Chernobyl evidence: INSAG and UNSCEAR

During a delayed safety test, reactor 4 of the RBMK-1000 plant underwent a rapid power excursion. Explosions destroyed the core and started a graphite fire. The event is classed as INES Level 7, the same top rank later assigned to Fukushima Daiichi in 2011 for a different accident sequence.

UNSCEAR records two immediate deaths and 28 ARS deaths among staff and emergency workers within four months — the 30 official early deaths often cited, sometimes listed as 31 with a later cardiac case. Later cancer totals are modelled. Thyroid cancer rose among those exposed as children; UNSCEAR does not treat a six-figure death toll as an observed count.

INSAG-1 (1986) emphasised operators. INSAG-7 (1992) concluded that design features and a weak safety culture were the main causes, with the night’s rule-breaking as the trigger. Both reports remain part of the public file.

On 27 April 1986, about 36 hours after the explosions. Residents were told the leave would be short. The city was not reoccupied. Slavutych was later built for plant staff.

A steel arch, the largest movable land structure of its kind, built beside unit 4 and slid over the 1986 sarcophagus on 29 November 2016, with later commissioning. It is meant to last about a century and to allow dismantling work.

The 1986 Early Notification and Assistance conventions, then the 1994 Convention on Nuclear Safety, plus IAEA safety-culture doctrine. Domestic Soviet criminal law produced the 1987 plant-management trial.