Background Information

Acknowledgement

World Nuclear Association is grateful to the International Atomic Energy Agency (IAEA) for access to its Power Reactor Information System (PRIS) database, and use of its data in the preparation of this report.

Definition of Capacity Factor

Capacity factors are calculated as the percentage obtained by dividing a reactor’s actual electricity output by the output expected if the reactor operated constantly at 100% of its net capacity. When calculating capacity factors, those reactors that do not generate any electricity during the calendar year are not included. For reactors that start-up or shut down during a calendar year the capacity factor for that year is calculated based on the electricity output that would have been generated were they to operate at 100% output for the fraction of the year in which they were in an operable status.

Reactor Statuses

The IAEA PRIS reactor database has a status type – Suspended Operation – differentiated from its Operating status. As of 15 August 2025, this status has been assigned to 19 reactors in Japan, which have not restarted since their outage after the 2011 accident at Fukushima Daiichi. It has also been assigned to four reactors in India: Madras 1, Rajasthan 1, Tarapur 1 and Tarapur 2.

World Nuclear Association uses the Operable status for reactors categorized by IAEA as Suspended Operation or Operable, with the exception of Rajasthan 1, which we consider to be in Permanent Shutdown status.

Ukraine

Performance data for reactors in Ukraine have not been provided to the IAEA PRIS database for 2022, 2023 and 2024. Estimates for output from Ukraine reactors are based on other data sources, principally data published in Energy Institute’s 2025 Statistical Review of World Energy.