slightly-enriched uranium

Noun

 * 1)  Enriched uranium with 0.9-2% uranium-235, requiring a special moderator with very low neutron absorption (such as heavy water or high-purity graphite) in order to be able to sustain a nuclear fission chain reaction.  Used to increase power output and efficiency in a few types of nuclear reactors capable of running on natural uranium, and for downblending of highly-enriched uranium from decommissioned nuclear weapons into low-enriched uranium suitable for use in commercial power reactors.