What is Nuclear reactor?
[[File:Scwr.svg|thumb|left|Supercritical-Water-Cooled Reactor.]] [[File:Three Mile Island (color)-2.jpg|thumb|left|Three Mile Island nuclear reactor and power plant]] A '''nuclear reactor''' is a [[machine]] that uses [[nuclear fission|fission]] to generate [[heat]]. There are different designs which use different [[fuel]]s. Most often, [[uranium|uranium-235]] or [[plutonium|plutonium-239]] are the main components of these fuels. Most nuclear reactors are power reactors, used to make electricity. In [[nuclear power plant]]s heat from the [[Nuclear fission|fission reactions]] in the reactor changes water into [[steam]]. The steam is then used to power [[electric]] [[turbine]]s which make [[electricity]]. Some small power reactors run nuclear submarines. As with other [[steam engine]]<nowiki/>s, the turbines take energy from the movement of the steam. Some reactors are used for other purposes. Some reactors make [[neutrons]] for scientific [[research]] and others make [[radioactive]] [[isotopes]]. Some [[universities]] have small nuclear reactors to teach students how reactors work. The first nuclear reactor was built in 1942 by a team of scientists led by [[Enrico Fermi]].<ref name=scw>{{cite encyclopedia |url= http://www.credoreference.com/entry/abccscience/nuclear_physics |title=Nuclear Physics (2005) |first= |last= |encyclopedia=Science in the Contemporary World: An Encyclopedia |year=2011 |accessdate=May 29, 2011}}</ref> This was a part of the [[Manhattan Project]] which needed the fuel from the reactor to make the [[atomic bomb]].<ref name=scw/> The first nuclear reactor to make electricity was a small experimental reactor built in [[Idaho]] in 1951.<ref name=scw/> It made just enough electricity for four light globes.<ref>http://www.inl.gov/factsheets/ebr-1.pdf Experimental Breeder Reactor 1</ref> Nuclear reactors are expensive to build because of the many safety features they need to have.<ref name=scw/> There is also a problem with the huge amount of radioactive waste from the reactors.<ref name=s