What was the Chernobyl nuclear disaster?

The Chernobyl Nuclear Power Plant lay roughly 15 kilometres northwest of the town of Chernobyl and about 110 kilometres north of Kyiv.

It was constructed as part of the Soviet Union’s large-scale plan to expand nuclear energy production during the Cold War.

The site selected for the plant was near the Pripyat River, which provided the necessary water supply for reactor cooling.

Construction began in the early 1970s, with the first reactor, Unit 1, becoming operational in September 1977.

This was followed by Units 2, 3, and 4 over the next six years. The plant used RBMK (Reaktor Bolshoy Moshchnosti Kanalny) reactors, a Soviet design that combined graphite moderation with water cooling. 

By the mid-1980s, the facility had become one of the most important power producers in the region.

It supplied electricity to much of northern Ukraine and western Russia. Its workforce lived primarily in the nearby city of Pripyat, which had been purpose-built in 1970 to house the plant’s engineers, technicians, and their families.

Pripyat was considered a model Soviet city, complete with schools, hospitals, sports complexes, and amusement parks.

At the time of the disaster, two more reactors, Units 5 and 6, were under construction, which showed the USSR’s continuing reliance on nuclear energy.

However, behind the plant’s impressive scale and strategic importance lay several critical design flaws and unsafe procedures. 

On the night of 25 to 26 April 1986, engineers at Reactor No. 4 prepared to carry out a safety test.

The goal was to test whether the reactor's turbines could keep producing enough electricity to power the cooling pumps in the event of a loss of external power.

To simulate this, operators planned to reduce the reactor’s output and disconnect it from the grid.

However, a series of mistakes disrupted the procedure from the beginning. Earlier delays had forced the test into the early hours of 26 April, and a shift change meant that poorly informed night staff were now overseeing the test.

The reactor was operating at an unstable low power level, and key safety systems had been manually disabled. 

As the test began, the operators made several serious errors. They withdrew the control rods to dangerously low levels, failed to maintain a stable reaction, and overlooked signs of increasing instability.

When they finally triggered the emergency shutdown, a design flaw in the RBMK reactor caused a sudden spike in reactivity.

The graphite displacers at the tips of the control rods momentarily increased reactivity when inserted, which accelerated the chain reaction instead of halting it.

Within seconds, an explosion tore through the reactor core, which blew off the 1,000-tonne steel and concrete lid.

A second explosion soon followed, likely caused by steam pressure and hydrogen build-up.

These blasts ruptured the building and released a large amount of radioactive material into the air. 

The initial explosion released fission products such as iodine-131, cesium-137, and strontium-90 directly into the atmosphere.

A graphite fire caught in the core and burned for approximately nine to ten days and threw radioactive smoke high into the sky.

The lack of a containment structure around the RBMK reactor meant there was no barrier to stop the material from escaping.

Soviet authorities struggled to estimate the size of the contamination, but external radiation levels near the plant reached thousands of times higher than normal.

Local plant workers and firefighters were exposed without adequate protective gear.

Many suffered from acute radiation syndrome and died within weeks. 

Carried by wind, the radioactive cloud spread over Belarus, Russia, Ukraine, and much of Europe.

Sweden was the first foreign country to detect high radiation levels, which caused people to ask questions and forced the Soviet Union to admit that an accident had occurred.

Over the following days, radioactive fallout was detected as far west as France and the United Kingdom.

The weather played a key role in where and how much radiation fell. Rainfall caused radioactive particles to settle into soil, forests, and lakes.

Areas in Belarus and Ukraine became heavily contaminated, and thousands of square kilometres were judged unsafe for living or farming. 

For the first 36 hours after the explosion, officials failed to warn the public. In Pripyat, life continued as normal, even as radiation levels rose to dangerous levels.

Children went to school, workers went to their jobs, and outdoor events took place.

It was only on the afternoon of 27 April that buses arrived to evacuate the city’s 49,000 residents.

They were told they would be away for only three days, and instructed to bring only essentials.

In reality, they would never return. The evacuation expanded to cover a 30-kilometre exclusion zone around the plant, eventually displacing over 100,000 people from dozens of towns and villages. 

Inside the plant, efforts to contain the fire and damage continued under harsh conditions.

Firefighters and soldiers known as “liquidators” were sent in with minimal protection to shovel debris, bury radioactive waste, and construct makeshift barriers.

Many of these men received fatal or long-term radiation exposure. Soviet authorities suppressed information out of fear of public panic and institutional embarrassment, worsened by confusion among government agencies.

Full details were only revealed gradually, and many health workers were not informed of the risks.

The scale of the disaster, combined with the disorganised and secretive response, shocked the international community and weakened global trust in the Soviet government. 

The human cost of the disaster remains hard to measure exactly. The Soviet reports first said there were only 31 deaths from the blast and radiation syndrome.

They did not include later health effects. The World Health Organization and other agencies later estimated that thousands of cancer cases, particularly thyroid cancer, were linked to the fallout.

Children and adolescents exposed to iodine-131 were especially at risk. In the years following the disaster, researchers documented significant rises in cancer rates and birth defects in affected regions.

They also recorded widespread psychological trauma in those areas. However, estimates vary, and the full toll may never be known. 

The disaster also caused widespread harm to the environment. Forests near the reactor, known as the “Red Forest,” turned orange and died within days of the explosion due to extreme radiation exposure.

Agricultural land was poisoned by radioactive isotopes, which rendered large areas unusable for farming.

Wildlife in the exclusion zone suffered initial die-offs but later rebounded in unexpected ways.

Some early studies suggested mutations in animals, but later research offered mixed results and found no consistent pattern of long-term genetic damage.

Economically, the disaster cost the USSR tens of billions of roubles, strained the healthcare system, and diverted resources from other sectors at a time when the Soviet economy was already under pressure. 

In the months after the disaster, Soviet engineers raced to build a concrete sarcophagus over Reactor No. 4.

Completed in November 1986, this structure was intended to seal off the damaged core and reduce radioactive leakage.

The hurried construction, however, used poor materials and suffered from cracks and structural weaknesses.

By the early 2000s, the sarcophagus had worn down until it risked collapsing and releasing more radioactive dust.

Plans for a lasting solution were made with help from other countries. 

In 2016, once engineers had completed years of planning and construction, a structure called the New Safe Confinement was moved over the old sarcophagus.

This large steel arch, 108 metres tall and 257 metres wide, was made to last at least 100 years and hold back any future leaks.

Funded by the European Bank for Reconstruction and Development, the project cost approximately €2.1 to €2.2 billion.

It included systems to monitor radiation levels, handle future deconstruction of the reactor, and ensure long-term environmental safety.

This new structure represented a significant engineering achievement and brought greater security to the Chernobyl site. 

Modern nuclear reactors are designed with several layers of safety features that did not exist in the RBMK design.

Most contemporary reactors use pressurised water systems and have reinforced containment buildings that can withstand explosions.

Operators must meet clear global safety rules, and regulators carry out checks on a regular basis.

Lessons from Chernobyl and later from the Fukushima disaster in 2011 led to widespread reviews of nuclear safety procedures across the world.

Training now emphasises disaster prevention and emergency planning. It also highlights the need for transparent communication. 

However, no system is completely free from risk. Human error, natural disasters, or acts of sabotage can still trigger accidents.

Countries with poor regulatory oversight, ageing reactors, or unstable political environments remain vulnerable.

In particular, Russia still operates several RBMK reactors, though many have undergone safety upgrades.

While another disaster on the scale of Chernobyl is less likely due to advances in technology and international cooperation, the event is still a stark warning about the potential dangers of nuclear energy when mismanaged.