Human error had played a major part in the disaster which followed the Chernobyl-4 accident. The operators did not give a chance to reactor's emergency core cooling systems and emergency shut down systems to operate by switching them off. In terms of radiation exposure and casualties it is the most serious of all the previous nuclear accidents. About 200 million people in western and central Europe are exposed to radiation, 135,000 were displaced from their homes and 31 died. This would not stop the peaceful use of nuclear energy for the benefit of mankind. It may help to make the nuclear power safer, in future.