SSTAR is an acronym for the "small, sealed, transportable, autonomous reactor" - being primarily researched and developed in the US by Lawrence Livermore National Laboratory. It is intended as a fast breeder reactor that is tamper resistant, passively safe, has a self-contained fuel source of Uranium-238 and an operative life of 30 years, which provides a constant power source between 10-100 megawatts.

Currently, no prototypes for SSTARs exist - one is expected by 2015, and they are being researched as the primary replacement for today's light water reactors.