The safety status of the Beznau and Leibstadt nuclear power plants (NPPs) was good. ENSI is not issuing an overall assessment for Gösgen NPP while the findings concerning its feedwater system are still being evaluated and the plant remains in an extended shutdown.
In 2025, Swiss nuclear installations recorded 43 reportable events that were relevant to nuclear safety. The corresponding number for the previous year was 36. The events were distributed across the nuclear installations as follows:
- 8 events at Beznau 1 NPP
- 5 events at Beznau 2 NPP
- 18 events at Gösgen NPP
- 6 events at Leibstadt NPP
- 3 events at the Paul Scherrer Institute (PSI)
- 2 events at the Central Interim Storage Facility in Würenlingen
- 1 event at the École Polytechnique Fédérale de Lausanne
- 0 events at Mühleberg NPP (undergoing decommissioning)
One event rated INES Level 1
ENSI classified the deviation during the loading of a transport and storage container at Leibstadt NPP as Level 1 (anomaly) on the International Nuclear and Radiological Event Scale (INES). ENSI classified all other events as INES Level 0 (events of minor safety deviation).
Prolonged shutdown at Gösgen NPP
During the reporting year, a possible design weakness in the feedwater system was identified at Gösgen NPP as a result of new calculation methods. Gösgen NPP had to prove that it can control the «break of a feedwater line» accident scenario in line with the current state of science and technology. This resulted in a prolonged shutdown.
The higher number of reportable events at Gösgen NPP in comparison with the previous year (2024: 10) was attributable to several factors: findings relating to the possible design weakness in the feedwater system, age-related findings, as well as operational errors and deviations. Some of the events also related to the firefighting water system in the power plant’s underground car park.
No impermissible releases
No impermissible releases of radioactive substances from Swiss nuclear installations were registered during the reporting year. The releases were significantly below the legal limits.
Radioactive waste management
In 2024, the National Cooperative for the Disposal of Radioactive Waste (Nagra) submitted the general licence applications for a deep geological repository in the North of Lägern site area and a fuel encapsulation plant in Würenlingen. On behalf of the Swiss Federal Office of Energy (SFOE), ENSI checked the completeness of the documents by February 2025 and requested additional information. Nagra submitted the revised application for the fuel encapsulation plant in May 2025, followed by the application for the deep geological repository in June. This marked the start of ENSI’s detailed review of the documents.
