Chernobyl Disaster timeline, fourth page of a chronology from a Department of Energy report
down of 4 main cooling pumps) and the power continued to increase. This led to a "crisis of convective heat transfer"; i.e. heating up of the fuel, its disintegration, rapid voiding of the coolant, sharp increase in pressure in the operating channels, rupture of the channels and a "thermal explosion." The steam formation and sharp temperature increase created conditions for steam zirconium and other exothermic reactions. A fuel failure specific energy release was greater than 300 cal/gm.
Recorded data shows the check valves between the coolant pumps on the fuel channel inlets closed, this was due to the rapid rise in the fuel channel pressure.
Time: 0123:40 Power: Unknown
Shift director gave order to press scram button. Operator saw rods were stopping before they reached bottom. He "felt shocks" (other translations are loud reports, banging). He released servo mechanism to allow rods to fall into core, but their actual movements are uncertain.
Two explosions were heard - "hot fragments and sparks flew up above the fourth plant, some of which fell on the roof of the turbogenerator room and started a fire".