The Lucens reactor was a 6 MW experimental nuclear power reactor built next to

Lucens Lucens () is a municipality in the Broye-Vully district in the canton of Vaud in Switzerland. In 2017 the former municipalities of Brenles, Chesalles-sur-Moudon, Cremin, Forel-sur-Lucens and Sarzens merged into the municipality of Lucens. Hist ...

Vaud Vaud ( ; french: (Canton de) Vaud, ; german: (Kanton) Waadt, or ), more formally the canton of Vaud, is one of the 26 cantons forming the Swiss Confederation. It is composed of ten districts and its capital city is Lausanne. Its coat of arms ...

, Switzerland. After its connection to the electrical grid on 29 January 1968, the reactor only operated for a few months before it suffered an accident on 21 January 1969. The cause was a corrosion-induced loss of heat dispersal leading to the destruction of a pressure tube which caused an adjacent pressure tube to fail, and partial meltdown of the core, resulting in radioactive contamination of the cavern.

Description

In 1962 the construction of a Swiss-designed pilot

nuclear power plant A nuclear power plant (NPP) is a thermal power station in which the heat source is a nuclear reactor. As is typical of thermal power stations, heat is used to generate steam that drives a steam turbine connected to a generator that produces ...

began. The heavy-water moderated,

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...

gas-cooled reactor was built in a

cave A cave or cavern is a natural void in the ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word ''cave'' can refer to smaller openings such as sea ...

rn. It produced 28 MW of heat, which was used to generate 6 MW of electricity, and it became critical 29 December 1966. It was fueled by 0.96%

enriched uranium Enriched uranium is a type of uranium in which the percent composition of uranium-235 (written 235U) has been increased through the process of isotope separation. Naturally occurring uranium is composed of three major isotopes: uranium-238 (238U ...

alloyed with

chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hard ...

cased in

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ...

alloy (magnesium with 0.6%

zirconium Zirconium is a chemical element with the symbol Zr and atomic number 40. The name ''zirconium'' is taken from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian '' zargun'' (zircon; ''zar-gun'' ...

) inserted into a

graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on la ...

matrix. Carbon dioxide gas was pumped into the top of the channels at 6.28

MPa MPA or mPa may refer to: Academia Academic degrees * Master of Performing Arts * Master of Professional Accountancy * Master of Public Administration * Master of Public Affairs Schools * Mesa Preparatory Academy * Morgan Park Academy * Mou ...

and 223 °C and exited the channels at a pressure of 5.79 MPa and at a temperature of 378 °C.

Nuclear accident

It was intended to operate until the end of 1969, but during a startup on 21 January 1969, it suffered a

loss-of-coolant accident A loss-of-coolant accident (LOCA) is a mode of failure for a nuclear reactor; if not managed effectively, the results of a LOCA could result in reactor core damage. Each nuclear plant's emergency core cooling system (ECCS) exists specifically ...

, leading to a partial core meltdown and the

radioactive contamination Radioactive contamination, also called radiological pollution, is the deposition of, or presence of radioactive substances on surfaces or within solids, liquids, or gases (including the human body), where their presence is unintended or undesirab ...

of the cavern, which was then sealed. Using the criteria of the

International Nuclear Event Scale The International Nuclear and Radiological Event Scale (INES) was introduced in 1990 by the International Atomic Energy Agency (IAEA) in order to enable prompt communication of safety significant information in case of nuclear accidents. The ...

, introduced in 1990 by the

International Atomic Energy Agency The International Atomic Energy Agency (IAEA) is an intergovernmental organization that seeks to promote the peaceful use of nuclear energy and to inhibit its use for any military purpose, including nuclear weapons. It was established in 195 ...

, the event has been assessed as a Level 4 "Accident with local consequences". The accident was caused by water condensation forming on some magnesium alloy

fuel element A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from n ...

components during shutdown and corroding them. These

corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...

products accumulated in some fuel channels. One of the vertical fuel channels was sufficiently blocked by it to impede the flow of carbon dioxide coolant, causing the magnesium alloy cladding to melt and further block the channel. The increase in temperature and exposure of the uranium metal fuel to the

coolant A coolant is a substance, typically liquid, that is used to reduce or regulate the temperature of a system. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, chemically inert and neither causes nor promotes corrosi ...

eventually caused the fuel to catch fire in the carbon dioxide coolant atmosphere. The pressure tube surrounding the fuel channel split because of overheating and bowing of the burning fuel assembly, and the carbon dioxide coolant leaked out of the reactor. No

irradiation Irradiation is the process by which an object is exposed to radiation. The exposure can originate from various sources, including natural sources. Most frequently the term refers to ionizing radiation, and to a level of radiation that will serve ...

of workers or the population occurred, though the reactor's cavern was seriously contaminated. The cavern was decontaminated, and the reactor was dismantled over the next few years. The plant was decommissioned in 1988, and the last radioactive waste was removed in 2003.

References

External links

Maps of Nuclear Power Reactors: Switzerland

Major Nuclear Power Plant Accidents
{{authority control Buildings and structures in the canton of Vaud Former nuclear research institutes Nuclear accidents and incidents Radioactively contaminated areas 1962 establishments in Switzerland 1969 disestablishments in Switzerland Former nuclear power stations in Switzerland

Description

Nuclear accident

See also

References

External links