The illustration depicts the process of steam production with a gas-cooled nuclear reactor.
The process encompasses several stages, beginning with regular water into tubes and ending with steam production. This is achieved by heating the water using the nuclear reactor and heaters until it transforms into hot steam.
A gas-cooled nuclear reactor consists of the reactor itself and a heat exchanger. The reactor contains 4 uranium fuel elements surrounded by graphite moderators and topped by charge tubes for loading fuel elements, and boron control rods. The whole reactor is contained in a pressure vessel surrounded by a concrete radiation shield.
From the reactor, the hot gas flows through a duct into the heat exchanger which is outside the concrete radiation shielding. In the heat exchanger, steam is generated in a secondary loop. There a pipe brings in water which is heated to steam, and this then flows out to the turbo-alternator. Meanwhile the hot gas sinks to the bottom of the heat exchanger and passes through a gas blower which pushes it into a cool gas duct and back to the reactor.
As can be seen, this is a continuous cycle that keeps the reactor from overheating, while carrying away the heat and steam, which will power the turbines.