Editing Integral fast reactor (section)

===Liquid metal sodium coolant===
{{See also|BN-600 reactor}}
Unlike reactors that use relatively slow low energy (thermal) neutrons, [[fast-neutron reactor]]s need [[nuclear reactor coolant]] that does not moderate or block neutrons (like water does in an LWR) so that they have sufficient energy to fission [[actinide]] isotopes that are [[fissionable]] but not [[fissile]]. The core must also be compact and contain the least amount of neutron-moderating material as possible. Metal sodium coolant in many ways has the most attractive combination of properties for this purpose. In addition to not being a neutron moderator, desirable physical characteristics include:

* Low melting temperature
* Low vapor pressure
* High boiling temperature
* Excellent thermal conductivity
* Low viscosity
* Light weight
* Thermal and radiation stability

Additional benefits to using liquid sodium include:

* Abundant and low-cost material
* Cleaning with chlorine produces non-toxic [[NaCl|table salt]]
* Compatible with other materials used in the core (does not react or dissolve stainless steel), so no special corrosion protection measures are needed
* Low pumping power (from lightweight and low viscosity)
* Protects other components from corrosion by maintaining an oxygen- and water-free environment (sodium would react with any trace amounts to make sodium oxide or sodium hydroxide and hydrogen)
* Lightweight (low density) improves resistance to seismic inertia events (earthquakes)

Significant drawbacks to using sodium are its extreme fire hazardousness in the presence of any significant amounts of air (oxygen) and its spontaneous combustion with water, rendering sodium leaks and flooding dangerous. This was the case at the [[Monju Nuclear Power Plant]] in a 1995 accident and fire. Reactions with water produce hydrogen which can be explosive. The sodium activation product (isotope) <sup>24</sup>Na releases dangerous energetic photons when it decays (albeit having only short half-life of 15 hours). The reactor design keeps <sup>24</sup>Na in the reactor pool and carries away heat for power production using a secondary sodium loop, but this adds costs to construction and maintenance.<ref>{{cite web |last=Fanning |first=Thomas H. |date=May 3, 2007 |title=Sodium as a Fast Reactor Coolant |url=http://www.ne.doe.gov/pdfFiles/SodiumCoolant_NRCpresentation.pdf |url-status=dead |archive-url=https://web.archive.org/web/20130113134710/http://www.ne.doe.gov/pdfFiles/SodiumCoolant_NRCpresentation.pdf |archive-date=2013-01-13 |access-date=2014-01-24 |website=Ne.doe.gov |publisher= |institution=Office of Nuclear Energy &#124; Department of Energy &#124; University of Chicago, [[Argonne National Laboratory|Argonne]]}}</ref>