The OK-650 reactor is the nuclear fission

Nuclear fission

In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...

 reactor

Nuclear reactor

A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...

 used singly to power the Soviet Navy

Soviet Navy

The Soviet Navy was the naval arm of the Soviet Armed Forces. Often referred to as the Red Fleet, the Soviet Navy would have played an instrumental role in a Warsaw Pact war with NATO, where it would have attempted to prevent naval convoys from bringing reinforcements across the Atlantic Ocean...

's
Project 685 Плавник (Mike),
Project 971 Щука-Б (Akula

Akula class submarine

Project 971 Щука-Б , is a nuclear-powered attack submarine first deployed by the Soviet Navy in 1986...

), and
Project 945 Барракуда, Кондор, and Марс (Sierra

Sierra class submarine

The Sierra I class or Project 945 nuclear submarine was the Soviet Union's successor class to the partly successful Project 705 Lira class submarine...

) submarine

Submarine

A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...

s, and in pairs to power the
Project 941 Акула (Typhoon

Typhoon class submarine

The Project 941 or Akula, Russian "Акула" class submarine is a type of nuclear-powered ballistic missile submarine deployed by the Soviet Navy in the 1980s...

) and
Project 949 Гранит and Антей (Oscar

Oscar class submarine

The Project 949 and Project 949A Soviet Navy/Russian Navy cruise missile submarines ....

) third generation submarines. It is a pressurized water reactor

Pressurized water reactor

Pressurized water reactors constitute a large majority of all western nuclear power plants and are one of three types of light water reactor , the other types being boiling water reactors and supercritical water reactors...

 (PWR), using 20-45% enriched

Enriched uranium

Enriched uranium is a kind of uranium in which the percent composition of uranium-235 has been increased through the process of isotope separation. Natural uranium is 99.284% 238U isotope, with 235U only constituting about 0.711% of its weight...

 uranium-235

Uranium-235

- References :* .* DOE Fundamentals handbook: Nuclear Physics and Reactor theory , .* A piece of U-235 the size of a grain of rice can produce energy equal to that contained in three tons of coal or fourteen barrels of oil. -External links:* * * one of the earliest articles on U-235 for the...

 fuel to produce 190 MW of power. It also powers the new Project 955 Borei

Borei class submarine

The Borei class is a class of nuclear-powered ballistic missile submarine produced and operated by the Russian Navy. The class is intended to replace the Delta III, Delta IV and Typhoon classes now in Russian Navy service...

submarines