The Fukushima disaster that occurred in Japan was only the second time every the international nuclear event scale rated a nuclear disaster as a 7 on a scale from 1 to 7. The disaster was caused on march 11th 2011 by a 9.0 earthquake that hit Japan, followed by a tsunami. When the earthquake hit it shut down the power to reactors 1, 2, and 3. When nuclear reactors shut down they must be cooled for days after in order to make sure a meltdown does not occur, so alternative energy systems were used to keep the reactors cool. About 50 minutes later, a tidal wave caused by the earthquake also hit the nuclear plant and caused the alternative energy sources to be flooded and stop working. Because the reactors were not being kept cool, they began to melt down shortly after due to the excess of heat created when the reaction occurs.
The Japanese government immediately evacuated the area 10km away from the power plant, and told people between 10km and 30km to not go outside and to stay in their houses until further notice. This caused widespread panic throughout the region. Only hours later when the owners of the plant decided to let it flood with sea water was the meltdown stopped. They did not do this immediately because they knew it would cause millions of dollars of damage to expensive equipment used.
Since the disaster, all but two of Japans nuclear reactors have been shut down due to safety issues. This is a huge problem for the country of japan because they were almost completely energy independent due to their extensive nuclear power generation. Now they need to import much of their energy from other countries because they do not have enough natural resources to harvest energy from to become independent another way. The disaster in Japan caused an outcry in many other countries to slow down their own nuclear programs. After the disaster public opinion in the United States about nuclear power shifted from about 50/50 to 40/60, making it less popular. It also hit stock markets around the world hard for companies that relied on nuclear energy to conduct business. Since then many new regulations have been proposed all over the world to make sure nuclear energy production is kept safer.