Top 9 Worst Nuclear Disasters In the World History
Top 9 Worst Nuclear Disasters In the World History. Photo KnowInsiders

What is a nuclear disaster?

A nucelar disaster is:

- An accident taking place in any nuclear facility of the nuclear fuel cycle including the nuclear reactor, or in a facility using radioactive sources, leading to a large-scale release of radioactivity in the environment.

- A ‘criticality’ accident in a nuclear fuel cycle facility where an uncontrolled nuclear chain reaction takes place inadvertently leading to bursts of neutrons and gamma radiation (as had happened at Tokaimura, Japan).

- An accident during the transportation of radioactive material.

How are nuclear accidents measured?

Nuclear accidents are measured in severity according to the International Nuclear and Radiological Event Scale (INES). Established in 1990 by the International Atomic Energy Agency (IAEA) this eight-point sliding scale is a bit like the nuclear equivalent of the Richter scale.

According to the IAEA:

“Events are classified on the scale at seven levels: Levels 1–3 are called 'incidents' and Levels 4–7 'accidents.' The scale is designed so that the severity of an event is about ten times greater for each increase in level on the scale. Events with no significant safety concerns are called 'deviations' and classed as Level 0.”

In descending order of magnitude, here are the five worst nuclear disasters to have shook the world over the last century.

We will be organizing nuclear disasters not by death toll but by their rating on the International Nuclear and Radiological Event Scale (INES). INES is a series of metrics that were created in 1990 as a way to measure the destruction caused by nuclear disasters and meltdowns. INES organizes nuclear disasters into the following categories:

Level 7 - Major Accident

Level 6 - Serious Accident

Level 5 - Accident With Wider Consequences

Level 4 - Accident With Local Consequences

Level 3 - Serious Incident

Level 2 - Incident

Level 1 - Anomaly

Level 0 – Deviation

9 Worst Nuclear Disasters In the World History

1. Chernobyl (Level 7)

The most serious nuclear accident took place on 26 April 1986 at the Chernobyl nuclear power plant in Ukraine (then part of the Soviet Union).

It is the only nuclear accident in the history of commercial nuclear power to have caused fatalities from radiation. Several factors, including reactor design issues and a poor safety culture, led to a failed safety test that caused two explosions, a fire that lasted for over a week, and the release of a large amount of radioactive material.

Top 9 Worst Nuclear Disasters In the World History
The New Safe Confinement with Chernobyl unit 4 behind it. The 36,000 tonne structure was pushed 327 metres on rails into position over the reactor building in November 2016. (Image: European Bank for Reconstruction and Development)

What caused the Chernobyl accident?

On April 26, 1986, the Number Four RBMK reactor at the nuclear power plant at Chernobyl, Ukraine, went out of control during a test at low-power, leading to an explosion and fire that demolished the reactor building and released large amounts of radiation into the atmosphere. Safety measures were ignored, the uranium fuel in the reactor overheated and melted through the protective barriers. RBMK reactors do not have what is known as a containment structure, a concrete and steel dome over the reactor itself designed to keep radiation inside the plant in the event of such an accident. Consequently, radioactive elements including plutonium, iodine, strontium and caesium were scattered over a wide area. In addition, the graphite blocks used as a moderating material in the RBMK caught fire at high temperature as air entered the reactor core, which contributed to emission of radioactive materials into the environment.

How many people died as an immediate result of the accident?

The initial explosion resulted in the death of two workers. Twenty-eight of the firemen and emergency clean-up workers died in the first three months after the explosion from Acute Radiation Sickness and one of cardiac arrest.

How large an area was affected by the radioactive fallout?

Some 150,000 square kilometres in Belarus, Russia and Ukraine are contaminated and stretch northward of the plant site as far as 500 kilometres. An area spanning 30 kilometres around the plant is considered the “exclusion zone” and is essentially uninhabited. Radioactive fallout scattered over much of the northern hemisphere via wind and storm patterns, but the amounts dispersed were in many instances insignificant.

Similar to Hiroshima

About 30,000 people were near Chernobyl's reactor when it exploded on April 26, 1986. Those exposed to the radiation are thought to have received about 45 rem (rem is a unit of radiation dosage), on average, which is similar to the average dose received by survivors after the atomic bomb was dropped on Hiroshima in 1945, according to the book "Physics for Future Presidents: The Science Behind the Headlines" (W. W. Norton & Company, 2008) by Richard Muller, a professor emeritus of physics at the University of California, Berkeley.

2. Mihama Nuclear Power Plant - Fukushima Prefecture, Japan (Level 7)

Top 9 Worst Nuclear Disasters In the World History
Photo AP

The 2011 Japan tsunami and earthquake devastated northeastern Japan, resulting in an outcome of around 15,000 deaths and thousands of injuries and missing people.

It was the worst earthquake in Japan's history and one of the worst tsunamis to strike the world in recorded history. To make a terrible situation even worse, the earthquake resulted in meltdowns at nuclear power plants in the country's Fukushima Prefecture. The meltdown directly resulted in the deaths of two people. The handling of the disaster, which many in the public perceived to be slow and inadequate, caused a massive uproar both in Japan and abroad. Like Chernobyl, the Fukushima disaster further deteriorated the world's faith in nuclear power. Several countries around the world, such as Germany and Italy, vowed to either close their nuclear power plants or cease building any new ones. However, in some countries such as India and Russia, nuclear power still reigns strong.

Do you know...?

Six months after the Fukushima meltdown, 28 percent of pale grass blue butterflies in the area had deformities such as altered wing patterns and malformed antennae and legs.

The first-ever study of radiation exposure on wild primates, conducted in 2012, found that monkeys near Fukushima had significantly lower red and white blood-cell counts compared with monkeys elsewhere in Japan.

3. Windscale on October 10, 1957 (Level 6)

Top 9 Worst Nuclear Disasters In the World History
Photo srp-uk

Designed to produce plutonium and other materials for the country’s burgeoning nuclear weapons program, Britain’s first nuclear reactor, known as Windscale, was built in northwest England in the late 1940s. On October 10, 1957, workers conducting standard maintenance at the massive facility noticed rising temperatures.

Upon further inspection, they discovered that the reactor’s uranium-filled graphite core had caught fire. With the reactor on the verge of collapse, plant operators risked their lives to fight the flames with cooling fans, carbon dioxide and water. The fire finally died out on October 12, but by that time a radioactive cloud was already spreading across the United Kingdom and Europe.

4. Kyshtym, Russia in 1957 (Level 6)

In the years following World War II, the United States was the foremost nuclear power in the world. In an effort to catch up, the Soviet Union quickly built nuclear power plants and cut corners in order to keep pace.

The Mayak plant near the city of Kyshtym had a tank with a substandard cooling system as a result, and when it failed, the increasing temperature caused an explosion that contaminated almost 500 miles of the surrounding area.

Initially, the Soviet government didn’t disclose what had happened, but one week later they had little choice. 10,000 people were evacuated from the area when some began to show signs of radiation sickness. Although the Soviet government refused to disclose any information about the accident, a study in Radiation and Environmental Biophysicsestimates that at least 200 people died from exposure to radiation. The Soviet government finally declassified information about the disaster in 1990.

5. Three Mile Island, Pennsylvania in 1979 (Level 5)

The most serious accident in U.S. commercial nuclear power plant operating history occurred at the Three Mile Island nuclear station in Pennsylvania. A combination of equipment failure and operator error led to the partial meltdown of the power plant’s Unit 2 reactor that resulted in the release of a small amount of radioactive material.

Top 9 Worst Nuclear Disasters In the World History
Photo BBC

No injuries, deaths or direct health effects were caused by the accident

Following the event, detailed studies of the accident’s radiological consequences were conducted by the Nuclear Regulatory Commission (NRC), the U.S. Department of Energy (DOE), the Environmental Protection Agency, the Department of Health, Education and Welfare (now Health and Human Services), and the Commonwealth of Pennsylvania.

No adverse effects to the surrounding environment

Months after the incident, concerns were raised about possible adverse effects from the radiation exposure on the people, animals, and plants in the areas near Three Mile Island. Various government agencies monitoring the area collected thousands of environmental samples of air, water, milk, vegetation, soil, and foodstuffs. It was determined that very low levels could be attributed to the accident and that the radioactive release had negligible effects on the physical health of the individuals or the environment.

6. Goiania Accident, Brazil in 1987 (Level 5)

On September 13th of 1987 a nuclear incident occurred in Goiania Brazil. The accident was caused primarily because of radioactive contamination of an abandoned piece of hospital machinery. The incident is considered one of the top 10 nuclear disasters to date, as it is classified as a level 5 accident.

When two opportunistic scrap metal thieves broke into an abandoned Brazilian hospital in 1987, they had no way of knowing that they were about to trigger one of the world’s worst nuclear contamination incidents. After scavenging parts from old hospital machinery, the thieves came across a teletherapy radiation capsule. Unaware of the danger the material possessed, they set about dismantling the unit with a screwdriver and sharing the glowing blue material amongst friends and family before selling the metal on. It wasn’t until local people began to fall ill that the source of radiation was discovered – at which point 249 people were found to have received significant radioactive contamination. Four people died as a direct result of the incident, and several houses were demolished in the aftermath.

7. Reactor Accidents at Chalk River (Level 5)

Back in the fifties, there were two rather serious nuclear reactor accidents at Chalk River, Ontario.

The first occurred in 1952, when the NRX reactor underwent a violent power excursion that destroyed the core of the reactor, causing some fuel melting. Unaccountably, the shut-off rods failed to fully descend into the core. A series of hydrogen gas explosions (or steam explosions) hurled the four-ton gasholder dome four feet through the air where it jammed in the superstructure. Thousands of curies of fission products were released into the atmosphere, and a million gallons of radioactively contaminated water had to be pumped out of the basement and "disposed of" in shallow trenches not far from the Ottawa River. The core of the NRX reactor could not be decontaminated; it had to be buried as radioactive waste. Young Jimmy Carter -- later U.S. President, then a nuclear engineer in the U.S. Navy -- was among the hundreds of Canadian and American servicemen who were ordered to participate in the NRX cleanup following the accident.

Six years later, in 1958, several metallic uranium fuel rods in the NRU reactor overheated and ruptured inside the reactor core. One of the damaged rods caught fire and was torn in two as it was being removed from the core by a robotic crane. As the remote-controlled crane passed overhead, carrying the larger portion of the damaged rod, a three-foot length of fiercely burning uranium fuel broke off and fell into a shallow maintenance pit. The burning fuel lay there, spreading deadly fission products and alpha-emitting particles throughout the reactor building. The ventilation system was jammed in the "open" position, thereby contaminating the accessible areas of the building as well as a sizable area downwind from the reactor site. A relay team of scientists and technicians eventually extinguished the fire by running past the maintenance pit at top speed wearing full protective gear, dumping buckets of wet sand on the burning uranium fuel.

8. Tokaimura, Japan 1999 (Level 4)

When a group of unqualified workers decided to put more highly enriched uranium in a precipitation tank than was permitted, disaster struck. Two of the workers eventually died with another fifty six plant workers also being exposed to high levels of radiation. To make matters worse, 21 civilians were also exposed to high doses of radiation and residents within a thousand feet of the plant were evacuated.

9. Saint Laurent Nuclear Accidents on March 19, 2017 (Level 4)

It was in 1969 that disaster struck the nuclear facility of Saint Laurent. The facility consists of two gas-cooled, graphite moderated reactors (GCR) known as A1 and A2 (see Fig. 1). It was on October 17, 1969 that uranium, necessary for the nuclear reaction to take place, melted and caused a partial meltdown.

Because of this, workers spent a full year cleaning and repairing the reactor, often working in a highly radioactive environment. It was this accident, coupled with an announcement given by the president of Électricité de France (EDF) Marcel Boiteux saying that France would stray away from GCRs, that signaled the end of the gas-graphite program in France. This novel experience in France's history did not change its future course in regards to nuclear development. French governmental leaders took a back seat as they justified the nuclear accident with the immense energy that nuclear yields.

Nearly a decade later the Saint Laurent plant experienced another nuclear accident, ranking a four out of seven on the International Nuclear Event Scale, equal to the level of the 1969 accident. Reactor A2 was shut down for two and a half years after two fuel elements melted where six to eight stack channels had become obstructed by a metal plate. [4] More information was requested about the 1980 incident and the subsequent cleanup at Saint Laurent A2, yet, Andrá Gauvenet, the Inspector General for Nuclear Safety and Protection, provided none. He only stated the accident resulted in no release of radioactivity to the environment.

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