Nuclear reactors are known for their operational reliability, which is crucial as newer technologies seek to join the existing fleet. In 2024, commercial reactors around the world achieved an average capacity factor of 83%, with North America reaching approximately 90%. This metric measures the ratio of actual energy output to the maximum theoretical output.
However, comparing this figure across different energy sources can be misleading. Natural-gas plants often exhibit lower capacity factors because they are more frequently turned on and off to manage fluctuating demand levels. It’s also important to note that high capacity factors for nuclear reactors do not account for the scheduled downtime required for refueling. Typically, reactors must refuel every 18 to 24 months, with operators planning these outages during low-demand seasons, such as spring and fall.
Data from the US Energy Information Administration illustrates that while reactor outages can vary significantly, a high operational capacity is often recorded during peak demand days. For instance, on July 28 of this year, the nuclear fleet operated at 99.6% capacity, contrasting with a drop to 77.6% on October 18, when maintenance and refueling outages occurred. As the industry approaches another season of increasing demand, many reactors are gradually returning to service.
Unexpected outages can also occur; for example, a generator failure at the Sequoyah nuclear power plant in Tennessee resulted in a year-long shutdown of one reactor. Additionally, the entire plant faced an unexpected closure shortly after its reactor resumed operations due to low water levels.
In another instance earlier this year, jellyfish caused operational challenges for two nuclear power plants in France by clogging cooling system filters, leading to significant but temporary output reductions. These situations underline the varied challenges that nuclear power facilities can face in maintaining consistent output.
Source: https://www.technologyreview.com/2025/12/04/1128754/nuclear-power-reliability/