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Historie: Pokusy s jaderným reaktorem na palubě - Tupolev-95LAL

Historie: Pokusy s jaderným reaktorem na palubě - Tupolev-95LAL
I.V. Kurchatov added aviation as a possible recipient of the new nuclear power plants

In the late 1940s, as the Cold War began to heat-up, the Soviet Union began research into the development of nuclear reactors as power sources to drive warships. The work was performed at first by an academic Russian engineer, I.V. Kurchatov, which added aviation as a possible recipient of the new nuclear power plants. On August 12th, 1955 the Council of Ministers of the USSR issued a Mandate which ordered certain groups within the aviation industry to join forces in this research. As a direct result of the Mandate, the design bureaus of Andrei Tupolev and Vladimir Myasishchev became the appointed chief design teams on a project to develop and produce several aircraft designs intended to be powered by nuclear propulsion while a bureau headed by N.D. Kuznetsov and A.M. Lyulka, were assigned to develop the engines for the aircraft.

They promptly decided on an energy transfer method: Direct Cycle. This method will enable the engines to use the energy supplied by the reactor, replacing the combustion chamber power supply that the jet engine utilizes. Several types of nuclear powered engines were tested: ramjet, turboprop and turbojet, with different transfer mechanisms for transmitting nuclear generated thermal energy across each one of them. After extensive experimentation with various engines and transfer systems, Soviet engineers concluded that the direct cycle turbojet engine offered the best alternative.

In the direct cycle power transfer configuration, the incoming air entered through the compressor mechanism of the turbojet engine, then, passed through a plenum that directed the air to the reactor core. Then the air, by this time acting as the reactor coolant additive, was constantly heated as it moved through the core. After exiting the core, the air went back to another plenum and from there was directed to the turbine section of the engines for thrust production. New coolant systems were also tested, as it was the protective shielding for the crew cabin. This and the size of the initial nuclear power plants were the main problem facing engineers working on the project. Shielding the crew and reducing the size and weight of the reactors in order to fit one on an airframe became the main technical hurdle in the project.

The Tupolev bureau, knowing the complexity of the task assigned to them, estimated that it would be two decades before the programme could produce a working prototype. They assumed that the first operational nuclear-assisted airplane could take to the air in the late 1970s or early 1980s. The programme was designed to operate in development phases. The first phase was designing and testing a small nuclear reactor, which properly began in late 1955. On March 1956, the Tupolev bureau was assigned by the Council of Ministers of the USSR the task of producing a flying test-bed plane as soon as possible. The Tupolev engineers decided to take an existing Tu-95M bomber and use it as a nuclear flying laboratory, the plane’s eventual designation was to be Tu-95LAL. By 1958, the ground phase of the programme, the rig used to install the nuclear reactor on the aircraft, was ready for testing. Some time during the summer of 1958, the nuclear power plant was turned on and testing commenced. Immediately, the required level of reactor power was achieved, thus opening the path for the flight test phase. Between May and August 1961, the Tu-95LAL completed 34 research flights.

Tu-95 LAL-Nuclear Reactor

Much of them made with the reactor shut down. The main purpose of the flight phase was examining the effectiveness of the radiation shielding which was one of the main concerns for the engineers. The massive amount of liquid sodium, beryllium oxide, cadmium, paraffin wax and steel plates; were the sole source of protection for the crew against the deadly radiation emerging from the core. The results were once again promising. Radiation levels were low in the crew cabin, paving the way for the bureau to design a new airframe. The next phase in the programme was to produce a test aircraft designed from the beginning to use nuclear power as its main propulsion force. This was to be the Aircraft 119. This aircraft was based on the Tu-95 design. The major distinction was that two of its four engines, inboard, were to be the new NK14a turboprops with heat exchangers. The NK14a operated in a very similar way to the direct cycle engines, the main difference being that the air, after passing through the compressor, did not go to the reactor, but directly to the heat exchange system. At the same time, the heat generated by the reactor, carried in the form of fluid; went to the heat exchange system. The combination of these two forces would enable the turbojet to produce the required amount of thrust. The other two outboard engines would remain NK12Ms.

The NK Kuznetsov Design Bureau commenced work on the engines at the same time that the schematics of Aircraft 119 were drawn. As in the Tu-95LAL, the internal bomb bay would house the reactor. The connections leading from the reactor to the engines would run through the main fuselage, up to the wings and then directly to the heat exchangers attached to the two inboard engines. Tupolev estimated that the first 119s were to be available for runway trials by late 1965. After trials, the 119’s engines were to be replaced by a four NK14a engine configurations based on the Tu-114 commercial liner. However, the 119 never made it off the drawing board. Budgetary constraints and the development of new conventional aircraft designs were cited as the main reason for the cancellation of the programme in August 1966. The cancellation of Aircraft 119 did not mean that the Soviet Union terminated its research into a nuclear powered aircraft. Several attempts were made in designing a nuclear-powered, supersonic bomber. Around the same time that Tupolev began working on the 119, there was a parallel program code named Aircraft 120.

A vast amount of research was invested on this project. Mainly on the design of a new turbojet engine and the layout of a new nuclear reactor system that would have been able to offer more protection to the crew and the aircraft sensitive avionics systems. Aircraft 120 was to be fitted with two turbojet engines based on the development by Kuznetsov. The reactor was to be installed near the rear part of the plane, as far from the cabin as possible. The crew consisted of the pilot, co-pilot, and navigator; enclosed in a heavy lead radiation shielding cabin. The 120 would have a conventional aerodynamics configuration with a high mounted 45 degrees swept wing, a swept empennage and a tricycle landing gear. Tupolev’s goal of reaching the testing phase for the 120 in the late 1970s never materialized, as with the 119, the 120 existence was only on the drawing board. Termination of the programme was mainly for the same reasons as for the 119’s.

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