Chernobyl Disaster Timeline

As planned, a gradual reduction in the output of power unit 4 began at 01:06 on 25 April 1986 as part of a scheduled reactor shutdown preparatory to a maintenance outage. By the beginning of the day shift, the power level had reached 1600 MW of its nominal 3200 MW thermal level.

On 26 April 1986, reactor 4 of the Chernobyl Nuclear Power Plant, located near Pripyat, Ukraine, exploded during the safety test. With dozens of direct casualties and thousands of health complications stemming from the disaster, it is one of only two nuclear accidents rated at the maximum severity on the International Nuclear Event Scale, the other being the 2011 Fukushima nuclear accident.

The fire in reactor no. 4 continued to burn until 10 May 1986; it is possible that well over half of the graphite ultimately burned out, releasing radioactive material into the atmosphere.

The test plan called for a gradual decrease in reactor power to a thermal level of 700–1000 MW, and an output of 720 MW was reached at 00:05 on 26 April 1986. The test procedure was to be run during this controlled power-down of reactor no. 4.

Starting from 27 April 1986 at 14:00, each apartment block in Pripyat was provided with a bus, supervised by police and city officials, to evacuate residents from the contaminated city following the explosion.

In October 1991, a fire occurred in the turbine building of reactor no. 2, contributing to decisions about the plant's future operations.

Image source: Chernobyl Nuclear Power Plant

Anatoli Zakharov, a fireman stationed in Chernobyl, offered a different description in 2008: 'I remember joking to the others, There must be an incredible amount of radiation here.' His recollections provided a personal perspective on the immediate response.

The design of the sarcophagus started on 20 May 1986, just 24 days after the disaster, with construction running from June to late November. From May 5, 1986, workers from NIKIET and other institutes contributed to decontamination and construction efforts.

Work began once again in late November 1986, as the Complex Expedition began work to assess the damage, while members of the Khoplin Radium Institute collected any fuel rods they found and took them back to their laboratory.

The Chernobyl Nuclear Power Plant sarcophagus, completed in December 1986, reduced the spread of radioactive contamination and provided radiological protection for the crews of the undamaged reactors.

In December 1986, after months of investigation, Vasya Koryagin accidentally found a large object that appeared to be molten lead that had dropped into the reactor core and melted, providing insight into conditions inside the destroyed reactor.

In 1987, Valery Legasov, first deputy director of the Kurchatov Institute of Atomic Energy in Moscow, said: 'We learned that robots are not the great remedy for everything,' reflecting the limits of robotic technology in the highly radioactive cleanup.

Image source: Valery Legasov

Reactor no. 1 was decommissioned in November 1996 as part of a deal between the Ukrainian government and international organizations such as the IAEA to end operations at the plant.

A contract was signed in 1999 with Areva NP (Framatome) for construction of ISF-2, an interim spent fuel storage facility. In 2003, technical deficiencies became apparent, and in 2007 Areva withdrew and Holtec International was contracted for a new design and construction.

On 15 December 2000, then-President Leonid Kuchma personally turned off reactor no. 3, ending nuclear power generation at the Chernobyl plant permanently.

On 12 February 2013, a 600 square metre section of the roof of the turbine-building collapsed, adjacent to the sarcophagus, causing a new release of radioactivity.

Image source: Chernobyl Nuclear Power Plant sarcophagus

The shelter was completed in 2016 and was moved into place over the sarcophagus on 29 November. It received €864 million from international donors in 2011 and was managed by the European Bank for Reconstruction and Development. In 2016–2018, the NSC was constructed around the old sarcophagus to enable removal of reactor debris, with clean-up scheduled for completion by 2065.

Image source: Chernobyl New Safe Confinement

While neutron activity has declined across most of the destroyed fuel, from 2017 until late 2020 a doubling in neutron density was recorded in the sub-reactor space, before levelling off in early 2021. As of 2021, some fuel had already degraded significantly.

The new ISF-2 design was approved in 2010, work started in 2011, and construction was completed in August 2017. Fuel transfers to ISF-1 were completed in June 2016.

Although a number of radioactive emergency vehicles were buried in trenches, many of the vehicles used by the liquidators still remained, as of 2018, parked in a field in the Chernobyl area.

In February 2025, a Russian drone struck the shelter causing a fire, damaging the outer and inner protective covering of the NSC and insulating layers inside. In December 2025, the IAEA said that the drone strike meant the structure could no longer perform its main safety function.

The first limited guided tours began in 2002. In 2011, Ukraine opened the sealed zone around the Chernobyl reactor to tourists, allowing wider public access to the site.

The video game S.T.A.L.K.E.R.: Shadow of Chernobyl, developed by GSC Game World and released by THQ in 2007, is a first-person shooter set in the Exclusion Zone. Its release increased the site's popularity, and tour operators estimated that 40,000 tourists visited between 2007 and 2017. A prequel, Clear Sky, followed in 2008 and a sequel, Call of Pripyat, in 2010.

Image source: S.T.A.L.K.E.R.: Shadow of Chernobyl

After its release in July 2019, the critically acclaimed historical drama television miniseries Chernobyl boosted interest in the disaster. Ukrainian president Volodymyr Zelenskyy announced that the Chernobyl site would become an official tourist attraction. Between 2017 and 2022, over 350,000 tourists visited the site, peaking at almost 125,000 visitors in 2019.

Image source: Chernobyl (miniseries)

Tourism rebounded after COVID in 2021, but the Russian invasion of Ukraine in early 2022 and fighting in the surrounding area forced the zone to be closed to all visitors. The zone remains closed to tourists as of April 2026.