In the early morning hours of April 26, 1986, the Chernobyl Nuclear Power Plant in Ukraine (formerly part of the Soviet Union) exploded, creating what many consider the worst nuclear disaster the world has ever seen.
Where is Chernobyl?
The Chernobyl Nuclear Power Plant is located about 81 miles (130 kilometers) north of the city of Kiev, Ukraine and about 12 miles (20 km) south of the border with Belarus, according to the World Nuclear Association. It is made up of four reactors that were designed and built during the 1970s and 1980s. A manmade reservoir, roughly 8.5 square miles (22 sq. km) in size and fed by the Pripyat River, was created to provide cooling water for the reactor.
The power plant
The Chernobyl plant used four Soviet-designed RBMK-1000 nuclear reactors — a design that’s now universally recognized as inherently flawed. RBMK reactors were of a pressure tube design that used an enriched U-235 uranium dioxide fuel to heat water, creating steam that drives the reactors’ turbines and generates electricity, according to the World Nuclear Association.
What happened?
The explosion occurred on April 26, 1986, during a routine maintenance check, according to U.N. Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). Operators were planning on testing the electrical systems when they turned off vital control systems, going against the safety regulations. This caused the reactor to reach dangerously unstable and low-power levels.
Reactor 4 had been shut down the day before in order to perform the maintenance checks to safety systems during potential power outages, according to the Nuclear Energy Agency (NEA). While there is still some disagreement over the actual cause of the explosion, it is generally believed that the first was caused by an excess of steam and the second was influenced by hydrogen. The excess steam was created by the reduction of the cooling water which caused steam to build up in the cooling pipes — the positive-void coefficient — which caused an enormous power surge that the operators could not shut down.
The explosions occurred at 1:23 a.m. on April 26, destroying reactor 4 and initiating a booming fire, according to NEA. Radioactive debris of fuel and reactor components rained over the area while fire spread from the building housing reactor 4 to adjacent buildings. Toxic fumes and dust were carried by the blowing wind, bringing fission products and the noble gas inventory with it.
Radioactive fallout
The explosions killed two plant workers — the first of several workers to die within hours of the accident. For the next several days, as emergency crews tried desperately to contain the fires and radiation leaks, the death toll climbed as plant workers succumbed to acute radiation sickness.
Evacuations of Pripyat commenced on April 27 — about 36 hours after the accident had occurred. By that time, many residents were already complaining about vomiting, headaches and other signs of radiation sickness. Officials closed off an 18-mile (30 km) area around the plant by May 14, evacuating another 116,000 residents. Within the next few years, 220,000 more residents were advised to move to less contaminated areas, according to the World Nuclear Association.
Chernobyl today
The area has recovered to some extent, but is far from returning to normal.. But in the areas just outside the exclusion zone, people are beginning to resettle. Tourists continue to visit the site, with visitation rates jumping 30-40% thanks to a new HBO series based on the disaster. And The catastrophe that occurred at Chernobyl resulted in a few significant changes for the nuclear industry: concern about reactor safety increased in eastern Europe as well as around the world; the remaining RBMK reactors were modified to reduce the risk in another disaster; and many international programs including the International Atomic Energy Agency (IAEA) and the World Association of Nuclear Operators (WANO) were founded as a direct result of Chernobyl, according to the World Nuclear Association. And around the globe, experts have continued researching ways to prevent future nuclear disasters.
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