Problems and Prospects for Nuclear Waste Disposal Policy Hardcove

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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.[1] The storage and disposal of radioactive waste is regulated by government agencies in order to protect human health and the environment.

Radioactive waste is broadly classified into 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 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 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 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 for 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. 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 - 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).[2]

Nature and significance

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 is harmful to humans and the environment. Different isotopes emit different types and levels of radiation, which last for different periods of time.

Physics Main article: Fission product yield See also: Radioactive decay Medium-lived fission products [further explanation needed ]
t ½ (year ) Yield (% ) Q (keV ) βγ
155Eu   4.76 0.0803   252 βγ
85Kr 10.76 0.2180   687 βγ
113mCd 14.1  0.0008   316 β
90Sr 28.9  4.505   2826 β
137Cs 30.23 6.337   1176 βγ
121mSn 43.9  0.00005 390 βγ
151Sm 88.8  0.5314   77 β
Long-lived fission products
  • v
  • t
  • e
Nuclide t 1 ⁄2 Yield Q [a 1] βγ
(Ma ) (%) [a 2] (keV )
99Tc 0.211 6.1385 294 β
126Sn 0.230 0.1084 4050[a 3] βγ
79Se 0.327 0.0447 151 β
135Cs 1.33  6.9110[a 4] 269 β
93Zr 1.53  5.4575 91 βγ
107Pd 6.5   1.2499 33 β
129I 15.7   0.8410 194 βγ
  • Decay energy is split among β , neutrino , and γ if any.
  • Per 65 thermal neutron fissions of 235U and 35 of 239Pu .
  • Has decay energy 380 keV, but its decay product 126Sb has decay energy 3.67 MeV.
    1. Lower in thermal reactors because 135Xe , its predecessor, readily absorbs neutrons .

    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 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 .[3] 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 the type of the ionizing radiation emitted by a radioactive substance are also important factors in determining its threat to humans.[4] 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.[5] This is further complicated by the fact that many radioisotopes do not decay immediately to a stable state but rather to radioactive decay products within a decay chain before ultimately reaching a stable state.

    Pharmacokinetics

    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,[6] and regulatory agencies assume the risk is linearly proportional to dose even for low doses. Ionizing radiation can cause deletions in chromosomes.[7] If 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[8]

    Depending on 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 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 the nature of the chemical compound which contains the radioisotope.

    Sources
    Actinides and fission products by half-life
    • v
    • t
    • e
    Actinides [9] by decay chain Half-life range (a ) Fission products of 235U by yield [10]
    4n 4n + 1 4n + 2 4n + 3 4.5–7% 0.04–1.25% <0.001%
    228 Ra№ 4–6 a 155 Euþ
    244 Cmƒ 241 Puƒ 250 Cf 227 Ac№ 10–29 a 90 Sr 85 Kr 113m Cdþ
    232 Uƒ 238 Puƒ 243 Cmƒ 29–97 a 137 Cs 151 Smþ 121m Sn
    248 Bk[11] 249 Cfƒ 242m Amƒ 141–351 a

    No fission products have a half-life in the range of 100 a–210 ka ...

    241 Amƒ 251 Cfƒ[12] 430–900 a
    226 Ra№ 247 Bk 1.3–1.6 ka
    240 Pu 229 Th 246 Cmƒ 243 Amƒ 4.7–7.4 ka
    245 Cmƒ 250 Cm 8.3–8.5 ka
    239 Puƒ 24.1 ka
    230 Th№ 231 Pa№ 32–76 ka
    236 Npƒ 233 Uƒ 234 U№ 150–250 ka 99 Tc₡ 126 Sn
    248 Cm 242 Pu 327–375 ka 79 Se₡
    1.53 Ma 93 Zr
    237 Npƒ 2.1–6.5 Ma 135 Cs₡ 107 Pd
    236 U 247 Cmƒ 15–24 Ma 129 I₡
    244 Pu 80 Ma

    ... nor beyond 15.7 Ma[13]

    232 Th№ 238 U№ 235 Uƒ№ 0.7–14.1 Ga
    • ₡,  has thermal neutron capture cross section in the range of 8–50 barns
    • ƒ,  fissile
    • №,  primarily a naturally occurring radioactive material (NORM)
    • þ,  neutron poison (thermal neutron capture cross section greater than 3k barns)

    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 a result of the processing or consumption of coal, oil, and gas, and some minerals, as discussed below.

    Nuclear fuel cycle Main articles: Nuclear fuel cycle and Spent nuclear fuel See also: Nuclear power

    Front end

    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 (UO2) concentrate from mining is a thousand or so times as radioactive as the granite used in buildings. It is refined from yellowcake (U3O8), then converted to uranium hexafluoride gas (UF6). 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 (UO2) for assembly as reactor fuel elements.[14]

    The main by-product of enrichment is depleted uranium (DU), principally the U-238 isotope, with a U-235 content of ~0.3%. It is stored, either as UF6 or as U3O8. 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 .[15] 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.

    Back end See also: Nuclear reprocessing

    The back-end of 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 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. 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.[16] The fission products removed from 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 [17] and Russia pursues closed cycle.[18]

    Fuel composition and long term radioactivity Activity of U-233 for three fuel types. In the case of MOX, the U-233 increases for the first 650 thousand years as it is produced by the decay of Np-237 which was created in the reactor by absorption of neutrons by U-235. See also: Spent nuclear fuel and High-level waste Main article: Long-lived fission product Total activity for three fuel types. In region 1, there is radiation from short-lived nuclides, in region 2, from Sr-90 and Cs-137 , and on the far right, the decay of Np-237 and U-233.

    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.[19]

    Long-lived radioactive waste from 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 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 around a million years. A comparison of the activity associated to U-233 for three different SNF types can be seen in 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 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 the MOX fuel results in a lower activity in region 3 of the figure on 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 ).

    Proliferation concerns See also: Nuclear proliferation and Reactor-grade plutonium

    Since uranium and plutonium are nuclear weapons materials, there have been proliferation concerns. Ordinarily (in spent nuclear fuel), plutonium 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).[20]

    High-level waste 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 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 a storage area, and the enrichment methods required have high capital costs.[21]

    Pu-239 decays to U-235 which is suitable for weapons and which has a very long half-life (roughly 109 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 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.

    Nuclear weapons decommissioning

    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 is a fissile material used in 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 bombs are normally not released to 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 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 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 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 is not fissile because it contains 99.3% of U-238 and only 0.7% of U-235.

    Legacy waste

    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 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."[22] Despite copious quantities of waste, the DOE has stated a goal of cleaning all presently contaminated sites successfully by 2025.[22] 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."[22] The United States has at least 108 sites designated as areas that are contaminated and unusable, sometimes many thousands of acres.[22] [23] DOE wishes to clean or mitigate many or all by 2025, using the recently developed method of geomelting ,[citation needed ] 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 , there were for example at least "167 known contaminant release sites" in one of the three subdivisions of the 37,000-acre (150 km2) site.[22] Some of the U.S. sites were smaller in nature, however, cleanup issues were simpler to address, and DOE has successfully completed cleanup, or at least closure, of several sites.[22]

    Medicine

    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:

    • Y-90 , used for treating lymphoma (2.7 days)
    • I-131 , used for thyroid function tests and for treating thyroid cancer (8.0 days)
    • Sr-89 , used for treating bone cancer , intravenous injection (52 days)
    • Ir-192 , used for brachytherapy (74 days)
    • Co-60 , used for brachytherapy and external radiotherapy (5.3 years)
    • Cs-137 , used for brachytherapy and external radiotherapy (30 years)
    • Tc-99 , product of the decay of Technetium-99m (221,000 years)

    Industry

    Industrial source waste can contain alpha, beta , neutron or gamma emitters. Gamma emitters are used in radiography while neutron emitting sources are used in a range of applications, such as oil well logging.[24]

    Naturally occurring radioactive material Annual release of uranium and thorium radioisotopes from coal combustion, predicted by ORNL to cumulatively amount to 2.9 Mt over the 1937–2040 period, from the combustion of an estimated 637 Gt of coal worldwide.[25]

    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).[26] A lot of this waste 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 (40K ), typically 17 milligrams in the body at a time and 0.4 milligrams/day intake.[27] 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 is 2.0 mSv per person a year worldwide.[28] 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 the nuclear fuel cycle).[28]

    TENORM is not regulated as restrictively as nuclear reactor waste, though there are no significant differences in the radiological risks of these materials.[29]

    Coal

    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 the ash content of 'dirty' coals.[25] [30] The more active ash minerals become concentrated in the fly ash precisely because they do not burn well.[25] 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.[31] 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 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".[25]

    Oil and gas

    Residues from the oil and gas industry often contain radium and its decay products. The sulfate scale from an oil well can be very 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 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.[32]

    Radioactive elements are an industrial problem in some oil wells where workers operating in direct contact with the crude oil and brine can be actually exposed to doses having negative health effects. Due to the relatively high concentration of these elements in the brine, its disposal is also a technological challenge. 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 since the 1980s.[33]

    Rare-earth mining

    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.[34]

    See also: Rare-earth_element § Environmental_considerations

    Classification

    Classification of radioactive waste varies by country. The IAEA, which publishes the Radioactive Waste Safety Standards (RADWASS), also plays a significant role.[35] The proportion of various types of waste generated in the UK:[36]

    • 94% – low-level waste (LLW)
    • ~6% – intermediate-level waste (ILW)
    • <1% – high-level waste (HLW)

    Mill tailings Main article: Uranium tailings See also: Uranium Mill Tailings Remedial Action Removal of very low-level waste

    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 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.[37]

    Low-level waste Main article: Low-level waste

    Low-level waste (LLW) 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 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.[38] LLW waste makes 94% of all radioactive waste volume in the UK.[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 Spent fuel flasks are transported by railway in the United Kingdom. Each flask is constructed of 14 in (360 mm) thick solid steel and weighs in excess of 50 t

    Intermediate-level waste (ILW) contains higher amounts of radioactivity compared to low-level waste. It generally requires shielding, but not cooling.[39] 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 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 6% of all radioactive waste volume in the UK.[1]

    High-level waste Main article: High-level waste

    High-level waste (HLW) is produced by nuclear reactors and the reprocessing of nuclear fuel.[40] 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.[41] 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 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 m3 of HLW.[1]

    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.[37] 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 a half-life that can stretch to as long as 24,000 years.[37]

    The amount of HLW worldwide is currently increasing by about 12,000 tonnes every year.[42] A 1000-megawatt nuclear power plant produces about 27 t of spent nuclear fuel (unreprocessed) every year.[43] For comparison, the amount of ash produced by coal power plants in the United States alone is estimated at 130,000,000 t per year[44] and fly ash is estimated to release 100 times more radiation than an equivalent nuclear power plant.[45]

    The current locations across the United States where nuclear waste is stored

    In 2010, it was estimated that about 250,000 t of nuclear HLW were stored globally.[46] This does not include amounts that have escaped into the environment from accidents or tests. Japan is estimated to hold 17,000 t of HLW in storage in 2015.[47] As of 2019, the United States has over 90,000 t of HLW.[48] HLW have been shipped to other countries to be stored or reprocessed and, in some cases, shipped back as active fuel.

    The ongoing controversy over high-level radioactive waste disposal is a major constraint on the nuclear power's global expansion.[49] Most scientists agree that the main proposed long-term solution is deep geological burial, either in a mine or a deep borehole.[50] [51] As of 2019 no dedicated civilian high-level nuclear waste site is operational[49] as small amounts of HLW did not justify the investment before. Finland is in the advanced stage of the construction of the Onkalo spent nuclear fuel repository , which is planned to open in 2025 at 400–450 m depth. France is in the planning phase for a 500 m deep Cigeo facility in Bure. Sweden is planning a site in Forsmark . Canada plans a 680 m deep facility near Lake Huron in Ontario. The Republic of Korea plans to open a site around 2028.[1] The site in Sweden enjoys 80% support from local residents as of 2020.[52]

    The Morris Operation in Grundy County, Illinois , is currently the only de facto high-level radioactive waste storage site in the United States.

    Transuranic waste Main article: Transuranic waste

    Transuranic waste (TRUW) as defined by U.S. regulations is, without regard to form or origin, waste that is contaminated with alpha-emitting transuranic radionuclides with half-lives greater than 20 years and concentrations greater than 100 nCi /g (3.7 MBq /kg), excluding high-level waste. Elements that have an atomic number greater than uranium are called transuranic ("beyond uranium"). Because of their long half-lives, TRUW is disposed of more cautiously than either low- or intermediate-level waste. In the United States, it arises mainly from nuclear weapons production, and consists of clothing, tools, rags, residues, debris, and other items contaminated with small amounts of radioactive elements (mainly plutonium ).

    Under U.S. law, transuranic waste is further categorized into "contact-handled" (CH) and "remote-handled" (RH) on the basis of the radiation dose rate measured at the surface of the waste container. CH TRUW has a surface dose rate not greater than 200 mrem per hour (2 mSv/h), whereas RH TRUW has a surface dose rate of 200 mrem/h (2 mSv/h) or greater. CH TRUW does not have the very high radioactivity of high-level waste, nor its high heat generation, but RH TRUW can be highly radioactive, with surface dose rates up to 1,000,000 mrem/h (10,000 mSv/h). The United States currently disposes of TRUW generated from military facilities at the Waste Isolation Pilot Plant (WIPP) in a deep salt formation in New Mexico .[53]

    Prevention

    A future way to reduce waste accumulation is to phase out current reactors in favor of Generation IV reactors , which output less waste per power generated. Fast reactors such as BN-800 in Russia are also able to consume MOX fuel that is manufactured from recycled spent fuel from traditional reactors.[54]

    The UK's Nuclear Decommissioning Authority published a position paper in 2014 on the progress on approaches to the management of separated plutonium, which summarises the conclusions of the work that NDA shared with UK government.[55]

    Management Modern medium to high-level transport container for nuclear waste See also: High-level radioactive waste management , List of nuclear waste treatment technologies , and Environmental effects of nuclear power

    Of particular concern in nuclear waste management are two long-lived fission products, Tc-99 (half-life 220,000 years) and I-129 (half-life 15.7 million years), which dominate spent fuel radioactivity after a few thousand years. The most troublesome transuranic elements in spent fuel are Np-237 (half-life two million years) and Pu-239 (half-life 24,000 years).[56] Nuclear waste requires sophisticated treatment and management to successfully isolate it from interacting with the biosphere . This usually necessitates treatment, followed by a long-term management strategy involving storage, disposal or transformation of the waste into a non-toxic form.[57] Governments around the world are considering a range of waste management and disposal options, though there has been limited progress toward long-term waste management solutions.[58]

    The Onkalo is a planned deep geological repository for the final disposal of spent nuclear fuel[59] [60] near the Olkiluoto Nuclear Power Plant in Eurajoki , on the west coast of Finland . Picture of a pilot cave at final depth in Onkalo.

    In the second half of the 20th century, several methods of disposal of radioactive waste were investigated by nuclear nations,[61] which are :

    • "Long-term above-ground storage", not implemented.
    • "Disposal in outer space" (for instance, inside the Sun), not implemented—as it would be currently too expensive.
    • "Deep borehole disposal ", not implemented.
    • "Rock melting", not implemented.
    • "Disposal at subduction zones", not implemented.
    • Ocean disposal , by the USSR, the United Kingdom,[62] Switzerland, the United States, Belgium, France, the Netherlands, Japan, Sweden, Russia, Germany, Italy and South Korea (1954–93). This is no longer permitted by international agreements.
    • "Sub-seabed disposal ", not implemented, not permitted by international agreements.
    • "Disposal in ice sheets", rejected in Antarctic Treaty
    • "Deep well injection", by USSR and USA.
    • Nuclear transmutation , using lasers to cause beta decay to convert the unstable atoms to those with shorter half-lives.

    In the United States, waste management policy completely broke down with the ending of work on the incomplete Yucca Mountain Repository .[63] At present there are 70 nuclear power plant sites where spent fuel is stored. A Blue Ribbon Commission was appointed by President Obama to look into future options for this and future waste. A deep geological repository seems to be favored.[63] 2018 Nobel Prize for Physics -winner Gérard Mourou has proposed using Chirped pulse amplification to generate high-energy and low-duration laser pulses to transmute highly radioactive material (contained in a target) to significantly reduce its half-life, from thousands of years to only a few minutes.[64] [65]

    Initial treatment

    Vitrification The Waste Vitrification Plant at Sellafield

    Long-term storage of radioactive waste requires the stabilization of the waste into a form that will neither react nor degrade for extended periods. It is theorized that one way to do this might be through vitrification.[66] Currently at Sellafield the high-level waste (PUREX first cycle raffinate ) is mixed with sugar and then calcined. Calcination involves passing the waste through a heated, rotating tube. The purposes of calcination are to evaporate the water from the waste and de-nitrate the fission products to assist the stability of the glass produced.[67]

    The 'calcine' generated is fed continuously into an induction heated furnace with fragmented glass .[68] The resulting glass is a new substance in which the waste products are bonded into the glass matrix when it solidifies. As a melt, this product is poured into stainless steel cylindrical containers ("cylinders") in a batch process. When cooled, the fluid solidifies ("vitrifies") into the glass. After being formed, the glass is highly resistant to water.[69]

    After filling a cylinder, a seal is welded onto the cylinder head. The cylinder is then washed. After being inspected for external contamination, the steel cylinder is stored, usually in an underground repository. In this form, the waste products are expected to be immobilized for thousands of years.[70]

    The glass inside a cylinder is usually a black glossy substance. All this work (in the United Kingdom) is done using hot cell systems. Sugar is added to control the ruthenium chemistry and to stop the formation of the volatile RuO4 containing radioactive ruthenium isotopes . In the West, the glass is normally a borosilicate glass (similar to Pyrex ), while in the former Soviet Union it is normal to use a phosphate glass .[71] The amount of fission products in the glass must be limited because some (palladium , the other Pt group metals, and tellurium ) tend to form metallic phases which separate from the glass. Bulk vitrification uses electrodes to melt soil and wastes, which are then buried underground.[72] In Germany a vitrification plant is in use; this is treating the waste from a small demonstration reprocessing plant which has since been closed down.[67] [73]

    Phosphate Ceramics

    Vitrification is not the only way to stabilize the waste into a form that will not react or degrade for extended periods. Immobilization via direct incorporation into a phosphate-based crystalline ceramic host is also used.[74] The diverse chemistry of phosphate ceramics under various conditions demonstrates a versatile material that can withstand chemical, thermal, and radioactive degradation over time. The properties of phosphates, particularly ceramic phosphates, of stability over a wide pH range, low porosity, and minimization of secondary waste introduces possibilities for new waste immobilization techniques.

    Ion exchange

    It is common for medium active wastes in the nuclear industry to be treated with ion exchange or other means to concentrate the radioactivity into a small volume. The much less radioactive bulk (after treatment) is often then discharged. For instance, it is possible to use a ferric hydroxide floc to remove radioactive metals from aqueous mixtures.[75] After the radioisotopes are absorbed onto the ferric hydroxide, the resulting sludge can be placed in a metal drum before being mixed with cement to form a solid waste form.[76] In order to get better long-term performance (mechanical stability) from such forms, they may be made from a mixture of fly ash , or blast furnace slag , and portland cement , instead of normal concrete (made with portland cement, gravel and sand).

    Synroc

    The Australian Synroc (synthetic rock) is a more sophisticated way to immobilize such waste, and this process may eventually come into commercial use for civil wastes (it is currently being developed for U.S. military wastes). Synroc was invented by Prof Ted Ringwood (a geochemist ) at the Australian National University .[77] The Synroc contains pyrochlore and cryptomelane type minerals. The original form of Synroc (Synroc C) was designed for the liquid high-level waste (PUREX raffinate) from a light-water reactor . The main minerals in this Synroc are hollandite (BaAl2Ti6O16), zirconolite (CaZrTi2O7) and perovskite (CaTiO3). The zirconolite and perovskite are hosts for the actinides . The strontium and barium will be fixed in the perovskite. The caesium will be fixed in the hollandite. A Synroc waste treatment facility began construction in 2018 at ANSTO .[78]

    Long-term management See also: Economics of nuclear power plants § Waste disposal costs

    The time frame in question when dealing with radioactive waste ranges from 10,000 to 1,000,000 years,[79] according to studies based on the effect of estimated radiation doses.[80] Researchers suggest that forecasts of health detriment for such periods should be examined critically.[81] [82] Practical studies only consider up to 100 years as far as effective planning[83] and cost evaluations[84] are concerned. Long term behavior of radioactive wastes remains a subject for ongoing research projects in geoforecasting .[85]

    Remediation

    Algae has shown selectivity for strontium in studies, where most plants used in bioremediation have not shown selectivity between calcium and strontium, often becoming saturated with calcium, which is present in greater quantities in nuclear waste. Strontium-90 with a half life around 30 years, is classified as high-level waste.[86]

    Researchers have looked at the bioaccumulation of strontium by Scenedesmus spinosus (algae ) in simulated wastewater. The study claims a highly selective biosorption capacity for strontium of S. spinosus, suggesting that it may be appropriate for use of nuclear wastewater.[87] A study of the pond alga Closterium moniliferum using non-radioactive strontium found that varying the ratio of barium to strontium in water improved strontium selectivity.[86]

    Above-ground disposal

    Dry cask storage typically involves taking waste from a spent fuel pool and sealing it (along with an inert gas ) in a steel cylinder, which is placed in a concrete cylinder which acts as a radiation shield. It is a relatively inexpensive method which can be done at a central facility or adjacent to the source reactor. The waste can be easily retrieved for reprocessing.[88]

    Geologic disposal Diagram of an underground low-level radioactive waste disposal site On Feb. 14, 2014, radioactive materials at the Waste Isolation Pilot Plant leaked from a damaged storage drum due to the use of incorrect packing material. Analysis showed the lack of a "safety culture" at the plant since its successful operation for 15 years had bred complacency.[89]

    The process of selecting appropriate deep final repositories for high-level waste and spent fuel is now underway in several countries with the first expected to be commissioned sometime after 2010.[citation needed ] The basic concept is to locate a large, stable geologic formation and use mining technology to excavate a tunnel, or large-bore tunnel boring machines (similar to those used to drill the Channel Tunnel from England to France) to drill a shaft 500 metres (1,600 ft) to 1,000 metres (3,300 ft) below the surface where rooms or vaults can be excavated for disposal of high-level radioactive waste. The goal is to permanently isolate nuclear waste from the human environment. Many people remain uncomfortable with the immediate stewardship cessation of this disposal system, suggesting perpetual management and monitoring would be more prudent.[citation needed ]

    Because some radioactive species have half-lives longer than one million years, even very low container leakage and radionuclide migration rates must be taken into account.[90] Moreover, it may require more than one half-life until some nuclear materials lose enough radioactivity to cease being lethal to living things. A 1983 review of the Swedish radioactive waste disposal program by the National Academy of Sciences found that country's estimate of several hundred thousand years—perhaps up to one million years—being necessary for waste isolation "fully justified."[91]

    The proposed land-based subductive waste disposal method disposes of nuclear waste in a subduction zone accessed from land and therefore is not prohibited by international agreement. This method has been described as the most viable means of disposing of radioactive waste,[92] and as the state-of-the-art as of 2001 in nuclear waste disposal technology.[93]

    Another approach termed Remix & Return[94] would blend high-level waste with uranium mine and mill tailings down to the level of the original radioactivi

    • Condition: Like New
    • Condition: This book is practically brand new; when I opened it the binding is very stiff so it has never been read
    • Book Title: Problems and Prospects for Nuclear Waste Disposal Policy Hardcove
    • ISBN: 9780313290589
    • Publication Name: Problems and Prospects for Nuclear Waste Disposal Policy
    • Item Length: 9.2in
    • Publisher: Bloomsbury Publishing USA
    • Series: Contributions in Political Science Ser.
    • Publication Year: 1993
    • Type: Textbook
    • Format: Hardcover
    • Language: English
    • Item Height: 0.4in
    • Author: Alvin H. Mushkatel
    • Item Width: 6.1in
    • Item Weight: 15.1 Oz
    • Number of Pages: 176 Pages

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