Energy (DOE) states there are "millions of gallons of radioactive waste" as well as "thousands of tons of spent nuclear fuel and material" and also "huge quantities of contaminated soil and water." Despite copious quantities of waste, in 2007,
4264-423: Is produced by nuclear reactors and the reprocessing of nuclear fuel. The exact definition of HLW differs internationally. After a nuclear fuel rod serves one fuel cycle and is removed from the core, it is considered HLW. Spent fuel rods contain mostly uranium with fission products and transuranic elements generated in the reactor core . Spent fuel is highly radioactive and often hot. HLW accounts for over 95% of
Marl - Misplaced Pages Continue
4368-528: Is refined from yellowcake (U 3 O 8 ), then converted to uranium hexafluoride gas (UF 6 ). As a gas, it undergoes enrichment to increase the U-235 content from 0.7% to about 4.4% (LEU). It is then turned into a hard ceramic oxide (UO 2 ) for assembly as reactor fuel elements. The main by-product of enrichment is depleted uranium (DU), principally the U-238 isotope, with a U-235 content of ~0.3%. It
4472-422: Is regulated by government agencies in order to protect human health and the environment. Radioactive waste is broadly classified into 3 categories: low-level waste (LLW), such as paper, rags, tools, clothing, which contain small amounts of mostly short-lived radioactivity; intermediate-level waste (ILW), which contains higher amounts of radioactivity and requires some shielding; and high-level waste (HLW), which
4576-432: Is stored, either as UF 6 or as U 3 O 8 . Some is used in applications where its extremely high density makes it valuable such as anti-tank shells , and on at least one occasion even a sailboat keel . It is also used with plutonium for making mixed oxide fuel (MOX) and to dilute, or downblend , highly enriched uranium from weapons stockpiles which is now being redirected to become reactor fuel. The back-end of
4680-639: Is the Wellenberg in central Switzerland. A marl lake is a lake whose bottom sediments include large deposits of marl. They are most often found in areas of recent glaciation and are characterized by alkaline water, rich in dissolved calcium carbonate, from which carbonate minerals are deposited. Marl lakes have frequently been dredged or mined for marl, often used for manufacturing Portland cement . However, they are regarded as ecologically important, and are vulnerable to damage by silting , nutrient pollution , drainage , and invasive species . In Britain, only
4784-426: Is to recycle the plutonium and use it as a fuel e.g. in fast reactors . In pyrometallurgical fast reactors , the separated plutonium and uranium are contaminated by actinides and cannot be used for nuclear weapons. Waste from nuclear weapons decommissioning is unlikely to contain much beta or gamma activity other than tritium and americium . It is more likely to contain alpha-emitting actinides such as Pu-239 which
4888-660: The Late Cretaceous . The cliffs, on both sides of the town of Dover in Kent , stretch for eight miles (13 km). The White Cliffs of Dover form part of the North Downs . A section of coastline encompassing the cliffs was purchased by the National Trust in 2016. The cliffs are part of the Dover to Kingsdown Cliffs Site of Special Scientific Interest and Special Area of Conservation . The point where Great Britain
4992-487: The National Trust , Natural England , and County Wildlife Trusts to maintain vegetation on nature reserves. The cliffs are the first landing point for many migratory birds flying inland from across the English Channel. After a 120-year absence, in 2009 it was reported that ravens had returned to the cliffs. Similar in appearance but smaller, the jackdaw is abundant. The rarest of the birds that live along
5096-473: The PUREX -process disposes of them as waste together with the fission products. The waste is subsequently converted into a glass-like ceramic for storage in a deep geological repository . The time radioactive waste must be stored depends on the type of waste and radioactive isotopes it contains. Short-term approaches to radioactive waste storage have been segregation and storage on the surface or near-surface of
5200-549: The little ships in the Dunkirk evacuation saw the welcoming sight of the cliffs. In the summer of 1940, reporters gathered at Shakespeare Cliff to watch aerial dogfights between German and British aircraft during the Battle of Britain . Vera Lynn , known as "The Forces' Sweetheart" for her 1942 wartime classic " (There'll Be Bluebirds Over) The White Cliffs of Dover " celebrated her 100th birthday in 2017. That year she led
5304-492: The silver-spotted skipper and straw belle . The well-known red admiral can be seen from February until November. The marbled white , black and white with a white wing border, can be seen from June to August. A possible Iron Age hillfort has been discovered at Dover, on the site of the later castle. The area was also inhabited during the Roman period when Dover was used as a port. A lighthouse survives from this era, one of
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#17327929575745408-467: The 18th century. The marl was normally extracted close to its point of use, so that almost every field had a marl pit, but some marl was transported greater distances by railroad. However, marl was gradually replaced by lime and imported mineral fertilizers early in the 19th century. A similar historical pattern was seen in Scotland. Marl was one of a few soil amendments available in limited quantities in
5512-715: The DOE has successfully completed cleanup, or at least closure, of several sites. Radioactive medical waste tends to contain beta particle and gamma ray emitters. It can be divided into two main classes. In diagnostic nuclear medicine a number of short-lived gamma emitters such as technetium-99m are used. Many of these can be disposed of by leaving it to decay for a short time before disposal as normal waste. Other isotopes used in medicine, with half-lives in parentheses, include: Industrial source waste can contain alpha, beta , neutron or gamma emitters. Gamma emitters are used in radiography while neutron emitting sources are used in
5616-569: The DOE stated a goal of cleaning all presently contaminated sites successfully by 2025. The Fernald , Ohio site for example had "31 million pounds of uranium product", "2.5 billion pounds of waste", "2.75 million cubic yards of contaminated soil and debris", and a "223 acre portion of the underlying Great Miami Aquifer had uranium levels above drinking standards." The United States has at least 108 sites designated as areas that are contaminated and unusable, sometimes many thousands of acres. The DOE wishes to clean or mitigate many or all by 2025, using
5720-411: The English Channel at least twice a year. Among the wildflowers are several varieties of orchids, the rarest of which is the early spider orchid , which has yellow-green to brownish green petals and looks like the body of a large spider. Rock samphire is an edible, salt tolerant succulent plant that grows on the cliff's slopes. The oxtongue broomrape is an unusual plant that lives on the roots of
5824-545: The MOX fuel results in a lower activity in region 3 of the figure at the bottom right, whereas for RGPu and WGPu the curve is maintained higher due to the presence of U-233 that has not fully decayed. Nuclear reprocessing can remove the actinides from the spent fuel so they can be used or destroyed (see Long-lived fission product § Actinides ). Since uranium and plutonium are nuclear weapons materials, there are proliferation concerns. Ordinarily (in spent nuclear fuel), plutonium
5928-660: The Napoleonic Wars, in particular, the defences were remodelled and a series of tunnels were dug into the cliff to act as barracks, adding space for an extra 2,000 soldiers. The tunnels mostly lay abandoned until the Second World War. South Foreland Lighthouse is a Victorian-era lighthouse on the South Foreland in St. Margaret's Bay , which was once used to warn ships approaching the nearby Goodwin Sands . Goodwin Sands
6032-408: The Pu-239; due to the relatively long half-life of these Pu isotopes, these wastes from radioactive decay of bomb core material would be very small, and in any case, far less dangerous (even in terms of simple radioactivity) than the Pu-239 itself. The beta decay of Pu-241 forms Am-241 ; the in-growth of americium is likely to be a greater problem than the decay of Pu-239 and Pu-240 as the americium
6136-1121: The Radioactive Waste Safety Standards (RADWASS), also plays a significant role. The proportion of various types of waste generated in the UK: Uranium tailings are waste by-product materials left over from the rough processing of uranium-bearing ore . They are not significantly radioactive. Mill tailings are sometimes referred to as 11(e)2 wastes , from the section of the US Atomic Energy Act of 1946 that defines them. Uranium mill tailings typically also contain chemically hazardous heavy metal such as lead and arsenic . Vast mounds of uranium mill tailings are left at many old mining sites, especially in Colorado , New Mexico , and Utah . Although mill tailings are not very radioactive, they have long half-lives. Mill tailings often contain radium, thorium and trace amounts of uranium. Low-level waste (LLW)
6240-591: The United Kingdom. Upper Cretaceous cyclic sequences in Germany and marl– opal -rich Tortonian - Messinian strata in the Sorbas Basin related to multiple sea drawdown have been correlated with Milankovitch orbital forcing. Marl as lacustrine sediment is common in post- glacial lake -bed sediments. Chara , a macroalga also known as stonewort, thrives in shallow lakes with high pH and alkalinity , where its stems and fruiting bodies become calcified. After
6344-477: The alga dies, the calcified stems and fruiting bodies break down into fine carbonate particles that mingle with silt and clay to produce marl. Marl ponds of the northeastern United States are often kettle ponds in areas of limestone bedrock that become poor in nutrients ( oligotrophic ) due to precipitation of essential phosphate . Normal pond life is unable to survive, and skeletons of freshwater molluscs such as Sphaerium and Planorbis accumulate as part of
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#17327929575746448-639: The ash content of 'dirty' coals. The more active ash minerals become concentrated in the fly ash precisely because they do not burn well. The radioactivity of fly ash is about the same as black shale and is less than phosphate rocks, but is more of a concern because a small amount of the fly ash ends up in the atmosphere where it can be inhaled. According to U.S. National Council on Radiation Protection and Measurements (NCRP) reports, population exposure from 1000-MWe power plants amounts to 490 person-rem/year for coal power plants, 100 times as great as nuclear power plants (4.8 person-rem/year). The exposure from
6552-448: The back end of the fuel cycle is especially relevant when designing a complete waste management plan for SNF. When looking at long-term radioactive decay, the actinides in the SNF have a significant influence due to their characteristically long half-lives. Depending on what a nuclear reactor is fueled with, the actinide composition in the SNF will be different. An example of this effect is the use of nuclear fuels with thorium . Th-232
6656-609: The bottom marl. In Hungary, Buda Marl is found that was formed in the Upper Eocene era. It lies between layers of rock and soil and may be defined it as both "weak rock and strong soil." Marl is the dominant rock type in the Vaca Muerta Formation in Argentina. Marl has been used as a soil conditioner and neutralizing agent for acid soil and in the manufacture of Portland cement . Because some marls have
6760-608: The castle to its current size, taking its curtain walls to the edge of the cliffs. During the First Barons' War the castle was held by King John's soldiers and besieged by the French between May 1216 and May 1217. The castle was also besieged in 1265 during the Second Barons' War . In the 16th century, cannons were installed at the castle, but it became less important militarily as Henry VIII had built artillery forts along
6864-405: The cliffs form a symbolic guard. The National Trust calls the cliffs "an icon of Britain", with "the white chalk face a symbol of home and wartime defence." Because crossing at Dover was the primary route to the continent before the advent of air travel, the white line of cliffs also formed the first or last sight of Britain for travellers. During the Second World War, thousands of allied troops on
6968-463: The cliffs is excellent for many species of wild flowers, butterflies and birds, and has been designated a Special Area of Conservation and a Site of Special Scientific Interest. Rangers and volunteers work to clear invasive plants that threaten the native flora. A grazing programme involving Exmoor ponies has been established to help to clear faster-growing invasive plants, allowing smaller, less robust native plants to survive. The ponies are managed by
7072-554: The cliffs is the peregrine falcon . In recent decline, the skylark also makes its home on the cliffs. The cliffs are home to fulmars and to colonies of black-legged kittiwake , a species of gull. Since bluebirds are not indigenous to the UK, some believe that bluebirds, as mentioned in the classic World War II song " (There'll Be Bluebirds Over) The White Cliffs of Dover ", composed by American artists, may actually refer to swallows and/or to house martins , which make an annual migration to continental Europe, many of them crossing
7176-473: The coast. Dover Castle was captured in 1642 during the Civil War when the townspeople climbed the cliffs and surprised the royalist garrison, giving a symbolic victory against royal control. Towards the end of the war many castles were slighted , but Dover was spared. The castle had renewed importance in the 1740s as the development of heavy artillery made capturing ports an important part of warfare. During
7280-452: The complete nuclear fuel cycle from mining to waste disposal is 136 person-rem/year; the corresponding value for coal use from mining to waste disposal is "probably unknown". Residues from the oil and gas industry often contain radium and its decay products. The sulfate scale from an oil well can be radium rich, while the water, oil, and gas from a well often contain radon . The radon decays to form solid radioisotopes which form coatings on
7384-425: The decay mode and the pharmacokinetics of an element (how the body processes it and how quickly), the threat due to exposure to a given activity of a radioisotope will differ. For instance, iodine-131 is a short-lived beta and gamma emitter, but because it concentrates in the thyroid gland, it is more able to cause injury than caesium -137 which, being water soluble , is rapidly excreted through urine. In
7488-651: The deposits to become consolidated into chalk . British chalk deposits are considered stratigraphically to belong in the Chalk Group . Due to the Alpine orogeny , a major mountain building event during the Cenozoic , the sea-floor deposits were raised above sea level. Until the end of the last glacial period , the British Isles were part of continental Europe, linked by the unbroken Weald-Artois Anticline ,
7592-607: The earth. Burial in a deep geological repository is a favored solution for long-term storage of high-level waste, while re-use and transmutation are favored solutions for reducing the HLW inventory. Boundaries to recycling of spent nuclear fuel are regulatory and economic as well as the issue of radioactive contamination if chemical separation processes cannot achieve a very high purity. Furthermore, elements may be present in both useful and troublesome isotopes, which would require costly and energy intensive isotope separation for their use –
7696-443: The end of the last glacial period, around 10,000 years ago, rising sea levels finally severed the last land connection. The cliffs' chalk face shows horizontal bands of dark-coloured flint which is composed of the remains of sea sponges and siliceous planktonic micro-organisms that hardened into the microscopic quartz crystals. Quartz silica filled cavities left by dead marine creatures which are found as flint fossils, especially
7800-411: The figure on the top right. The burnt fuels are thorium with reactor-grade plutonium (RGPu), thorium with weapons-grade plutonium (WGPu), and Mixed oxide fuel (MOX, no thorium). For RGPu and WGPu, the initial amount of U-233 and its decay for around a million years can be seen. This has an effect on the total activity curve of the three fuel types. The initial absence of U-233 and its daughter products in
7904-567: The fuel are a concentrated form of high-level waste as are the chemicals used in the process. While most countries reprocess the fuel carrying out single plutonium cycles, India is planning multiple plutonium recycling schemes and Russia pursues closed cycle. The use of different fuels in nuclear reactors results in different spent nuclear fuel (SNF) composition, with varying activity curves. The most abundant material being U-238 with other uranium isotopes, other actinides, fission products and activation products. Long-lived radioactive waste from
8008-416: The half-life rule, the rate of decay is inversely proportional to the duration of decay. In other words, the radiation from a long-lived isotope like iodine-129 will be much less intense than that of a short-lived isotope like iodine-131 . The two tables show some of the major radioisotopes, their half-lives, and their radiation yield as a proportion of the yield of fission of uranium-235. The energy and
8112-411: The hundreds of thousands to millions of years. The minor actinides meanwhile are heavy elements other than uranium and plutonium which are created by neutron capture . Their half lives range from years to millions of years and as alpha emitters they are particularly radiotoxic. While there are proposed – and to a much lesser extent current – uses of all those elements, commercial scale reprocessing using
8216-412: The inside of pipework. In an oil processing plant, the area of the plant where propane is processed is often one of the more contaminated areas of the plant as radon has a similar boiling point to propane. Radioactive elements are an industrial problem in some oil wells where workers operating in direct contact with the crude oil and brine can be exposed to doses having negative health effects. Due to
8320-411: The internal moulds of Micraster echinoids. Several different ocean floor species such as brachiopods , bivalves , crinoids , and sponges can be found in the chalk deposits, as can sharks' teeth. In some areas, layers of soft, grey chalk known as a hardground complex can be seen. Hardgrounds are thought to reflect disruptions in the steady accumulation of sediment when sedimentation ceased and/or
8424-461: The loose surface sediments were stripped away by currents or slumping, exposing the older hardened chalk sediment. A single hardground may have been exhumed 16 or more times before the sediments were compacted and hardened ( lithified ) to form chalk. Thousands of years ago, the cliffs were eroding at 20–60 mm (0.75–2.3 in) a year. Research shows that the erosion rate over the last 150 years has increased to 220–320 mm (8.7–12.6 in)
8528-617: The major shipping lanes through the Straits of Dover . It went out of service in 1988 and is now owned by the National Trust for Places of Historic Interest or Natural Beauty . The cliffs have great symbolic value in Britain because they face towards continental Europe across the narrowest part of the English Channel (approximately 20 miles (32 km) between coasts), where invasions have historically threatened and against which
8632-581: The manufacture of Portland cement. It is abundant and yields better physical and mechanical properties than metakaolin as a supplementary cementitious material and can be calcined at a considerably lower temperature. The Channel Tunnel was constructed in the West Melbury Marly Chalk, a geological formation containing marl beds. This formation was chosen because of its very low permeability, absence of chert , and lack of fissures found in overlying formations. The underlying Glauconitic Marl
8736-487: The marl lakes of the more remote parts of northern Scotland are likely to remain pristine into the near future. White cliffs of Dover The White Cliffs of Dover are the region of English coastline facing the Strait of Dover and France. The cliff face, which reaches a height of 350 feet (110 m), owes its striking appearance to its composition of chalk accented by streaks of black flint , deposited during
8840-565: The nature of the chemical compound which contains the radioisotope. No fission products have a half-life in the range of 100 a–210 ka ... ... nor beyond 15.7 Ma Radioactive waste comes from a number of sources. In countries with nuclear power plants, nuclear armament, or nuclear fuel treatment plants, the majority of waste originates from the nuclear fuel cycle and nuclear weapons reprocessing. Other sources include medical and industrial wastes, as well as naturally occurring radioactive materials (NORM) that can be concentrated as
8944-891: The north of Scotland is the Dounreay site which is prepared to withstand a 4m tsunami. [1] Some high-activity LLW requires shielding during handling and transport but most LLW is suitable for shallow land burial. To reduce its volume, it is often compacted or incinerated before disposal. Low-level waste is divided into four classes: class A , class B , class C , and Greater Than Class C ( GTCC ). Intermediate-level waste (ILW) contains higher amounts of radioactivity compared to low-level waste. It generally requires shielding, but not cooling. Intermediate-level wastes includes resins , chemical sludge and metal nuclear fuel cladding, as well as contaminated materials from reactor decommissioning. It may be solidified in concrete or bitumen or mixed with silica sand and vitrified for disposal. As
9048-577: The nuclear fuel cycle). TENORM is not regulated as restrictively as nuclear reactor waste, though there are no significant differences in the radiological risks of these materials. Coal contains a small amount of radioactive uranium, barium, thorium, and potassium, but, in the case of pure coal, this is significantly less than the average concentration of those elements in the Earth's crust . The surrounding strata, if shale or mudstone, often contain slightly more than average and this may also be reflected in
9152-491: The nuclear fuel cycle, mostly spent fuel rods , contains fission products that emit beta and gamma radiation, and actinides that emit alpha particles , such as uranium-234 (half-life 245 thousand years), neptunium-237 (2.144 million years), plutonium-238 (87.7 years) and americium-241 (432 years), and even sometimes some neutron emitters such as californium (half-life of 898 years for californium-251). These isotopes are formed in nuclear reactors . It
9256-440: The open literature. Some designs might contain a radioisotope thermoelectric generator using Pu-238 to provide a long-lasting source of electrical power for the electronics in the device. It is likely that the fissile material of an old nuclear bomb, which is due for refitting, will contain decay products of the plutonium isotopes used in it. These are likely to include U-236 from Pu-240 impurities plus some U-235 from decay of
9360-590: The point where Great Britain is closest to continental Europe – the Strait of Dover is approximately 20 miles (32 km) across. On a clear day the cliffs are visible from the French coast. The chalk cliffs of the Alabaster Coast of Normandy in France are part of the same geological system. The White Cliffs are at one end of the Kent Downs designated Area of Outstanding Natural Beauty . In 1999
9464-402: The potential to become "plutonium mines", from which material for nuclear weapons can be acquired with relatively little difficulty. Critics of the latter idea have pointed out the difficulty of recovering useful material from sealed deep storage areas makes other methods preferable. Specifically, high radioactivity and heat (80 °C in surrounding rock) greatly increase the difficulty of mining
9568-400: The public on 20 July 2015. Nuclear waste Radioactive waste is a type of hazardous waste that contains radioactive material . Radioactive waste is a result of many activities, including nuclear medicine , nuclear research , nuclear power generation, nuclear decommissioning , rare-earth mining, and nuclear weapons reprocessing. The storage and disposal of radioactive waste
9672-477: The recently developed method of geomelting , however the task can be difficult and it acknowledges that some may never be completely remediated. In just one of these 108 larger designations, Oak Ridge National Laboratory (ORNL), there were for example at least "167 known contaminant release sites" in one of the three subdivisions of the 37,000-acre (150 km ) site. Some of the U.S. sites were smaller in nature, however, cleanup issues were simpler to address, and
9776-498: The reduced content of calcium carbonate versus straight lime, expressed as the calcium carbonate equivalent. Because the carbonate in marl is predominantly calcium carbonate, magnesium deficiency may be seen in crops treated with marl if they are not also supplemented with magnesium. Marl has been used in Pamlico Sound to provide a suitable artificial substrate for oysters in a reef-like environment. Marl has been used in
9880-588: The relatively high concentration of these elements in the brine, its disposal is also a technological challenge. Since the 1980s, in the United States, the brine is however exempt from the dangerous waste regulations and can be disposed of regardless of radioactive or toxic substances content. Due to natural occurrence of radioactive elements such as thorium and radium in rare-earth ore , mining operations also result in production of waste and mineral deposits that are slightly radioactive. Classification of radioactive waste varies by country. The IAEA, which publishes
9984-457: The same material disposed of in a non-active area, such as a normal office block. Example LLW includes wiping rags, mops, medical tubes, laboratory animal carcasses, and more. LLW makes up 94% of all radioactive waste volume in the UK. Most of it is disposed of in Cumbria , first in landfill style trenches, and now using grouted metal containers that are stacked in concrete vaults. A new site in
10088-541: The southern United States, where soils were generally poor in nutrients, prior to about 1840. By the late 19th century, marl was being mined on an industrial scale in New Jersey and was increasingly being used on a more scientific basis, with marl being classified by grade and the state geological survey publishing detailed chemical analyses. Marl continues to be used for agriculture into the 21st century, though less frequently. The rate of application must be adjusted for
10192-530: The sugary secretions from the larval "honey glands" and, in return, protect the larvae from predators and parasitoids, even going so far as to bury them at night. The larvae pupate in the upper soil, and continue to be protected by the ants, often in their nests, until the adults emerge in the spring or autumn. Similar in appearance, but more abundant, is the chalkhill blue , a chalk grassland specialist that can be seen in July and August. Threatened species include
10296-637: The total radioactivity produced in the process of nuclear electricity generation but it contributes to less than 1% of volume of all radioactive waste produced in the UK. Overall, the 60-year-long nuclear program in the UK up until 2019 produced 2150 m of HLW. The radioactive waste from spent fuel rods consists primarily of cesium-137 and strontium-90, but it may also include plutonium, which can be considered transuranic waste. The half-lives of these radioactive elements can differ quite extremely. Some elements, such as cesium-137 and strontium-90 have half-lives of approximately 30 years. Meanwhile, plutonium has
10400-403: The type of the ionizing radiation emitted by a radioactive substance are also important factors in determining its threat to humans. The chemical properties of the radioactive element will determine how mobile the substance is and how likely it is to spread into the environment and contaminate humans. This is further complicated by the fact that many radioisotopes do not decay immediately to
10504-516: Was derived from the Latin albus (meaning 'white') as an allusion to the white cliffs. Dover Castle , the largest castle in England, was founded in the 11th century. It has been described as the "Key to England" owing to its defensive significance throughout history. The castle was founded by William the Conqueror in 1066 and rebuilt for Henry II , King John , and Henry III . This expanded
10608-446: Was named in honour of Dame Vera Lynn. Dover Museum was founded in 1836. Shelled from France in 1942 during the Second World War, the museum lost much of its collections, including nearly all its natural history collections. Much of the surviving material was left neglected in caves and other stores until 1946. In 1948 a temporary museum was opened and in 1991 a new museum of three storeys, built behind its original Victorian façade,
10712-476: Was opened. In 1999, a new gallery on the second floor centred on the Dover Bronze Age Boat was opened. Samphire Hoe Country Park is a nature reserve on a new piece of land created from the rock excavated during the construction of the Channel Tunnel . It covers a 74-acre (30 ha) site at the foot of Shakespeare Cliff , between Dover and Folkestone . There is an education shelter with
10816-603: Was used sporadically in Britain beginning in prehistoric times and its use was mentioned by Pliny the Elder in the 1st century. Its more widespread use from the 16th century on contributed to the early modern agricultural revolution. However, the lack of a high-energy economy hindered its large-scale use until the Industrial Revolution . Marl was used extensively in Britain, particularly in Lancashire , during
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