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Experimental Breeder Reactor-II (EBR-II) is a reactor designed, built and operated by Argonne National Laboratory in Idaho.〔(Experimental Breeder Reactor II ), Argonne National Laboratory〕 It was shut down in 1994. Custody of the reactor was transferred to Idaho National Laboratory after its founding in 2005. It is a sodium cooled reactor with a thermal power rating of 62.5 megawatts (MW), an intermediate closed loop of secondary sodium, and a steam plant that produces 19 MW of electrical power through a conventional turbine generator. The original emphasis in the design and operation of EBR-II was to demonstrate a complete breeder-reactor power plant with on-site reprocessing of metallic fuel. The demonstration was successfully carried out from 1964 to 1969. The emphasis was then shifted to testing fuels and materials for future, larger, liquid metal reactors in the radiation environment of the EBR-II reactor core. It operated as the Integral Fast Reactor prototype. Costing more than US$32 million, it achieved first criticality in 1965 and ran for 30 years. It was designed to produce about 62.5 megawatts of heat and 20 megawatts of electricity, which was achieved in September 1969 and continued for most of its lifetime. Over its lifetime it has generated over two billion kilowatt-hours of electricity, providing a majority of the electricity and also heat to the facilities of the Argonne National Laboratory-West. In controlled testing in 1986, with the EBR-II reactor running at full power and the emergency shutdown systems disabled, the reactor's supply of electricity was intentionally turned off, causing the coolant pumps to stop. This is a worse scenario than what happened in the Fukushima Nuclear Disaster. (At Fukushima, which began operation in 1971, the emergency shutdown system turned off the reactor as soon as it detected the earthquake. However the tsunami destroyed the electric generators powering the coolant pumps, which needed to continue running after the reactor shutdown. Subsequently, the core overheated and meltdown occurred.) EBR-II, in contrast, handled the event without creating a dangerous situation. EBR-II had a negative thermal coefficient of reactivity that shut down the reactor when the temperature increased due to loss of the coolant pumps; the time required to heat the large pool of sodium surrounding the reactor provided a sufficient time buffer for the passive decay heat removal system to prevent the EBR-II reactor from melting down. The safe shutdown of the EBR-II relied only on the laws of physics and did not require operator or control system intervention. == Design == The fuel consists of uranium rods 5 millimeters in diameter and 33 cm (13 inches) long . Enriched to 67% uranium-235 when fresh, the concentration dropped to approximately 65% upon removal. The rods also contained 10% zirconium. Each fuel element is placed inside a thin-walled stainless steel tube along with a small amount of sodium metal. The tube is welded shut at the top to form a unit 73 cm (29 inches) long. The purpose of the sodium is to function as a heat-transfer agent. As more and more of the uranium undergoes fission, it develops fissures and the sodium enters the voids. It extracts an important fission product, caesium-137, and hence becomes intensely radioactive. The void above the uranium collects fission gases, mainly krypton-85. Clusters of the pins inside hexagonal stainless steel jackets 234 cm (92 inches) long are assembled honeycomb-like; each unit has about 4.5 kg (10 lbs) of uranium. All together, the core contains about 308 kg (680 lbs) of uranium fuel, and this part is called the driver. The EBR-II core can accommodate as many as 65 experimental sub-assemblies for irradiation and operational reliability tests, fueled with a variety of metallic and ceramic fuels—the oxides, carbides, or nitrides of uranium and plutonium, and metallic fuel alloys such as uranium-plutonium-zirconium fuel. Other sub-assembly positions may contain structural-material experiments. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Experimental Breeder Reactor II」の詳細全文を読む スポンサード リンク
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