World construction for nuclear reactors peaked in the mid-1970s and dropped precipitously through the early 2000s. The modest resurgence in new construction in the 21st century has not been sufficient to prevent a significant increase in the average age of nuclear reactors. In 1990, the average age (from grid connection) of the operating reactors in the world was 11 years; in 2023, it was 31 years.1 The United States (41 years) and France (36 years) had the oldest reactor fleets in 2023.
The oldest operating reactor in the United States is Nine Mile Point Unit 1 in New York State, which entered commercial service in December 1969. The newest reactor to enter service is Vogtle Unit 3 at the Alvin W. Vogtle Electric Generating Plant in Georgia which began commercial operation on July 31, 2023.2
As of 2023, nine of the 41 units that have been closed in the United States had reached 40 years of age. All nine had obtained licenses to operate up to 60 years but they closed for mainly for economic reasons. In other words, at least one-quarter of the 134 reactors connected to the grid in the United States never reached their initial design lifetime of 40 years. The mean age at the closure of those 41 units was 22.8 years.1
In France, the United States, and other countries, the operating lifetime of a reactor can be extended through relicensing in which a government regulatory agency extends the right to operate beyond the initial license period. There are multiple incentives to relicense. Nuclear power plants are expensive to build. Relicensing enables operators to continue generating revenue from existing infrastructure without the need for significant new capital investment.
Nuclear power is a widely deployed low-carbon source of electricity. The push to relicense may be boosted by the Declaration to Triple Nuclear Energy by 2050 signed by 20 countries at the 28th United Nations Climate Change Conference or Conference of the Parties of the UNFCCC (COP28).3
In Europe, the loss of Russian natural gas since the invasion of Ukraine has prompted some countries to examine whether they can extend the lives of their aging nuclear reactors to maintain a secure supply of low-carbon electricity.4
In the United States, the Nuclear Regulatory Commission (NRC) issues licenses for commercial power reactors to operate for up to 40 years. These licenses can be renewed for an additional 20 years at a time. As of January 2022, the NRC had renewed the operating licenses of 94 commercial nuclear reactors. Fifty-eight entered their extended period of operation; eight of those have since ceased operations.5 In 2019 and 2020 the NRC approved the first licenses for reactors in Florida and Pennsylvania to operate for 80 years.6
In 2023, the Finnish Government granted a new operating license for both units at Fortum’s Loviisa nuclear power plant until the end of 2050, when they will be 70 years old.7
The wisdom of relicensing has been questioned by some who suggest that safety concerns multiply as reactors age. Like any physical structure, components of nuclear power plants degrade with use including the reactor core and the equipment inside it, concrete, electronics, etc. The degradation of some materials through exposure to ionizing radiation adds additional challenges. Routine operation and maintenance take care of most wear and tear.
But are older nuclear reactors “less safe?” There is remarkably little independent, rigorous research that addresses this question due to limited data availability and the challenge of defining “safety.” One study assessed the impact of age and reactor technology on safety in the French nuclear fleet between 1997 and 2015 using data on 19,000 nuclear safety events declared by plant managers to the French regulatory agency. The study concluded that older reactors did experience some types of safety events more frequently. For one class of reactors, one additional year of age led to a 15% increase in the expected number of automatic shut-downs per year in 1997, but just 6% in 2014. The researchers concluded that technological improvements and “significant progresses in the management of aging” were behind the gains in safety.8
The aging of the world’s fleet of nuclear reactors will remain a central issue in discussions of energy security and the decarbonization of the world’s energy system. Informed decision-making demands better data on the relationship among aging, economic performance, and safety. Equally important is greater transparency regarding how operators of nuclear power plants and the government agencies that regulate them assess and report safety.
1 Mycle Schneider and Antony Froggatt, “The World Nuclear Industry Status Report 2023,” A Mycle Schneider Consulting Project, 2023, Link
2 U.S. Energy Information Administration, “How old are U.S. nuclear power plants, and when was the newest one built?” August 3, 2023, https://www.eia.gov/tools/faqs/faq.php?id=228&t=3
3 Nuclear Energy Agency, “Countries launch joint declaration to triple nuclear energy capacity by 2050 at COP28,” December 2, 2023, Link
4 Hernandez, America, Forrest Crellin, Prasanta Kumar Dutta, Anurag Rao and Aditi Bhandari, “The Nuclear Aged,” Reuters, August 22, 2023, Link
5 United States Nuclear Regulatory Commission, “Reactor License Renewal,” accessed March 15, 2024, https://www.nrc.gov/reactors/operating/licensing/renewal.html
6 Bandyk, Matthew, “How long can a nuclear plant run? Regulators consider 100 years,” Utility Dive, March 29, 2021, Link
7 Fortum, “The Finnish Government has granted a new operating licence for Fortum’s Loviisa nuclear power plant,” 16 February 2023, Link
8 Romain Bizet, Petyo Bonev, and François Lévêque, “Are older nuclear reactors less safe? Evidence from incident data in the French fleet, i3 Working Papers Series, 17-CER-02, https://minesparis-psl.hal.science/hal-01695160/file/WP-17-CER-02.pdf
