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Monday, April 5, 2021

Nuclear fuel cycle

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Nuclear_fuel_cycle

The nuclear fuel cycles describes how nuclear fuel is extracted, processed, used, and disposed of

The nuclear fuel cycle, also called nuclear fuel chain, is the progression of nuclear fuel through a series of differing stages. It consists of steps in the front end, which are the preparation of the fuel, steps in the service period in which the fuel is used during reactor operation, and steps in the back end, which are necessary to safely manage, contain, and either reprocess or dispose of spent nuclear fuel. If spent fuel is not reprocessed, the fuel cycle is referred to as an open fuel cycle (or a once-through fuel cycle); if the spent fuel is reprocessed, it is referred to as a closed fuel cycle.

Basic concepts

The lifecycle of fuel in the present US system. If put in one place the total inventory of spent nuclear fuel generated by the commercial fleet of power stations in the United States, would stand 7.6 metres (25 ft) tall and be 91 metres (300 ft) on a side, approximately the footprint of one American football field.

Nuclear power relies on fissionable material that can sustain a chain reaction with neutrons. Examples of such materials include uranium and plutonium. Most nuclear reactors use a moderator to lower the kinetic energy of the neutrons and increase the probability that fission will occur. This allows reactors to use material with far lower concentration of fissile isotopes than are needed for nuclear weapons. Graphite and heavy water are the most effective moderators, because they slow the neutrons through collisions without absorbing them. Reactors using heavy water or graphite as the moderator can operate using natural uranium.

A light water reactor (LWR) uses water in the form that occurs in nature, and requires fuel enriched to higher concentrations of fissile isotopes. Typically, LWRs use uranium enriched to 3–5% U-235, the only fissile isotope that is found in significant quantity in nature. One alternative to this low-enriched uranium (LEU) fuel is mixed oxide (MOX) fuel produced by blending plutonium with natural or depleted uranium, and these fuels provide an avenue to utilize surplus weapons-grade plutonium. Another type of MOX fuel involves mixing LEU with thorium, which generates the fissile isotope U-233. Both plutonium and U-233 are produced from the absorption of neutrons by irradiating fertile materials in a reactor, in particular the common uranium isotope U-238 and thorium, respectively, and can be separated from spent uranium and thorium fuels in reprocessing plants.

Some reactors do not use moderators to slow the neutrons. Like nuclear weapons, which also use unmoderated or "fast" neutrons, these fast-neutron reactors require much higher concentrations of fissile isotopes in order to sustain a chain reaction. They are also capable of breeding fissile isotopes from fertile materials; a breeder reactor is one that generates more fissile material in this way than it consumes.

During the nuclear reaction inside a reactor, the fissile isotopes in nuclear fuel are consumed, producing more and more fission products, most of which are considered radioactive waste. The buildup of fission products and consumption of fissile isotopes eventually stop the nuclear reaction, causing the fuel to become a spent nuclear fuel. When 3% enriched LEU fuel is used, the spent fuel typically consists of roughly 1% U-235, 95% U-238, 1% plutonium and 3% fission products. Spent fuel and other high-level radioactive waste is extremely hazardous, although nuclear reactors produce orders of magnitude smaller volumes of waste compared to other power plants because of the high energy density of nuclear fuel. Safe management of these byproducts of nuclear power, including their storage and disposal, is a difficult problem for any country using nuclear power.

Front end

1 Uranium ore – the principal raw material of nuclear fuel
2 Yellowcake – the form in which uranium is transported to a conversion plant
3 UF₆ – used in enrichment
4 Nuclear fuel – a compact, inert, insoluble solid

Exploration

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

Naturally occurring uranium consists primarily of two isotopes U-238 and U-235, with 99.28% of the metal being U-238 while 0.71% is U-235, and the remaining 0.01% is mostly U-234. The number in such names refers to the isotope's atomic mass number, which is the number of protons plus the number of neutrons in the atomic nucleus.

The atomic nucleus of U-235 will nearly always fission when struck by a free neutron, and the isotope is therefore said to be a "fissile" isotope. The nucleus of a U-238 atom on the other hand, rather than undergoing fission when struck by a free neutron, will nearly always absorb the neutron and yield an atom of the isotope U-239. This isotope then undergoes natural radioactive decay to yield Pu-239, which, like U-235, is a fissile isotope. The atoms of U-238 are said to be fertile, because, through neutron irradiation in the core, some eventually yield atoms of fissile Pu-239.

Mining

Uranium ore can be extracted through conventional mining in open pit and underground methods similar to those used for mining other metals. In-situ leach mining methods also are used to mine uranium in the United States. In this technology, uranium is leached from the in-place ore through an array of regularly spaced wells and is then recovered from the leach solution at a surface plant. Uranium ores in the United States typically range from about 0.05 to 0.3% uranium oxide (U₃O₈). Some uranium deposits developed in other countries are of higher grade and are also larger than deposits mined in the United States. Uranium is also present in very low-grade amounts (50 to 200 parts per million) in some domestic phosphate-bearing deposits of marine origin. Because very large quantities of phosphate-bearing rock are mined for the production of wet-process phosphoric acid used in high analysis fertilizers and other phosphate chemicals, at some phosphate processing plants the uranium, although present in very low concentrations, can be economically recovered from the process stream.

Milling

Mined uranium ores normally are processed by grinding the ore materials to a uniform particle size and then treating the ore to extract the uranium by chemical leaching. The milling process commonly yields dry powder-form material consisting of natural uranium, "yellowcake", which is sold on the uranium market as U₃O₈. Note that the material isn't always yellow.

Uranium conversion

Usually milled uranium oxide, U₃O₈ (triuranium octoxide) is then processed into either of two substances depending on the intended use.

For use in most reactors, U₃O₈ is usually converted to uranium hexafluoride (UF₆), the input stock for most commercial uranium enrichment facilities. A solid at room temperature, uranium hexafluoride becomes gaseous at 57 °C (134 °F). At this stage of the cycle, the uranium hexafluoride conversion product still has the natural isotopic mix (99.28% of U-238 plus 0.71% of U-235).

For use in reactors such as CANDU which do not require enriched fuel, the U₃O₈ may instead be converted to uranium dioxide (UO₂) which can be included in ceramic fuel elements.

In the current nuclear industry, the volume of material converted directly to UO₂ is typically quite small compared to that converted to UF₆.

Enrichment

Nuclear fuel cycle begins when uranium is mined, enriched and manufactured to nuclear fuel (1) which is delivered to a nuclear power plant. After usage in the power plant the spent fuel is delivered to a reprocessing plant (if fuel is recycled) (2) or to a final repository (if no recycling is done) (3) for geological disposition. In reprocessing 95% of spent fuel can be recycled to be returned to usage in a nuclear power plant (4).

The natural concentration (0.71%) of the fissionable isotope U-235 is less than that required to sustain a nuclear chain reaction in light water reactor cores. Accordingly UF₆ produced from natural uranium sources must be enriched to a higher concentration of the fissionable isotope before being used as nuclear fuel in such reactors. The level of enrichment for a particular nuclear fuel order is specified by the customer according to the application they will use it for: light-water reactor fuel normally is enriched to 3.5% U-235, but uranium enriched to lower concentrations is also required. Enrichment is accomplished using any of several methods of isotope separation. Gaseous diffusion and gas centrifuge are the commonly used uranium enrichment methods, but new enrichment technologies are currently being developed.

The bulk (96%) of the byproduct from enrichment is depleted uranium (DU), which can be used for armor, kinetic energy penetrators, radiation shielding and ballast. As of 2008 there are vast quantities of depleted uranium in storage. The United States Department of Energy alone has 470,000 tonnes. About 95% of depleted uranium is stored as uranium hexafluoride (UF₆).

Fabrication

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

The alloy used for the tubes depends on the design of the reactor. Stainless steel was used in the past, but most reactors now use a zirconium alloy. For the most common types of reactors, boiling water reactors (BWR) and pressurized water reactors (PWR), the tubes are assembled into bundles with the tubes spaced precise distances apart. These bundles are then given a unique identification number, which enables them to be tracked from manufacture through use and into disposal.

Service period

Transport of radioactive materials

Transport is an integral part of the nuclear fuel cycle. There are nuclear power reactors in operation in several countries but uranium mining is viable in only a few areas. Also, in the course of over forty years of operation by the nuclear industry, a number of specialized facilities have been developed in various locations around the world to provide fuel cycle services and there is a need to transport nuclear materials to and from these facilities. Most transports of nuclear fuel material occur between different stages of the cycle, but occasionally a material may be transported between similar facilities. With some exceptions, nuclear fuel cycle materials are transported in solid form, the exception being uranium hexafluoride (UF₆) which is considered a gas. Most of the material used in nuclear fuel is transported several times during the cycle. Transports are frequently international, and are often over large distances. Nuclear materials are generally transported by specialized transport companies.

Since nuclear materials are radioactive, it is important to ensure that radiation exposure of those involved in the transport of such materials and of the general public along transport routes is limited. Packaging for nuclear materials includes, where appropriate, shielding to reduce potential radiation exposures. In the case of some materials, such as fresh uranium fuel assemblies, the radiation levels are negligible and no shielding is required. Other materials, such as spent fuel and high-level waste, are highly radioactive and require special handling. To limit the risk in transporting highly radioactive materials, containers known as spent nuclear fuel shipping casks are used which are designed to maintain integrity under normal transportation conditions and during hypothetical accident conditions.

In-core fuel management

A nuclear reactor core is composed of a few hundred "assemblies", arranged in a regular array of cells, each cell being formed by a fuel or control rod surrounded, in most designs, by a moderator and coolant, which is water in most reactors.

Because of the fission process that consumes the fuels, the old fuel rods must be replaced periodically with fresh ones (this is called a (replacement) cycle). During a given replacement cycle only some of the assemblies (typically one-third) are replaced since fuel depletion occurs at different rates at different places within the reactor core. Furthermore, for efficiency reasons, it is not a good policy to put the new assemblies exactly at the location of the removed ones. Even bundles of the same age will have different burn-up levels due to their previous positions in the core. Thus the available bundles must be arranged in such a way that the yield is maximized, while safety limitations and operational constraints are satisfied. Consequently, reactor operators are faced with the so-called optimal fuel reloading problem, which consists of optimizing the rearrangement of all the assemblies, the old and fresh ones, while still maximizing the reactivity of the reactor core so as to maximise fuel burn-up and minimise fuel-cycle costs.

This is a discrete optimization problem, and computationally infeasible by current combinatorial methods, due to the huge number of permutations and the complexity of each computation. Many numerical methods have been proposed for solving it and many commercial software packages have been written to support fuel management. This is an ongoing issue in reactor operations as no definitive solution to this problem has been found. Operators use a combination of computational and empirical techniques to manage this problem.

The study of used fuel

Used nuclear fuel is studied in Post irradiation examination, where used fuel is examined to know more about the processes that occur in fuel during use, and how these might alter the outcome of an accident. For example, during normal use, the fuel expands due to thermal expansion, which can cause cracking. Most nuclear fuel is uranium dioxide, which is a cubic solid with a structure similar to that of calcium fluoride. In used fuel the solid state structure of most of the solid remains the same as that of pure cubic uranium dioxide. SIMFUEL is the name given to the simulated spent fuel which is made by mixing finely ground metal oxides, grinding as a slurry, spray drying it before heating in hydrogen/argon to 1700 °C. In SIMFUEL, 4.1% of the volume of the solid was in the form of metal nanoparticles which are made of molybdenum, ruthenium, rhodium and palladium. Most of these metal particles are of the ε phase (hexagonal) of Mo-Ru-Rh-Pd alloy, while smaller amounts of the α (cubic) and σ (tetragonal) phases of these metals were found in the SIMFUEL. Also present within the SIMFUEL was a cubic perovskite phase which is a barium strontium zirconate (Ba_xSr_1−xZrO₃).

The solid state structure of uranium dioxide, the oxygen atoms are in green and the uranium atoms in red

Uranium dioxide is very insoluble in water, but after oxidation it can be converted to uranium trioxide or another uranium(VI) compound which is much more soluble. Uranium dioxide (UO₂) can be oxidised to an oxygen rich hyperstoichiometric oxide (UO_2+x) which can be further oxidised to U₄O₉, U₃O₇, U₃O₈ and UO₃.2H₂O.

Because used fuel contains alpha emitters (plutonium and the minor actinides), the effect of adding an alpha emitter (²³⁸Pu) to uranium dioxide on the leaching rate of the oxide has been investigated. For the crushed oxide, adding ²³⁸Pu tended to increase the rate of leaching, but the difference in the leaching rate between 0.1 and 10% ²³⁸Pu was very small.

The concentration of carbonate in the water which is in contact with the used fuel has a considerable effect on the rate of corrosion, because uranium(VI) forms soluble anionic carbonate complexes such as [UO₂(CO₃)₂]²⁻ and [UO₂(CO₃)₃]⁴⁻. When carbonate ions are absent, and the water is not strongly acidic, the hexavalent uranium compounds which form on oxidation of uranium dioxide often form insoluble hydrated uranium trioxide phases.

Thin films of uranium dioxide can be deposited upon gold surfaces by ‘sputtering’ using uranium metal and an argon/oxygen gas mixture. These gold surfaces modified with uranium dioxide have been used for both cyclic voltammetry and AC impedance experiments, and these offer an insight into the likely leaching behaviour of uranium dioxide.

Fuel cladding interactions

The study of the nuclear fuel cycle includes the study of the behaviour of nuclear materials both under normal conditions and under accident conditions. For example, there has been much work on how uranium dioxide based fuel interacts with the zirconium alloy tubing used to cover it. During use, the fuel swells due to thermal expansion and then starts to react with the surface of the zirconium alloy, forming a new layer which contains both fuel and zirconium (from the cladding). Then, on the fuel side of this mixed layer, there is a layer of fuel which has a higher caesium to uranium ratio than most of the fuel. This is because xenon isotopes are formed as fission products that diffuse out of the lattice of the fuel into voids such as the narrow gap between the fuel and the cladding. After diffusing into these voids, it decays to caesium isotopes. Because of the thermal gradient which exists in the fuel during use, the volatile fission products tend to be driven from the centre of the pellet to the rim area. Below is a graph of the temperature of uranium metal, uranium nitride and uranium dioxide as a function of distance from the centre of a 20 mm diameter pellet with a rim temperature of 200 °C. The uranium dioxide (because of its poor thermal conductivity) will overheat at the centre of the pellet, while the other more thermally conductive forms of uranium remain below their melting points.

Temperature profile for a 20 mm diameter fuel pellet with a power density of 1 kW per cubic meter. The fuels other than uranium dioxide are not compromised.

Normal and abnormal conditions

The nuclear chemistry associated with the nuclear fuel cycle can be divided into two main areas; one area is concerned with operation under the intended conditions while the other area is concerned with maloperation conditions where some alteration from the normal operating conditions has occurred or (more rarely) an accident is occurring.

The releases of radioactivity from normal operations are the small planned releases from uranium ore processing, enrichment, power reactors, reprocessing plants and waste stores. These can be in different chemical/physical form from releases which could occur under accident conditions. In addition the isotope signature of a hypothetical accident may be very different from that of a planned normal operational discharge of radioactivity to the environment.

Just because a radioisotope is released it does not mean it will enter a human and then cause harm. For instance, the migration of radioactivity can be altered by the binding of the radioisotope to the surfaces of soil particles. For example, caesium (Cs) binds tightly to clay minerals such as illite and montmorillonite, hence it remains in the upper layers of soil where it can be accessed by plants with shallow roots (such as grass). Hence grass and mushrooms can carry a considerable amount of ¹³⁷Cs which can be transferred to humans through the food chain. But ¹³⁷Cs is not able to migrate quickly through most soils and thus is unlikely to contaminate well water. Colloids of soil minerals can migrate through soil so simple binding of a metal to the surfaces of soil particles does not completely fix the metal.

According to Jiří Hála's text book, the distribution coefficient K_d is the ratio of the soil's radioactivity (Bq g⁻¹) to that of the soil water (Bq ml⁻¹). If the radioisotope is tightly bound to the minerals in the soil, then less radioactivity can be absorbed by crops and grass growing on the soil.

Cs-137 K_d = 1000
Pu-239 K_d = 10000 to 100000
Sr-90 K_d = 80 to 150
I-131 K_d = 0.007 to 50

In dairy farming, one of the best countermeasures against ¹³⁷Cs is to mix up the soil by deeply ploughing the soil. This has the effect of putting the ¹³⁷Cs out of reach of the shallow roots of the grass, hence the level of radioactivity in the grass will be lowered. Also after a nuclear war or serious accident, the removal of top few cm of soil and its burial in a shallow trench will reduce the long-term gamma dose to humans due to ¹³⁷Cs, as the gamma photons will be attenuated by their passage through the soil.

Even after the radioactive element arrives at the roots of the plant, the metal may be rejected by the biochemistry of the plant. The details of the uptake of ⁹⁰Sr and ¹³⁷Cs into sunflowers grown under hydroponic conditions has been reported. The caesium was found in the leaf veins, in the stem and in the apical leaves. It was found that 12% of the caesium entered the plant, and 20% of the strontium. This paper also reports details of the effect of potassium, ammonium and calcium ions on the uptake of the radioisotopes.

In livestock farming, an important countermeasure against ¹³⁷Cs is to feed animals a small amount of Prussian blue. This iron potassium cyanide compound acts as an ion-exchanger. The cyanide is so tightly bonded to the iron that it is safe for a human to eat several grams of Prussian blue per day. The Prussian blue reduces the biological half-life (different from the nuclear half-life) of the caesium. The physical or nuclear half-life of ¹³⁷Cs is about 30 years. This is a constant which can not be changed but the biological half-life is not a constant. It will change according to the nature and habits of the organism for which it is expressed. Caesium in humans normally has a biological half-life of between one and four months. An added advantage of the Prussian blue is that the caesium which is stripped from the animal in the droppings is in a form which is not available to plants. Hence it prevents the caesium from being recycled. The form of Prussian blue required for the treatment of humans or animals is a special grade. Attempts to use the pigment grade used in paints have not been successful. Note that a good source of data on the subject of caesium in Chernobyl fallout exists at (Ukrainian Research Institute for Agricultural Radiology).

Release of radioactivity from fuel during normal use and accidents

The IAEA assume that under normal operation the coolant of a water-cooled reactor will contain some radioactivity but during a reactor accident the coolant radioactivity level may rise. The IAEA states that under a series of different conditions different amounts of the core inventory can be released from the fuel, the four conditions the IAEA consider are normal operation, a spike in coolant activity due to a sudden shutdown/loss of pressure (core remains covered with water), a cladding failure resulting in the release of the activity in the fuel/cladding gap (this could be due to the fuel being uncovered by the loss of water for 15–30 minutes where the cladding reached a temperature of 650–1250 °C) or a melting of the core (the fuel will have to be uncovered for at least 30 minutes, and the cladding would reach a temperature in excess of 1650 °C).

Based upon the assumption that a Pressurized water reactor contains 300 tons of water, and that the activity of the fuel of a 1 GWe reactor is as the IAEA predicts, then the coolant activity after an accident such as the Three Mile Island accident (where a core is uncovered and then recovered with water) can be predicted.

Releases from reprocessing under normal conditions

It is normal to allow used fuel to stand after the irradiation to allow the short-lived and radiotoxic iodine isotopes to decay away. In one experiment in the US, fresh fuel which had not been allowed to decay was reprocessed to investigate the effects of a large iodine release from the reprocessing of short cooled fuel. It is normal in reprocessing plants to scrub the off gases from the dissolver to prevent the emission of iodine. In addition to the emission of iodine the noble gases and tritium are released from the fuel when it is dissolved. It has been proposed that by voloxidation (heating the fuel in a furnace under oxidizing conditions) the majority of the tritium can be recovered from the fuel.

A paper was written on the radioactivity in oysters found in the Irish Sea. These were found by gamma spectroscopy to contain ¹⁴¹Ce, ¹⁴⁴Ce, ¹⁰³Ru, ¹⁰⁶Ru, ¹³⁷Cs, ⁹⁵Zr and ⁹⁵Nb. Additionally, a zinc activation product (⁶⁵Zn) was found, which is thought to be due to the corrosion of magnox fuel cladding in spent fuel pools. It is likely that the modern releases of all these isotopes from the Windscale event is smaller.

On-load reactors

Some reactor designs, such as RBMKs or CANDU reactors, can be refueled without being shut down. This is achieved through the use of many small pressure tubes to contain the fuel and coolant, as opposed to one large pressure vessel as in pressurized water reactor (PWR) or boiling water reactor (BWR) designs. Each tube can be individually isolated and refueled by an operator-controlled fueling machine, typically at a rate of up to 8 channels per day out of roughly 400 in CANDU reactors. On-load refueling allows for the optimal fuel reloading problem to be dealt with continuously, leading to more efficient use of fuel. This increase in efficiency is partially offset by the added complexity of having hundreds of pressure tubes and the fueling machines to service them.

Interim storage

After its operating cycle, the reactor is shut down for refueling. The fuel discharged at that time (spent fuel) is stored either at the reactor site (commonly in a spent fuel pool) or potentially in a common facility away from reactor sites. If on-site pool storage capacity is exceeded, it may be desirable to store the now cooled aged fuel in modular dry storage facilities known as Independent Spent Fuel Storage Installations (ISFSI) at the reactor site or at a facility away from the site. The spent fuel rods are usually stored in water or boric acid, which provides both cooling (the spent fuel continues to generate decay heat as a result of residual radioactive decay) and shielding to protect the environment from residual ionizing radiation, although after at least a year of cooling they may be moved to dry cask storage.

Transportation

Reprocessing

Spent fuel discharged from reactors contains appreciable quantities of fissile (U-235 and Pu-239), fertile (U-238), and other radioactive materials, including reaction poisons, which is why the fuel had to be removed. These fissile and fertile materials can be chemically separated and recovered from the spent fuel. The recovered uranium and plutonium can, if economic and institutional conditions permit, be recycled for use as nuclear fuel. This is currently not done for civilian spent nuclear fuel in the United States.

Mixed oxide, or MOX fuel, is a blend of reprocessed uranium and plutonium and depleted uranium which behaves similarly, although not identically, to the enriched uranium feed for which most nuclear reactors were designed. MOX fuel is an alternative to low-enriched uranium (LEU) fuel used in the light water reactors which predominate nuclear power generation.

Currently, plants in Europe are reprocessing spent fuel from utilities in Europe and Japan. Reprocessing of spent commercial-reactor nuclear fuel is currently not permitted in the United States due to the perceived danger of nuclear proliferation. The Bush Administration's Global Nuclear Energy Partnership proposed that the U.S. form an international partnership to see spent nuclear fuel reprocessed in a way that renders the plutonium in it usable for nuclear fuel but not for nuclear weapons.

Partitioning and transmutation

As an alternative to the disposal of the PUREX raffinate in glass or Synroc matrix, the most radiotoxic elements could be removed through advanced reprocessing. After separation, the minor actinides and some long-lived fission products could be converted to short-lived or stable isotopes by either neutron or photon irradiation. This is called transmutation. Strong and long-term international cooperation, and many decades of research and huge investments remain necessary before to reach a mature industrial scale where the safety and the economical feasibility of partitioning and transmutation (P&T) could be demonstrated.

Waste disposal

Actinides and fission products by half-life
Actinides by decay chain				Half-life range (a)	Fission products of ²³⁵U by yield
4n	4n+1	4n+2	4n+3		Fission products of ²³⁵U by yield
4n	4n+1	4n+2	4n+3			4.5–7%	0.04–1.25%	<0.001%
²²⁸Ra^№				4–6 a	†		¹⁵⁵Eu^þ
²⁴⁴Cm^ƒ	²⁴¹Pu^ƒ	²⁵⁰Cf	²²⁷Ac^№	10–29 a		⁹⁰Sr	⁸⁵Kr	^113mCd^þ
²³²U^ƒ		²³⁸Pu^ƒ	²⁴³Cm^ƒ	29–97 a		¹³⁷Cs	¹⁵¹Sm^þ	^121mSn
²⁴⁸Bk	²⁴⁹Cf^ƒ	^242mAm^ƒ		141–351 a	No fission products have a half-life in the range of 100–210 ka ...
	²⁴¹Am^ƒ		²⁵¹Cf^ƒ	430–900 a
		²²⁶Ra^№	²⁴⁷Bk	1.3–1.6 ka
²⁴⁰Pu	²²⁹Th	²⁴⁶Cm^ƒ	²⁴³Am^ƒ	4.7–7.4 ka
	²⁴⁵Cm^ƒ	²⁵⁰Cm		8.3–8.5 ka
			²³⁹Pu^ƒ	24.1 ka
		²³⁰Th^№	²³¹Pa^№	32–76 ka
²³⁶Np^ƒ	²³³U^ƒ	²³⁴U^№		150–250 ka	‡	⁹⁹Tc^₡	¹²⁶Sn
²⁴⁸Cm		²⁴²Pu		327–375 ka			⁷⁹Se^₡
				1.53 Ma		⁹³Zr
	²³⁷Np^ƒ			2.1–6.5 Ma		¹³⁵Cs^₡	¹⁰⁷Pd
²³⁶U			²⁴⁷Cm^ƒ	15–24 Ma			¹²⁹I^₡
²⁴⁴Pu				80 Ma	... nor beyond 15.7 Ma
²³²Th^№		²³⁸U^№	²³⁵U^ƒ№	0.7–14.1 Ga	... nor beyond 15.7 Ma
Legend for superscript symbols ₡ has thermal neutron capture cross section in the range of 8–50 barns ƒ fissile m metastable isomer № primarily a naturally occurring radioactive material (NORM) þ neutron poison (thermal neutron capture cross section greater than 3k barns) † range 4–97 a: Medium-lived fission product ‡ over 200 ka: Long-lived fission product

A current concern in the nuclear power field is the safe disposal and isolation of either spent fuel from reactors or, if the reprocessing option is used, wastes from reprocessing plants. These materials must be isolated from the biosphere until the radioactivity contained in them has diminished to a safe level.^[22] In the U.S., under the Nuclear Waste Policy Act of 1982 as amended, the Department of Energy has responsibility for the development of the waste disposal system for spent nuclear fuel and high-level radioactive waste. Current plans call for the ultimate disposal of the wastes in solid form in a licensed deep, stable geologic structure called a deep geological repository. The Department of Energy chose Yucca Mountain as the location for the repository. Its opening has been repeatedly delayed. Since 1999 thousands of nuclear waste shipments have been stored at the Waste Isolation Pilot Plant in New Mexico.

Fast-neutron reactors can fission all actinides, while the thorium fuel cycle produces low levels of transuranics. Unlike LWRs, in principle these fuel cycles could recycle their plutonium and minor actinides and leave only fission products and activation products as waste. The highly radioactive medium-lived fission products Cs-137 and Sr-90 diminish by a factor of 10 each century; while the long-lived fission products have relatively low radioactivity, often compared favorably to that of the original uranium ore.

Horizontal drillhole disposal describes proposals to drill over one kilometer vertically, and two kilometers horizontally in the earth’s crust, for the purpose of disposing of high-level waste forms such as spent nuclear fuel, Caesium-137, or Strontium-90. After the emplacement and the retrievability period, drillholes would be backfilled and sealed. A series of tests of the technology were carried out in November 2018 and then again publicly in January 2019 by a U.S. based private company. The test demonstrated the emplacement of a test-canister in a horizontal drillhole and retrieval of the same canister. There was no actual high-level waste used in this test.

Fuel cycles

Although the most common terminology is fuel cycle, some argue that the term fuel chain is more accurate, because the spent fuel is never fully recycled. Spent fuel includes fission products, which generally must be treated as waste, as well as uranium, plutonium, and other transuranic elements. Where plutonium is recycled, it is normally reused once in light water reactors, although fast reactors could lead to more complete recycling of plutonium.

Once-through nuclear fuel cycle

A once through (or open) fuel cycle

Not a cycle per se, fuel is used once and then sent to storage without further processing save additional packaging to provide for better isolation from the biosphere. This method is favored by six countries: the United States, Canada, Sweden, Finland, Spain and South Africa. Some countries, notably Finland, Sweden and Canada, have designed repositories to permit future recovery of the material should the need arise, while others plan for permanent sequestration in a geological repository like the Yucca Mountain nuclear waste repository in the United States.

Plutonium cycle

A fuel cycle in which plutonium is used for fuel

The integral fast reactor concept (color), with the reactor above and integrated pyroprocessing fuel cycle below. A more detailed animation and demonstration is available.

IFR concept (Black and White with clearer text)

Several countries, including Japan, Switzerland, and previously Spain and Germany, are using or have used the reprocessing services offered by BNFL and COGEMA. Here, the fission products, minor actinides, activation products, and reprocessed uranium are separated from the reactor-grade plutonium, which can then be fabricated into MOX fuel. Because the proportion of the non-fissile even-mass isotopes of plutonium rises with each pass through the cycle, there are currently no plans to reuse plutonium from used MOX fuel for a third pass in a thermal reactor. If fast reactors become available, they may be able to burn these, or almost any other actinide isotopes.

The use of a medium-scale reprocessing facility onsite, and the use of pyroprocessing rather than the present day aqueous reprocessing, is claimed to considerably reduce the proliferation potential or possible diversion of fissile material as the processing facility is in-situ/integral. Similarly as plutonium is not separated on its own in the pyroprocessing cycle, rather all actinides are "electro-won" or "refined" from the spent fuel, the plutonium is never separated on its own, instead it comes over into the new fuel mixed with gamma and alpha emitting actinides, species that "self-protect" it in numerous possible thief scenarios.

Beginning in 2016 Russia has been testing and is now deploying Remix Fuel in which the spent nuclear fuel is put through a process like Pyroprocessing that separates the reactor Grade Plutonium and remaining Uranium from the fission products and fuel cladding. This mixed metal is then combined with a small quantity of medium enriched Uranium with approximately 17% U-235 concentration to make a new combined metal oxide fuel with 1% Reactor Grade plutonium and a U-235 concentration of 4%. These fuel rods are suitable for use in standard PWR reactors as the Plutonium content is no higher than that which exists at the end of cycle in the spent nuclear fuel. As of February 2020 Russia was deploying this fuel in some of their fleet of VVER reactors.

Minor actinides recycling

It has been proposed that in addition to the use of plutonium, the minor actinides could be used in a critical power reactor. Tests are already being conducted in which americium is being used as a fuel.

A number of reactor designs, like the Integral Fast Reactor, have been designed for this rather different fuel cycle. In principle, it should be possible to derive energy from the fission of any actinide nucleus. With a careful reactor design, all the actinides in the fuel can be consumed, leaving only lighter elements with short half-lives. Whereas this has been done in prototype plants, no such reactor has ever been operated on a large scale.

It so happens that the neutron cross-section of many actinides decreases with increasing neutron energy, but the ratio of fission to simple activation (neutron capture) changes in favour of fission as the neutron energy increases. Thus with a sufficiently high neutron energy, it should be possible to destroy even curium without the generation of the transcurium metals. This could be very desirable as it would make it significantly easier to reprocess and handle the actinide fuel.

One promising alternative from this perspective is an accelerator-driven sub-critical reactor / subcritical reactor. Here a beam of either protons (United States and European designs) or electrons (Japanese design) is directed into a target. In the case of protons, very fast neutrons will spall off the target, while in the case of the electrons, very high energy photons will be generated. These high-energy neutrons and photons will then be able to cause the fission of the heavy actinides.

Such reactors compare very well to other neutron sources in terms of neutron energy:

Thermal 0 to 100 eV
Epithermal 100 eV to 100 keV
Fast (from nuclear fission) 100 keV to 3 MeV
DD fusion 2.5 MeV
DT fusion 14 MeV
Accelerator driven core 200 MeV (lead driven by 1.6 GeV protons)
Muon-catalyzed fusion 7 GeV.

As an alternative, the curium-244, with a half-life of 18 years, could be left to decay into plutonium-240 before being used in fuel in a fast reactor.

A pair of fuel cycles in which uranium and plutonium are kept separate from the minor actinides.

The minor actinide cycle is kept within the green box.

Fuel or targets for this actinide transmutation

To date the nature of the fuel (targets) for actinide transformation has not been chosen.

If actinides are transmuted in a Subcritical reactor, it is likely that the fuel will have to be able to tolerate more thermal cycles than conventional fuel. An accelerator-driven sub-critical reactor is unlikely to be able to maintain a constant operation period for equally long times as a critical reactor, and each time the accelerator stops then the fuel will cool down.

On the other hand, if actinides are destroyed using a fast reactor, such as an Integral Fast Reactor, then the fuel will most likely not be exposed to many more thermal cycles than in a normal power station.

Depending on the matrix the process can generate more transuranics from the matrix. This could either be viewed as good (generate more fuel) or can be viewed as bad (generation of more radiotoxic transuranic elements). A series of different matrices exists which can control this production of heavy actinides.

Fissile nuclei (such as ²³³U, ²³⁵U, and ²³⁹Pu) respond well to delayed neutrons and are thus important to keep a critical reactor stable; this limits the amount of minor actinides that can be destroyed in a critical reactor. As a consequence, it is important that the chosen matrix allows the reactor to keep the ratio of fissile to non-fissile nuclei high, as this enables it to destroy the long-lived actinides safely. In contrast, the power output of a sub-critical reactor is limited by the intensity of the driving particle accelerator, and thus it need not contain any uranium or plutonium at all. In such a system, it may be preferable to have an inert matrix that does not produce additional long-lived isotopes.

Actinides in an inert matrix

The actinides will be mixed with a metal which will not form more actinides; for instance, an alloy of actinides in a solid such as zirconia could be used.

The raison d’être of the Initiative for Inert Matrix Fuel (IMF) is to contribute to Research and Development studies on inert matrix fuels that could be used to utilise, reduce and dispose both weapon- and light water reactor-grade plutonium excesses. In addition to plutonium, the amounts of minor actinides are also increasing. These actinides have to be consequently disposed in a safe, ecological and economical way. The promising strategy that consists of utilising plutonium and minor actinides using a once-through fuel approach within existing commercial nuclear power reactors e.g. US, European, Russian or Japanese Light Water Reactors (LWR), Canadian Pressured Heavy Water Reactors, or in future transmutation units, has been emphasised since the beginning of the initiative. The approach, which makes use of inert matrix fuel is now studied by several groups in the world. This option has the advantage of reducing the plutonium amounts and potentially minor actinide contents prior to geological disposal. The second option is based on using a uranium-free fuel leachable for reprocessing and by following a multi-recycling strategy. In both cases, the advanced fuel material produces energy while consuming plutonium or the minor actinides. This material must, however, be robust. The selected material must be the result of a careful system study including inert matrix – burnable absorbent – fissile material as minimum components and with the addition of stabiliser. This yields a single-phase solid solution or more simply if this option is not selected a composite inert matrix–fissile component. In screening studies e.g. pre-selected elements were identified as suitable. In the 90s an IMF once through strategy was adopted considering the following properties: • neutron properties i.e. low absorption cross-section, optimal constant reactivity, suitable Doppler coefficient e.g., • phase stability, chemical inertness, and compatibility e.g., • acceptable thermo-physical properties i.e. heat capacity, thermal conductivity e.g., • good behaviour under irradiation i.e. phase stability, minimum swelling e.g. , • retention of fission products or residual actinides e.g., • optimal properties after irradiation with insolubility for once through then out e.g. This once through then out strategy may be adapted as a last cycle after multi-recycling if the fission yield is not large enough, in which case the following property is required good leaching properties for reprocessing and multi-recycling.

Actinides in a thorium matrix

Upon neutron bombardment, thorium can be converted to uranium-233. ²³³U is fissile, and has a larger fission cross section than both ²³⁵U and ²³⁸U, and thus it is far less likely to produce higher actinides through neutron capture.

Actinides in a uranium matrix

If the actinides are incorporated into a uranium-metal or uranium-oxide matrix, then the neutron capture of ²³⁸U is likely to generate new plutonium-239. An advantage of mixing the actinides with uranium and plutonium is that the large fission cross sections of ²³⁵U and ²³⁹Pu for the less energetic delayed neutrons could make the reaction stable enough to be carried out in a critical fast reactor, which is likely to be both cheaper and simpler than an accelerator driven system.

Mixed matrix

It is also possible to create a matrix made from a mix of the above-mentioned materials. This is most commonly done in fast reactors where one may wish to keep the breeding ratio of new fuel high enough to keep powering the reactor, but still low enough that the generated actinides can be safely destroyed without transporting them to another site. One way to do this is to use fuel where actinides and uranium is mixed with inert zirconium, producing fuel elements with the desired properties.

Uranium cycle in renewable mode

To fulfill the conditions required for a nuclear renewable energy concept, one has to explore a combination of processes going from the front end of the nuclear fuel cycle to the fuel production and the energy conversion using specific fluid fuels and reactors, as reported by Degueldre et al (2019). Extraction of uranium from a diluted fluid ore such as seawater has been studied in various countries worldwide. This extraction should be carried out parsimoniously, as suggested by Degueldre (2017). An extraction rate of kilotons of U per year over centuries would not modify significantly the equilibrium concentration of uranium in the oceans (3.3 ppb). This equilibrium results from the input of 10 kilotons of U per year by river waters and its scavenging on the sea floor from the 1.37 exatons of water in the oceans. For a renewable uranium extraction, the use of a specific biomass material is suggested to adsorb uranium and subsequently other transition metals. The uranium loading on the biomass would be around 100 mg per kg. After contact time, the loaded material would be dried and burned (CO2 neutral) with heat conversion into electricity. The uranium ‘burning’ in a molten salt fast reactor helps to optimize the energy conversion by burning all actinide isotopes with an excellent yield for producing a maximum amount of thermal energy from fission and converting it into electricity. This optimisation can be reached by reducing the moderation and the fission product concentration in the liquid fuel/coolant. These effects can be achieved by using a maximum amount of actinides and a minimum amount of alkaline/earth alkaline elements yielding a harder neutron spectrum. Under these optimal conditions the consumption of natural uranium would be 7 tons per year and per gigawatt (GW) of produced electricity. The coupling of uranium extraction from the sea and its optimal utilisation in a molten salt fast reactor should allow nuclear energy to gain the label renewable. In addition, the amount of seawater used by a nuclear power plant to cool the last coolant fluid and the turbine would be ∼2.1 giga tons per year for a fast molten salt reactor, corresponding to 7 tons of natural uranium extractable per year. This practice justifies the label renewable.

Thorium cycle

In the thorium fuel cycle thorium-232 absorbs a neutron in either a fast or thermal reactor. The thorium-233 beta decays to protactinium-233 and then to uranium-233, which in turn is used as fuel. Hence, like uranium-238, thorium-232 is a fertile material.

{\displaystyle {\ce {{\overset {neutron}{n}}+ ^{232}_{90}Th -> ^{233}_{90}Th ->[\beta^-] ^{233}_{91}Pa ->[\beta^-] {\overset {fuel}{^{233}_{92}U}}}}}

After starting the reactor with existing U-233 or some other fissile material such as U-235 or Pu-239, a breeding cycle similar to but more efficient than that with U-238 and plutonium can be created. The Th-232 absorbs a neutron to become Th-233 which quickly decays to protactinium-233.

Protactinium-233 in turn decays with a half-life of 27 days to U-233. In some molten salt reactor designs, the Pa-233 is extracted and protected from neutrons (which could transform it to Pa-234 and then to U-234), until it has decayed to U-233. This is done in order to improve the breeding ratio which is low compared to fast reactors.

Thorium is at least 4-5 times more abundant in nature than all of uranium isotopes combined; thorium is fairly evenly spread around Earth with a lot of countries having huge supplies of it; preparation of thorium fuel does not require difficult and expensive enrichment processes; the thorium fuel cycle creates mainly Uranium-233 contaminated with Uranium-232 which makes it harder to use in a normal, pre-assembled nuclear weapon which is stable over long periods of time (unfortunately drawbacks are much lower for immediate use weapons or where final assembly occurs just prior to usage time); elimination of at least the transuranic portion of the nuclear waste problem is possible in MSR and other breeder reactor designs.

One of the earliest efforts to use a thorium fuel cycle took place at Oak Ridge National Laboratory in the 1960s. An experimental reactor was built based on molten salt reactor technology to study the feasibility of such an approach, using thorium fluoride salt kept hot enough to be liquid, thus eliminating the need for fabricating fuel elements. This effort culminated in the Molten-Salt Reactor Experiment that used ²³²Th as the fertile material and ²³³U as the fissile fuel. Due to a lack of funding, the MSR program was discontinued in 1976.

Thorium was first used commercially in the Indian Point Unit 1 reactor which began operation in 1962. The cost of recovering U-233 from the spent fuel was deemed uneconomical, since less than 1% of the thorium was converted to U-233. The plant's owner switched to uranium fuel, which was used until the reactor was permanently shut down in 1974.

Current industrial activity

Currently the only isotopes used as nuclear fuel are uranium-235 (U-235), uranium-238 (U-238) and plutonium-239, although the proposed thorium fuel cycle has advantages. Some modern reactors, with minor modifications, can use thorium. Thorium is approximately three times more abundant in the Earth's crust than uranium (and 550 times more abundant than uranium-235). There has been little exploration for thorium resources, and thus the proved resource is small. Thorium is more plentiful than uranium in some countries, notably India.

Heavy water reactors and graphite-moderated reactors can use natural uranium, but the vast majority of the world's reactors require enriched uranium, in which the ratio of U-235 to U-238 is increased. In civilian reactors, the enrichment is increased to 3-5% U-235 and 95% U-238, but in naval reactors there is as much as 93% U-235.

The term nuclear fuel is not normally used in respect to fusion power, which fuses isotopes of hydrogen into helium to release energy.

Renewable portfolio standard

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Renewable_portfolio_standard

A renewable portfolio standard (RPS) is a regulation that requires the increased production of energy from renewable energy sources, such as wind, solar, biomass, and geothermal. Other common names for the same concept include Renewable Electricity Standard (RES) at the United States federal level and Renewables Obligation in the UK.

The RPS mechanism places an obligation on electricity supply companies to produce a specified fraction of their electricity from renewable energy sources. Certified renewable energy generators earn certificates for every unit of electricity they produce and can sell these along with their electricity to supply companies. Supply companies then pass the certificates to some form of regulatory body to demonstrate their compliance with their regulatory obligations. RPS can rely on the private market for its implementation. In jurisdictions such as California, minimum RPS requirements are legislated. California Senate Bill 350 passed in October 2015 requires retail sellers and publicly owned utilities to procure 50 percent of their electricity from eligible renewable energy resources by 2030. RPS programs tend to allow more price competition between different types of renewable energy, but can be limited in competition through eligibility and multipliers for RPS programs. Those supporting the adoption of RPS mechanisms claim that market implementation will result in competition, efficiency, and innovation that will deliver renewable energy at the lowest possible cost, allowing renewable energy to compete with cheaper fossil fuel energy sources.

RPS-type mechanisms have been adopted in several countries, including the United Kingdom, Italy, Poland, Sweden, Belgium, and Chile, as well as in 29 of 50 U.S. states, and the District of Columbia.

Policy by country

China

China adopted a renewable energy target in 2006 and modified it in 2009 to the following targets:

Renewable electricity – 500 GW by 2020 (300 from hydro, 150 from wind, 30 from biomass, and 20 from solar PV)
Renewable energy – 15% by 2020 (15% non-fossil fuel, which includes nuclear)

European Union

The European Union passed the Directive on Electricity Production from Renewable Energy Sources in 2001 and expanded it in 2007 to the following EU-wide targets (although member states are free to pass more aggressive targets):

Renewable electricity – 33% by 2020
Renewable energy – 20% by 2020

Germany

The German Renewable Energy Act, since its adoption in 2000, is producing strong growth in renewable power capacity by encouraging private investors through guaranteed Feed-in tariffs. Germany adopted targets more aggressive than the EU mandated targets in September 2010:

Renewable electricity – 35% by 2020 and 80% by 2050
Renewable energy – 18% by 2020, 30% by 2030, and 60% by 2050

Japan

Based on the 1997 Act on the Promotion of New Energy Usage, 118 million KWh was targeted in 2012 (METI).

Republic of Korea

The Republic of Korea adopted the Act on the Promotion of the Development, Use, and Diffusion of New and Renewable Energy since 2012.

United Kingdom

The Renewables Obligation (RO) is designed to encourage generation of electricity from eligible renewable sources in the United Kingdom. It was introduced in England and Wales and in a different form (the Renewables Obligation (Scotland)) in Scotland in April 2002 and in Northern Ireland in April 2005, replacing the Non-Fossil Fuel Obligation which operated from 1990.

The RO places an obligation on licensed electricity suppliers in the United Kingdom to source an increasing proportion of electricity from renewable sources, similar to a renewable portfolio standard. In 2010/11 it is 11.1% (4.0% in Northern Ireland). This figure was initially set at 3% for the period 2002/03 and under current political commitments will rise to 15.4% (6.3% in Northern Ireland) by the period 2015/16 and then it runs until 2037 (2033 in Northern Ireland). The extension of the scheme from 2027 to 2037 was declared on 1 April 2010 and is detailed in the National Renewable Energy Action Plan. Since its introduction the RO has more than tripled the level of eligible renewable electricity generation (from 1.8%^{[citation needed]} of total UK supply to 7.0% in 2010).

United States

Selected state renewable portfolio standards with 2018 revisions. 29 states have adopted policies targeting a percentage of their energy to come from renewable sources.

The Public Utility Regulatory Policies Act is a law, passed in 1978 by the United States Congress as part of the National Energy Act. It was meant to promote greater use of renewable energy.

In 2009, the US Congress considered Federal level RPS requirements. The American Clean Energy and Security Act reported out of committee in July by the Senate Committee on Energy & Natural Resources includes a Renewable Electricity Standard that called for 3% of U.S. electrical generation to come from non-hydro renewables by 2013, but the full Senate did not pass the bill.

Different state RPS programs issue a different number of Renewable Energy Credits depending on the generation technology; for example, solar generation counts for twice as much as other renewable sources in Michigan and Virginia.

The Lawrence Berkeley National Laboratory claims that RPS requirements were responsible for 60% of the total increase in American renewable electricity generation since the year 2000. However, the LBNL also reports that RPSs' role has been declining in recent years from 71% of the annual American renewables builds in the year 2013 to 46% just two years later, in 2015.

Nuclear power proposed as renewable energy

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Nuclear_power_proposed_as_renewable_energy

Whether nuclear power should be considered a form of renewable energy is an ongoing subject of debate. Statutory definitions of renewable energy usually exclude many present nuclear energy technologies, with the notable exception of the state of Utah. Dictionary-sourced definitions of renewable energy technologies often omit or explicitly exclude mention of nuclear energy sources, with an exception made for the natural nuclear decay heat generated within the Earth.

The most common fuel used in conventional nuclear fission power stations, uranium-235 is "non-renewable" according to the Energy Information Administration, the organization however is silent on the recycled MOX fuel. Similarly, the National Renewable Energy Laboratory does not mention nuclear power in its "energy basics" definition.

In 1987, the Brundtland Commission (WCED) classified fission reactors that produce more fissile nuclear fuel than they consume (breeder reactors, and if developed, fusion power) among conventional renewable energy sources, such as solar power and hydropower. The American Petroleum Institute does not consider conventional nuclear fission renewable, but considers breeder reactor nuclear fuel renewable and sustainable, and while conventional fission leads to waste streams that remain a concern for millennia, the waste from efficiently recycled spent fuel requires a more limited storage supervision period of about thousand years. The monitoring and storage of radioactive waste products is also required upon the use of other renewable energy sources, such as geothermal energy.

Definitions of renewable energy

Renewable energy flows involve natural phenomena, which with the exception of tidal power, ultimately derive their energy from the sun (a natural fusion reactor) or from geothermal energy, which is heat derived in greatest part from that which is generated in the earth from the decay of radioactive isotopes, as the International Energy Agency explains:

Renewable energy is derived from natural processes that are replenished constantly. In its various forms, it derives directly from the sun, or from heat generated deep within the earth. Included in the definition is electricity and heat generated from sunlight, wind, oceans, hydropower, biomass, geothermal resources, and biofuels and hydrogen derived from renewable resources.

Renewable energy resources exist over wide geographical areas, in contrast to other energy sources, which are concentrated in a limited number of countries.

In ISO 13602-1:2002, a renewable resource is defined as "a natural resource for which the ratio of the creation of the natural resource to the output of that resource from nature to the technosphere is equal to or greater than one".

Conventional fission, breeder reactors as renewable

Nuclear fission reactors are a natural energy phenomenon, having naturally formed on earth in times past, for example a natural nuclear fission reactor which ran for thousands of years in present-day Oklo Gabon was discovered in the 1970s. It ran for a few hundred thousand years, averaging 100 kW of thermal power during that time.

Conventional, human manufactured, nuclear fission power stations largely use uranium, a common metal found in seawater, and in rocks all over the world, as its primary source of fuel. Uranium-235 "burnt" in conventional reactors, without fuel recycling, is a non-renewable resource, and if used at present rates would eventually be exhausted.

A cutaway model of the 2nd most powerful presently operating fast breeder reactor in the world. The (BN-600), at 600 MW of nameplate capacity is equivalent in power output to a natural gas CCGT. It dispatches 560 MW to the Middle Urals power grid. Construction of a second breeder reactor, the BN-800 reactor was completed in 2014.

This is also somewhat similar to the situation with a commonly classified renewable source, geothermal energy, a form of energy derived from the natural nuclear decay of the large, but nonetheless finite supply of uranium, thorium and potassium-40 present within the Earth's crust, and due to the nuclear decay process, this renewable energy source will also eventually run out of fuel. As too will the Sun, and be exhausted.

Nuclear fission involving breeder reactors, a reactor which breeds more fissile fuel than they consume and thereby has a breeding ratio for fissile fuel higher than 1 thus has a stronger case for being considered a renewable resource than conventional fission reactors. Breeder reactors would constantly replenish the available supply of nuclear fuel by converting fertile materials, such as uranium-238 and thorium, into fissile isotopes of plutonium or uranium-233, respectively. Fertile materials are also nonrenewable, but their supply on Earth is extremely large, with a supply timeline greater than geothermal energy. In a closed nuclear fuel cycle utilizing breeder reactors, nuclear fuel could therefore be considered renewable.

In 1983, physicist Bernard Cohen claimed that fast breeder reactors, fueled exclusively by natural uranium extracted from seawater, could supply energy at least as long as the sun's expected remaining lifespan of five billion years. This was based on calculations involving the geological cycles of erosion, subduction, and uplift, leading to humans consuming half of the total uranium in the Earth's crust at an annual usage rate of 6500 tonne/yr, which was enough to produce approximately 10 times the world's 1983 electricity consumption, and would reduce the concentration of uranium in the seas by 25%, resulting in an increase in the price of uranium of less than 25%.

Proportions of the isotopes, U-238 (blue) and U-235 (red) found in natural uranium, versus grades that are enriched. light water reactors and the natural uranium capable CANDU reactors, are primarily powered only by the U-235 component, failing to extract much energy from U-238. While by contrast uranium breeder reactors mostly use U-238/the primary constituent of natural uranium as their fuel.

Advancements at Oak Ridge National Laboratory and the University of Alabama, as published in a 2012 issue of the American Chemical Society, towards the extraction of uranium from seawater have focused on increasing the biodegradability of the process and reducing the projected cost of the metal if it was extracted from the sea on an industrial scale. The researchers' improvements include using electrospun Shrimp shell Chitin mats that are more effective at absorbing uranium when compared to the prior record setting Japanese method of using plastic amidoxime nets. As of 2013 only a few kilograms (picture available) of uranium have been extracted from the ocean in pilot programs and it is also believed that the uranium extracted on an industrial scale from the seawater would constantly be replenished from uranium leached from the ocean floor, maintaining the seawater concentration at a stable level. In 2014, with the advances made in the efficiency of seawater uranium extraction, a paper in the journal of Marine Science & Engineering suggests that with, light water reactors as its target, the process would be economically competitive if implemented on a large scale. In 2016 the global effort in the field of research was the subject of a special issue in the journal of Industrial & Engineering Chemistry Research.

In 1987, the World Commission on Environment and Development(WCED), an organization independent from, but created by, the United Nations, published Our Common Future, in which a particular subset of presently operating nuclear fission technologies, and nuclear fusion were both classified as renewable. That is, fission reactors that produce more fissile fuel than they consume - breeder reactors, and when it is developed, fusion power, are both classified within the same category as conventional renewable energy sources, such as solar and falling water.

Presently, as of 2014, only 2 breeder reactors are producing industrial quantities of electricity, the BN-600 and BN-800. The retired French Phénix reactor also demonstrated a greater than one breeding ratio and operated for ~30 years, producing power when Our Common Future was published in 1987.

Fusion fuel supply

If it is developed, fusion power would provide more energy for a given weight of fuel than any fuel-consuming energy source currently in use, and the fuel itself (primarily deuterium) exists abundantly in the Earth's ocean: about 1 in 6500 hydrogen (H) atoms in seawater (H₂O) is deuterium in the form of (semi-heavy water). Although this may seem a low proportion (about 0.015%), because nuclear fusion reactions are so much more energetic than chemical combustion and seawater is easier to access and more plentiful than fossil fuels, fusion could potentially supply the world's energy needs for millions of years.

In the deuterium + lithium fusion fuel cycle, 60 million years is the estimated supply lifespan of this fusion power, if it is possible to extract all the lithium from seawater, assuming current (2004) world energy consumption. While in the second easiest fusion power fuel cycle, the deuterium + deuterium burn, assuming all of the deuterium in seawater was extracted and used, there is an estimated 150 billion years of fuel, with this again, assuming current (2004) world energy consumption.

Legislation in the United States

If nuclear power were classified as renewable energy (or as low-carbon energy), additional government support would be available in more jurisdictions, and utilities could include nuclear power in their effort to comply with Renewable portfolio standard (RES).

In 2009 the State of Utah passed the "Renewable Energy Development Act" which in part defined nuclear power as a form of renewable energy.

Sunday, April 4, 2021

Carbon bubble

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Carbon_bubble

Carbon Bubble according to data by the Carbon Tracker Initiative (2013)

The carbon bubble is a hypothesized bubble in the valuation of companies dependent on fossil-fuel-based energy production, because the true costs of carbon dioxide in intensifying global warming are not yet taken into account in a company's stock market valuation.Currently the price of fossil fuels companies' shares is calculated under the assumption that all fossil fuel reserves will be consumed. An estimate made by Kepler Chevreux puts the loss in value of the fossil fuel companies due to the impact of the growing renewables industry at US$28 trillion over the next two decades-long. A more recent analysis made by Citi puts that figure at $100 trillion.

Analysts in both the petroleum and financial industries are concluding that the "age of oil" has already reached a new stage where the excess supply that appeared in late 2014 may continue to prevail in the future. A consensus appears to be emerging that an international agreement will be reached to introduce measures to constrain the combustion of hydrocarbons in an effort to limit global temperature rise to the nominal 2 °C that is consensually predicted to limit environmental harm to tolerable levels.

According to the UK's Committee on Climate Change, overvaluing companies that produce fossil fuels and greenhouse gases poses a serious threat to the economy. The committee warned the British government and Bank of England of the risks of the carbon bubble in 2014. The following year, Mark Carney, the Governor of the Bank of England, in his lecture to Lloyd's of London, warned that limiting global warming to 2 °C appears to require that the "vast majority" of fossil fuel reserves be "stranded assets", or "literally unburnable without expensive carbon-capture technology", resulting in "potentially huge" exposure to investors in that sector. He concluded that "the window of opportunity is finite and shrinking" for responding to the threat that climate change poses to financial resilience and longer-term prosperity, which he called the "tragedy of the horizon". That same month, the Prudential Regulation Authority of the Bank of England issued a report discussing the risks and opportunities that climate change presents to the insurance industry.

In his speech announcing his denial of the proposal to build the Keystone XL oil pipeline, United States President Barack Obama gave as one reason for the decision "... ultimately, if we're going to prevent large parts of this Earth from becoming not only inhospitable but uninhabitable in our lifetimes, we're going to have to keep some fossil fuels in the ground...".

Etymology

The term "carbon bubble" arose in the early 21st century from the increasing awareness of the impact of fossil fuel combustion on global temperatures. The term was coined by the Carbon Tracker Initiative which published key reports in July 2011 and April 2013. and it was further popularised in the New Scientist magazine in October 2011. A widely shared article by Bill McKibben was published in Rolling Stone magazine in July 2012, bringing the idea to the attention of a popular audience. These were followed later in 2013 by a report from the Demos think tank.

Value

Author Bill McKibben has estimated that to sustain human life in the world, up to $20 trillion worth of fossil fuel reserves will need to remain in the ground. The Stern report in 2006 stated that the benefits of strong, early action to decrease the use of oil, coal and gas considerably outweigh the costs. Fossil fuel contributors, the building industry, and land use practices ignore the responsibility of the external costs and ignore the polluter pays principle according to which climate change costs will be paid by historical climate polluters.

Prospects for orderly bubble deflation

A planned and orderly transition away from dependence on fossil fuels could prevent a disruptive "bursting of the carbon bubble". A number of developments are supporting such a transition.

Government action on climate change

A detailed academic study of the consequences for the producers of the various hydrocarbon fuels concluded in early 2015 that a third of global oil reserves, half of gas reserves and over 80% of current coal reserves should remain underground from 2010 to 2050 in order to meet the target of no more than a 2 °C rise in average global temperature. Hence continued exploration or development of reserves would be extraneous to needs. To meet the 2 °C target, strong measures would be needed to suppress demand, such as a substantial carbon tax leaving a lower price for the producers from a smaller market. The impact on producers would vary widely depending on the cost of production in their areas of operation. For example, the impact in Canada would be far larger than in the United States. Open-pit mining of bituminous sands in Canada would soon drop to negligible levels after 2020 in all scenarios considered because it is considerably less economic than other methods of production.

In mid-2015, the Centre for Science and Policy, University of Cambridge published a report assessing the risks from climate change in order to estimate the amount of resources that should be allocated to address them. The report notes that "standard economic estimates of the global costs of climate change are wildly sensitive both to assumptions about the science, and to judgments about the value of human life. They are also likely to be systematically biased towards underestimation of risk, as they tend to omit a wide range of impacts that are difficult to quantify".

Awareness in the financial industry

By 2013, there was significant awareness in the financial industry of the risks associated with exposure to companies involved in extraction of fossil fuels. In early 2014, the FTSE Group, BlackRock and the Natural Resources Defense Council collaborated in the creation of a stock market index series that excludes companies linked to exploration, ownership or extraction of carbon-based fossil fuel reserves. These indices are intended to make it easier for investors to steer their investments away from such companies. It has been proposed that companies be required by law to report on their greenhouse gas emissions and assess the risk this could pose to their future financial performance. According to Christiana Figueres, UNFCCC, companies have a duty to shareholders to move to a low-carbon economy, because of the effects of the carbon bubble.

Inflatable carbon bubble asking the Swiss National Bank to divest from fossil fuels (2019).

Divestment campaigning

The ongoing fossil fuels divestment campaign in universities, churches and pension funds contributes to divestiture from fossil fuel companies. By late 2015, this divestiture was reported to reach $2.6 trillion, by September 2019, total divestment commitments had grown to an approximate value of $11.48 trillion.

In September 2019, when the University of California announced, it will divest its $83 billion in endowment and pension funds from the fossil fuel industry, UC officials said, they made it for financial reasons: "We believe hanging on to fossil fuel assets is a financial risk."

Cheaper clean energy

The price of renewable energy is continually dropping. As of 2014 new wind power is cheaper than new coal and gas power in Australia, China and the United States. Also the electricity produced from a photovoltaic roof system is cheaper than the electricity from the grid in many countries and places in the world.

Real pollution control

Fossil fuels are known for their huge negative externalities or hidden costs. Tackling this market failure will make alternative energies more competitive and will reduce the consumption of fossil fuels.

Cancellation of government energy subsidies

According to the International Monetary Fund, governments around the world gave $523 billion direct subsidies for fossil fuels in 2011. If a carbon tax of $25 per ton of CO
2 is included the subsidies total $1.9 trillion only for 2011. Removing fossil fuels subsidies will further reduce their consumption and make the alternative energies even more competitive.

Renewable corporations lobbying

As the penetration of the renewable energy increases so will the wealth of the renewable energy corporations. This and the increasing number of employees in the renewable energy sector will inevitably transform into political lobbying against fossil fuels.

Urbanization and Electric transportation

Urbanization combined with increasing availability of convenient, safe and efficient public transport, green buildings and efficient energy distribution, as well as extended product life/use/re-use, increased local recycling and self-sustainability in raw materials drive down energy consumption. Perversely, ready access to travel and luxury, more batteries (energy storage and conversion losses) and proliferation of low cost LED technology, e.g. for advertising and decorative uses, may negate some of the potential energy savings. Switching to renewables sourced, electricity based transportation will reduce the demand for fossil fuels, particularly petroleum. Combining roof photovoltaics with second hand EV batteries will further reduce the dependence on fossil fuels as they will provide the needed grid storage for the times when the intermittent renewable energy sources are not producing electricity.

Innovation and Efficiency

Innovations in, for example, information technology, miniaturisation, LEDs, virtual reality, 3D printing, new materials and biotechnology enable energy reduction in the areas of human sustenance and travel, as well as physical product creation and distribution. They also offer new avenues for economic growth and technological leadership, and are thus especially important for sustained wealth creation in the most developed, net-energy importing nations. Energy consumption may be expected to decrease as the service sector of the economy continues to grow whilst heavy industry, construction, manufacturing and agricultural sectors reduce. Increased investments in energy efficiency may lead to less consumed energy even when the economy grows. Without growth in energy usage the prices of fossil fuels will decrease and most of the mega energy projects may be uneconomical.

Demographics and Changes in consumer behavior

A shrinking and ageing, already materially prosperous, satisfied and individualistic society may be less motivated towards additional, energy consuming material goods and new construction. On the other hand, longer life expectancy and increasing leisure and travel time will increase total energy use over an individual's lifetime. According to research by U.S. PIRG Education Fund reported in late 2014: "Over the last decade – after 60-plus years of steady increases – the number of miles driven by the average American has been falling. Young Americans have experienced the greatest changes: driving less; taking public transport, biking and walking more; and seeking out places to live in cities and walkable communities where driving is an option, not a necessity." Data from the U.S. Energy Information Administration show that U.S. consumption of both coal and petroleum liquids peaked in 2005, and at the end of 2014 had fallen by 21% and 13% respectively. Consumption of natural gas continued to climb, resulting in the rate of total fossil fuel consumption in terms of energy units falling only 6% from its peak in 2007 to a plateau. On the other hand, global consumption of petroleum climbed steadily a total of 32% from 1995 to 2014.

Media coverage of climate change

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Media_coverage_of_climate_change

Global warming was the cover story of this 2007 issue of the liberal-leaning feminist Ms. magazine

Media coverage of climate change has had effects on public opinion on climate change, as it mediates the scientific opinion on climate change that the global temperature has increased in recent decades and that the trend is mainly caused by human-induced emissions of greenhouse gases. Almost all scientific bodies of national or international standing agree with this view, although a few organisations hold non-committal positions.

Climate change communication research frequently studies the effectiveness of that media. Some researchers and journalists believe that media coverage of political issues is adequate and fair, while a few feel that it is biased. However, most studies on media coverage of the topic are neither recent nor concerned with coverage of environmental issues. Moreover, they are only rarely concerned specifically with the question of bias.

Despite recent trends in increased coverage on climate change, media coverage is not constant, and researchers wonder if the current increase in attention will be sustained.

History

Media attention is especially high in carbon dependent countries with commitments under the Kyoto Protocol. The way the media report on climate change in English-speaking countries, especially in the United States, has been widely studied, while studies of reporting in other countries have been less expansive. A number of studies have shown that particularly in the United States and in the UK tabloid press, the media significantly understated the strength of scientific consensus on climate change established in IPCC Assessment Reports in 1995 and in 2001.

A peak in media coverage occurred in early 2007, driven by the IPCC Fourth Assessment Report and Al Gore's documentary An Inconvenient Truth. A subsequent peak in late 2009, which was 50% higher, may have been driven by a combination of the November 2009 Climatic Research Unit email controversy and December 2009 United Nations Climate Change Conference.

The Media and Climate Change Observatory team at the University of Colorado Boulder found that 2017 “saw media attention to climate change and global warming ebb and flow” with June seeing the maximum global media coverage on both subjects. This rise is “largely attributed to news surrounding United States (US) President Donald J. Trump’s withdrawal from the 2015 United Nations (UN) Paris Climate Agreement, with continuing media attention paid to the emergent US isolation following through the G7 summit a few weeks later.”

Common distortions

Factual

Bord et al. claim that a substantial portion of the United States public has a flawed understanding of global warming, seeing it as linked to general "pollution" and causally connected in some way to atmospheric ozone depletion. Scientists and media scholars who express frustrations with inadequate science reporting argue that it can lead to at least three basic distortions. First, journalists distort reality by making scientific errors. Second, they distort by keying on human-interest stories rather than scientific content. And third, journalists distort by rigid adherence to the construct of balanced coverage. Bord, O’Connor, & Fisher (2000) argue that responsible citizenry necessitates a concrete knowledge of causes and that until, for example, the public understands what causes climate change it cannot be expected to take voluntary action to mitigate its effects.

Narrative

According to Shoemaker and Reese, controversy is one of the main variables affecting story choice among news editors, along with human interest, prominence, timeliness, celebrity, and proximity. Coverage of climate change has been accused of falling victim to the journalistic norm of "personalization". W.L Bennet defines this trait as: "the tendency to downplay the big social, economic, or political picture in favor of human trials, tragedies and triumphs" The culture of political journalism has long used the notion of balanced coverage in covering the controversy. In this construct, it is permissible to air a highly partisan opinion, provided this view is accompanied by a competing opinion. But recently scientists and scholars have challenged the legitimacy of this journalistic core value with regard to matters of great importance on which the overwhelming majority of the scientific community has reached a well-substantiated consensus view.

Yet there is evidence that this is exactly what the media is doing. In a survey of 636 articles from four top United States newspapers between 1988 and 2002, two scholars found that most articles gave as much time to the small group of climate change doubters as to the scientific consensus view. Given real consensus among climatologists over global warming, many scientists find the media's desire to portray the topic as a scientific controversy to be a gross distortion. As Stephen Schneider put it:

“a mainstream, well-established consensus may be ‘balanced’ against the opposing views of a few extremists, and to the uninformed, each position seems equally credible.”

Science journalism concerns itself with gathering and evaluating various types of relevant evidence and rigorously checking sources and facts. Boyce Rensberger, the director of the Massachusetts Institute of Technology (MIT) Knight Center for Science Journalism, said, “balanced coverage of science does not mean giving equal weight to both sides of an argument. It means apportioning weight according to the balance of evidence.”

The claims of scientists also get distorted by the media by a tendency to seek out extreme views, which can result in portrayal of risks well beyond the claims actually being made by scientists. Journalists tend to overemphasize the most extreme outcomes from a range of possibilities reported in scientific articles. A study that tracked press reports about a climate change article in the journal Nature found that "results and conclusions of the study were widely misrepresented, especially in the news media, to make the consequences seem more catastrophic and the timescale shorter."

A 2020 study in PNAS found that newspapers tended to give greater coverage of press releases that opposed action on climate change than those that supported action. The study attributes it to false balance.

Alarmism

Alarmism is using inflated language, including an urgent tone and imagery of doom. In a report produced for the Institute for Public Policy Research Gill Ereaut and Nat Segnit suggested that alarmist language is frequently used in relation to environmental matters by newspapers, popular magazines and in campaign literature put out by the government and environment groups. It is claimed that when applied to climate change, alarmist language can create a greater sense of urgency.

The term alarmist can be used as a pejorative by critics of mainstream climate science to describe those that endorse it. MIT meteorologist Kerry Emanuel wrote that labeling someone as an "alarmist" is "a particularly infantile smear considering what is at stake." He continued that using this "inflammatory terminology has a distinctly Orwellian flavor."

It has been argued that using sensational and alarming techniques, often evoke "denial, paralysis, or apathy" rather than motivating individuals to action and do not motivate people to become engaged with the issue of climate change. In the context of climate refugees—the potential for climate change to displace people—it has been reported that "alarmist hyperbole" is frequently employed by private military contractors and think tanks.

Some media reports have used alarmist tactics to challenge the science related to global warming by comparing it with a purported episode of global cooling. In the 1970s, global cooling, a claim with limited scientific support (even during the height of a media frenzy over global cooling, "the possibility of anthropogenic warming dominated the peer-reviewed literature") was widely reported in the press. Several media pieces have claimed that since the even-at-the-time-poorly-supported theory of global cooling was shown to be false, that the well-supported theory of global warming can also be dismissed. For example, an article in The Hindu by Kapista and Bashkirtsev wrote: "Who remembers today, they query, that in the 1970s, when global temperatures began to dip, many warned that we faced a new ice age? An editorial in The Time magazine on June 24, 1974, quoted concerned scientists as voicing alarm over the atmosphere 'growing gradually cooler for the past three decades', 'the unexpected persistence and thickness of pack ice in the waters around Iceland,' and other harbingers of an ice age that could prove 'catastrophic.' Man was blamed for global cooling as he is blamed today for global warming"., and the Irish Independent published an article claiming that "The widespread alarm over global warming is only the latest scare about the environment to come our way since the 1960s. Let's go through some of them. Almost exactly 30 years ago the world was in another panic about climate change. However, it wasn't the thought of global warming that concerned us. It was the fear of its opposite, global cooling. The doom-sayers were wrong in the past and it's entirely possible they're wrong this time as well." Numerous other examples exist.

Media, politics, and public discourse

As McCombs et al.’s 1972 study of the political function of mass media showed, media coverage of an issue can “play an important part in shaping political reality”. Research into media coverage of climate change has demonstrated the significant role of the media in determining climate policy formation. The media has considerable bearing on public opinion, and the way in which issues are reported, or framed, establishes a particular discourse.

In more general terms, media coverage of climate change in the USA is related to the controversy about media ownership and fairness. While most media scholars uphold the view that the media in the USA is free and unbiased, a minority disagrees. Historian Michael Parenti, for instance, alleges that the American media serves corporate interests by "inventing reality."

Media-policy interface

The relationship between media and politics is reflexive. As Feindt & Oels state, “[media] discourse has material and power effects as well as being the effect of material practices and power relations”. Public support of climate change research ultimately decides whether or not funding for the research is made available to scientists and institutions.

As highlighted above, media coverage in the United States during the Bush Administration often emphasized and exaggerated scientific uncertainty over climate change, reflecting the interests of the political elite. Hall et al. suggest that government and corporate officials enjoy privileged access to the media, so their line quickly becomes the ‘primary definer’ of an issue. Furthermore, media sources and their institutions very often have political leanings which determine their reporting on climate change, mirroring the views of a particular party. However, media also has the capacity to challenge political norms and expose corrupt behaviour, as demonstrated in 2007 when The Guardian revealed that American Enterprise Institute received $10,000 from petrochemical giant Exxon Mobil to publish articles undermining the IPCC’s 4th assessment report.

Ever-strengthening scientific consensus on climate change means that skepticism is becoming less prevalent in the media (although the email scandal in the build up to Copenhagen reinvigorated climate skepticism in the media).

Discourses of action

The polar bear has become a symbol for those attempting to generate support for addressing climate change

Commentators have argued that the climate change discourses constructed in the media have not been conducive to generating the political will for swift action. The polar bear has become a powerful discursive symbol in the fight against climate change. However, such images may create a perception of climate change impacts as geographically distant, and MacNaghten argues that climate change needs to be framed as an issue 'closer to home'. On the other hand, Beck suggests that a major benefit of global media is that it brings distant issues within our consciousness.

Furthermore, media coverage of climate change (particularly in tabloid journalism but also more generally), is concentrated around extreme weather events and projections of catastrophe, creating “a language of imminent terror” which some commentators argue has instilled policy-paralysis and inhibited response. Moser et al. suggest using solution-orientated frames will help inspire action to solve climate change. The predominance of catastrophe frames over solution frames may help explain the apparent value-action gap with climate change; the current discursive setting has generated concern over climate change but not inspired action.

Breaking the prevailing notions in society requires discourse that is traditionally appropriate and approachable to common people. For example, Bill McKibben, an environmental activist, provides one approach to inspiring action: a war-like mobilization, where climate change is the enemy. This approach would resonate with working Americans who normally find themselves occupied with other news headlines. Dispelling the capitalist commodification of the environment also requires different rhetoric that breaks certain ingrained notions concerning the human relationship with the environment. This could include incorporating traditional Indigenous knowledge that prioritizes human existence with the environment as a mutualistic and protective one.

Additionally, international movements in developing countries in the Global South are usually excluded in developed nations that assert hegemony over the economies of developing nations. This especially applies to the people of Latin America, that are battling multinational oil and mineral corporations that seek to cooperate with the ruling class and exploit fragile ecosystems, rather than provide real solutions to working people that mutually benefit the environment. This is apparent in Ecuador, where former President Rafael Correa, a left-leaning populist, incited “economic growth” as a reason to sell portions of the Amazon rainforest to oil companies. These popular movements usually are neglected by the United States due to corporate relationships within the political sphere of influence.

Compared to what experts know about traditional media's and tabloid journalism's impacts on the formation of public perceptions of climate change and willingness to act, there is comparatively little knowledge of the impacts of social media, including message platforms like Twitter, on public attitudes toward climate change.

Coverage of youth

Published in the journal Childhood, the article "Children's protest in relation to the climate emergency: A qualitative study on a new form of resistance promoting political and social change" considers how children have evolved into prominent actors to create a global impact on awareness of climate change. It highlights the work of children like Greta Thunberg and the significance of their resistance to the passivity of world leaders regarding climate change. It also discusses how individual resistance can directly be linked to collective resistance and that this then creates a more powerful impact, empowering young people to act more responsibly and take authority over the future. The article offers a holistic view of the impact of youth to raise awareness whilst also inspiring action, and using social media platforms such as YouTube, Facebook and Instagram to share the youth message.

Coverage by country

Canada

During the Harper government (2006-2015), Canadian media, mostly notably the CBC, made little effort to balance the claims of global warming deniers with voices from science. The Canadian coverage appeared to be driven more by national and international political events rather than the changes to carbon emissions or various other ecological factors. The discourse was dominated by matters of government responsibility, policy-making, policy measures for mitigation, and ways to mitigate climate change; with the issue coverage by mass media outlets continuing to act as an important means of communicating environmental concerns to the general public, rather than introducing new ideas about the topic itself.

Within various provincial and language media outlets, there are varying levels of articulation regarding scientific consensus and the focus on ecological dimensions of climate change. Within Quebec, specifically, these outlets are more likely to position climate change as an international issue, and to link climate change to social justice concerns in order to depict Quebec as a pro-environmental society

Across various nations, including Canada, there has been an increased effort in the use of celebrities in climate change coverage, which is able to gain audience attention, but in turn, it reinforces individualized rather than structural interpretations of climate change responsibility and solutions .