The Chernobyl Disaster took place in 1986 in the Soviet Union (present-day Ukraine) and is considered the worst nuclear accident in history. The reactor used at Chernobyl was an RBMK type, which had a major design flaw. Unlike safer reactors, it used graphite as a moderator and did not have a strong containment structure to trap radiation in case of an accident. The disaster began during a safety test in which operators wanted to check whether the reactor could still be cooled during a power outage. To conduct this test, they reduced the reactor’s power and, critically, switched off several safety systems.

At low power levels, the RBMK reactor became highly unstable. Instead of slowing down, the nuclear reaction started behaving unpredictably due to increased steam formation, which actually accelerated the reaction rather than controlling it. When the operators realised things were going wrong, they pressed the emergency shutdown button. However, due to a flaw in the control rods, this action initially increased the reaction instead of stopping it. Within seconds, there was a massive power surge, leading to a steam explosion that blew off the reactor lid. The exposed core released radioactive material into the atmosphere, and the graphite caught fire, further spreading radiation.

The situation became extremely dangerous because there was no proper containment building, the reactor design was flawed, and human errors worsened the situation. Initially, the Soviet government tried to suppress information and delayed evacuation. Eventually, nearby areas like Pripyat were evacuated, and a massive concrete structure, known as a sarcophagus, was built to contain the radiation. The disaster spread radioactive material across large parts of Europe. The key lesson from Chernobyl is that a combination of poor reactor design and human error can lead to catastrophic consequences.