01 Overview
At 1:23 AM on April 26, 1986, Reactor No. 4 at the Chernobyl Nuclear Power Plant suffered a catastrophic steam explosion followed by an open-air reactor core fire. The explosion was caused by a combination of design flaws in the RBMK reactor and operator errors during a safety test. The immediate blast destroyed the reactor building and killed two workers instantly.
02 Cause
The disaster originated from a flawed reactor design (positive void coefficient) combined with a culture of secrecy in the Soviet nuclear program. During a low-power test to verify safety systems, operators violated safety protocols by withdrawing nearly all control rods. When the test began, the reactor became unstable - a massive power surge occurred, causing superheated steam to rupture fuel channels, leading to a steam explosion and subsequent chemical explosions that blew off the 1,000-tonne reactor lid.
03 Impact
The explosion released 400 times more radiation than the atomic bomb dropped on Hiroshima. About 350,000 people were ultimately evacuated from the surrounding area. The Exclusion Zone - a 30km radius around the plant - remains largely uninhabited today. The Soviet government's initial cover-up delayed international response by days. Long-term health effects include thousands of thyroid cancer cases.
04 Response
Firefighters arrived within minutes, unaware of the radiation danger. Liquidators - over 600,000 people - were ultimately drafted to contain the disaster, building a concrete sarcophagus over the reactor. The town of Pripyat (population 50,000) was evacuated 36 hours after the explosion. In 2016, a New Safe Confinement structure was slid over the old sarcophagus.
05 Legacy
Chernobyl accelerated the collapse of the Soviet Union by exposing governmental failures. It directly contributed to the creation of INSAG international safety standards. The disaster became a symbol of the dangers of nuclear power and Soviet-era secrecy. Today the site receives hundreds of thousands of tourists annually.