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VM-4 Atomic Reactor, Submarine

The successful creation of a nuclear submarine flotilla with a VM-A reactor became the basis for the further development of the nuclear submarine fleet. The development of atomic science and technology, the expansion of theoretical knowledge and experimental data have opened the possibility for the development of a more advanced transport reactor, which is a second-generation installation, which would take into account all the mistakes of the previous project and use the latest materials, designs and devices. New nuclear power plants received the indices “VM-4” and “V-5”.

The main requirements for the new generation of submarines were to increase their reliability and survivability, as well as to reduce the size of the nuclear installation. The basis for the start of work was the Resolution of the Central Committee of the CPSU and the Council of Ministers of the USSR, adopted in August 1958.

From the very beginning, the design of reactors went in two alternative directions, whose supervisor was A.P. Alexandrov. The scientific innovations and designers identified the main innovations that distinguish the second-generation reactor:

• the exception of a branched system of pipelines of the primary circuit;
• the use of several compensation grids with individual drives;
• transition to two-speed primary circulation pumps;
• increasing the resource of all PPU equipment up to 12 thousand hours, and campaigns in the core — up to 5 thousand hours.

The first direction, which was entrusted to the Design Bureau of Plant No. 92 (Gorky, chief designer I.I.Afrikantov), involved a transition to completely new design solutions that eliminated the shortcomings of the previous design of a nuclear power plant. The OKB project was handled by sector “B”, which already had experience in creating a nuclear superheater installation (PPU) for the atomic icebreaker “Lenin”. The design bureau development reactor received the BM-4 index.

The second direction, where NII-8 (the chief designer N. A. Dollezhal) was the ideological leader, was to preserve the main circuit layout solutions of the VM-A reactor and to modernize its bottlenecks as much as possible. The second generation reactor for the NII-8 design submarine received the “B-5” index.

At the first stage of the design of the installation, the designers of the Design Bureau of Plant No. 92 provided for large-scale prospecting to select the type of installation and basic layout solutions. On their basis, the choice was made in favor of the block design of PPU with a water coolant. The main design features of installations of this type were two block assemblies: a “reactor-steam generator” with a “pipe in pipe” and a “steam generator-pump” primary circuit connection.

As the main technical solution, a two-reactor version of a nuclear steam generating unit (NAPP) with an on-board arrangement of two groups of main equipment was adopted.

After consideration of the proposals of NII-8 and Design Bureau of Plant No. 92 by the scientific supervisor and gas supplier, it was recognized that the latter more fully meets the requirements for second-generation nuclear submarines and can be recommended for further study. Subsequently, the BM-4 installation was created immediately for three nuclear submarine projects - projects 670, 671 and 667, developed by various design bureaus.

The first project - for the nuclear submarines of project 671 - received the OK-300 index, the second - for the nuclear submarines of the project 670 - the OK-350 index, the third - for the nuclear submarines of the project 667 - the OK-700 index. The main equipment of various installation options was almost completely unified, and the PUFs differed only in the number of loops (4 or 5 per reactor) and the bindings to the fundamental structures of the reactor compartments. One 90 MW reactor and one turbine were installed on Project 670 nuclear submarines, two 72 MW reactors each and one turbine on Project 671 nuclear submarines, and two 90 MW reactors and two turbines on Project 667 nuclear submarines. The technical projects for the VMU-4 (OK-300) PPU, the VM-4-1 (OK-350) PPU and the VM-4-2 (OK-700) PPU were approved in April 1960, March 1961 and August 1963 respectively.

The creation of reliable in operation PPU OK-300, OK-350, and OK-700 with minimum weight and size characteristics was made possible thanks to the compact arrangement of equipment around the reactor, which made it possible to simultaneously use it as biological protection elements, and significantly reduce the length of primary circuit systems and welds greatly increased equipment reliability.

The equipment of the installation was made with firmly-dense housings designed for primary pressure. So, the hulls and bottoms of the OK-300 and OK-350 reactors were made of pearlitic steels and welded by automatic welding. Inside the case was lined with anticorrosive cladding, which increased the manufacturability and reliability of the equipment.

A one-way flow diagram of the coolant circulation through the core was adopted, which simplified the design of the reactor internal block and made it possible to use natural coolant circulation to cool the reactor.

In the reactor core, rod and double-ring fuel rods with uranium enrichment of 21% were used (the zone with 2 ring fuel rods was the only one that completely developed its energy resource). The design core recharge cycle was 8 years.

Designers and designers had to abandon the bench prototype, and the first full-time products for PPU came immediately for installation in the nuclear submarine. To compensate for the lack of a full-fledged stand, the Design Bureau focused on step-by-step inspection and testing of equipment, for which more than 200 stands were created. In particular, thermocyclic tests of full-scale models of connecting nozzles of the reactor-generator, head samples of the reactor vessels were carried out. In 1964, prototype reactors of the OK-300 and OK-350 units underwent comprehensive tests for the collection of reactors and the functioning of control and protection systems, after which they were adopted by interagency commissions.

The experience of creating the first generation nuclear submarines has shown that the installation of nuclear-powered submarines in the reactor compartment due to the cramped space of the latter is the most difficult stage in the manufacture of nuclear submarines. New layout solutions created the prerequisites for transferring a large amount of installation work to prefabricated sections, which shortened the installation time and improved its quality. To supervise the installation of nuclear power substations, special crew monitors recruited from the OKB specialists were sent to the nuclear submarine manufacturers. However, this did not become a 100% guarantee to exclude incidents on land - they happened, including nuclear ones.

There have been other incidents. So, in November 1966, at the Sevmash enterprise, during hydrotesting of the reactor for the Project 667 nuclear powered submarines, a significant amount of dirt and metal shavings was discovered in the apparatus manufactured at the Volgograd Barrikady Plant. This incident was immediately qualified as an “emergency”, as it called into question the absence of foreign objects in previously manufactured equipment. This provoked a check of all previously mounted reactors, which delayed the deadline for the delivery of a number of nuclear submarines of projects 670 and 667. The incident ended with the release of a special regulatory document regulating the procedure for closing and opening equipment of the primary circuit of the nuclear submarine fleet.

In the early 70s, two serious shortcomings of BM-4 type PUFs were revealed: premature depressurization of rod-type fuel rods and the formation of cracks in the risers of the reactor caps. To eliminate them, new core designs with upgraded rod and ring fuel rods were developed and the design of the reactor cover was improved.

During the operation of the second generation nuclear submarines, nuclear installations have demonstrated significantly increased reliability of systems and equipment. With more intensive operation of these nuclear submarines, the number of equipment failures or malfunctions was ten times smaller compared to the first generation of boats.

Project 671 nuclear submarines (Ruff) was created as a hunter boat and was intended to destroy American nuclear submarines with ballistic missiles. The main boat K-38 was laid in April 1963 in Leningrad at the Novo-Admiralty Plant (now the Admiralty Shipyards). The project 671 nuclear submarine used one propeller shaft, which allowed to reduce the displacement and noise of the ship and to obtain a significantly higher underwater speed than its foreign counterparts. The implementation of the single-shaft scheme also made it possible to place the main turbo-gear unit and both autonomous turbogenerators with all associated equipment in one compartment, which ensured a decrease in the relative length of the boat hull. In the construction of a durable case, it was decided to use new AK-29 steel, which allowed to increase the depth of immersion. On November 5, 1967, an act was signed on acceptance of the K-38 project 671 lead boat into the USSR Navy, and it became part of the Northern Fleet. A total of 15 boats of Project 671 were built, most of them served in the Northern Fleet.

Project 670 nuclear submarines (Skat) were designed to destroy ships traveling as part of convoys, mainly aircraft carriers as part of aircraft carrier strike groups. Their construction was carried out at the Krasnoye Sormovo plant, Gorky. The submarine had a two-hull architecture with spindle-shaped contours of the light hull, which has an elliptical section in the bow due to the placement of missile weapons.

The first nuclear submarine was launched on August 2, 1966. The acceptance certificate for the lead ship K-43 of series 670 was signed on November 6, 1967, and it became part of the Northern Fleet.

In total, 11 nuclear submarines of project 670 were built.

Project 667 nuclear submarines were created as a carrier for ballistic missiles with a nuclear warhead. After the government’s decision to change the weapons used on it, the project received index 667A (Navaga). New missile carriers became known as the SSBN (strategic missile submarine cruiser).

The project 667 boat was a two-hull, the fore end had an oval shape, the stern end - spindle-shaped. The robust case of cylindrical cross section with a diameter of 9.4 m was divided into 10 compartments, of which the 7th compartment was the reactor compartment. Main power plant with a rated power of 52 thousand hp consisted of autonomous starboard and port side blocks. Each unit included a water-water reactor VM-4-2 (OK-700), a steam turbine unit with a turbo-gear unit, and a turbogenerator.

The construction of submarines under project 667A was carried out rapidly. The first K-137 submarine of project 667A was laid down at the Northern Machine-Building Plant on November 9, 1964. Launching took place on August 28, 1966, and acceptance tests began on September 1. The K-137 nuclear submarine went into operation on November 5, 1967 and was transferred to the Northern Fleet on November 24.

Series 667A became the largest of all the projects of the Soviet submarines and had a large number of modifications. Between 1967 and 1974 34 ships of projects 667A and 667AU were built.

All boats of projects 671, 670 and 667 were withdrawn from the fleet from 1989 to 1997.