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Core of CROCUS, a small nuclear reactor used for research at the EPFL in Switzerland.
Core of CROCUS, a small nuclear reactor used for research at the EPFL in Switzerland. CROCUS is a Research reactor at École Polytechnique Fédérale de Lausanne in Switzerland, sometimes described as zero power but in fact limited Switzerland (English pronunciation; Schweiz Swiss German: Schwyz or Schwiiz Suisse Svizzera Svizra officially the Swiss Confederation
This article is a subarticle of Nuclear power. Nuclear power is any Nuclear technology designed to extract usable Energy from atomic nuclei via controlled Nuclear reactions

A nuclear reactor is a device in which nuclear chain reactions are initiated, controlled, and sustained at a steady rate, as opposed to a nuclear bomb, in which the chain reaction occurs in a fraction of a second and is uncontrolled causing an explosion. A nuclear chain reaction occurs when one Nuclear reaction causes an average of one or more nuclear reactions thus leading to a self-propagating number of these reactions A nuclear weapon is an explosive device that derives its destructive force from Nuclear reactions either fission or a combination of fission and fusion.

The most significant use of nuclear reactors is as an energy source for the generation of electrical power (see Nuclear power) and for the power in some ships (see Nuclear marine propulsion). Electric power is defined as the rate at which Electrical energy is transferred by an Electric circuit. Nuclear power is any Nuclear technology designed to extract usable Energy from atomic nuclei via controlled Nuclear reactions Nuclear marine propulsion is propulsion of a ship powered by a Nuclear reactor. This is usually accomplished by methods that involve using heat from the nuclear reaction to power steam turbines. In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature A steam turbine is a mechanical device that extracts Thermal energy from pressurized Steam, and converts it into useful mechanical work There are also other less common uses as discussed below.


Contents

How it works

NC State's PULSTAR Reactor is a 1 MW pool-type research reactor with 4% enriched, pin-type fuel consisting of UO2 pellets in zircaloy cladding.
NC State's PULSTAR Reactor is a 1 MW pool-type research reactor with 4% enriched, pin-type fuel consisting of UO2 pellets in zircaloy cladding. North Carolina State University at Raleigh is a public, Coeducational extensive Research University located in Raleigh North Carolina Research reactors are Nuclear reactors that serve primarily as a Neutron source. Zircaloy, also incorrectly called zircalloy, is a group of high- Zirconium Alloys One of the main uses of zircaloys is in Nuclear technology,
The control room of NC State's Pulstar Nuclear Reactor.
The control room of NC State's Pulstar Nuclear Reactor. North Carolina State University at Raleigh is a public, Coeducational extensive Research University located in Raleigh North Carolina

The key components common to most types of nuclear power plants are:

Conventional electrical power plants all have a fuel source to provide heat. In Nuclear engineering, a neutron moderator is a medium which reduces the velocity of Fast neutrons thereby turning them into Thermal neutrons capable A coolant is a fluid which flows through a device in order to prevent its overheating transferring the heat produced by the device to other devices that utilize or dissipate it A control rod is a rod made of Chemical elements capable of absorbing many Neutrons without fissioning themselves A pressure vessel is a closed container designed to hold gases or liquids at a Pressure different from the ambient Pressure. An Emergency Core Cooling System (ECCS is a component in Nuclear power plants designed to deal with a Loss of coolant accident (LOCA by providing massive backup A Reactor Protective System (RPS is a set of Nuclear safety components in a Nuclear power plant designed to safely shutdown the reactor and prevent the This is an article about nuclear power plant equipment For other uses see Steam generator. A boiling water reactor ( BWR) is a type of Nuclear reactor developed by the General Electric in the mid 1950s A containment building, in its most common usage is a Steel or reinforced concrete structure enclosing a Nuclear reactor. A boiler feedwater pump is a specific type of Pump used to pump Feedwater into a Steam Boiler. A steam turbine is a mechanical device that extracts Thermal energy from pressurized Steam, and converts it into useful mechanical work In Electricity generation, an electrical generator is a device that converts Mechanical energy to Electrical energy, generally using Electromagnetic Surface condenser is the commonly used term for a water cooled Shell and tube heat exchanger installed on the exhaust Steam from a Steam turbine in Examples are natural gas, coal, and fuel oil. For a nuclear power plant, this heat is provided by nuclear fission inside the nuclear reactor. Nuclear fission is the splitting of the nucleus of an atom into parts (lighter nuclei) often producing Free neutrons and other smaller nuclei which may When a relatively large fissile atomic nucleus (usually uranium-235 or plutonium-239) is struck by a neutron it forms two or more smaller nuclei as fission products, releasing energy and neutrons in a process called nuclear fission. In Nuclear engineering, a fissile material is one that is capable of sustaining a Chain reaction of Nuclear fission. The nucleus of an Atom is the very dense region consisting of Nucleons ( Protons and Neutrons, at the center of an atom Uranium-235 is an isotope of uranium that differs from the element's other common isotope Uranium-238, by its ability to cause a rapidly expanding fission Plutonium-239 is an Isotope of Plutonium. Plutonium-239 is the primary Fissile isotope used for the production of Nuclear weapons although This article is a discussion of neutrons in general For the specific case of a neutron found outside the nucleus see Free neutron. Fission products are the atomic fragments left after a large nucleus fissions. Nuclear fission is the splitting of the nucleus of an atom into parts (lighter nuclei) often producing Free neutrons and other smaller nuclei which may The neutrons then trigger further fission. And so on. When this nuclear chain reaction is controlled, the energy released can be used to heat water, produce steam and drive a turbine that generates electricity. A nuclear chain reaction occurs when one Nuclear reaction causes an average of one or more nuclear reactions thus leading to a self-propagating number of these reactions A turbine is a rotary Engine that extracts Energy from a Fluid flow It should be noted that a nuclear explosive involves an uncontrolled chain reaction, and the rate of fission in a reactor is not capable of reaching sufficient levels to trigger a nuclear explosion (even if the fission reactions increased to a point of being out of control, it would melt the reactor assembly rather than form a nuclear explosion). A nuclear explosive is an Explosive device that derives its energy from Nuclear reactions Almost all nuclear explosive devices that have been designed and produced A nuclear explosion occurs as a result of the rapid release of energy from an intentionally high-speed Nuclear reaction. A nuclear meltdown is a term for a severe Nuclear reactor accident Enriched uranium is uranium in which the percent composition of uranium-235 has been increased from that of uranium found in nature. Enriched uranium is a kind of Uranium in which the percent composition of Uranium-235 has been increased through the process of Isotope separation. Natural uranium is only 0. 72% uranium-235, with the rest being mostly uranium-238 (99. Uranium-238 (U-238 is the most common isotope of Uranium found in nature 2745%) and a tiny fraction is uranium-234 (0. Uranium-234 is an isotope of Uranium. In Natural uranium and uranium ore 234U occurs as an indirect Decay product of 238U 0055%).

Reactor types

Classifications

Nuclear Reactors are classified by several methods; a brief outline of these classification schemes is provided.

Classification by type of nuclear reaction

Classification by moderator material

Used by thermal reactors.

Classification by coolant

In thermal nuclear reactors (LWRs in specific), the coolant acts as a moderator that must slow down the neutrons before they can be efficiently absorbed by the fuel.
In thermal nuclear reactors (LWRs in specific), the coolant acts as a moderator that must slow down the neutrons before they can be efficiently absorbed by the fuel.

Classification by generation

Classification by phase of fuel

Classification by use

Current technologies

There are two types of nuclear power in current use:

  1. The nuclear fission reactor produces heat through a controlled nuclear chain reaction in a critical mass of fissile material. This article is a subarticle of Nuclear power. A nuclear reactor is a device in which Nuclear chain reactions are initiated controlled A nuclear chain reaction occurs when one Nuclear reaction causes an average of one or more nuclear reactions thus leading to a self-propagating number of these reactions A critical mass is the smallest amount of Fissile material needed for a sustained Nuclear chain reaction. In Nuclear engineering, a fissile material is one that is capable of sustaining a Chain reaction of Nuclear fission.
    All current nuclear power plants are critical fission reactors, which are the focus of this article. Nuclear power is any Nuclear technology designed to extract usable Energy from atomic nuclei via controlled Nuclear reactions The output of fission reactors is controllable. There are several subtypes of critical fission reactors, which can be classified as Generation I, Generation II and Generation III. A generation II reactor is a Nuclear reactor of one of several types developed from the first generation I reactors. A generation III reactor is a development of any of the generation II Nuclear reactor designs incorporating evolutionary improvements in design which have been developed All reactors will be compared to the Pressurized Water Reactor (PWR), as that is the standard modern reactor design. Pressurized water reactor ( PWR s (also VVER if of Russian design are generation II nuclear power reactors that use ordinary Water
Diablo Canyon - a PWR
Diablo Canyon - a PWR
  1. A. The Diablo Canyon Power Plant is an electricity-generating Nuclear power plant in San Luis Obispo County, California. Pressurized Water Reactors (PWR)
    These reactors use a pressure vessel to contain the nuclear fuel, control rods, moderator, and coolant. Pressurized water reactor ( PWR s (also VVER if of Russian design are generation II nuclear power reactors that use ordinary Water They are cooled and moderated by high pressure liquid water. The hot radioactive water that leaves the pressure vessel is looped through a steam generator, which in turn heats a secondary (non-radioactive) loop of water to steam that can run turbines. They are the majority of current reactors, and are generally considered the safest and most reliable technology currently in large scale deployment. This is a thermal neutron reactor design, the newest of which are the Advanced Pressurized Water Reactor and the European Pressurized Reactor. The neutron temperature, also called the neutron energy, indicates a free neutron's Kinetic energy, usually given in Electron volts The term This article is about the Mitsubishi Heavy Industry's design for the Westinghouse AP series see AP1000 The Mitsubishi APWR is an Advanced The EPR (or US-EPR for the United States specific design is a third generation Pressurized water reactor (PWR design United States Naval reactors are of this type. United States Naval reactor refers to Nuclear reactors used by the United States Navy.
Laguna Verde nuclear power plant - a BWR
Laguna Verde nuclear power plant - a BWR
  1. B. Laguna Verde is a Mexican Nuclear power plant, located in the municipality of Alto Lucero, Veracruz. Boiling Water Reactors (BWR)
    A BWR is like a PWR without the steam generator. A boiling water reactor ( BWR) is a type of Nuclear reactor developed by the General Electric in the mid 1950s A boiling water reactor is cooled and moderated by water like a PWR, but at a lower pressure, which allows the water to boil inside the pressure vessel producing the steam that runs the turbines. Unlike a PWR, there is no primary and secondary loop. The thermal efficiency of these reactors can be higher, and they can be simpler, and even potentially more stable and safe. These reactors make up a substantial percentage of modern reactors. This is a thermal neutron reactor design, the newest of which are the Advanced Boiling Water Reactor and the Economic Simplified Boiling Water Reactor. The Advanced Boiling Water Reactor (ABWR is a Generation III reactor Boiling water reactor. The reactor formally known as Economic Simplified Boiling Water Reactor ( ESBWR) is a Passively safe generation III+ reactor which builds on the success
The CANDU Qinshan Nuclear Power Plant
The CANDU Qinshan Nuclear Power Plant
  1. C. The CANDU reactor is a Canadian-invented Pressurized heavy water reactor developed initially in the late 1950s and 1960s by a partnership between Atomic Energy of The Qinshan Nuclear Power Plant is a multi-unit nuclear plant under construction in China Pressurized Heavy Water Reactor (PHWR)
    A Canadian design, (known as CANDU) these reactors are heavy-water-cooled and -moderated Pressurized-Water reactors. A pressurised heavy water reactor (PHWR is a nuclear power reactor, commonly using unenriched Natural uranium as its fuel that uses Heavy water ( Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page The CANDU reactor is a Canadian-invented Pressurized heavy water reactor developed initially in the late 1950s and 1960s by a partnership between Atomic Energy of Heavy water is water which contains a higher proportion than normal of the Isotope Deuterium, as deuterium oxide, D2O or ²H2O Instead of using a single large pressure vessel as in a PWR, the fuel is contained in hundreds of pressure tubes. These reactors are fueled with natural uranium and are thermal neutron reactor designs. Uranium (jʊˈreɪniəm is a silvery-gray Metallic Chemical element in the PHWRs can be refueled while at full power, which makes them very efficient in their use of uranium (it allows for precise flux control in the core). CANDU PHWR's have been built in Canada, Argentina, China, India (pre-NPT), Pakistan (pre-NPT), Romania, and South Korea. For a topic outline on this subject see List of basic Argentina topics. China ( Wade-Giles ( Mandarin) Chung¹kuo² is a cultural region, an ancient Civilization, and depending on perspective a National India, officially the Republic of India (भारत गणराज्य inc-Latn Bhārat Gaṇarājya; see also other Indian languages) is a country Pakistan () officially the Islamic Republic of Pakistan, is a country located in South Asia, Southwest Asia, Middle East and Romania ( dated: Rumania, Roumania South Korea, officially the Republic of Korea and often referred to as Korea ( Korean: 대한민국 tɛː India also operates a number of PHWR's, often termed 'CANDU-derivatives', built after the Government of Canada halted nuclear dealings with India following the 1974 Smiling Buddha nuclear weapon test. The Smiling Buddha was the first nuclear test explosion by India on May 18, 1974 at Pokhran.
The Ignalina Nuclear Power Plant - a still operating RBMK
The Ignalina Nuclear Power Plant - a still operating RBMK
  1. D. Ignalina Nuclear Power Plant is a two-unit RBMK -1500 Nuclear power station in Visaginas, Lithuania. Reaktor Bolshoy Moshchnosti Kanalniy (High Power Channel Reactor) (RBMK)
    A Soviet Union design, built to produce plutonium as well as power. RBMK is an acronym for the Russian reaktor bolshoy moshchnosti kanalniy (Реактор Большой Мощности Канальный which means "High Power Channel RBMKs are water cooled with a graphite moderator. The Mineral graphite, as with Diamond and Fullerene, is one of the Allotropes of carbon. RBMKs are in some respects similar to CANDU in that they are refuelable during power operation and employ a pressure tube design instead of a PWR-style pressure vessel. However, unlike CANDU they are very unstable and too large to have containment buildings, making them dangerous in the case of an accident. A containment building, in its most common usage is a Steel or reinforced concrete structure enclosing a Nuclear reactor. A series of critical safety flaws have also been identified with the RBMK design, though some of these were corrected following the Chernobyl accident. The Chernobyl disaster was a nuclear reactor accident in the Chernobyl Nuclear Power Plant in the Soviet Union. RBMK reactors are generally considered one of the most dangerous reactor designs in use. The Chernobyl plant had four RBMK reactors.
The Torness nuclear power station - an AGR
The Torness nuclear power station - an AGR
  1. E. Torness nuclear power station was the last of the United Kingdom's second generation nuclear power plants to be commissioned Gas Cooled Reactor (GCR) and Advanced Gas Cooled Reactor (AGR)
    These are generally graphite moderated and CO2 cooled. An advanced gas-cooled reactor (AGR is a type of Nuclear reactor. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single They can have a high thermal efficiency compared with PWRs due to higher operating temperatures. There are a number of operating reactors of this design, mostly in the United Kingdom, where the concept was developed. The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located Older designs (i. e. Magnox stations) are either shut down or will be in the near future. For other uses of the term see Magnox (disambiguation. Magnox is a now obsolete type of nuclear power reactor which was designed However, the AGCRs have an anticipated life of a further 10 to 20 years. This is a thermal neutron reactor design. Decommissioning costs can be high due to large volume of reactor core.
    F. Liquid Metal Fast Breeder Reactor (LMFBR)
The Superphenix, one of the few FBRs
The Superphenix, one of the few FBRs
  1. This is a reactor design that is cooled by liquid metal, totally unmoderated, and produces more fuel than it consumes. A breeder reactor is a Nuclear reactor that generates new Fissile or fissionable material at a greater rate than it consumes such material The fast breeder or fast breeder reactor ( FBR) is a Fast neutron reactor designed to breed fuel by producing more Fissile material Superphénix ( English: Superphoenix) or SPX is a Nuclear power station on the Rhône River at Creys-Malville in France, They are said to "breed" fuel, because they produce fissionable fuel during operation because of neutron capture. Neutron capture is a kind of Nuclear reaction in which an Atomic nucleus collides with one or more Neutrons and they merge to form a heavier nucleus These reactors can function much like a PWR in terms of efficiency, and do not require much high pressure containment, as the liquid metal does not need to be kept at high pressure, even at very high temperatures. Superphénix in France was a reactor of this type, as was Fermi-I in the United States. Superphénix ( English: Superphoenix) or SPX is a Nuclear power station on the Rhône River at Creys-Malville in France, The Enrico Fermi Nuclear Generating Station is a Nuclear power plant on the shore of Lake Erie near Monroe in Frenchtown Charter Township, Monroe The Monju reactor in Japan suffered a sodium leak in 1995 and was approved for restart in 2008. is Japan 's only Fast breeder reactor. Located in Tsuruga, Fukui Prefecture in Japan, the reactor began construction in 1985 and first achieved All three use/used liquid sodium. Sodium (ˈsoʊdiəm is an element which has the symbol Na( Latin natrium, from Arabic natrun) atomic number 11 atomic mass 22 These reactors are fast neutron, not thermal neutron designs. The neutron temperature, also called the neutron energy, indicates a free neutron's Kinetic energy, usually given in Electron volts The term These reactors come in two types:
    Lead cooled
    Using lead as the liquid metal provides excellent radiation shielding, and allows for operation at very high temperatures. The lead-cooled fast reactor is a Nuclear power Generation IV reactor that features a Fast neutron spectrum molten Lead or Lead-bismuth Characteristics Lead has a dull luster and is a dense, Ductile, very soft highly Also, lead is (mostly) transparent to neutrons, so fewer neutrons are lost in the coolant, and the coolant does not become radioactive. Unlike sodium, lead is mostly inert, so there is less risk of explosion or accident, but such large quantities of lead may be problematic from toxicology and disposal points of view. Often a reactor of this type would use a lead-bismuth eutectic mixture. LBE redirects here For the US airport see Arnold Palmer Regional Airport. In this case, the bismuth would present some minor radiation problems, as it is not quite as transparent to neutrons, and can be transmuted to a radioactive isotope more readily than lead.
    Sodium cooled
    Most LMFBRs are of this type. The Sodium-cooled fast reactor or SFR is a Generation IV reactor project to design an advanced Fast neutron reactor. The sodium is relatively easy to obtain and work with, and it also manages to actually prevent corrosion on the various reactor parts immersed in it. However, sodium explodes violently when exposed to water, so care must be taken, but such explosions wouldn't be vastly more violent than (for example) a leak of superheated fluid from a SCWR or PWR. The Supercritical water reactor (SCWR is a Generation IV reactor concept that uses supercritical water as the working fluid EBR-I, the first reactor to have a core meltdown, was of this type. Experimental Breeder Reactor I (EBR-I is a Decommissioned Research reactor and U
    G. Aqueous Homogeneous Reactor
  2. The radioisotope thermoelectric generator produces heat through passive radioactive decay. Aqueous homogeneous reactors (AHR are a type of Nuclear reactor in which soluble nuclear salts (usually Uranium sulfate or Uranium nitrate) A radioisotope thermoelectric generator ( RTG, RITEG) is an Electrical generator which obtains its power from Radioactive decay. Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation.
    Some radioisotope thermoelectric generators have been created to power space probes (for example, the Cassini probe), some lighthouses in the former Soviet Union, and some pacemakers. Cassini–Huygens is a joint NASA / ESA / ASI Robotic spacecraft mission currently studying the planet Saturn and its A lighthouse is a Tower, building or framework designed to emit light from a system of lamps and lenses or in older times from a fire and used as an The Union of Soviet Socialist Republics (USSR was a constitutionally Socialist state that existed in Eurasia from 1922 to 1991 The heat output of these generators diminishes with time; the heat is converted to electricity utilising the thermoelectric effect. The thermoelectric effect is the direct conversion of temperature differences to electric Voltage and vice versa

Advanced reactors

More than a dozen advanced reactor designs are in various stages of development. [3] Some are evolutionary from the PWR, BWR and PHWR designs above, some are more radical departures. Pressurized water reactor ( PWR s (also VVER if of Russian design are generation II nuclear power reactors that use ordinary Water A boiling water reactor ( BWR) is a type of Nuclear reactor developed by the General Electric in the mid 1950s A pressurised heavy water reactor (PHWR is a nuclear power reactor, commonly using unenriched Natural uranium as its fuel that uses Heavy water ( The former include the Advanced Boiling Water Reactor (ABWR), two of which are now operating with others under construction, and the planned passively safe ESBWR and AP1000 units (see Nuclear Power 2010 Program). The Advanced Boiling Water Reactor (ABWR is a Generation III reactor Boiling water reactor. Passive Nuclear safety describes a safety feature of a Nuclear reactor that does not require operator action or electronic feedback in order to shut down safely in The reactor formally known as Economic Simplified Boiling Water Reactor ( ESBWR) is a Passively safe generation III+ reactor which builds on the success The " Nuclear Power 2010 Program " was unveiled by the U

Generation IV reactors

Generation IV reactors are a set of theoretical nuclear reactor designs currently being researched. Generation IV reactors (Gen IV are a set of theoretical nuclear reactor designs currently being researched These designs are generally not expected to be available for commercial construction before 2030. Current reactors in operation around the world are generally considered second- or third-generation systems, with the first-generation systems having been retired some time ago. Research into these reactor types was officially started by the Generation IV International Forum (GIF) based on eight technology goals. The primary goals being to improve nuclear safety, improve proliferation resistance, minimize waste and natural resource utilization, and to decrease the cost to build and run such plants. [5]

Generation V+ reactors

Designs which are theoretically possible, but which are not being actively considered or researched at present. The Gas-Cooled Fast Reactor (GFR system is a nuclear reactor design which is currently in development The lead-cooled fast reactor is a Nuclear power Generation IV reactor that features a Fast neutron spectrum molten Lead or Lead-bismuth A molten salt reactor (MSR is a type of Nuclear reactor where the primary coolant is a Molten salt. The Sodium-cooled fast reactor or SFR is a Generation IV reactor project to design an advanced Fast neutron reactor. The Supercritical water reactor (SCWR is a Generation IV reactor concept that uses supercritical water as the working fluid The Very High Temperature Reactor is a Generation IV reactor concept that uses a Graphite - moderated Nuclear reactor with a once-through Though such reactors could be built with current or near term technology, they trigger little interest for reasons of economics, practicality, or safety.

Fusion reactors

Controlled nuclear fusion could in principle be used in fusion power plants to produce power without the complexities of handling actinides, but significant scientific and technical obstacles remain. Similar to how the Fission-fragment rocket produces thrust a fission fragment reactor is a Nuclear reactor that generates Electricity by decelerating an In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus Fusion power is power generated by Nuclear fusion reactions In this kind of reaction two light atomic nuclei fuse History of the actinoid series From the earlier known chemical properties of actinium (89 up to uranium (92 indicating a relation to the Transition metals it was generally Several fusion reactors have been built, but as yet none has 'produced' more thermal energy than electrical energy consumed. Despite research having started in the 1950s, no commercial fusion reactor is expected before 2050. The ITER project is currently leading the effort to commercialize fusion power. ITER is an international Tokamak ( Magnetic confinement fusion) research/engineering proposal for an experimental project that will help to make the transition from

Nuclear fuel cycle

Main article: Nuclear fuel cycle

Thermal reactors generally depend on refined and enriched uranium. The nuclear fuel cycle, also called nuclear fuel chain, is the progression of Nuclear fuel through a series of differing stages Enriched uranium is a kind of Uranium in which the percent composition of Uranium-235 has been increased through the process of Isotope separation. Some nuclear reactors can operate with a mixture of plutonium and uranium (see MOX). Mixed oxide, or MOX fuel, is a blend of oxides of Plutonium and Natural uranium, Reprocessed uranium, or Depleted uranium which behaves The process by which uranium ore is mined, processed, enriched, used, possibly reprocessed and disposed of is known as the nuclear fuel cycle. Nuclear reprocessing separates components of Spent nuclear fuel such as Reprocessed uranium Plutonium Minor The nuclear fuel cycle, also called nuclear fuel chain, is the progression of Nuclear fuel through a series of differing stages

Under 1% of the uranium found in nature is the easily fissionable U-235 isotope and as a result most reactor designs require enriched fuel. Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides Enrichment involves increasing the percentage of U-235 and is usually done by means of gaseous diffusion or gas centrifuge. Gaseous diffusion is a technology used to produce Enriched uranium by forcing gaseous Uranium hexafluoride, UF6 through semi-permeable membranes A gas centrifuge is a separating machine specifically developed to separate Uranium-235 from Uranium-238. The enriched result is then converted into uranium dioxide powder, which is pressed and fired into pellet form. Uranium dioxide (2 an Oxide of Uranium, also known as urania or uranic oxide is a black radioactive crystalline powder These pellets are stacked into tubes which are then sealed and called fuel rods. Nuclear fuel is any material that can be consumed to derive Nuclear energy, by analogy to chemical Fuel that is burned to derive energy Many of these fuel rods are used in each nuclear reactor.

Most BWR and PWR commercial reactors use uranium enriched to about 4% U-235, and some commercial reactors with a high neutron economy do not require the fuel to be enriched at all (that is, they can use natural uranium). Neutron economy is defined as the ratio of an adjoint weighted average of the excess Neutron production divided by an adjoint Weighted average of the fission According to the International Atomic Energy Agency there are at least 100 research reactors in the world fueled by highly enriched (weapons-grade/90% enrichment uranium). The International Atomic Energy Agency ( IAEA) is an international organization that seeks to promote the peaceful use of nuclear energy and to inhibit its Research reactors are Nuclear reactors that serve primarily as a Neutron source. Theft risk of this fuel (potentially used in the production of a nuclear weapon) has led to campaigns advocating conversion of this type of reactor to low-enrichment uranium (which poses less threat of proliferation). [6]

It should be noted that fissionable U-235 and non-fissionable U-238 are both used in the fission process. U-235 is fissionable by thermal (i. e. slow-moving) neutrons. A thermal neutron is one which is moving about the same speed as the atoms around it. Since all atoms vibrate proportionally to their absolute temperature, a thermal neutron has the best opportunity to fission U-235 when it is moving at this same vibrational speed. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature On the other hand, U-238 is more likely to capture a neutron when the neutron is moving very fast. This U-239 atom will soon decay into plutonium-239, which is another fuel. Pu-239 is a viable fuel and must be accounted for even when a highly enriched uranium fuel is used. Plutonium fissions will dominate the U-235 fissions in some reactors, especially after the initial loading of U-235 is spent. Plutonium is fissionable with both fast and thermal neutrons, which make it ideal for either nuclear reactors or nuclear bombs.

Most reactor designs in existence are thermal reactors and typically use water as a neutron moderator (moderator means that it slows down the neutron to a thermal speed) and as a coolant. But in a fast breeder reactor, some other kind of coolant is used which will not moderate or slow the neutrons down much. The fast breeder or fast breeder reactor ( FBR) is a Fast neutron reactor designed to breed fuel by producing more Fissile material This enables fast neutrons to dominate, which can effectively be used to constantly replenish the fuel supply. By merely placing cheap unenriched uranium into such a core, the non-fissionable U-238 will be turned into Pu-239, "breeding" fuel.

Fueling of nuclear reactors

The amount of energy in the reservoir of nuclear fuel is frequently expressed in terms of "full-power days," which is the number of 24-hour periods (days) a reactor is scheduled for operation at full power output for the generation of heat energy. Nuclear fuel is any material that can be consumed to derive Nuclear energy, by analogy to chemical Fuel that is burned to derive energy The number of full-power days in a reactor's operating cycle (between refueling outage times) is related to the amount of fissile uranium-235 (U-235) contained in the fuel assemblies at the beginning of the cycle. In Nuclear engineering, a fissile material is one that is capable of sustaining a Chain reaction of Nuclear fission. Uranium-235 is an isotope of uranium that differs from the element's other common isotope Uranium-238, by its ability to cause a rapidly expanding fission A higher percentage of U-235 in the core at the beginning of a cycle will permit the reactor to be run for a greater number of full-power days.

At the end of the operating cycle, the fuel in some of the assemblies is "spent" and is discharged and replaced with new (fresh) fuel assemblies, although in practice it is the buildup of reaction poisons in nuclear fuel that determines the lifetime of nuclear fuel in a reactor. A nuclear poison, also called a neutron poison is a substance with a large neutron absorption cross-section in applications such as Nuclear reactors Long before all possible fission has taken place, the buildup of long-lived neutron absorbing fission byproducts impedes the chain reaction. The fraction of the reactor's fuel core replaced during refueling is typically one-fourth for a boiling-water reactor and one-third for a pressurized-water reactor.

Not all reactors need to be shut down for refueling; for example, pebble bed reactors, RBMK reactors, molten salt reactors, Magnox, AGR and CANDU reactors allow fuel to be shifted through the reactor while it is running. The pebble bed reactor ( PBR) is a graphite- moderated, gas-cooled Nuclear reactor. RBMK is an acronym for the Russian reaktor bolshoy moshchnosti kanalniy (Реактор Большой Мощности Канальный which means "High Power Channel A molten salt reactor (MSR is a type of Nuclear reactor where the primary coolant is a Molten salt. For other uses of the term see Magnox (disambiguation. Magnox is a now obsolete type of nuclear power reactor which was designed An advanced gas-cooled reactor (AGR is a type of Nuclear reactor. The CANDU reactor is a Canadian-invented Pressurized heavy water reactor developed initially in the late 1950s and 1960s by a partnership between Atomic Energy of In a CANDU reactor, this also allows individual fuel elements to be situated within the reactor core that are best suited to the amount of U-235 in the fuel element.

The amount of energy extracted from nuclear fuel is called its "burn up," which is expressed in terms of the heat energy produced per initial unit of fuel weight. Burn up is commonly expressed as megawatt days thermal per metric ton of initial heavy metal.

Safety

Main article: Nuclear safety
See also: Nuclear safety in the U.S.

Natural nuclear reactors

Main article: Natural nuclear fission reactor

Although nuclear fission reactors are often thought of as being solely a product of modern technology, the first nuclear fission reactors were in fact naturally occurring. See also Nuclear debate Nuclear safety covers the actions taken to prevent Nuclear and radiation accidents or to limit their consequences Nuclear safety in the US is governed by federal regulations and continues to be studied by the Nuclear Regulatory Commission (NRC A natural nuclear fission reactor is a Uranium deposit where analysis of Isotope Ratios has shown that self-sustaining Nuclear chain reactions A natural nuclear fission reactor can occur under certain circumstances that mimic the conditions in a constructed reactor. A natural nuclear fission reactor is a Uranium deposit where analysis of Isotope Ratios has shown that self-sustaining Nuclear chain reactions [7] Fifteen natural fission reactors have so far been found in three separate ore deposits at the Oklo mine in Gabon, West Africa. Oklo is a region near the town of Franceville, in the Haut-Ogooué province of the Central African state of Gabon. Gabon (gəˈbɒn or /gaˈbõ/ in French) is a country in west central Africa sharing borders with Equatorial Guinea, Cameroon, Republic West Africa or Western Africa is the Westernmost Region of the African Continent. First discovered in 1972 by French physicist Francis Perrin, they are collectively known as the Oklo Fossil Reactors. Francis Perrin ( Paris, 1901 - id 1992 was a French Physicist, the son of Jean Perrin. A natural nuclear fission reactor is a Uranium deposit where analysis of Isotope Ratios has shown that self-sustaining Nuclear chain reactions Self-sustaining nuclear fission reactions took place in these reactors approximately 1. Nuclear fission is the splitting of the nucleus of an atom into parts (lighter nuclei) often producing Free neutrons and other smaller nuclei which may 5 billion years ago, and ran for a few hundred thousand years, averaging 100 kW of power output during that time. [8] The concept of a natural nuclear reactor was theorized as early as 1956 by Paul Kuroda at the University of Arkansas[9][10]

Such reactors can no longer form on Earth: radioactive decay over this immense time span has reduced the proportion of U-235 in naturally occurring uranium to below the amount required to sustain a chain reaction. The University of Arkansas, often shortened to U of A or just UA, is a public Co-educational Land-grant university

The natural nuclear reactors formed when a uranium-rich mineral deposit became inundated with groundwater that acted as a neutron moderator, and a strong chain reaction took place. The water moderator would boil away as the reaction increased, slowing it back down again and preventing a meltdown. The fission reaction was sustained for hundreds of thousands of years.

These natural reactors are extensively studied by scientists interested in geologic radioactive waste disposal. They offer a case study of how radioactive isotopes migrate through the earth's crust. This is a significant area of controversy as opponents of geologic waste disposal fear that isotopes from stored waste could end up in water supplies or be carried into the environment.

See also

References

  1. ^ A Technology Roadmap for Generation IV Neuclear Energy SystemsPDF (4. Auxiliary feedwater is a backup Water supply system found in Pressurized water reactor Nuclear power plants This system sometimes known as Emergency feedwater A containment building, in its most common usage is a Steel or reinforced concrete structure enclosing a Nuclear reactor. David Hahn (born October 30, 1976) is a man known for his attempt to build a Fast breeder Nuclear reactor in 1994 in his backyard shed in Energy development is the ongoing effort to provide sufficient Primary energy sources and secondary Energy forms to meet civilization's needs List of nuclear reactors is a comprehensive annotated list of all the Nuclear reactors of the world sorted by country List of United States Naval reactors is a comprehensive annotated list of all naval reactors designed built or used by the United States Navy. Nuclear marine propulsion is propulsion of a ship powered by a Nuclear reactor. Nuclear physics is the field of Physics that studies the building blocks and interactions of Atomic nuclei. Nuclear power is a method for generating energy by harnessing the radioactivity of atoms The Nuclear Reactor Operator Badge is a decoration of the United States Army which was issued between the years of 1965 and 1990. See also Critical mass Most Nuclear reactors use a Chain reaction to induce a controlled rate of Nuclear fission in fissile material releasing This article is about nuclear reactors For other meanings see Scram (disambiguation. Safety engineering is an applied science strongly related to Systems engineering and the subset System Safety Engineering Technology assessment ( TA, German Technikfolgenabschätzung) is the study and Evaluation of new technologies. 33 MiB); see "Fuel Cycles and Sustainability"
  2. ^ World Nuclear Association Information Brief -Research Reactors
  3. ^ Advanced Nuclear Power Reactors. A mebibyte (a contraction of me ga bi nary byte) is a unit of Information or Computer storage, abbreviated MiB. Uranium Information Centre. The Uranium Information Centre is an Australian organisation primarily concerned with increasing the public understanding of Uranium mining and nuclear Retrieved on June 28, 2006.
  4. ^ Dr. Charles Till. Nuclear Reaction: Why Do Americans Fear Nuclear Power?. Public Broadcasting Service (PBS). Retrieved on 2006-11-09. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 694 - Egica, a king of the Visigoths of Hispania, accuses Jews of aiding Muslims sentencing all
  5. ^ Generation IV Nuclear Reactors. Uranium Information Centre. The Uranium Information Centre is an Australian organisation primarily concerned with increasing the public understanding of Uranium mining and nuclear Retrieved on June 28, 2006.
  6. ^ IAEA, Improving Security at World's Nuclear Research Reactors: Technical and Other Issues Focus of June Symposium in Norway (7 June 2006).
  7. ^ Video of physics lecture - at Google Video; a natural nuclear reactor is mentioned at 42:40 mins into the video
  8. ^ Meshik, Alex P. "The Workings of an Ancient Nuclear Reactor. " Scientific American. November, 2005. Pg. 82.
  9. ^ Oklo: Natural Nuclear Reactors. Office of Civilian Radioactive Waste Management. Retrieved on June 28, 2006.
  10. ^ Oklo's Natural Fission Reactors. American Nuclear Society. The American Nuclear Society (ANS is an international not-for-profit 501(c (3 scientific and educational organization consisting of approximately 11000 engineers Retrieved on June 28, 2006.

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