There were seven reportable incidents at Beznau 1 Nuclear Power Plant (NPP), eight at Gösgen NPP and seven at Leibstadt NPP. Their importance for nuclear safety was low and all incidents were rated Level 0 on the International Nuclear and Radiological Event Scale (INES). The Paul Scherrer Institut suffered two incidents, which were likewise rated INES Level 0. There were no reportable incidents at Beznau 2 NPP, the Zwilag Central Interim Storage Facility in Würenlingen or the Federal Institute of Technology in Lausanne (EPFL). At Mühleberg NPP, which is currently undergoing decommissioning, there was one security-relevant incident. Emissions of radioactive material into the environment via waste water and exhaust air from the nuclear installations were significantly below the allowed limits. Safety of people and the environment was ensured at all times.

Periodic Safety Review

In addition to the ongoing oversight activities, the Periodic Safety Review (PSR), which is carried out every ten years, is an important basis for assessing the condition of nuclear power plants. If a nuclear power plant is to be in operation for more than 40 years, the operator must provide an additional safety case as part of the PSR demonstrating that it can also ensure safety during long-term operation. In 2025, Leibstadt NPP will be the last of the nuclear power plants operating in Switzerland to switch over to long-term operation. It submitted its PSR with the safety case for long-term operation in 2022, and ENSI subjected this to a first review during the reporting year. ENSI also completed the review of the 2018 PSR of the Gösgen NPP. ENSI’s assessment of the PSR, the safety case for long-term operation and the backfit concept was positive.

Mühleberg Nuclear Power Plant is now undergoing decommissioning. ENSI has overseen the decommissioning and dismantling of numerous systems. In the year under review, Mühleberg NPP completed the transport of its remaining 215 fuel elements to the Zwilag central interim storage facility in Würenlingen. They will remain stored there until they are disposed of in a deep geological repository.

Waste management programme reviewed

The relevant sectoral plan process for disposal of the radioactive waste is in its third and final stage. Nagra plans to submit two general licence applications in 2024: one for a combined storage facility for all radioactive waste in the Stadel (ZH) site area and one for a fuel element encapsulation plant next to the Zwilag facility in Würenlingen (AG). In the year under review, ENSI continued the preparations for the safety review of these applications. ENSI has also completed its review of the five-year waste management programme that Nagra is working on. In its expert opinion, ENSI concludes that the waste producers responsible for disposal have fulfilled their legal mandate.