A thermonuclear fusion power plant is expected to provide low-carbon electricity with important safety and sustainability advantages. The fuel will be deuterium extracted from water and tritium bred inside the reactor from lithium. The D–T reaction produces helium, while activated structural materials will require radioactive waste management. Several countries are developing demonstration fusion power plants, mainly based on tokamaks, while other concepts are also being pursued. Many projects will build on knowledge gained from ITER and other fusion experiments. Some aim to supply electricity to the grid around 2040 or later.