To maintain a chain reaction in a nuclear reactor, the number of neutrons produced in the core by fissions must at all times be exactly equal to the number of neutrons that disappear into or escape from the core. The ratio of production to disappearance is called the multiplication coefficient , noted K, and must therefore be strictly equal to 1, which is called criticality , and the reactor is called critical. If this number K is less than 1, the neutrons disappear quickly, the chain reaction stops and so does the reactor: the core is said to be subcritical.
It is then said that the heart is over-critical. We generally use 3 types of absorbents:. It is these delayed neutrons as opposed to the prompt neutrons emitted during fission itself that give the time needed to adjust poisons, such as raising or lowering control rods, and control reactor power.
Without delayed neutron, there is no control of the chain reaction, and therefore no nuclear reactor. The fission of a plutonium nucleus gives more neutrons 2.
On the other hand, the proportion of delayed neutrons is lower in plutonium fission 0. Figure 3. These reactors are robust, reliable and competitive. The vast majority of these reactors use ordinary water as coolant. It is the Chernobyl accident, which we will describe below, that is at the origin of Generation III under construction: these reactors are required that if the major accident of total core meltdown occurs, the radioactivity remains confined in the site, i.
It is a high-power MW pressurised water reactor, highly protected and equipped with highly redundant backup systems that ensure its robustness and safety. The first two EPRs under construction in Finland and France experienced major construction difficulties, resulting in considerable delays and additional costs. The next two, recently achieved in China, do not have these problems because they benefit from the feedback of the first ones.
Generation IV is expected to meet the requirements of a context that will be different from today. This is expected to lead to better use of fissile materials, more efficient management of long-lived radioactive waste, better resistance to proliferation [2] , safety at least as high as that of Generation III, and the ability to open up to applications other than just the supply of electricity: desalination of seawater, heat production for industry, hydrogen production for the manufacture or improvement of synthetic fuels, etc.
When a heavy nucleus is fissioned, the loss of mass of the components releases considerable energy. Similarly or conversely , the fusion of two very light nuclei leads to a loss of mass and an even greater release of energy in terms of the mass of the components.
This is the type of reaction that occurs in the core of stars Figure 4. Fission and fusion were both discovered in , but while the first fission generator reactor was commissioned in , the use of fusion to produce electricity is still a distant prospect today.
The problem is that the light cores in question have a positive electrical charge and therefore repel each other. At the heart of the stars, the gigantic forces of gravity solve this problem, but on Earth we must find another method. Most hopes are based on the very high temperature million degrees of a deuterium and tritium plasma, two hydrogen isotopes whose nucleus contains one or two neutrons respectively [3].
The speeds of the nuclei at these temperatures allow electrostatic repulsion to be overcome. Of course, at this temperature, this plasma must have no contact with a material wall: it is confined by a combination of magnetic and electric fields in a machine called a tokamak. ITER, the most powerful of these machines, has been under construction in Cadarache since in a very multinational setting. Around , ITER should produce its first deuterium-tritium plasma: by then the equivalent for the fission of the Fermi experiment in December will have been more or less reached for fusion.
Figure 5. Emission of greenhouse gases from different electricity sources, expressed in g of CO2 per kWh. Weisser, IAEA May ] In terms of the environment, one of the major advantages of nuclear electricity is that its production — in a complete life-cycle analysis — causes very little release of greenhouse gases, gases responsible for climate change, as illustrated in the diagram in Figure 5.
Excluding accidents, nuclear power plants are characterized by very low levels of radioactive releases to the environment, which are closely monitored. The total amount of radioactivity released into the atmosphere from a nuclear power plant is less than that released from a coal-fired power plant due to the uranium and thorium impurities contained in it. Before the systematization of the treatment of certain well-known mineral waters by passage over ion exchange resins, they would have been too radioactive to be authorized as liquid discharges from a power plant.
At the exit of any thermal power plant, nuclear or other, the water is discharged at a higher temperature than at the entrance. For seaside power plants, this is not a problem.
For power plants cooled by rivers, the temperature difference is limited by regulation to a level that does not risk disturbing aquatic fauna. This often leads to not releasing the water into the environment without having cooled it by evaporation in these large air coolers , the plume of which can be identified from a distance plume due to the condensation in the atmosphere of this evaporated river water.
In France, these towers are associated with nuclear power plants, but in Germany, these same towers most often report coal-fired power plants. While effluents and discharges are diluted into the environment due to their minimal radioactivity, radioactive waste is, by contrast, concentrated and immobilized in matrices appropriate to its nature. These solid packages are stored under control until they are stored under conditions that ensure their containment for as long as they present a danger.
A radioactive substance is a substance that contains radioelements whose quantity or concentration requires protective measures. Radioactive waste is radioactive material for which no use is planned or envisaged.
For radioactive waste, the usual French classification is based on two important parameters to define the appropriate management method: the level of activity , which corresponds to the number of disintegrations per unit of time of the radioactive elements contained in the waste and the radioactive half-life of these radioelements.
In particular, a distinction is made between waste whose radioactivity comes mainly from radioelements with a period of less than 31 years so-called short-lived waste and waste whose radioactivity comes mainly from radioelements with a period of more than 31 years so-called long-lived waste. Figure 6. Classification of radioactive waste[Source : ASN] These two criteria, activity level and half-life, make it possible to classify the waste and associate one or more management channels to each category, as shown in Figure 6.
The most hazardous waste MAVL and HA is the waste from spent nuclear fuel after the treatment that allows the recycling of uranium and plutonium.
They are vitrified and encapsulated in stainless steel containers awaiting deep storage in the CIGEO centre provided for by the law, which is due to come into service in For the ultimate management of radioactive waste, Great Britain and Japan have chosen the same options as France and China are about to do the same, Sweden and Finland have chosen the geological storage of spent fuel without treatment, and most other countries are storing spent fuel pending a decision.
Figure 7. This is why, to communicate on events affecting a nuclear installation, the INES International Nuclear Event Scale has been created, similar to the Richter scale for earthquakes. We will only mention here the most well-known ones, as well as the lessons that have been learned. The generated heat is removed from the reactor by a circulating fluid, typically water.
This heat can then be used to generate steam, which drives turbines for electricity production. In order to ensure the nuclear reaction takes place at the right speed, reactors have systems that accelerate, slow or shut down the nuclear reaction, and the heat it produces. This is normally done with control rods, which typically are made out of neutron-absorbing materials such as silver and boron. Two examples of nuclear fissioning of uranium, the most commonly used fuel in nuclear reactors.
Nuclear reactors come in many different shapes and sizes — some use water to cool their cores, whilst others use gas or liquid metal. Further information on the many different types of reactor around the world can be found in the Nuclear Power Reactors section of the Information Library.
Nuclear reactors are very reliable at generating electricity, capable of running for 24 hours a day for many months, if not years, without interruption, whatever the weather or season. Additionally, most nuclear reactors can operate for very long periods of time — over 60 years in many cases.
A number of different materials can be used to fuel a reactor, but most commonly uranium is used. All communities would have to be evacuate d. This is what happened in Chernobyl, Ukraine, in A steam explosion at one of the power plants four nuclear reactors caused a fire, called a plume. This plume was highly radioactive, creating a cloud of radioactive particles that fell to the ground, called fallout.
The fallout spread over the Chernobyl facility, as well as the surrounding area. The fallout drifted with the wind, and the particles entered the water cycle as rain. Radioactivity traced to Chernobyl fell as rain over Scotland and Ireland. Most of the radioactive fallout fell in Belarus. The environmental impact of the Chernobyl disaster was immediate. For kilometers around the facility, the pine forest dried up and died. The red color of the dead pine s earned this area the nickname the Red Forest.
Fish from the nearby Pripyat River had so much radioactivity that people could no longer eat them. Cattle and horses in the area died. More than , people were relocate d after the disaster , but the number of human victim s of Chernobyl is difficult to determine.
The effects of radiation poisoning only appear after many years. Cancers and other diseases can be very difficult to trace to a single source. Future of Nuclear Energy Nuclear reactors use fission, or the splitting of atoms, to produce energy. Nuclear energy can also be produced through fusion, or joining fusing atoms together. The sun, for instance, is constantly undergoing nuclear fusion as hydrogen atoms fuse to form helium.
Because all life on our planet depends on the sun, you could say that nuclear fusion makes life on Earth possible.
Nuclear power plants do not have the capability to safely and reliably produce energy from nuclear fusion. It's not clear whether the process will ever be an option for producing electricity.
Nuclear engineers are researching nuclear fusion, however, because the process will likely be safe and cost-effective. Nuclear Tectonics The decay of uranium deep inside the Earth is responsible for most of the planet's geothermal energy, causing plate tectonics and continental drift.
The cooling system in one of the two reactors malfunctioned, leading to an emission of radioactive fallout. No deaths or injuries were directly linked to the accident. Also called "the country. Unstable atomic nuclei lose energy by emitting radiation and subatomic particles. The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit.
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Any interactives on this page can only be played while you are visiting our website. You cannot download interactives. However, over time, there has been a shift in demand for cheaper and cleaner fuel options, such as the nonrenewable energy source of natural gas, and renewable options like solar power and wind energy. Each energy resource has its advantages and disadvantages.
Explore nonrenewable and renewable options with this collection on energy resources. Different regions have access to different renewable or nonrenewable natural resources such as freshwater, fossil fuels, fertile soil, or timber based on their geographic location and past geologic processes.
For example, the Great Plains region of the United States is known for its abundance of fertile soil. As a result, its main industry is agriculture. Corn, soybeans, and wheat are globally exported from this region and serve as the main economy. On the other side of the spectrum, the desert southwestern region of the United States depends on the Central Arizona Project canals to transport water from the Colorado River in order to support agriculture and urban areas. Use these materials to explore the interconnected nature of resources and their distribution.
How does nuclear energy work? Is radiation a risk?
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