Chernobyl Incident Timeline

2 May 1986, Friday.

No time was confirmed.

Two floors of bubbler pools beneath the reactor served as a large water reservoir for the emergency cooling pumps. After the disaster, the pools and the basement were flooded because of ruptured cooling water pipes and accumulated firefighting water.

The smoldering graphite, fuel, and other material above at a temperature of more than 1200 °C started to burn through the reactor floor and mixed with molten concrete from the reactor lining, creating corium, a radioactive semi-liquid material comparable to lava. If this mixture had melted through the floor into the pool of water, it was feared it would create a serious steam explosion that would eject even more radioactive material from the reactor. It was therefore necessary to drain the pool.

Three engineers volunteered, Alexei Ananenko (who knew where the valves were), Valeri Bezpalov, and, Boris Baranov, whose job was to hold a submersible light. Their light failed almost immediately, and they were forced to proceed in darkness, often underwater, to find the valves. The sluice gates opened, and the water was drained. All of them returned to the surface and according to Ananenko, their colleagues jumped for joy when they heard they had managed to open the valves.

Despite wading through contaminated water, all three survived the mission, and in 2018 were awarded the Order For Courage by Ukrainian President Petro Poroshenko. During the April 2018 ceremony, Poroshenko said that the three men had been quickly forgotten at the time, with the Soviet news agency still hiding many of the details of the catastrophe. At the time they had reported that all three had died and been buried in "tightly sealed zinc coffins". Ananenko and Bespalov received their awards in person, while Baranov, who died in 2005 of a heart attack, was awarded him posthumously.

With the bubbler pool gone, a meltdown was less likely to produce a powerful steam explosion. To do so, the molten core would now have to reach the water table below the reactor. To reduce the likelihood of this, it was decided to freeze the earth beneath the reactor, which would also stabilize the foundations. Using oil drilling equipment, the injection of liquid nitrogen began on 4 May. It was estimated that 25 metric tons of liquid nitrogen per day would be required to keep the soil frozen at −100 °C. This idea was soon scrapped and the room where the cooling system would have been installed was filled with concrete.

Miners and Metro construction workers start tunnel under Unit 3 to construct heat exchanger under No.4 reactor (shown 3.09 minutes in to clip below).

A 30 kilometer zone around the reactor is designated for evacuation (90.000 people).