The OK-150 reactor and its successor, the OK-900 reactor are Soviet marine nuclear fission reactors used to power ships at sea. They are pressurized water reactors (PWRs) that use enriched uranium-235 fuel. They have been used in various Russian nuclear-powered icebreaker ships. OK-150 Specifications: Distillate water was used for heat transfer and as a moderator. The core was 1.6 m high by 1 m diameter. It consisted of 219 fuel assemblies, totalling 7,704 fuel pins. There was a biological shield made of concrete mixed with metal shavings. OK-900A Specifications: