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

Watch an animated, step-by-step reconstruction of the Chernobyl explosion

This video shows how a 1986 safety test at Chernobyl spiraled out of control—leading to a massive rise in temperatures, an explosion and reactor meltdown that produced the largest civilian nuclear disaster in history.

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.

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 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.

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.

Russia's invasion of Ukraine has destabilized safety and oversight at Chernobyl

Russian forces cut power and disabled monitoring of the decommissioned nuclear power plant in 2022, endangering operators at Chernobyl. In February 2025, a Russian drone struck the confinement structure—part of broader efforts to pressure Ukraine's energy infrastructure—punching a hole in the containment shell.

Nuclear weapons release energy through rapid atomic reactions

Nuclear weapons work by unleashing energy from atomic fission—or fusion—reactions. In fission bombs, a critical mass triggers a runaway chain reaction in milliseconds. This video explains the basic science behind their immense explosive power.

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.

Chernobyl pushed the world to create rapid-alert systems for nuclear accidents

In the aftermath of the disaster, nations adopted new agreements requiring immediate international notification of nuclear accidents. They coordinated emergency assistance—efforts led by the International Atomic Energy Agency to prevent future disasters from being concealed when radiation emergencies occur.

Water acts as a coolant and a moderator of nuclear reactions in reactors

Nuclear reactions within a containment structure boil water into steam, which drives a turbine that generates electricity. This water is then recirculated via pumps back into the containment structure to repeat the process, with reaction rates lowered by the insertion of control rods that absorb neutrons, which trigger reactions.

View a list of the worst nuclear meltdowns before 2013

Nuclear meltdowns occur when a reactor overheats and radioactive materials leach into the surrounding environment. While rare, the reasons for each occurrence—as detailed in this piece—can help establish new safety protocols for future reactors.

Thermal runaway reactions can cause batteries to catch fire or explode

If a lithium-ion battery is heated, punctured, crushed, or short-circuits due to manufacturing flaws or degradation, the cathode and anode can make contact without the resistance provided by a circuit. The ensuing spike in chemical reactions increases the temperature and can release oxygen, initiating and intensifying burning of the battery's interior.

Radioactive elements can introduce software errors because the ionizing radiation they produce can detach electrons from atoms, and computer code relies on the distribution of electrons.

The Chernobyl virus earned its name for activating on the meltdown's anniversary

Affecting Windows 95 and 98 computers, it filled gaps in the code of any program opened after infecting a computer, earning it the nickname "Spacefiller." On April 26, 1999, the virus overwrote part of the software responsible for booting up a computer, rendering it unusable.

Exposure to ionizing radiation from nuclear accidents can damage DNA

The damage can increase the risks of cancer, cataracts, heart disease, and other illnesses based on exposure times and intensities. Contaminated food, water, air, or soil from near nuclear accidents can further prolong one's exposure.

Radioactive elements can introduce software errors because the ionizing radiation they produce can detach electrons from atoms, and computer code relies on the distribution of electrons.

How fusion—which releases energy when two lighter atoms combine to form a heavier atom—differs from fission

In 1984, Operation Smash Hit intentionally crashed a 239-ton train into a nuclear waste canister at 100 miles per hour to prove the canister's safety, which remained completely intact and lost just 0.29 of its 100 pounds of pressure.

In 1984, Operation Smash Hit intentionally crashed a 239-ton train into a nuclear waste canister at 100 miles per hour to prove the canister's safety, which remained completely intact and lost just 0.29 of its 100 pounds of pressure.

Explosive volcanic eruptions happen when magma pressure overcomes rock strength

Magma usually stays underground because of a balance between its upward pressure, the weight of the Earth’s crust above, and the crust’s rock strength. Landslides can reduce crust weight, while built-up gas pressure can strengthen magmastatic pressure.

Learn more about the three sites that powered the Manhattan Project

The Manhattan Project relied on three main sites: Oak Ridge, which enriched uranium; Hanford, which produced plutonium in large reactors; and Los Alamos, which designed and assembled the bombs—work that culminated in the Trinity nuclear test in 1945.

Radioactivity was accidentally discovered when uranium left marks on photographic plates

In 1896, Henri Becquerel had been exploring phosphorescence—the emission of light of one color after an object is exposed to another color. He expected these emissions to come from objects exposed to sunlight, but he observed emissions after an overcast day.

Faulty wiring and flammable materials caused a fire in the Apollo 1 command module

During a launch rehearsal test on Jan. 27, 1967, the fire took the lives of astronauts Gus Grissom, Ed White, and Roger Chaffee. The tragedy led to improvements to CM construction and the development of a single-piece hatch for escapes.

The East Palestine, Ohio, train derailment explained

A train transporting a number of potentially dangerous chemicals derailed near the Ohio–Pennsylvania border in early February 2023. The extent of the leak has caused a number of environmental concerns and required a controlled burn to clear most...

Economic stagnation and the arms race pushed the USSR toward collapse

By the 1980s, chronic economic stagnation and soaring military costs forced Gorbachev to launch sweeping reforms—perestroika and glasnost—to revive the Soviet system. Instead, openness fueled independence movements across the republics, accelerating the regime’s rapid downfall.

Explaining why solving the solar neutrino problem revealed that neutrinos could transform

Electron neutrinos are byproducts of the nuclear reactions within the sun's core. Based on the sun's energy output, scientists modeled reaction rates and predicted neutrino production, but the observed values were consistently one-third the predicted values. Experiments later showed that these neutrinos could change into other types on their way to Earth, causing the discrepancy.

More than 90% of the atoms in the human body were forged by stars

Excluding all of the universe's hydrogen and most of its helium and lithium that formed in the Big Bang, elements found in significant amounts in our bodies formed through nuclear fusion within stars, collisions between neutron stars, or stars undergoing supernova. For example, all of the oxygen (65% of our mass) came from massive stars exploding.

Internal-combustion engines convert fuel into motion using controlled explosions

Gasoline engines mix fuel and air, compressing it and igniting it to create thousands of tiny explosions that push pistons up and down. This movement spins the crankshaft, which moves a vehicle's wheels.

Fireworks make a loud booming sound after exploding due to air expanding faster than the speed of sound.

Dirty lightning is a thunderstorm created from friction between rising and falling flows of ash and smoke during volcanic eruptions.

Neutron stars, the remains of some massive stars after they explode in a supernova, are the densest directly observable objects in the universe.

Before writing 'Walden,' transcendentalist Henry David Thoreau nearly burned down his hometown with a campfire that grew out of control.

Volcanic activity may have triggered the Black Death by spewing gases that led to crop failures in Europe, thus forcing the import of grain ships with plague-infested fleas.

Discover the catastrophic consequences of a failure of the US electrical grid—something that is more likely than many Americans think.

Chaos theory—informally known as the butterfly effect—is the reason why weather forecasts are presented with probabilities rather than certainties.

Volcanoes 'die' when their supply of magma runs out, if they are shifted away from their underlying magma reservoir, or if they get clogged by collapsing or their magma cooling back into rock.

An investigation suggests a Scottish island became awash in forever chemicals via seafoam and seaspray—raising questions about what that means for the safety of other coastal areas.

How the most famous Ebola book, The Hot Zone, which sold 3.5 million copies and was translated into 30 languages, got aspects of the disease so wrong.

Poison ivy's characteristic rash is caused by an allergic response to an oily compound in the plant called urushiol.

Sunflowers have long been a symbol of nuclear disarmament because they can extract large amounts of radioactive cesium from soil.

The Russia-Ukraine conflict is the largest ground war in Europe since World War II in casualties, forces mobilized, and displacement of civilians.

While the sun's gravity keeps the planets in orbit, their gravity also pulls on the sun, causing it and everything else in the solar system to orbit around a mutual balance point called the barycenter—the true center of the solar system.

The history of many kitchen appliances involves unexpected discoveries and applications, including wartime radar turned hamster defroster and replacing an 'ice king' with heat-stealing boxes.

Pure water does not conduct electricity because this flow of energy requires the movement of charged particles, and water is a neutral molecule.

Some Pokémon have been named after real and fictional organisms, while some real-world species have been named after Pokémon, such as Chilicola charizard and Binburrum zapdos.

US intelligence allegedly pursued more than 600 schemes to assassinate Cuban revolutionary Fidel Castro.

Bone marrow (soft tissue found inside certain bones) generates roughly 500 billion new blood cells each day

Long before Major League Baseball began allowing instant replay for balls and strikes, an umpire reluctantly used the technology to determine whether a hit was a home run, a move that inadvertently ushered in a new era for the sport.

Double world record holder Hunter Ewen helped conquer his fear of balloons, called globophobia, by training to win Guinness World Record titles for balloon inflation.

Gerrymandering works through two techniques: cracking opposing voters across districts to dilute their power, and packing them into a few to waste their votes in lopsided majorities.