WHAT IT IS
KN-3 (КН-3) is the Soviet/Russian naval pressurized-water reactor designed by OKBM (chief designer F. M. Mitenkov) to steam the Project 1144 Orlan battlecruisers. Two reactors make one ship plant. The core is the VM-16 type. Western and some Russian notes also call the plant OK-900B — a compact, hotter cousin of the OK-900A icebreaker module, not a submarine OK-650. It is a two-loop-circuit, four-primary-loop, thermal-neutron PWR. It is not RITM-200 and not a liquid-metal Alfa plant.
The same family was intended for the unfinished Project 1143.7 Ulyanovsk carrier and appears against Project 1941 Titan in some reactor tables. Four KN-3 pairs were built, one pair per Orlan hull.
HISTORY
Early studies for a nuclear cruiser asked for two steam-generating units of at least 300 MWt each — more than three times a second-generation Soviet SSN plant and about twice an icebreaker OK-900. Compact mass was mandatory: the reactor sits in a surface hull that also carries belt armor and a Granit battery. OKBM delivered a working design in 1972. New hull steel (VK-2), stainless piping with organosilicate anticorrosion coat, and longer fuel assemblies than the icebreaker core (about 1.1 m versus 0.9 m; zone height raised ~1.3×) were part of that drawing. Fuel came from the Elektrostal machine works.
Kirov (later Admiral Ushakov) cold-criticalled both reactors on 18 and 19 April 1980. On natural circulation the plant reached 22.5 % power against a 15 % design claim, which let the core run about 8 °C cooler at the same superheated-steam temperature. The ship made about 30 knots despite a 100 mm armor belt and more than 25,000 t displacement. A 1983 CIA note on trials has been cited for 40 knots at 83 % plant power; treat that as an intelligence figure, not a Navy brochure.
HOW THE REACTOR WORKS
Primary: high-purity water (bidistillate) is both moderator and coolant. It is pumped through the core at high pressure — about 14 MPa (140 bar) at reactor outlet in one engineering sheet, “about 200 atmospheres” in the Project 1144 encyclopedia article — picks up heat, and does not boil. Four circulation loops per reactor. Core flow on that same sheet: 3,381 t/h per reactor.
Secondary: primary heat boils a separate water inventory. That steam drives the turbines. Two GTZA (turbine-reduction units), 70,000 hp (about 51 MW) each, two shafts, five-blade screws. Combined published shaft power of the nuclear-plus-boiler plant: 140,000 shp.
CONAS — Combined Nuclear And Steam — is the ship-level trick. Two oil-fired auxiliary boilers (about 115–120 t/h steam each) can be cut in for sprint or can drive the ship alone at 14–17 knots if both reactors are down. Nuclear steam covers cruise (about 20 knots in some Western write-ups). Full plant: 30–32 knots in open naval lists. Fuel oil for boiler-only running is good for roughly 1,000 nmi.
The automated plant occupies three compartments. Reactor spaces have splinter protection cited at 76 mm in one Western survey and a 100 mm side / 35 mm end scheme in German-language Project 1144 notes.
CORE AND RATINGS
Thermal power is the number that wanders. Design requirement and most English cards: ~300 MWt per reactor. Russian Project 1144 page: two reactors, 150 MWt each in one table line, and 342 MWt combined thermal in the plant paragraph. A paper that treated KN-3 as a possible buried civilian module used 230 MWt × 2. Report the spread: the plant was sized as a pair of ~300 MWt-class PWRs; some Russian tables quote lower.
Fuel: HEU. Open figures cluster at about 70 % U-235; Western naval-reactor tables give 55–90 %. First-load U-235 mass in the buried-plant paper: 448 kg per reactor at 53.3 % average enrichment — a different core assumption, listed here so the reader sees the range. Core campaign: 10–11 years in the cruiser article; 27,500 hours in the module paper. Unreplaceable equipment life talked at up to 40 years.
Ship electrical: four 3 MW turbo-generators and four 1.5 MW gas-turbine generators (18 MW of stations in the Russian table).
WHERE IT WAS FITTED
Project 1144 / 1144.2 Orlan — Kirov, Frunze, Kalinin, Yuri Andropov; later Admiral Ushakov, Admiral Lazarev, Admiral Nakhimov, Pyotr Velikiy. Four ships, eight reactors. Project 1143.7 Ulyanovsk — same plant on the drawing; hull scrapped incomplete. Project 1941 Titan — listed with VM-16 / KN-3 (OK-900B) in some inventories.
As of the mid-2020s open fleet picture: Pyotr Velikiy has been the steaming KN-3 cruiser; Admiral Nakhimov has been in a long modernization; Ushakov and Lazarev were not funded back to steam.
WHAT IT IS NOT
Not OK-650 (Oscar, Akula, Typhoon, Yasen-class SSN/SSGN plants). Not RITM-200 (LK-60 icebreakers and later surface projects). Not KN-3 the laboratory oil-in-water meter, and not a KN-series DC contactor.
IN ONE SENTENCE
KN-3 is OKBM’s four-loop surface PWR — VM-16 core, OK-900 family, ~300 MWt class, HEU, ten-year core — fitted in pairs with oil boilers as the CONAS plant that drives Project 1144 Orlan at 30 knots and was meant to steam Ulyanovsk.