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OK-900 Atomic Reactor, Icebreaker

In 1966, during the preparation of the atomic icebreaker Lenin for the next navigation, a leak was discovered in the reactor vessel No. 1, which was impossible to eliminate without replacing the reactor. Replacing the housing was associated with a violation of the sealing of the 1st circuit. Dismantling was to be carried out in a difficult radiation environment.

Taking into account that the experimental nuclear installation used on the icebreaker corresponded to the level of scientific knowledge and technical capabilities of the domestic industry of the fifties, that over the elapsed time since the icebreaker was built, experience was gained in operating nuclear plants on the Lenin icebreaker, submarines and ground power stations of the USSR Council of Ministers No. 148-62 of February 18, 1967 decided to completely replace the OK-150 nuclear installation with an OK-900 type installation, the technical design of which was developed for icebreakers of the Arctic type ."

OKBM carried out studies on the layout of the OK-900 installation in the dimensions of the reactor compartment of the Lenin icebreaker. One of the options successfully "fit" into the space allotted for installation. Chief Designer of APPU I.I. Afrikantov, appreciating the advantages of this idea, achieved support for the proposed option to repair the icebreaker in MSM. After that, the first deputy minister of secondary engineering A.M. Petrosyants instructed OKBM to develop detailed materials (calculations, schedules, demonstration drawings, etc.) to replace the installation, the timing and cost of the work, the technology for dismantling and installing the equipment, and the manufacturing plants of APPU OK-900 equipment.

The generally accepted dismantling of equipment was unacceptable under the conditions of severe radiation conditions, therefore, a method was proposed for the aggregate removal of the entire nuclear installation without violating its sealing.

The large weight of the nuclear installation with biological protection did not allow it to be removed through the deck upward or across the board to the shore or a watercraft. Therefore, it was decided to remove the APPU through the bottom. At the same time, the desirability of unloading together with the atomic steam production installation and those structures and equipment that had operational radioactive contamination and could not be used in the layout solutions of the new nuclear installation was taken into account.

After studying, the method of free discharge at the burial place (Tsivolki Bay, Novaya Zemlya) using cumulative charges was adopted. The ship was towed to the burial area, where underwater electric cutting of the bottom of the bulkheads by divers was made, remote gas cutting of the lower sections of the bulkheads by cumulative charges and unloading the compartment with its simultaneous burial at sea.

Dismantling continued from September 8 to 19, 1967. September 26, 1967 a / l "Lenin" arrived in Murmansk, October 5 entered dock. To restore the bottom, the Iceberg Central Design Bureau and the Admiralty Plant used an original technological system: a new section, made according to the size of the cutout in the bottom, was towed through the water from the place of its assembly to the floating dock and installed on the keel track, the dock was melted to the required depth, and the icebreaker located in the dock with a bottom cutout just above the section. When the dock surfaced, the new section entered the cutout of the bottom of the icebreaker, after which it was welded with the main body. Work on the restoration of the bottom and installation of overboard reinforcement under the new modernization project was completed on November 20, 1967.

The developed and implemented project for the aggregate unloading of the OK-150 nuclear power plant unit on the Lenin icebreaker without breaking the compartment’s seal, with a launch weight of 3,700 tons and directly in the burial area is a unique project in terms of scale and engineering courage, clear in execution, completed for the first time in practice world shipbuilding. To fit and dock the new OKP-900 APPU reactor installation into the icebreaker’s hull, out of 675 ship’s premises 204 were re-formed or completely refitted. During the modernization, 6.2 thousand units of new mechanisms and equipment were installed, of which over 30 prototypes of the main equipment were installed.

The birth date of the OK-900 reactor installation can be considered 1964, when two Decrees of the USSR Council of Ministers (No. 667-271 of 08/06/1964 and No. 680-280 of 08/10/1964) were issued, providing for the design and construction of a series of new nuclear icebreakers of project 1052, and also design and supply of equipment PPU OK-900 for the lead icebreaker of this series. The basis for them was the positive results of the operation of the atomic icebreaker "Lenin" in 1960-1963. and the important economic role played by icebreakers in the development of remote regions of Siberia and the Far East,

A technical meeting on choosing an installation option (out of five options developed by OKBM) for the icebreaker of project 1052 was held in Gorky on April 22, 1965. The meeting recommended for further development the 4th option - PPU 0K-900 in a two-reactor version with 4 steam generators and 4 TsNPK. The main design feature of the installation was a block assembly unit for the main equipment of the reactor – steam generator – hydrochamber, connected by thick-walled pipes on the principle of “pipe in pipe”. This original solution allowed to exclude long pipelines of large diameter of the primary circuit. The pressure compensation system was selected gas. Steam generators for polyurethane foam should be made in the following variant: the medium of the first circuit is located in the annulus, and the medium of the second circuit is inside the pipe system.

The preliminary design of the OKP-900 PPU with a capacity of 159 MW was completed in September of the same year.

The Council of Ministers of the USSR set the task of “reviving” the icebreaker by April 22, 1970 - the 100th anniversary of the birth of V.I. Lenin. Due to time constraints, OKBM proposed to put into production the main PPU equipment with a long manufacturing cycle (reactor shells, volume compensators, KR and A3 drives, etc.), without waiting for approval of the OK-900 technical project developed under the scientific supervision of the Atomic Institute Energy imeni I.V.Kurchatov.

The decree of the USSR Council of Ministers on project 1052 did not provide for testing the installation on its ground-based prototype, and complex tests of the PUF were supposed to be carried out as part of the mooring tests of the lead icebreaker of project 1052. The use of PU-OK-900 on the Lenin atomic icebreaker made it possible to verify all the adopted design and design decisions in real conditions, test the systems and equipment before launching them into serial production for the icebreakers of project 1052.

The technical and working projects of PPU 0K-900 were approved on May 18, 1967. The main structural differences of the new OK-900 RU from OK-150 are:

• the transition to the block layout of the main equipment, involving the connection of its elements with short pipelines using the principle of "pipe in pipe";
• refusal of a two-way coolant circulation circuit in the core;
• placement of inlet and outlet nozzles in the upper part of the reactor vessel in order to prevent exposure of fuel assemblies when the primary circuit breaks;
• increase in the number of loops of the primary circuit to four, with the placement of one two-speed main circulation pump for each loop;
• application of gas pressure compensation.

One of the important innovations was the reversal of the circulation scheme in the circuits: the coolant of the first circuit began to be supplied to the annulus of the steam generator, and the water of the second circuit was introduced through the pipes. Such a scheme, which was later applied to other naval switchgears, simplified the fight against coolant leaks and made it possible to reduce their probability by replacing tensile stresses in the GHG pipes with compressive ones. At the same time, it presented additional requirements for the bodies of steam generators, which, however, under the conditions of more intense loads on ship RPs, were technically easier to satisfy than to achieve the reliability of a branched pipe system. A number of materials were replaced with alloys more resistant to stress corrosion.

The maintainability of the reactor plant has increased significantly, which constituted a serious problem of the previous reactor. This was ensured by changing the layout of some nodes (increasing their availability), using removable biological protection elements, and so on.

In OK-900 RU, dispersion fuel with an enrichment of 35-40% is used. The height of the active zone is reduced to 100 cm with an increased (up to 117 cm) diameter. Experiments with the cladding material of the fuel rods ceased - the choice was made in favor of steel.

The main manufacturers and suppliers of equipment for PPU 0K-900 steel:

Machine-building plant (Gorky) - reactors, auxiliary equipment of the 1st circuit (filter coolers, filters), piping parts, circulation pumps of the 1st circuit, control and protection system drives and other equipment. Barricades Plant (Volgograd) - reactor vessels, pressure chambers and auxiliary equipment, volume compensators. Baltic Plant (Leningrad) - new steam generators. Izhorskiy Zavod (Kolpino city) - blanks for reactor caps, steam generator housings and slabs for biological protection.

Preparation for production and installation of PPU at the Zvezdochka machine-building enterprise began in March 1967. Based on the production capabilities of the enterprise, which had cranes with a maximum lifting capacity of 150 tons, the installation of biological protection equipment and piping PPU OK-900 was carried out by the aggregate-node method, the essence of which was that the PUF of each side was divided into 2 main units, manufactured in the workshop conditions of the Zvyozdochka enterprise:

• Unit No. 1 (reactor, 4 hydraulic chambers TsNPK) with a total weight of 85 tons;
• Unit No. 2 (ZhVZ tank) with a total weight of 130 tons.

In parallel with the manufacture and installation of the OK-900 installation, the production and testing of prototypes of equipment and systems were underway, which were also the prototypes (reactor, steam generator, TsNPK, emergency protection drives and compensating gratings, CPS systems, etc.) from manufacturers. Tests of experimental samples were carried out, as a rule, at special stands at OKBM and at manufacturing plants, which, basically, were successful, confirming the characteristics inherent in the design. The exception was the PG-18t steam generator developed by SKBK, the tests of which were carried out at the special stand of the Admiralty Plant in the summer of 1968.

The first trouble was clarified when the steam generator reached its rated load, in which, due to parasitic overflows of the primary coolant, in addition to the pipe system, the superheated steam produced by the steam generator did not meet the specification temperature (238 ° C instead of 290°C).

The second drawback of the PG-18t design was identified during the emergency cooling mode, when the main body connector with the pipe system “opened”, throwing part of the primary coolant into the atmosphere. The selection committee rejected the product. The situation was further complicated by the fact that the blanks of the steam generator bodies were already at that moment on the machines of the Izhora plant, while the Zvezdochka enterprise delayed the manufacture and installation of unit No. 1, which was originally supposed to include 4 steam generators. Therefore, it was decided to ship unit No. 1 to order without steam generators, and install the steam generator and weld the main pipes to the reactor directly on the icebreaker.

SKBK found a solution that eliminates parasitic leaks of the primary coolant in the steam generator in addition to the pipe system, which led to a decrease in the temperature of the steam behind the steam generator, within two months the steam generators were finalized, the tests were continued and successfully completed, which allowed the OK-900 installation to be completed by the deadline.

On March 16, 1970, factory mooring trials of the nuclear installation of the Lenin icebreaker began. April 20, 1970, the interagency commission began work. She praised the quality of installation of the OK-900 installation, mechanisms, assemblies, integrated automation systems. By mid-April 1970, all installation work on the OKP-900 APPU and its systems was almost completely completed.

On April 22, 1970, after lifting the rods of the compensating groups, the OK-900 reactor showed the first signs of “life”, “breathed” and the OK-900 installation began its long and successful journey. On April 23, at 2:30 a.m., reactor No. 2 of the port side installation was launched. Thus, the task is to introduce the OKP-900 APPU into action on the birthday of V.I. Lenin was executed.

The physical launch of the No. 1 starboard installation was carried out on May 1, 1970.

The output of the reactors to the energy level of power was carried out: Reactor No. 1 - May 4, 1970, No. 2 - April 29, 1970. Dynamic tests and analysis of the results were carried out by specialists of the Institute of Atomic Energy named after I.V. Kurchatov under the direction of O.A. Lebedev.

The mooring tests of the automatic control and control system when the icebreaker was parked near the wall of the plant ended on May 18, 1970. After that, during the period from May 19 to May 24, when passing the icebreaker from Severodvinsk to Murmansk, sea acceptance tests were carried out. On May 24, the Lenin atomic icebreaker returned from sea trials from the Barents Sea to the home port of Murmansk.

On June 20, the interdepartmental commission accepted the OKP-900 APPU with all the mechanisms and systems serving it, as well as all modernization work and repairs of the Lenin icebreaker, and handed the icebreaker to the Murmansk Shipping Company for operation. For the first time in the practice of shipbuilding, the creation of the automatic control system was carried out for 6 years from the start of design to the commissioning of the vessel.

June 21, 1970 the icebreaker "Lenin" went into the Arctic navigation.

The work of the icebreaker confirmed the high efficiency of the use of nuclear energy on ships of the icebreaker fleet. The icebreaker for five years exceeded the life expectancy granted to it by the project and worked on ice tracks for 30 years. During this time, 3741 transport and icebreaking ships were spent in the ice of the Arctic, 654.4 thousand nautical miles were covered. As a result of the commissioning of the atomic icebreaker, navigation in the western region of the Arctic was extended from 3 to 11 months.

The icebreaker was withdrawn from the Atomflot in 1989. After lengthy technical activities and restoration on December 3, 2009, a museum was opened on the icebreaker "Lenin", standing at the pier of the Murmansk Marine Station.

Subsequently, two OK-900A reactors were installed on the nuclear powered icebreakers of Project 1052 “Arktika”, which are an improved, somewhat more powerful (171 MW) version of the OK-900 reactor. RU OK-900A also stood on the SSV-33 Ural large nuclear reconnaissance ship, the only ship of the 1941 USSR Navy project.