It’s hard for those of us in the modern era to grasp the true horror of the Chernobyl disaster. Even a deep dive into the Chernobyl meltdown timeline can only reveal so much about the very real, visceral consequences of the event. Putting the sequence of events that led to Chernobyl into context takes an event that American history books casually summarize as a horrible accident and paints the incident for what it really was: a series of compounding mistakes that produced one of the greatest environmental tragedies in human history.
The Chernobyl disaster occurred in the early morning hours of April 26, 1986, in a nuclear power plant next to the Ukrainian city of Pripyat. Multiple detonations spewed out vast quantities of toxic nuclear material and produced ongoing leaks that caused radiation levels to spike around the globe. At least 30 people lost their lives as a direct result of Chernobyl - but the true toll of the event, including increased rates of cancer and other illnesses along with environmental concerns, is impossible to measure. What is possible to track, however, are the series of unfortunate decisions that led to the tragedy in the first place.
The biggest (and arguably, the most easily avoided) mistake that led to the Chernobyl meltdown was an overall lack of safety culture at the power plant. Not only was the experiment that ultimately caused the event poorly planned and executed, but it also ignored several established safety protocols in the name of expediency.
To make matters worse, the experiment needed to be started by one shift and completed by another, further complicating the situation.
According to the International Atomic Energy Agency:
If the Chernobyl accident is assessed in terms of this safety culture concept, it can be seen that not only those involved in the operational stage lacked an adequate safety culture, but also those involved in other stages of the lifetime of a nuclear power plant (designers, engineers, constructors, equipment manufacturers, ministerial and regulatory bodies, etc.).
Before the experiment on Chernobyl’s Unit 4 reactor - which was an attempt to determine whether its emergency systems could operate under inertial force in the wake of a power outage - the emergency core cooling system was disconnected.
This system was disconnected throughout the duration of the test. While further mistakes ultimately caused the detonations, the exclusion of this safety measure further complicated the situation and reflected a general lack of interest in safety by the plant’s operators.
The experiment called for the reactor to be stabilized at a power level of about 1000 megawatts, but a human error let that level tank to 30 MWt. The reaction within the plant destabilized.
As the operators did their best to increase the power, they were able to raise it to a level of 200 MWt - still dangerous, but stable for the time being. Unfortunately, the steps they took in doing so led directly to the accident that would soon rock the plant.
As the Chernobyl experiment carried on throughout the night of April 25, 1986, operators became frustrated at their inability to raise the power level in the reactor. They started to remove control rods.
Safety protocol called for at least 15 rods to be present, but the operators withdrew them until just eight remained. This caused the reactor to cross the minimum operating reactivity margin, which created a "positive void coefficient" that RBMK reactors are prone to developing. This left the reactor prone to a power surge and a growing potential for a complete nuclear meltdown.