Chernobyl – the world’s worst nuclear disaster

The catastrophic Chernobyl nuclear accident in Ukraine, then part of the Soviet Union, marked its 34th anniversary on Sunday.

“Sunday is International Chernobyl Disaster Remembrance Day. The women, men & children affected by radioactive contamination must never be forgotten,” the UN said, designating April 26 the International Chernobyl Disaster Remembrance Day.

What is Chernobyl?

On April 26, 1986, a sudden surge of power during a reactor systems test destroyed Unit 4 of the nuclear power station at Chernobyl, some 110 kilometers from Ukraine’s capital, Kiev.

The newly built city of Pripyat was the nearest town to the power plant, just under 2 miles away and housed almost 50,000 people in 1986. A smaller and older town, Chernobyl, was about 9 miles away and home to about 12,000 residents.

According to the World Nuclear Association, Chernobyl is made up of four reactors that were designed and built during the 1970s and 1980s. The Chernobyl plant used four Soviet-designed RBMK-1000 nuclear reactors – a design 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.

In most nuclear reactors, water is also used as a coolant and to moderate the reactivity of the nuclear core by removing the excess heat and steam. The RBMK-1000 used graphite to moderate the core’s reactivity and to keep a continuous nuclear reaction occurring in the core.

As the nuclear core heated and produced more steam bubbles, the core became more reactive, not less, creating a positive-feedback loop that engineers refer to as a “positive-void coefficient.”

The incident

The explosion occurred on April 26, 1986, during a routine maintenance check.  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.

The explosions occurred at 1:23 a.m. on April 26, destroying reactor 4 and initiating a booming fire. Toxic fumes and dust were carried by the blowing wind, bringing fission products and the noble gas inventory with it.

According to the official figures, 31 people were killed in the immediate aftermath of the accident, while millions more were affected. Around 8.4 million people in the former Soviet territories of Belarus, Russia, and Ukraine received the largest exposure to radiation.

Around 155,000-square-kilometer area of these three countries were contaminated, and over 400,000 people were displaced. Later research into the accident showed that the radioactive clouds reached as far as the US and China.

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. Within the next few years, 220,000 more residents were advised to move to less contaminated areas.

Chernobyl today

Today, Chernobyl including within the exclusion zone, is filled with a variety of wildlife that have thrived without interference from humans but the region is far from returning to normal.

Tourists continue to visit the site, with visitation rates jumping thanks to a TV series based on the disaster. The UN has recognized the April 26 as International Chernobyl Disaster Remembrance Day.

On 8 December 2016, the United Nations General Assembly adopted a resolution designating 26 April as International Chernobyl Disaster Remembrance Day.

In its resolution, the General Assembly recognised that three decades after the disaster there remains persistent serious long-term consequences and that the affected communities and territories are experiencing continuing related needs. It called on member states to observe the day.

The 1986 reactor meltdown and explosion at Chernobyl is considered the worst civilian nuclear disaster in history.

Message by Ukraine

Ukrainian President Volodymyr Zelenskiy honoured the memory of those who risked their lives to help contain radiation at the site in the months after the explosion and fire at the nuclear power plant in 1986.

“On this day we bow our heads to the blessed memory of those heroes who saved the future from the danger of radiation,” Zelenskiy said in a statement for the anniversary.

Zelenskiy also expressed “deep respect” for the firefighters and others currently working in the zone to “protect these lands from new natural disasters.”

Rehabilitation

Regarding the recent developments, the UN said the completion of the placement of the new safe confinement over the old shelter was a major milestone achieved in 2019.

Over 2.2 billion euros were provided by 45 donor nations through funds managed by the European Bank for Reconstruction and Development.

“The new safe confinement was handed over to the Government of Ukraine on 10 July 2019. The scope of the project in terms of international cooperation is one of the largest ever seen in the field of nuclear safety,” it added.

The Chernobyl disaster has resulted in a few significant changes for the nuclear industry. Experts around the world have continued researching ways for further safety to prevent future nuclear disasters.