This prototype of a bomber has been developing in U.S.S.R. in the late 1940, in time of cold war. Different to the U.S.A. projects this one had a new innovation, that had been developed by Russian engineers. They developed a new energy transfer method- Direct Cycle. This method enabled the energy created by the reactor in the plane to get used by the turbines, and replaced the combustion chamber of the jet engine. In the process the air entered through a compressor mechanism of the turbojet engine, where it passed through a plenum to the reactors core. It works there like a coolant additive, and gets heated. Next, it travels through another plenum to the turbine section where it works like a thrust. This project was planed to start flying somewhere between 1970 and 1980 but the first plane flew up in 1955! This serie was used by the U.S.S.R. as bombers and had later models. 

Credits to www.aviation-history.com