The OK-650 reactor is the nuclear fission reactor used for powering the Soviet Navy's Project 685 Плавник/Plavnik, Project 971 Щука-Б/Shchuka-B, and Project 945 Барракуда/Barrakuda, Кондор/Kondor, and Марс/Mars submarines, and in pairs to power the Project 941 Акула/Akula and Project 949 Гранит/Granit and Антей/Antei third generation submarines. Wikipedia