The Zircaloy casing is the second barrier to release that separates the radioactive fuel from the rest of the reactor. The solid fuel pellet is the first barrier that retains many of the radioactive fission products produced by the fission process. These fuel rods are then put together to form an assembly of which several hundred make up the reactor core.Ĭourtesy of Nuclear Fuel Industries, Ltd ( The "defence-in-depth" principle is used by the nuclear industry to achieve a high level of safety. The fuel is manufactured in pellets put into a long tube made of Zircaloy (an alloy of zirconium) with a failure temperature of 1,200☌ (caused by the auto-catalytic oxidation of water), and sealed tight. The nuclear fuel used is Uranium Oxide, a ceramic with a very high melting point of about 2,800☌. below how the boiling water reactor works. The 6 reactors at Fukushima Daiichi NPP are of the type known as boiling water reactor (BWR). * The moderator slows the free neutrons to ensure that they will be absorbed by the nucleus upon collision, hence sustaining the fission process. High-Temperature Gas- Cooled Reactor (HTGR) Light Water cooled Graphite moderated Reactor (LWGR)/ (RBMK) Pressurized Heavy Water moderated Reactor (PHWR)/ (CANDU) They are generally classified according to the type of coolant and moderator*, as listed below: Types of Nuclear ReactorsĪt present, there are 7 types of reactors in operation globally. More than 99% of the radioactivity produced during the fission reaction is retained in the fuel rods. In addition, when uranium is 'split' into two during the fission process, significant quantities of highly radioactive wastes are created. It is therefore important to ensure safe operation of the nuclear power plant so that there is no accident or leakage of radiation which could cause harmful effects to people and the environment. Radiation is given out as a by-product of the chain reaction. The energy generated in the nuclear fission process is harvested to produce electricity in a NPP.Ĭlick here for an illustration of the fission process. burning, nuclear fission gives off an enormous quantity of energy. When enough of these neutrons produce further fissions, the process becomes self-sustaining. If the ejected neutrons go on to strike other unstable atoms nearby, those too can break apart, releasing further neutrons in a process known as a chain reaction. It results in two lighter atoms and the ejection of two or three neutrons. This phenomenon occurs when certain heavy atoms are struck by a neutron - they absorb it, become unstable and split apart. Click here for Japan Nuclear Accident FAQĬurrently, all nuclear power plants derive power from nuclear fission.This brief provides some technical background on nuclear reactors and the major accident that occurred at the Fukushima Daiichi Nuclear Power Plant (NPP) on 11 March 2011. Technical Background on Fukushima Daiichi Nuclear Power Plant Accident
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