The KLT-40 and KLT-40M reactors are nuclear fission reactors used to power the Taymyr-class icebreakers (KLT-40M, 171 MW) and the LASH carrier Sevmorput (KLT-40, 135 MW). They are pressurized water reactors (PWR) fueled by either 30–40% or 90 %[note 1] enriched uranium-235 fuel to produce 135 to 171 MW of thermal power.
The KLT-40S variant is used in the Russian floating nuclear power station Akademik Lomonosov. It was developed by OKBM Afrikantov and produced by NMZ. The KLT-40S produces 150 MW thermal (about 52 MWe at 35% efficiency). The KLT-40S also uses low-enriched uranium at 14.1% enrichment to meet international proliferation standards.