Encyclopedia
Articles
Long-form educational entries. Featured pieces sit on the homepage; this index is the full set.
nuclear power
Radioactivity
Radioactivity is a natural phenomenon. Unstable atom nuclei release particles: helium nuclei (alpha); electrons or positrons (beta); photons (gamma).
5 min read
nuclear power
Ionising Radiation
Ionizing radiation can be classified into alpha, beta, gamma, X-rays, and neutrons, while cosmic radiation is composed primarily of high-energy protons.
4 min read
radiation
Natural and Human-Made Radiation
Background radiation is unavoidable. Medicine, industry, and nuclear energy add further doses that are managed differently.
6 min read
nuclear power
Half-life
A half-life is a period after which half of the radioactive material has decayed. The half-life of isotopes is used in medicine or radiocarbon dating.
3 min read
nuclear power industry
Fission Chain Reaction
When a neutron splits the 235U nucleus, 2-3 neutrons are released. The fission chain reaction occurs when they split other nuclei, releasing more neutrons.
3 min read
nuclear power industry
Control and Reaction States
The chain fission reaction in a nuclear reactor is controlled by the neutron absorber content. The reactor can be subcritical, critical, or supercritical.
3 min read
fission physics
Coolant and Moderator
The coolant removes heat. The moderator slows neutrons. Sometimes they are the same fluid.
8 min read
nuclear fuel
Fuel Production
Uranium ore is turned into U3O8 (yellowcake) or UF6 (hex), enriched up to 3—5% of 235U, and as a UO2 compressed into pellets inserted into zircalloy tubes.
3 min read
nuclear fuel
Fuel Enrichment
Enrichment is a physical process that raises the concentration of the 235U isotope to 3—5%. Gaseous diffusion, centrifuges, or laser excitation are used.
4 min read
nuclear fuel
Interim Storage
Spent fuel is first stored in water pools near the reactor to be cooled. Then it is moved to dry interim storage, located usually on-site.
3 min read
nuclear fuel
Reprocessing
Spent fuel can be reprocessed. Extracted uranium and plutonium can be used for MOX or uranium fuel production. The remaining waste is vitrified.
4 min read
nuclear fuel
Final Repositories
The highly radioactive vitrified waste in special leak-tight flasks will be stored for thousands of years in a deep underground final repository.
3 min read
nuclear reactors
Gas-cooled Reactor (GCR) and Advanced Gas-cooled Reactor (AGR)
Gas cooled reactors (GCR), used in Japan and the UK, use graphite as a moderator and pressurized CO2 as a coolant. It is a double-circuit power plant.
3 min read
nuclear reactors
RBMK Type Reactor
The Soviet RBMK reactor uses graphite as a moderator and light water, that boils in the channels, as a coolant. Chernobyl reactor was of RBMK type.
3 min read
nuclear reactors
High Temperature Reactor (HTGR)
In a High Temperature Gas-cooled Reactor (HTGR), the highly enriched uranium spheres are dispersed in graphite (moderator) balls. Helium is a coolant.
3 min read
nuclear reactors
Reactor Using Fast Neutrons (FR)
A reactor using fast neutron (FR) burns a mixture of uranium and plutonium. Fast breeder reactors (FBR) produce more plutonium than they consume.
3 min read
safety
INES and Nuclear Accidents
The International Nuclear Event Scale ranks events. Three Mile Island, Chernobyl, and Fukushima are the reference severe accidents.
6 min read
nuclear fuel
Fuel Assembly
There are different types of nuclear fuel. A typical fuel assembly for PWR consists of fuel rods, long cylinders of zircaloy filled with UO2 pellets.
4 min read
nuclear fuel
Fuel Cycle
In a closed fuel cycle, spent nuclear fuel (used fuel removed from a reactor) is reprocessed. In an open cycle, it is stored in interim storage.
4 min read
nuclear power industry
Principle of Operation
The binding energy that holds nucleons together is different for each isotope. When fusing light nuclei or splitting heavy nuclei, energy is released.
3 min read
nuclear reactors
The First Reactor
The first fission reactor was Chicago Pile No. 1, constructed by Enrico Fermi (2.12.1942). The first experimental nuclear power plant was the EBR-1.
3 min read
nuclear reactors
Pressurized Water Reactor (PWR)
The pressurized water reactor (PWR) uses light water at a pressure of 15.7 MPa as a coolant. Steam in the secondary circuit propels the turbine.
3 min read
nuclear reactors
Boiling Water Reactor (BWR)
In a boiling water reactor (BWR), the water boils directly inside the reactor. Dried steam propels the turbogenerator. It is a single-circuit power plant.
3 min read
nuclear reactors
Heavy Water Reactor (PHWR)
The pressurized heavy water reactor (PHWR) uses natural uranium as fuel and heavy water as coolant and moderator. Most of them are of the CANDU type.
3 min read
nuclear reactors
Small Modular Reactors
Inside a nuclear reactor, a fission reaction takes place. Released energy is removed by coolant and used to generate electricity. A common reactor is PWR.
16 min read
radioactive waste
Radioactive Waste
Radioactive waste is classified as low-level, intermediate-level, or high-level; as solid, gaseous, or liquid. Each type needs different handling.
3 min read
nuclear plant safety
The Safety of Nuclear Power Plants
Safety is an important aspect of nuclear power plants. Safe operation and fuel handling have to be ensured to reduce the risk of a nuclear accident.
3 min read
nuclear power
Natural Sources
Natural sources of radioactivity can be found in the air, soil, cosmic rays, or humans. The annual dose received from them is called "natural background".
4 min read
nuclear power
Man-made Sources
Man-made radioactivity sources are mostly used in medicine for diagnostics and treatment. Coal and nuclear plants produce radioactive waste.
4 min read
nuclear power
Decay Series
Unstable isotopes decay in four decay series (thorium, neptunium, uranium, actinium) into other radionuclides and finally into stable atoms.
3 min read
nuclear power
Quantities and Units
The radioactivity and its effects are measured by detectors and dosimeters (activity in becquerels, dose in grays, equivalent dose in sieverts).
4 min read
nuclear power
Effects of Ionising Radiation
Ionising radiation could change material properties. In living tissue, it could damage DNA and lead to cell death. This is used in tumor treatment.
3 min read
nuclear power
Radiation Doses and Activities
A chart of the radioactivity of various objects (e.g., nuts or coal) and the doses produced by some activities (like eating bananas or visiting Chernobyl).
3 min read
nuclear power
Nuclear Power Summary
Nuclear energy originates from the makeup of the atom. Ionizing radiation caused by decay of the atom nuclei is a natural part of our environment.
17 min read
nuclear power industry
Types of Nuclear Reactions
Nuclear reactions can lead to scattering, capture, or splitting depending on neutron velocity. So-called "slow" neutrons (0.02 eV) can split 235U nuclei.
3 min read
nuclear power industry
Moderator
To increase the chance of fission, the moderator slows down neutrons by collisions. The usual moderators are water, heavy water, and graphite.
3 min read
nuclear power industry
Absorber
The absorber (boron, cadmium) captures the neutrons and thus regulates the nuclear reactor output. It can be part of the coolant or control rods.
3 min read
nuclear power industry
Coolant
The coolant removes heat from the fission reaction. The most commonly used is water, but also helium, CO2, molten sodium, lead, or fluoride salts are used.
3 min read
nuclear power industry
Fission Products
After fission, the uranium nucleus decays into two approximately equal halves. Typical products are iodine and cesium, but other ways of decay exist.
3 min read
nuclear power industry
The Largest Nuclear Power Plants
In 2012, there were 436 reactors in use worldwide. The largest nuclear power plant is Japan's Kashiwazaki Kariwa with 7,965 MW of installed power output.
3 min read
nuclear fuel
Transportation
Fresh fuel, yellowcake or uranium ore are transported normally, while highly radioactive materials like spent fuel are transported in special flasks.
3 min read
nuclear reactors
The Nuclear Power Plant — How it Works
Inside the nuclear power plant reactor, a controlled fission reaction takes place. Heat removed by coolant is used to produce steam to propel the turbine.
5 min read
nuclear reactors
The Future of Fission Reactors
Several types of Generation IV reactors are under development: fast reactors cooled by lead, molten salts, or sodium; HTGR, or supercritical water reactor.
4 min read
radioactive waste
Production of Radioactive Waste
Radioactive waste, produced in medicine or industry, is low-level or intermediate-level waste. Spent nuclear fuel is high-level radioactive waste.
3 min read
radioactive waste
Types of Radioactive Waste
The radioactive waste is classified by radioisotope content, activity level (low, intermediate, high-level), or state (solid, gas, liquid).
4 min read
radioactive waste
The Processing of Radioactive Waste
Liquid radioactive waste can be evaporated, filtered, biocleaned or flocculated. Solid waste can be pressed, incinerated, vitrified or fixed in synrock.
5 min read
radioactive waste
The Disposal of Radioactive Waste
For radioactive waste with short-lived isotopes, a surface repository is sufficient, while long-lived isotopes must be isolated in a deep repository.
3 min read
nuclear plant safety
Nuclear Safety
Nuclear safety is the ability of a nuclear facility to keep the fission process and resulting radioactive products always under control.
3 min read
nuclear plant safety
Safety Systems
The safety of nuclear power plants is ensured by inherent safety measures that rely on physical laws, bariers, and systems redundancy.
8 min read
nuclear plant safety
External Hazards
The nuclear power plant has to withstand terrorist attack, operator error, system malfunction, or natural disasters like floods, earthquakes, or tsunami.
3 min read
nuclear plant safety
INES Scale
INES, the international nuclear and radiological event scale from 1 to 7, is used to clearly communicate the severity of a nuclear accident.
4 min read
nuclear plant safety
Nuclear Accidents
In the nuclear power industry, only three large accidents have occurred: Three Mile Island (1979), Chernobyl (1986) and Fukushima Daiichi (2011).
15 min read
nuclear plant safety
International Nuclear Organizations
There are several organizations supervising the nuclear power industry, like the International Atomic Energy Agency or the World Nuclear Association.
3 min read
nuclear plant safety
Nuclear Power Plants and the Environment
Nuclear power plants are safe and clean. They release no CO2 or emissions. Almost all of their waste is in solid form, albeit highly radioactive.
3 min read