Chernobyl: The Disaster That Shook the World

The bombs dropped on Hiroshima and Nagasaki created explosions equal to 15 kilotons of TNT. The radioactive gases released into the atmosphere by those blasts were 400 times less than the gases released by another disaster.

At that disaster site today, a huge dome can be seen. This dome is 354 feet high and 840 feet wide, covering the location of one of the worst accidents in history—an accident that even shocked the biggest enemy of the United States at that time, the Soviet Union.

This explosion is known as the Chernobyl Nuclear Disaster.

The Chernobyl Nuclear Power Plant was built near the city of Pripyat, about 100 km from Kyiv, the capital of Ukraine. Today, this city is completely abandoned. At that time, Ukraine was part of the Soviet Union.

It was the era of the Cold War, and the Soviet Union had started building many nuclear power plants using nuclear energy. One of them was the Chernobyl plant.

This power plant had four nuclear reactors, named Reactor 1, 2, 3, and 4. Reactor 4 was the newest one, and today a massive dome stands over it.

Each reactor could produce 1,000 megawatts of electricity, enough to supply power to nearly half of the Soviet Union’s population.

In simple terms, the reactors worked by heating water through a nuclear reaction. The water turned into steam, which rotated turbines. The spinning turbines generated electricity.

However, a nuclear reaction is a chain reaction. Once it starts, it cannot easily be controlled. To control it, each reactor had 211 control rods.

These control rods were made of materials that absorb neutrons released during nuclear reactions. Neutrons are the particles that collide with uranium atoms and sustain the nuclear reaction. If the neutrons are absorbed by control rods instead of uranium, the reaction slows down.

At Chernobyl, the control rods were made of boron carbide, but their tips were made of graphite.

The reactor process ran 24/7, and temperatures inside the reactor could reach 1,600°C, about one-third the temperature of the Sun’s surface. Because of this extreme heat, the reactor had to be constantly cooled.

Water pipes inside the reactor continuously circulated water using pumps, similar to how coolant keeps a car engine from overheating.

However, there was a major design flaw.

In a car engine, water circulation stops when the engine turns off. But in a nuclear reactor, water circulation must never stop, even if the reaction stops, because the reactor continues producing heat for some time.

The water pumps required electricity to operate. Normally, this electricity came from the reactor’s own turbines. If power failed, diesel generators would start as backup.

But there was a problem: switching to diesel generators took about 60 seconds, meaning the water pumps would stop during that time.

Engineers wanted to ensure the pumps would keep running during those 60 seconds. So they installed a safety system where the reactor would gradually reduce electricity production, allowing the remaining power to run the pumps until the backup generators started.

However, this system still needed testing.

On April 25, 1986, engineers prepared to perform this safety test on Reactor 4, under the supervision of Deputy Chief Engineer Anatoly Dyatlov.

According to the rulebook, the test should be done when the reactor was producing 700 megawatts. Normally it produced 1,000 megawatts.

To reduce power, control rods were inserted. But too many rods were inserted, and the power suddenly dropped from 1,000 megawatts to only 30 megawatts.

To increase the power again, engineers began removing control rods. The power rose from 30 to 200 megawatts. They removed even more rods.

Out of 211 control rods, only eight remained inside the reactor, which violated safety rules requiring at least 15 rods.

Because of this violation, the nuclear reaction accelerated rapidly. Power surged from 200 megawatts to several thousand megawatts.

The extreme heat caused water in the pipes to evaporate rapidly. At this moment, panic spread in the control room, and the reactor began vibrating violently.

The only solution was to press the emergency shutdown button, which would insert all control rods and stop the reaction.

Engineers pressed the button.

But the moment the rods entered the reactor, a massive explosion occurred.

The explosion was equivalent to 225 tons of TNT.

The reason was the graphite tips of the control rods. While boron carbide absorbs neutrons and slows reactions, graphite actually increases the reaction.

Since the reactor was already unstable, the graphite tips accelerated the reaction even more, causing the reactor walls to rupture and explode.

Two engineers died instantly, and two others were severely burned.

The explosion caused a fire in the reactor building. Firefighters arrived quickly and tried to extinguish it with water, thinking it was a normal fire. But it was actually a graphite fire, which is extremely difficult to put out.

Soon after the accident, the entire city of Pripyat, home to about 50,000 people, was evacuated overnight.

Over the next 10 days, helicopters dropped more than 5,000 tons of sand, clay, and other materials onto the reactor to control the fire.

Eventually the fire was extinguished, but radioactive gases continued to leak into the atmosphere.

Many firefighters became sick from radiation exposure, and some died in the following weeks and months.

Initially, the Soviet Union tried to hide the disaster, fearing damage to its reputation during the Cold War. But the truth could not stay hidden for long.

36 hours after the explosion, a radiation monitoring station in Sweden detected rising radiation levels in the air coming from Ukraine.

The Soviet government was finally forced to reveal the accident.

Even after the fire was extinguished, danger remained. Beneath the reactor was a large pool of water contaminated with radioactive material. If it turned into steam, it could spread even more radiation.

Three brave men volunteered for a dangerous mission:

Alexei Ananenko, Valeri Bezpalov, and Boris Baranov.

They entered the radioactive water and opened the drainage valves, preventing an even bigger explosion.

Their mission was called a “suicide mission,” but fortunately all three survived.

However, the damage had already been done.

Radioactive materials like iodine-131 spread through the atmosphere, causing thousands of people to develop thyroid cancer. Many of those affected were firefighters and cleanup workers.

Radioactive fallout spread across Europe, damaging forests and contaminating grass eaten by animals.

In the first four months, 31 people died, but long-term radiation exposure is estimated to have caused around 4,000 deaths, though the true number may be much higher.

Today, the area around Chernobyl is still restricted. Even after nearly 40 years, radiation continues to leak from the site and may remain dangerous for hundreds of years.

To contain the radiation, a massive protective dome costing about $3 billion was built over the reactor. This structure is expected to prevent radioactive materials from escaping into the atmosphere for about 100 years.