Chernobyl Disaster

An imbalance in nuclear reactivity factors caused Chernobyl's reactor to explode

The initial explosion resulted from excessive steam pressure that had built up in a runaway manner due to design flaws and violations of safety protocols. Once exposed to atmospheric oxygen, the hot graphite in the control rods underwent a combustion reaction, resulting in a secondary explosion.

The Chernobyl disaster released more radioactive material than the Hiroshima bomb

A reactor explosion during a safety test resulted in a series of evacuations and resettlements that displaced over 300,000 people and left areas uninhabitable for up to 20,000 years. The Soviet government initially tried to hide the disaster, but rising radiation levels were identified by detectors in Sweden.

Chernobyl's remaining reactors kept running for 14 years after the explosion

Due to energy shortages in Ukraine, Chernobyl's other undamaged reactors continued operating for years. Units 1 and 2 operated until 1996 and 1991, respectively, while Reactor 3 remained online until December 15, 2000, when Ukraine finally shut down the plant.

The 'Elephant's Foot' in Chernobyl is part of the largest documented mass of corium

The nuclear disaster produced around 200 tons of nuclear fuel that mixed with the surrounding melted reactor core materials. As of 2025, corium has been naturally formed four other times in history: once during the Three Mile Island accident and three times at the Fukushima Daiichi plant disaster.

View the abandoned town of Pripyat, a year after the Chernobyl nuclear disaster

The town's 50,000 residents were evacuated more than a day after the explosions at Chernobyl, leaving behind schools, apartments, and streets seemingly frozen in time. Most evacuees were resettled to Slavutych, about 50 kilometers (31 miles) east of the plant.

Limited transparency soon after Chernobyl made it a source of conspiracy theories

Some rumors about the event became perceived as more reliable than the Soviet mass media, which had omitted key information during the early days of uncertainty. The resulting theories included CIA involvement in the disaster, three-headed birds, aliens, and a weaponized earthquake.

The Chernobyl exclusion zone remains a region restricted to public access

It now spans beyond the initial 30-kilometer radius around the nuclear plant to include surrounding areas found to have significant radioactive contamination. Aside from a handful of elderly self-settlers, permanent residency is banned, and access remains tightly controlled due to lingering radioactive contamination.

More than 500,000 people worked to contain Chernobyl's fallout

The group—collectively referred to as "liquidators"—included firefighters, military troops, miners, engineers and sanitation crews. Beyond clearing radioactive debris and performing decontamination work, they confined radioactive material to prevent its spread into groundwater.

The disaster affected the Soviet Union's credibility at home and abroad

The USSR's secretive, chaotic response to Chernobyl dealt a significant blow to its legitimacy. Public anger over deception, health risks, and propaganda fueled mass protests, strengthened independence movements in Ukraine and Belarus, and convinced many Soviets that the system was failing.

Watch a visualization of the construction of Chernobyl's sarcophagus

Built to contain the remains of Reactor 4 after the nuclear disaster, the "shelter structure" was constructed from about 400,000 cubic meters of concrete—enough to fill 160 Olympic-sized swimming pools. Construction required vehicles and cranes modified with special shielding to protect workers.