As much as 25% of the existing nuclear generating capacity in the United States could shut by 2050 as natural gas and renewable energy resources continue to grow.

The Energy Department's Energy Information Administration (EIA) says that nuclear power currently accounts for about 20% of electricity generation in the United States.

Nearly all nuclear plants now in use began operation between 1970 and 1990. EIA says these plants would require a license renewal before 2050 to operate beyond the 60-year period covered by their original 40-year operating license and the 20-year license extension that nearly 90% of plants have either already received or have applied for.

Nuclear retirements through 2050 are forecast to cut its share of the generation mix to 11%.EIA’s 2017 Annual Energy Outlook (AEO2017) Reference case does not envision a large amount of new nuclear capacity additions. By 2050, four reactors currently under construction and some uprates at existing plants are projected to come online.

A January 2017 white paper by the National Conference of State Legislatures says that since 2013, six nuclear reactors in the United States have closed for good. Another 12 are slated to shut down. And operators of several more have warned of possible closures.

On April 14, Energy Secretary Rick Perry ordered a study of the U.S. grid in an effort to determine whether policies that boost renewable energy are speeding the retirement of coal and nuclear plants and threatening power reliability.

Indeed, many operators point out that nuclear energy has long been the source of emission-free generation that clean-energy advocates love to hate. (Read "Facing Threats, Nukes Work to Polish Their Green Cred.")

Except during maintenance or refueling cycles, nuclear plants operate around the clock as baseload generators. That means nuclear plants make up a disproportionately large share of generation compared with their share of electricity generating capacity. Generating capacity using other fuels is typically dispatched at much lower rates than nuclear units.

EIA says that as more nuclear capacity is retired than built, and as other fuels such as natural gas and renewables gain market share, the nuclear share of the U.S. electricity generation mix declines from 20% in 2016 to 11% in 2050.

Coal and nuclear capacity decline while natural gas and renewables continue to grow.From 2018 through 2050, 9.1 gigawatts (GW) of nuclear capacity is added in EIA's reference case estimate, which assumes that current laws and policies do not change.

Two projects under construction—V.C. Summer in South Carolina and Vogtle in Georgia—each have two reactors and are expected to add 4.4 GW of new nuclear capacity. However, their progress has been uncertain since the company manufacturing their reactors, Westinghouse Electric, filed for bankruptcy protection in late March.

EIA says that another 4.7 GW of added nuclear capacity results from uprates, or operational changes that allow existing plants to produce more electricity. Increases from uprates are expected to end by 2040, as EIA expects that all plants planning to uprate will have completed the projects by then.

More than offsetting the total addition of 9.1 GW of nuclear capacity from new plants and uprates are projected retirements of 29.9 GW from 2018 through 2050.

Since the outlook's assumptions were finalized, legislation passed in Illinois created financial incentives through 2026 to support the continued operation of Quad Cities and Clinton. Operators of these two plants subsequently withdrew their announcements to retire those plants, reducing the amount of capacity likely to retire in 2017 and 2018.

However, in the months since the outlook was finalized, Entergy announced plans to retire three plants: Michigan’s Palisades in 2018 and New York’s Indian Point Units 2 and 3 around 2020.

New commercial nuclear power plants are licensed by the Nuclear Regulatory Commission (NRC) for 40 years. Because many nuclear plants were built more than 40 years ago, nearly 90% of currently operating nuclear plants are currently operating under or have applied for 20-year license renewals. Plant operators may apply for subsequent license renewals to continue operating for an additional 20 years (a total of 80 years).