Timeline of events in 19864/25•Decrease in plant power indicating the start of reactor shutdown.•The emergency core cooling system was deactivated .•The automated regulation system has been turned off.•Power reduced to 30 Mtw.•Power reduction resumed.4/26•Operational reactivity margin reduced to less than 30 Mtw.•Power increased to 200 Mtw by withdrawing the bars and starting two additional recirculation pumps.◦Decrease the vacuum.◦Withdraw all but six of the bars. ◦Emergency protection signals obstructed by operators.•The flow of feed water to the drums increased.◦The control room shows excessive reactivity.◦This required an immediate shutdown, however, the warning was ignored and the test was started.•Feedwater flow to the steam drums decreased - 30 seconds later reactor inlet temperatures begin to rise.◦The recirculation pumps begin to slow down along with the turbine.◦ Reactor flow decreases.•Turbine power valves closed.◦Power increased.◦The test was finished.◦An operator noticed the rods moving on the core map. •Emergency scram initiated by the AZ-5 button. This was driven because:◦Doppler decreases the addition of reactivity.◦Fuel fragments caused rapid depletion.◦Power and ram pressure increased rapidly.•Power increased rapidly due to positive vacuum effect.•An explosion occurs, then a second explosion occurs a few seconds later. Summary of what happened: The operators were running tests to see how the reactor would perform in the event of an electrical failure, when a flaw in the reactor caused a severe surge in current. The core had not been turned off before running the test. The power surge triggered events that sent the nuclear reaction spiraling out of control, causing both explosions. The reactor was not equipped with a containment structure... full of paper... even their cooling systems would have been able to function. What happened: When a huge earthquake occurred, the subsequent tsunami knocked out the electricity at the TEPC and caused many problems for workers struggling to repair and maintain water levels in the damaged reactors. Water was desperately needed to prevent the fuel rods from overheating and there was a huge possibility of radioactive exposure due to the lack of cooling water and the overheating of the fuel rods. I don't think this accident could have been avoided because the main damage was a result of the tsunami and the rest was due to the damaged reactors which caused damage to others that were not affected by the tsunami. I think we have learned as a society that ultimately we will never be able to create a completely safe nuclear facility that guarantees no radiation release..