The 5 Worst Nuclear Disasters of All Time, and What Caused Them


Written by Marisa Wilson

Published: September 14, 2022

Share on:


Since the first reactors were built in 1954, the effects of nuclear accidents have been a subject of discussion and a significant source of public anxiety regarding nuclear facilities. However, human error still exists, and there have been several mishaps with varied repercussions, near misses, and incidents. 

Technical methods have been implemented to lessen the chance of accidents or to minimize the quantity of radioactivity released into the environment. Nuclear accidents are graded on a scale of severity (INES). This eight-point sliding scale, developed in 1990 by the International Atomic Energy Agency (IAEA), might be considered the nuclear version of the Richter scale. 

The scale categorizes events into seven levels, with levels 1-3 labeled “incidents” and levels 4–7 being “accidents.” With each level on the scale that is raised, the severity of an event becomes roughly ten times greater. We’ll cover some of the worst accidents in history, so grab your PPE and get ready to read a radioactive article. 

5. Three Mile Island

The nuclear plant at Three Mile Isaland released radioactive material in 1979

©A L Spangler/

The removal of heat from the core of the Three Mile Island Unit 2 reactor was hindered in 1979. This was due to technical malfunctions and a stuck open relief valve. This is a crucial process for preventing reactor damage. When the required pressure levels were reached, the instrumentation misinformed plant operators that the valve had successfully reclosed. Operators made decisions that ultimately made the loss of coolant worse. This is because they were unaware that it was happening at the plant. 

Due to the malfunction and operator error, the reactor core did not receive proper cooling water circulation, which led to overheating and a partial meltdown. As a result, some radioactive material was emitted in a minor amount. Experts say the 2 million or so surrounding residents were exposed to very little radiation at the time of the catastrophe. The exposure from the accident had no observable effects on the health of the plant’s employees or the general population. 

Concerns regarding potential radiation exposure harm to people, animals, and plants in the vicinity of Three Mile Island were voiced months after the catastrophe. Various government organizations that monitored the area took thousands of environmental samples. The mishap had little impact on the environment or people’s physical well-being. This was the best possible outcome for Three Mile Island, Pennsylvania

4. Windscale Fire

It was thought that the Windscale project in the United Kingdom, built-in 1950 with Winston Churchill’s prior permission, would one day aid in creating a terrifyingly devastating hydrogen bomb. A few brave individuals stopped a catastrophic event with their good deeds, but due to a “cover-up” by the government, their efforts went unappreciated. A horrific chain of events began on October 10, 1957, when uranium fuel at the plant overheated and caught fire. Tom Tuohy, Windscale’s deputy general manager, took the initiative that day and was tasked with attempting to put out the fire. The 39-year-old quickly raced to the factory after saying farewell to his family and ordering them to keep the windows closed. 

Tuohy bravely put on protective gear to better grasp the situation and climbed 80 feet to the concrete shaft at the top of the Number 1 nuclear pile. To his dismay, he looked down and noticed an odd red glow which meant that uranium was burning hotly inside. Tuohy ultimately decided to halt all ventilation and cooling systems to prevent air entering the building. To their delight, this strategy worked, and water was hosed through holes into the reactor to kill the fire. The issue was finally over when the flames subsided over the following 24 hours and eventually disappeared altogether. 

Thirty people developed thyroid cancer due to radioactive material entering the nearby countryside. Malignancies associated with Windscale may have killed 240 people. Farms nearby were contaminated by dangerous particles, and milk from cows was gathered from a vast 500 km area close to Sellafield. It was 1,000 times diluted before being discharged into the Irish Sea, where it became slightly contaminated. But if it weren’t for one man’s foresight, the incident’s radioactive contamination might have been much worse.

3. Kyshtym

Techa River was the site of the dumping of nuclear waste

Hazardous nuclear waste was dumped in the Techa River


The plant was hazardous right away. The Techa River was used as a dump site for radioactive waste. Solid waste was dumped on the property without regard for its contents, and smoke was let go. The employees had very little protective equipment, and most of the job was thought to have been performed using local prisoners as forced labor. There was a nuclear accident in 1953, but nobody discovered it until a worker got radiation poisoning. Additionally, four other employees were impacted. 

It was the first of numerous occurrences at the institution over many years. One of the cooling systems at the Mayak plant collapsed on September 29, 1957. Nobody became aware until it was too late. A waste tank explosion released a radioactive cloud into the atmosphere that covered 20,000 square kilometers. Only 11,000 of the 270,000 residents were evacuated (which took two years to do). The survivors were forced to clean up the mess by putting contaminated animals and crops to death. 

They worked without radiation protection and then returned to their houses. Three hundred of the village’s 5000 population died from radiation sickness within a short period of time. Only (ethnic) Russians were relocated despite plans for an evacuation. The Tatars made up the remaining half of the community. Additionally, it is very challenging to conduct current research on the occurrence. This is due to the Soviets suppression of information and documentation. Even now, Russia is not open to having its official account of events contested.

2. Fukushima

The second worse nuclear disaster occurred in Fukashima

The Fukashima nuclear disaster was triggered by an earthquake which also caused a tsunami

©Fly & Dive/

The Fukushima plant accident in 2011 in northern Japan was the second deadliest nuclear accident in the development of nuclear power. Authorities stated that the backup generators at the Fukushima Daiichi plant were impacted by the tsunami waves. The waves were produced by the main shock of the Japan earthquake on March 11, 2011. Although the cooling systems in each of the three active reactors failed within the first few days of the catastrophe, all three reactors were successfully turned down. 

The fuel rods in reactors 1 through 3 were overheated. They were partially melted down due to increasing residual heat within each reactor’s core. This occasionally resulted in the release of radiation. By injecting saltwater and boric acid into the three cores, workers hoped to stabilize and cool them. The evacuation zone was increased to 30 km surrounding the facility at the end of March. 

The ocean water nearby was contaminated with high levels of iodine-131. This is because the loss of radioactive water through breaks in the trenches and tunnels. They were connecting the plant to the ocean. According to plant authorities, those cracks were patched on April 6. Later that month, employees started pumping the radioactive water to a nearby storage structure until it could be treated. On April 12, nuclear authorities raised the nuclear emergency level from 5 to 7. Which is the highest possible rating on the scale. This is the same classification that Chernobyl received. Over 1,000 people perished. The number of people affected by radiation in Japan has more than tripled that of Chernobyl.

1. Chernobyl

the worst nuclear disaster of all time occurred at Chernobyl nuclear plant.

The Chernobyl nuclear disaster left behind a ghost town where people can never return to


The worst nuclear disaster occurred at Chernobyl nuclear plant in Ukraine. On April 25th and 26th, 1986, personnel at reactor Unit 4 of the conducted an unplanned experiment. Workers turned off the reactor’s power control and emergency safety systems. They also removed many of the control rods from the reactor’s core but allowed it to continue operating at 7 percent power. Others exacerbated these errors, and by 1:13 a.m. on April 26, the chain reaction in the core had gotten out of hand. A giant fireball was created by several explosions, which blasted off the reactor’s massive steel and concrete lid. 

This caused a fire in the graphite reactor core, which released a large amount of radioactive material into the atmosphere. The material was blown across large distances by air currents. The core was partially melted as well. The evacuation of Pripyat’s 30,000 residents began on April 27. On April 28, The heat and radiation seeping from the reactor core had been contained by May 4, although at a high risk to personnel. Debris was buried at 800 temporary locations, and the highly radioactive reactor core was sealed in a concrete-and-steel sarcophagus later that year. According to some estimates, 50 people were killed in the initial explosions, while others claim it was two. 

Dozens more people became ill from radiation poisoning, and some died as a result. This radioactivity was carried by the wind across Russia and Ukraine all the way to France and Italy. Millions of acres of forest and farmland were damaged. Despite the evacuation of many thousands of people, hundreds of thousands stayed in hazardous areas. Animals were born deformed in the following years. Thousands of radiation-induced illnesses and cancer deaths were projected in the long run among people. The Chernobyl tragedy fueled criticism of Soviet reactors’ risky practices, and poor designs. It caused opposition to constructing new such units. 

Up Next:

Share this post on:
About the Author

Creepy-crawly creatures enthrall Marisa. Aside from raising caterpillars, she has a collection of spiders as pets. The brown recluse is her favorite spider of all time. They're just misunderstood. You don't have to worry about squishing the creatures as her catching, and relocating abilities can safely move stray centipedes or snakes to a new location that's not your living room.

Thank you for reading! Have some feedback for us? Contact the AZ Animals editorial team.