Nuclear power plants currently operate in 31 countries. Here are top 4 countries which have the most nuclear power plants. The United States is the largest producer of nuclear power, while France has the largest share of electricity generated by nuclear power. China has the fastest growing nuclear power program with 28 new reactors under construction. After Fukushima, Japan shut down all of its 54 nuclear reactors, 12 of them permanently; 42 remain in operational condition, of which 24 have requested permission to restart, and 5 reactors have been restarted.