Infomanya-English

On the night of April 26, 1986, the world remained unaware that the Chernobyl Nuclear Power Plant in the Soviet Union was about to witness one of the worst nuclear disasters in history. What was intended to be a routine safety test on an RBMK reactor quickly turned catastrophic due to critical human errors, disabled safety systems, and inherent design flaws, creating a radioactive crisis whose environmental and human consequences continue to be felt decades later.

What Was the Chernobyl Nuclear Test?

The experiment conducted in Reactor No. 4 of the Chernobyl Nuclear Power Plant was essentially a safety test, scientifically known as the Turbine Coastdown Test. The main goal of this test was to determine whether, if power suddenly went out, the turbines could continue producing electricity long enough for the reactor’s cooling pumps to operate continuously until the diesel generators fully started. These generators took about 40 to 60 seconds to start, and protecting against this dangerous gap was the main purpose of the experiment.

Errors Before the Nuclear Test

The biggest mistake before the test was that Reactor No. 4 was run at around 1600 megawatts during the day to meet the electricity needs of Kyiv, instead of shutting it down during daytime as planned. Because of high electricity demand, the scheduled test was postponed to the night, when the experienced daytime staff had left and the control room was staffed by a relatively less experienced night shift.

Dangerous Accumulation of Xenon-135

Running the reactor at

low power for a long time caused Xenon-135 to accumulate, which absorbs neutrons and suppresses the nuclear reaction. To counter this, operators withdrew more control rods than allowed, even though safety protocols required a minimum number of rods to remain inserted.

Deliberate Violation of Safety Rules

Under pressure to complete the test, several fundamental safety protocols were ignored. Automatic shutdown systems and warning systems were temporarily disabled or ignored to prevent the reactor from shutting down on its own.

Incomplete Technical Briefing for Night Shift

The daytime shift, which had run the reactor for an extended period, left without giving a full technical briefing. The night shift operators were not fully aware of the reactor’s internal conditions, Xenon poisoning, or the dangers of low power operation, this was a serious administrative mistake.

Ignorance of Flaws in Reactor Design

The RBMK reactor had a major scientific flaw: the Positive Void Coefficient and graphite-tipped control rods. In an emergency, when control rods were inserted, the graphite tips would first enter the reactor and accelerate the reaction. Operators were neither fully informed about these risks nor were these dangers considered in the test planning—making it a hidden but lethal mistake from the start.

The Test Begins — The First Moment of Danger

On the night of April 26, 1986, the Turbine Coastdown Test began. Steam supply to the turbines was cut to see how long the turbines could provide electricity to the cooling pumps using rotational inertia. As turbine speed decreased, water

flow in the reactor dropped and steam levels increased, a highly dangerous condition for the RBMK reactor because higher steam accelerates the nuclear reaction. Meanwhile, the reactor was already unstable due to low power, Xenon-135 accumulation, and excessively withdrawn control rods, causing a sudden spike in power generation.

The Emergency Button and Disaster

When the control room pressed the AZ-5 emergency button to control the power, the graphite-tipped control rods entered the reactor first, causing power to surge instead of decrease. Pressure increased so much that a first steam explosion occurred, followed immediately by a second explosion that completely destroyed Reactor No. 4.

Were Anyone Punished for the Failed Test?

After the Chernobyl nuclear disaster, the Soviet government launched an official investigation, concluding that serious violations of safety protocols had occurred during the failed test. Following the investigation, Chernobyl plant director Viktor Bryukhanov, chief engineer Nikolai Fomin, and the test supervisor Anatoly Dyatlov were held responsible for negligence and misuse of authority, and all three were sentenced to ten years in prison. Later scientific reports also acknowledged that a major cause of the accident was the RBMK reactor’s flawed design and the secrecy around it. Initially, however, legal responsibility was imposed only on these officers.

Chernobyl — A Warning

Ultimately, the Chernobyl disaster is not only a story of a failed test but also a warning: no matter how powerful technology is, human negligence and violation of safety rules can push it onto a path of destruction.