Swiss energy group BKW (formerly Bernische Kraftwerke) has completed defueling of the decommissioned Mühleberg NPP (KKM Kernkraftwerk Mühleberg). The 418 used fuel elements have all now been transferred to the interim storage facility in Würenlingen in northern Switzerland, reducing radioactivity by more than 99%. BKW noted that removal of the fuel was completed 16 months ahead of the original scheduled set in 2015.

The 373 MWe boiling water reactor plant, some 15 kilometres from the Swiss capital Bern, began operation in 1972 and provided 5% of Switzerland’s electricity. BKW decided to close the plant in 2013 for economic reasons and it was disconnected from the grid in December 2019. In 2020 its operating licence was replaced by a decommissioning order.

KKM is the first of five Swiss nuclear power reactors due to be decommissioned. Following the nuclear disaster at Japan’s Fukushima Daiichi NPP in 2011, the Swiss government decided to phase out nuclear energy production. Parliament approved the decision but no deadline has been set to shut down the remaining nuclear stations.

Dismantling work is going according to plan, but has been slightly complicated by the discovery of asbestos in a building which dates back to the 1960s, according to BKW. Decommissioning is scheduled to take place in three phases. The first phase (planned for 2021-24) includes removal of all fuel assemblies with highly radioactive components from inside the reactor being dismantled and packaged under water. During the second phase, from 2025, all remaining parts of the system that came into contact with radioactivity will be dismantled. These include the reactor pressure vessel, parts of the containment container or the fuel element storage pool that is no longer required.

All dismantled components will be sorted, cleaned if possible, checked for radioactivity and packed. Cleaned and released material will be landfilled as normal waste or recycled where possible. Building structures that may have come into contact with radioactivity during operation will be inspected and cleaned to ensure that there is no radioactivity left. KKM will submit an application to the authorities for conventional dismantling by 2027. This phase will end with the lifting or clearing of controlled zones. By the end of 2030, KKM should be free of radioactive material and, if no more radiological hazards are identified, the authorities will release the site for new use.

The final phase should demonstrate that the site is no longer a source of radiological hazard. Depending on whether the area will be used for industrial or natural purposes, the area will be available for further use from 2034.

Image (top): The Mühleberg nuclear power plant (courtesy of BKW)

Image (mid-right): All 418 nuclear fuel elements have now been removed from the NPP (image courtesy of Keystone/Peter Klaunzer)