"The policy debate over the role of nuclear power in the nation's energy mix is rooted in the technology's fundamental characteristics. Nuclear reactors can produce potentially vast amounts of energy with relatively low consumption of natural resources and emissions of greenhouse gases and other pollutants. However, facilities that produce nuclear fuel for civilian power reactors can also produce materials for nuclear weapons. The process of nuclear fission (splitting of atomic nuclei) to generate power also results in the production of radioactive material that must be contained in the reactor and can remain hazardous for thousands of years. How to manage the weapons proliferation and safety risks of nuclear power, or whether nuclear power is worth those risks, are issues that have long been debated in Congress. The 104 licensed nuclear power reactors at 65 sites in the United States generate about 20% of the nation's electricity. Five new reactors are currently licensed for construction. About a dozen more are planned, but whether they move forward will depend largely on their economic competitiveness with natural gas and coal plants. Throughout the world, 436 reactors are currently in service, and 62 more are under construction."
CRS Report for Congress, R42853