Wigner energy is created inside nuclear reactors that use graphite, a form of carbon, as neutron moderator. When the graphite is bombarded with neutrons from the reactor core, crystalline dislocations occur as a result of the Wigner effect, causing the graphite rods to swell and begin storing the energy. This energy is problematic for nuclear reactors because it can be spontaneously and rapidly released from the graphite in the form of heat, and unplanned excess heat is not a desirable situation within a nuclear reactor. Nuclear power station at Leibstadt, Switzerland. ... Graphite (named by Abraham Gottlob Werner in 1789, from the Greek γραφειν: to draw/write, for its use in pencils) is one of the allotropes of carbon. ... General Name, Symbol, Number Carbon, C, 6 Chemical series Nonmetals Group, Period, Block 14 (IVA), 2, p Density, Hardness 2267 kg/m3 0. ... In nuclear engineering, a neutron moderator is a medium which reduces the velocity of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a chain reaction. ... Properties In physics, the neutron is a subatomic particle with no net electric charge and a mass of 940 MeV/c² (1. ... The Wigner effect, also known as the discomposition effect, is a change in the physical or chemical properties of a crystalline solid resulting from damage caused by radiation. ... A red-hot iron rod cooling after being worked by a blacksmith. ...

The Windscale fire was an incident where plant operators used a process known as annealing in an attempt to reduce stored Wigner energy. This required shutting off the core's cooling system and allowing internal temperatures to rise, resulting in a gradual bleeding-off of Wigner energy. The first fifteen attempts of this process was completed successfully, but due to inaccurate temperature monitoring in the core, the sixteenth resulted in extremely high temperatures and a chain reaction. This led to canisters of materials in the core rupturing and subsequently igniting, causing a release of radioactive gases and particulates into the atmosphere. A more serious incident was averted when the fire was extinguished using a high-risk strategy of flooding the core with water. On October 10, 1957, the graphite core of a British nuclear reactor at the Windscale site, near Sellafield, caught fire, releasing substantial amounts of radioactive contamination into the surrounding area. ... The word anneal has several meanings: In metallurgy and materials science annealing is a heat treatment wherein the microstructure of a material is altered, causing changes in its properties such as strength and hardness. ... A chain reaction is a sequence of reactions where a reactive product or biproduct causes more additional reactions. ... Radioactive decay is the set of various processes by which unstable atomic nuclei (nuclides) emit subatomic particles. ... Gas (actually, as), the GNU assembler, is the default GCC back-end. ... Particulates, alternately referred to as Particulate Matter (PM) , aerosols or fine particles are tiny particles of solid or liquid suspended in the air. ... Atmosphere may refer to: a celestial body atmosphere, e. ... Fire is a form of combustion. ... Water (from the Old English word wæter) is a colorless, tasteless, and odorless substance that is essential to all known forms of life and is known also as the most universal solvent. ...

No currently-operating US nuclear reactor uses graphite. The dozen RBMKs left over from the Soviet Union are likely the last nuclear power plants to do so - although in the world there may be some graphite-containing nuclear reactors producing plutonium for weapons. US,Us or us may stand for the United States of America us, the oblique case form of the English language pronoun we. ... Nuclear power station at Leibstadt, Switzerland. ... RBMK is an acronym for the Russian reaktor bolshoi moshchnosty kanalny which means reactor (of) large power (with) channels, and describes a now-obsolete class of nuclear power reactor which was built only in the Soviet Union. ... A nuclear power plant in Cattenom, France. ...

External links

• An article on the Windscale fire, by the Lake District Tourist Board (http://www.lakestay.co.uk/1957.htm)