Editing Subcritical reactor (section)

==Subcritical hybrid systems==
While ADS was originally conceptualized as a part of a [[light water reactor]] design, other proposals have been made that incorporate an ADS into other [[generation IV reactor]] concepts.{{citation needed|date=April 2014}}

One such proposal calls for a [[gas-cooled fast reactor]] that is fueled primarily by [[plutonium]] and [[americium]]. The neutronic properties of americium make it difficult to use in any critical reactor, because it tends to make the [[void coefficient|moderator temperature coefficient]] more positive, decreasing stability. The inherent safety of an ADS, however, would allow americium to be safely burned. These materials also have good neutron economy, allowing the pitch-to-diameter ratio to be large, which allows for improved natural circulation and economics.