Final answer:
The world’s worst nuclear disaster occurred in Ukraine after the Chernobyl nuclear plant exploded in April 1986, causing acute radiation sickness and long-term health effects.
Step-by-step explanation:
The world’s worst nuclear disaster occurred in Ukraine after the Chernobyl nuclear plant exploded in April 1986. The accident was caused by an unauthorized experiment that resulted in an uncontrollable chain reaction and a steam explosion.
The explosion released a large amount of radioactive material into the atmosphere, causing acute radiation sickness among workers and firefighters and leading to long-term health effects and an increased risk of cancer.