One of the remarkable features of nuclear power in the United States is that it has provided an annual average of about 19% of the country’s electricity since 1990 even though just one new plant has become operational in over 30 years. Many factors are at work here, including increased fuel enrichment level, more efficient “burnup” of the fuel, a significant increase in the average capacity factor for nuclear plants, and license extensions that allow some plants to operate for 60 years or more.
An important but lesser-known boost for nuclear power comes through the phenomenon known as the “uprating” of existing plants. Uprating generally involves physically modifying a plant to increase its generating capacity.1 Since 1977, the Nuclear Regulatory Commission (NRC) has approved 144 power uprates with at least one in every state with operational reactors.
There are three categories of power uprates:2
- Measurement uncertainty recaptures power uprates are less than two percent and are achieved using better feedwater flow measurement devices to measure feedwater flow more precisely, which is used to calculate reactor power.
- Stretch power uprates are typically between 2 and 7 percent and usually involve changes to instrumentation settings but do not require major plant modifications.
- Extended power uprates can be as high as 20% and are achieved by significant modifications to major equipment such as high-pressure turbines, condensate pumps and motors, main generators, and/or transformers.
The cumulative uprates from 1977 to 2021 amount to 24,080 megawatts thermal (MWt), or 8030 megawatts electric (MWe). To put this in perspective, Unit 3 at Plant Vogtle, southeast of Augusta, Georgia, which became operational in July 2023 has a nameplate capacity of 1100 MWe. Thus, the power uprates of the entire fleet of nuclear plants are the equivalent of more than seven of the new Vogtle units. That is a lot of electricity. At its full output of 1,100 megawatts of electricity, Unit 3 at Plant Vogtle can power 500,000 homes and businesses.3
A large majority of the approved upratings are in the range of zero to five percent. These tend to be cheaper and faster to implement and be approved by the NRC. As of November 2023, the NRC had no new applications for uprating under review.
1 U.S. Energy Information Administration, “Uprates can increase U.S. nuclear capacity substantially without building new reactors,” July 17, 2012, Link
2 U.S. Nuclear Regulatory Commission, “Types of Power Uprates,” March 10, 2020, Link
3 Amy, Jeff, “The first US nuclear reactor built from scratch in decades enters commercial operation in Georgia,” AP News, July 31, 2023, Link
