Flaws in the Machine
The RBMK reactor's fatal design flaw, graphite-tipped control rods, and the chain of decisions that turned a safety test into catastrophe.
The Positive Void Coefficient
Unlike Western reactors, the RBMK design became more reactive when it lost coolant, creating a dangerous feedback loop that led to the explosion.
Graphite-Tipped Traps
The control rods, meant to stop the reaction, had graphite tips. When they were first inserted during the emergency shutdown (AZ-5), they actually displaced water and increased power for a crucial few seconds.
The Safety Test Delay
The test was supposed to be run by the day shift, who were prepared for it. A power demand delay forced the inexperienced night shift to handle the complex procedure with little warning.
Disabling the Safety Systems
To perform the test, operators manually disabled several automated emergency systems, leaving the reactor with no "brakes" when things started to go wrong.
Prior Warnings Ignored
Similar (though less severe) incidents had occurred at other RBMK plants years earlier, but the findings were classified and never shared with the Chernobyl staff.