What exactly is a nuclear disaster?
A nuclear disaster is defined as An accident that occurs in any nuclear facility of the nuclear fuel cycle, including the nuclear reactor, or in a facility that employs radioactive sources, resulting in a large-scale release of radioactivity into the environment.
A ‘criticality’ accident in a nuclear fuel cycle facility in which an uncontrolled nuclear chain reaction occurs inadvertently, resulting in neutron and gamma radiation bursts (as had happened at Tokaimura, Japan).
An accident occurred while transporting radioactive material.
How are nuclear disasters measured?
The International Nuclear and Radiological Event Scale is used to assess the severity of nuclear accidents (INES). The International Atomic Energy Agency (IAEA) established this eight-point sliding scale in 1990, which is similar to the Richter scale in nuclear terms.
The IAEA states that:
“On the scale, events are classified into seven levels: incidents (Levels 1-3) and accidents (Levels 4-7).” The scale is designed so that each increase in level on the scale increases the severity of an event by about ten times. Events with no significant safety concerns are referred to as ‘deviations,’ and they are classified as Level 0.”
Here are the five worst nuclear disasters that have shaken the world in descending order of magnitude over the last century.
We will organize nuclear disasters based on their rating on the International Nuclear and Radiological Event Scale rather than their death toll (INES). INES is a set of metrics developed in 1990 to assess the devastation caused by nuclear disasters and meltdowns. Nuclear disasters are classified as follows by INES:
Level Seven – Serious Accident
Level Six – Serious Mishap
Level Five – Serious Accident with Serious Repercussions
Level Four – Local Consequences Accident
Level Three – Incident of Serious Importance
Level Two – Incident
Level One – Anomaly
Level Zero – Deviation
The 9 Worst Nuclear Disasters in History
1.the Chernobyl disaster (Level 7)
On April 26, 1986, the most serious nuclear accident occurred at the Chernobyl nuclear power plant in Ukraine (then part of the Soviet Union).
It is the only nuclear accident in commercial nuclear power history to result in radiation fatalities. Several factors, including reactor design issues and poor safety culture, contributed to a failed safety test, which resulted in two explosions, a week-long fire, and the release of a large amount of radioactive material.
What caused the Chernobyl disaster?
On April 26, 1986, the Number Four RBMK reactor at the Chernobyl nuclear power plant in Ukraine lost control during a low-power test, resulting in an explosion and fire that destroyed the reactor building and released large amounts of radiation into the atmosphere. Because safety precautions were disregarded, the reactor’s uranium fuel overheated and melted through the protective barriers. RBMK reactors lack a containment structure, which is a concrete and steel dome over the reactor that is designed to keep radiation inside the plant in the event of an accident. As a result, radioactive elements such as plutonium, iodine, strontium, and caesium were dispersed over a large area. Furthermore, as air entered the reactor core, the graphite blocks used as a moderating material in the RBMK caught fire at high temperatures, contributing to the release of radioactive materials into the environment.
How many people were killed as a direct result of the accident?
Two workers were killed in the initial explosion. In the three months following the explosion, twenty-eight firemen and emergency clean-up workers died of Acute Radiation Sickness and one of cardiac arrest.
What was the extent of the radioactive fallout?
Some 150,000 square kilometres of Belarus, Russia, and Ukraine have been contaminated, stretching up to 500 kilometres north of the plant site. The “exclusion zone,” which stretches for 30 kilometres around the plant, is essentially uninhabited. Wind and storm patterns dispersed radioactive fallout over much of the northern hemisphere, but the amounts dispersed were often insignificant.
As with Hiroshima,
On April 26, 1986, approximately 30,000 people were in the vicinity of the Chernobyl reactor when it exploded. According to the book “Physics for Future Presidents: A Primer,” those exposed to the radiation are thought to have received about 45 rem (rem is a unit of radiation dosage), which is similar to the average dose received by survivors after the atomic bomb was dropped on Hiroshima in 1945.”The Science Behind the Headlines,” by Richard Muller, emeritus professor of physics at the University of California, Berkeley (W. W. Norton & Company, 2008).
2.Fukushima Prefecture’s Mihama Nuclear Power Plant (Level 7)
The 2011 Japan tsunami and earthquake devastated northeastern Japan, killing approximately 15,000 people and leaving thousands injured and missing.
It was the worst earthquake in Japanese history, as well as one of the worst tsunamis in recorded history. To make matters worse, the earthquake caused meltdowns at nuclear power plants in the country’s Fukushima Prefecture. Two people were killed as a direct result of the meltdown. The disaster’s handling, which many in the public perceived as slow and inadequate, sparked a massive uproar both in Japan and abroad. The Fukushima disaster, like Chernobyl, eroded the world’s trust in nuclear power. Several countries around the world, including Germany and Italy, have pledged to either close or stop building new nuclear power plants. However, nuclear power remains dominant in some countries, including India and Russia.
3.Windscale on 10 October 1957 (Level 6)
Britain’s first nuclear reactor, known as Windscale, was built in northwest England in the late 1940s to produce plutonium and other materials for the country’s burgeoning nuclear weapons programme. Workers performing routine maintenance at the massive facility noticed rising temperatures on October 10, 1957.
Further investigation revealed that the reactor’s uranium-filled graphite core had caught fire. With the reactor on the verge of collapsing, plant operators put their lives in danger by using cooling fans, carbon dioxide, and water to extinguish the flames. The fire was finally extinguished on October 12, but by then, a radioactive cloud had spread across the United Kingdom and Europe.
4.In 1957, Kyshtym, Russia (Level 6)
In the years following World War II, the United States was the world’s leading nuclear power. In order to keep up, the Soviet Union quickly constructed nuclear power plants and cut corners.
The Mayak plant near Kyshtym had a tank with a subpar cooling system, and when it failed, the rising temperature caused an explosion that contaminated nearly 500 miles of the surrounding area.
The Soviet government initially refused to reveal what had occurred, but after a week, they had little choice. When some people began to show signs of radiation sickness, 10,000 people were evacuated from the area. Despite the Soviet government’s refusal to release any information about the accident, a study published in Radiation and Environmental Biophysics estimates that at least 200 people died as a result of radiation exposure. In 1990, the Soviet government finally declassified information about the disaster.
5.In 1979, Three Mile Island, Pennsylvania (Level 5)
The Three Mile Island nuclear power plant in Pennsylvania experienced the most serious accident in commercial nuclear power plant history. The partial meltdown of the power plant’s Unit 2 reactor was caused by a combination of equipment failure and operator error, resulting in the release of a small amount of radioactive material.
The accident resulted in no injuries, deaths, or direct health effects.
Following the accident, the Nuclear Regulatory Commission (NRC), the United States 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 conducted detailed studies of the accident’s radiological consequences.
6.Accident in Goiania, Brazil, in 1987 (Level 5)
A nuclear incident occurred in Goiania, Brazil, on September 13, 1987. The accident was primarily caused by radioactive contamination of a piece of hospital machinery that had been abandoned. As a level 5 accident, the incident is regarded as one of the top ten nuclear disasters of all time.
When two opportunistic scrap metal thieves broke into an abandoned Brazilian hospital in 1987, they had no idea they were about to set off one of the worst nuclear contamination incidents in history. The thieves discovered a teletherapy radiation capsule while scavenging parts from old hospital machinery. Unaware of the danger the material posed, they proceeded to dismantle it with a screwdriver and distribute the glowing blue material to friends and family before selling the metal. It wasn’t until locals started getting sick that the source of the radiation was discovered, and 249 people were found to have received significant radioactive contamination. Four people were killed as a direct result of the incident, and several houses were destroyed as a result.
7.Chalk River Reactor Mishaps (Level 5)
Two major nuclear reactor accidents occurred in Chalk River, Ontario, in the 1950s.
The first occurred in 1952 when the NRX reactor experienced a violent power excursion that destroyed the reactor’s core and caused some fuel to melt. Surprisingly, the shut-off rods did not fully descend into the core. A series of hydrogen gas explosions (or steam explosions) propelled the four-ton gasholder dome four feet into the air, where it became entangled in the superstructure. Thousands of cubic kilometres 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 near the Ottawa River. The NRX reactor core could not be decontaminated and had to be buried as radioactive waste. Young Jimmy Carter, later President of the United States and then a nuclear engineer in the United States Navy, was among the hundreds of Canadian and American servicemen ordered to participate in the NRX cleanup following the accident.
Six years later, in 1958, the NRU reactor’s metallic uranium fuel rods overheated and ruptured inside the reactor core. One of the damaged rods caught fire and was ripped in half while being extracted from the core by a robotic crane. A three-foot length of fiercely burning uranium fuel broke off and fell into a shallow maintenance pit as the remote-controlled crane passed overhead carrying the majority of the damaged rod. The smouldering fuel spread lethal fission products and alpha-emitting particles throughout the reactor building. The ventilation system was stuck in the “open” position, contaminating the building’s accessible areas as well as a large area downwind from the reactor site.A relay team of scientists and technicians eventually extinguished the fire by running at full speed past the maintenance pit, dumping buckets of wet sand on the burning uranium fuel.
8.1999, Tokaimura, Japan (Level 4)
When an unqualified group of workers decided to put more highly enriched uranium than was permitted in a precipitation tank, disaster struck. Two of the workers died, and another fifty-six plant workers were also exposed to high levels of radiation. In addition, 21 civilians were exposed to high doses of radiation, and residents within a thousand feet of the plant were evacuated.
9. On March 19, 2017, there were nine nuclear accidents in Saint Laurent (Level 4)
The Saint Laurent nuclear power plant was destroyed in 1969. The facility is made up of two gas-cooled, graphite-moderated reactors (GCR) called A1 and A2 (see Fig. 1). On October 17, 1969, uranium, which was required for the nuclear reaction to occur, melted, resulting in a partial meltdown.
As a result, workers spent an entire year cleaning and repairing the reactor, often in a highly radioactive environment. This accident, combined with an announcement by the president of Électricité de France (EDF), Marcel Boiteux, that France would abandon GCRs, signalled the end of the French gas-graphite programme. This novel experience in French history did not alter the country’s future nuclear development plans. French leaders took a back seat as they justified the nuclear accident with the enormous energy that nuclear generates.
Nearly a decade later, the Saint Laurent plant experienced another nuclear accident, this time rated a four out of seven on the International Nuclear Event Scale, the same as the 1969 accident. After two fuel elements melted were six to eight stack channels had become obstructed by a metal plate, Reactor A2 was shut down for two and a half years.  More information about the 1980 incident and subsequent cleanup at Saint Laurent A2 was requested, but Andrá Gauvenet, the Inspector General for Nuclear Safety and Protection, refused to provide any. He only stated that there was no radioactivity released into the environment as a result of the accident.