Chicago woodpile - 1: The world's first nuclear reactor

What do you think is depicted in the photo? Yes, of course, the answer is given in the title, but still, only a person familiar with the history of the development of nuclear energy and well-known can recognize a nuclear reactor in this pile of “logs”. Polennitsa was created in 1942 to test the possibility of a controlled nuclear chain reaction.

There was a “woodpile” of graphite blocks that were neatly packed, and in each second layer the blocks were hollow, and inside was nuclear fuel — pressed uranium oxides and metal ingots.
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Since such a reactor was used to test the possibility of a controlled reaction, there were also a kind of “controls” - several types of rods of cadmium and boron steel. There were a total of three types of rods. The first type - was controlled from the console, it was the control rods. The second type - emergency rods. Rather, it was the only rod that was suspended above the reactor on a rope. If an emergency situation arose, the rope was planned to be cut, and the rod that fell into the reactor jammed the reaction. Well, there was also a rod that was manually removed in order to create the conditions for conducting a controlled nuclear reaction (that is, to bring the reactor itself to a critical state).

All this is incomparable with modern reactors - neither the cooling system was provided (that is, it was, the reactor was planned to be watered with ordinary water in case of strong heating), or the system for protecting humans from radioactive radiation.

He worked the reactor for several tens of minutes (28, to be precise), and during this time, scientists received real evidence of the possibility of a nuclear reaction (controlled) - the experiment was completely successful.

Via dvice + wikipedia