Chernobyl Nuclear Disaster
Reactor four at Chernobyl exploded at 1.23 on the morning of 26 April 1986 during a safety test. The test was to determine whether the turbine's rotational energy could power the coolant pumps during a power cut, and it had been postponed and rescheduled to a night shift that had not been briefed on it. The reactor was an RBMK design with two defects the operators did not know about: a positive void coefficient, meaning that steam bubbles in the coolant increase reactivity rather than damping it, and control rods tipped with graphite, so that the first metre of insertion accelerates the reaction instead of stopping it. The staff, trying to recover from a power drop, withdrew almost all the rods and disabled safety systems, and when the emergency shutdown was pressed the reactor's power rose in seconds by a factor of hundreds. Two explosions blew the 1,200-tonne upper shield off and set the graphite core burning. The initial response was denial. The plant reported no reactor damage for hours, the town of Pripyat was evacuated thirty-six hours later, and the Soviet government said nothing until Swedish monitors detected the plume and asked. Some 600,000 liquidators worked on the site, and the first responders received doses that killed twenty-eight of them within months. The long-term toll is contested and runs from 4,000 to tens of thousands. Gorbachev later said the accident, more than his own reforms, was what broke the Soviet system's authority. The exclusion zone of 2,600 square kilometres is still in place and has become one of Europe's largest de facto nature reserves, with wolves, lynx and wild horses in the villages. Russian troops dug trenches in the contaminated forest in 2022.
- Year: 1986 CE
- Category: Technological
