The vision of fission energy is compelling. In the last two decades it has become the world's largest single source of emission-free energy, and it creates a waste stream sufficiently small and compact that we can conceive of isolating this waste permanently from the environment. For fission to provide more energy in the future, our grand challenge is to continue to improve the safety, economic performance, waste minimization, and proliferation resistance of fission power plants.
The U.S. has 103 nuclear power plants providing over 20 % of its electricity; worldwide the number is 433. These plants have helped stabilize electricity costs, particularly with the recent volatility of natural gas prices. Our nuclear plants reduce substantially the amount of carbon dioxide that world-wide electricity use releases to the atmosphere. Nuclear fission is the only non-fossil energy source that has been demonstrated at large scale, and that could be expanded substantially further. Nuclear's current contribution is sufficiently large that every year since 1999 the increases in the operating capacity of existing U.S. nuclear power plants from improving equipment reliability accounted for over half of all carbon-dioxide reductions reported by the U.S. electrical industry.
We now expect most existing U.S. nuclear plants to apply for 20-year license extensions , which means that the existing U.S. nuclear fleet will operate out past 2030. Many of our U.S. plants has been sold by regulated utilities to large owner-operator companies like Excelon and Entergy. Besides encouraging further improvements in reliability and safety, the large technical expertise and financial resources available to these new nuclear-focused companies provides the best possible conditions for new plant orders. Designing the next generation of fission plants is where some of our most interesting work is now, ranging from planning for light water reactors with new passive safety features, to gas-cooled reactors with extremely durable fuel, to lead-cooled reactors that can burn more waste than they generate.