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OK-150 Atomic Reactor, Icebreaker

In 1957, the Lenin icebreaker, the world's first atomic surface ship, set sail. Nuclear-powered icebreaker "Lenin" became the leading one in a special class of domestic ships designed for complex routes of the Northern Sea Route. Having relied on the creation of an atomic icebreaker, the Soviet Union solved two problems at once: it worked out the use of reactors in the surface fleet and commissioned a ship, the need for which for Arctic navigation was absolutely impossible to overestimate.

The decision to build an atomic icebreaker was adopted by the USSR Council of Ministers on November 20, 1953. The need for such an icebreaker was very acute. The fuel supply for diesel icebreakers was enough for a maximum of a month of travel, which was not enough for northern navigation. Therefore, a ship was required that could accompany the caravans of ships for a longer time. Nuclear-powered icebreaker can operate on average for 6-8 months without a break, and if there are special tasks, up to 12-14 months.

The following government decree of August 18, 1954 specified the task of creating the atomic icebreaker "Lenin" in terms, stages and main contractors. The design of the nuclear icebreaker was assigned to the Leningrad TsKB-15 (later the Iceberg Central Design Bureau). The chief designer of the icebreaker was appointed V.I. Neganov. The design of the atomic steam generating installation (APPU) was entrusted to the Design Bureau of the Gorky Plant No. 92 (later OKBM). The chief designer of APPU was approved by I.I. Africans. The scientific management of the icebreaker project was entrusted to A.P. Alexandrov, and a nuclear reactor - on I.V. Kurchatov, who later transferred his authority to A.P. Alexandrov.

Three APPU OK-150 reactors developed at the Design Bureau of the Gorky Plant No. 92 with a capacity of 90 MW each provided a total production of 360 t / h of steam with a temperature of up to 3100°C and a pressure of 28 atm. Each reactor had two circulation loops with two steam generators, two circulation pumps and one emergency pump. A steam pressure compensation system in the primary circuit was used. In the reactor core, uranium dioxide fuel with 5% enrichment in uranium-235 was used.

The technical design of OKPU OK-150 was developed in March 1955, and on June 17, 1955, it was approved and recommended for launch into production at the section of the NPS NTS of the Ministry.

When developing the APPU project for the first time, a whole series of complex scientific and technical problems were solved. One of them was a significant increase in the duration of the core campaign and the economical use of nuclear fuel. The implementation of the decision proposed by the scientific leadership on introducing burnable absorbers into the active zone to compensate for excess reactivity made it possible to increase the core campaign up to 200 days, and the use of zirconium alloys in the structural elements of the zone allowed a 1.5-fold decrease in uranium consumption compared to stainless steel core steels.

APPU OK-150 is a reactor installation (RU) with a loop layout, i.e. The main equipment of the circuit was located in separate buildings, interconnected by pipelines. Reactors of the OK-150 type belong to pressurized-water reactors of the vessel type, in which water under pressure is used as a heat carrier, as well as a neutron moderator. The reactor is made in the form of a thick-walled cylindrical vessel (body) with a flat lid and a bottom.

The material of the reactor vessel is carbon steel. The diameter of the cylindrical part of the casing is 186 cm, the wall thickness is 14 cm. The active zone, located in the central region of the casing, is surrounded by several cylindrical shells made of 1X18H10T stainless steel, between which cooling water flows.

The 3 reactors of the Lenin icebreaker differed in the structural material of the claddings of fuel elements (fuel elements). Reactor No. 1 had fuel rods with stainless steel cladding; in reactors No. 2 and No. 3, the claddings of the fuel rods were made of zirconium alloy. In accordance with this, nuclear fuel in reactor No. 1 is enriched in the 235U isotope of 6.5%, and in reactors No. 2 and No. 3 - 5%. In other parameters, all OK-150 reactor units were identical.

The active zone (AZ) of the OK-150 reactor is formed by 219 working channels (RK), or fuel assemblies (FAs) located in nodes of a regular triangular lattice with a pitch of 64 mm, which determines the equivalent diameter of the AZ cross section of 99.7 cm. Each RK contains a bundle of 36 cylindrical fuel rods placed in casing tubes made of zirconium alloy. Nuclear fuel in the form of tablets of uranium dioxide with a diameter of 4.5 mm is placed in zirconium tubes. The height of the fuel column of tablets, equal to 160 cm, corresponds to the height of the AZ. Neutron reflectors are steel screens of radiation protection of the reactor vessel and channels of cooling water. The active zone is cooled by water at a pressure of 160 atm at an inlet and outlet temperature of 248 and 325 ° C, respectively. The thermal operational capacity of the reactor is about 55 MW with an energy resource of 21.

Instead of the initially designed emergency protection submersible rods introduced into the active zone by the pump pressure, the rods moving inside the dry sleeves and introduced into the core under the action of springs were used as organs for regulating the reactivity of the reactor. In biological protection, low-deficiency and cheaper materials were used: steel, water, heavy concrete.

The atomic icebreaker Lenin was laid down at the Admiralteysky Zavod shipyard in Leningrad on July 27, 1956, and on December 5, 1957 the icebreaker was launched and was being built at the factory wall. In August 1959, the physical launch of the reactors took place. In 1958-1959 it was the main body of work on the installation of systems and equipment of a nuclear installation. The most stressful was the final stage of construction, installation and testing of automatic control systems. As the installation of equipment, fittings and pipelines of the APPU progressed, specialists from the Design Bureau and Plant No. 92 were sent to the Admiralty Plant to provide technical assistance.

The clear organization of work and the dedicated work of the many teams involved in the creation of the first APPU, in many respects contributed to the timely, record-breaking delivery of the Lenin nuclear-powered icebreaker. Its construction was completed on September 12, 1959, and on December 5, 1959 the icebreaker was handed over for trial operation to the Murmansk Shipping Company of the USSR MMF, and the state flag of the USSR was hoisted on it. From this date, not only the biography of the first atomic icebreaker is counted, it is celebrated as the birthday of the domestic atomic icebreaker fleet. The icebreaker became the world's first surface ship with a nuclear power plant, and in terms of power it had no equal among the icebreakers of the whole world.

Already in the course of its first use, the icebreaker "Lenin" demonstrated excellent performance, which helped to significantly increase the navigation period. The first Arctic navigation of the nuclear icebreaker began on August 19, 1960 and lasted three months for 10 days. During this time, he traveled more than 10 thousand miles, of which about seven thousand - in severe ice conditions, navigated 92 ships through the Kara Sea and the Laptev Sea.

In just the first six years of operation, the icebreaker traveled over 82,000 nautical miles and independently conducted more than 400 vessels. During this time, the icebreaker during the trial operation of a nuclear power plant revealed its design flaws, problems with the configuration and layout of equipment. In addition, there were cases of equipment failure.

In February 1965, an accident occurred during a scheduled refueling operation at reactor No. 2 with an active zone having fuel rods with Zr-Nb alloy claddings. Part of the fuel in the emergency zone (94 fuel assemblies) was transferred to the Lepse FTB, and the remaining part (125 fuel assemblies) was transferred to a special container, which was subsequently flooded in the Kara Sea.

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."