SSTAR's an acronym for the "small, sealed, transportable, autonomous reactor" - being primarily researched and developed in the USA by Lawrence Livermore National Laboratory. It's designed as a fast breeder nuclear reactor that's passively safe. It's a self-contained fuel source of Uranium-235 containing also Uranium-238 which will be partly consumed by fast-neutron fission and, more importantly, converted into more fissile material ("breeding" Plutonium). It should've an operative life of 30 ye… (More on Sstar)