There have been two explosions at a nuclear power plant in Japan which was damaged in Friday's earthquake.
Nuclear reactors create electricity from tiny little particles called atoms. When these atoms are split, huge amounts of heat burst out. This heat is then turned into electricity which is then used to power people's homes.
When nuclear power works well, it's clean, efficient and gives off lots and lots of energy.
But when things go wrong, it can be really serious. Check out Sonali's report to find out more.