From plant construction through the 1986 accident, INSAG reports, the 1987 trial and the 2016 confinement.
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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.
Engineering time is a night; institutional time is thirty years of reports and a second shelter.
Health time is longer still and must be cited as models with dates, not as a single toll.
JanuaryFebruaryMarchAprilMayJuneJulyAugustSeptemberOctoberNovemberDecember
Work starts on the Chernobyl station beside the new town of Pripyat in the Ukrainian SSR.
The fourth RBMK-1000 unit is commissioned. The design lacks a Western-style full containment building.
The turbine-rundown test ends in a prompt power excursion, explosions and a graphite fire in unit 4.
Buses empty the atomgrad. A wider 30-kilometre exclusion zone is drawn in the following days.
Forsmark’s alarm and European monitoring force a first Soviet public statement.
IAEA’s first advisory report, based on limited data, stresses operator actions at the Post-Accident Review Meeting.
Bryukhanov, Fomin and Dyatlov receive prison sentences after a public trial held in the Chernobyl area.
The update names RBMK design and safety culture as principal causes and records hardware fixes at remaining units.
UN agencies publish a synthesis on health, environment and social costs, including modelled death ranges that remain debated.
The arch is slid over the 1986 sarcophagus, the largest move of its kind, opening a long dismantling phase.
Each public-record claim on this dossier sits beside the timeline chapter already on the page.
Public-record encyclopedia. Not legal advice, not a how-to, not a private file.
Claim The official death toll is in the hundreds of thousands.
Timeline beat 1970 — Construction begins
That figure is a high-end model or a confusion with all later deaths in large populations. UNSCEAR’s documented early radiation deaths are 28 plus two blast deaths.
Claim The accident was a Western-style containment meltdown.
Timeline beat 1983 — Unit 4 online
RBMK unit 4 had no full containment. The sequence was a power excursion, explosions and a graphite fire.
Claim Pripyat was left in place for weeks.
Timeline beat 26 Apr 1986 — Explosion at 01:23
The city was evacuated on 27 April 1986, the day after the explosions.
Claim INSAG never changed its mind.
Timeline beat 27 Apr 1986 — Pripyat evacuated
INSAG-7 (1992) explicitly updated INSAG-1 (1986) once design data were available.
Mark each timeline beat already on this dossier as supported, contested or unknown, using the public-record claims already filed here. Not a verdict.
Editorial marks on this device only. Public-record encyclopedia — not legal advice, not a how-to, not a private file.
| Timeline beat | Supported / Contested / Unknown |
|---|---|
| 1970 — Construction begins Claim already on file: The official death toll is in the hundreds of thousands. | |
| 1983 — Unit 4 online Claim already on file: The accident was a Western-style containment meltdown. | |
| 26 Apr 1986 — Explosion at 01:23 Claim already on file: Pripyat was left in place for weeks. | |
| 27 Apr 1986 — Pripyat evacuated Claim already on file: INSAG never changed its mind. | |
| 28 Apr 1986 — Sweden detects the plume Claim already on file: INSAG never changed its mind. | |
| Aug 1986 — INSAG-1 in Vienna Claim already on file: INSAG never changed its mind. | |
| Jul 1987 — Plant managers tried Claim already on file: INSAG never changed its mind. | |
| 1992 — INSAG-7 revises cause Claim already on file: INSAG never changed its mind. | |
| 2005 — Chernobyl Forum Claim already on file: INSAG never changed its mind. | |
| 29 Nov 2016 — New Safe Confinement Claim already on file: INSAG never changed its mind. |
After 2016 the accident’s hardware is under a new roof; the health argument remains a dated literature, not a closed census.
Public-record encyclopedia. Not legal advice. Not a how-to. Graphic detail is withheld. Wars belong in a separate atlas.