BERN, 8-9-2015 — /EuropaWire/ — The Mühleberg nuclear power plant (KKM) is back online. The plant had been shut down since 3 August for annual maintenance work. During this period, the cooling water supply system that operates independently of the Aare was also finalised. The return to operation means the annual maintenance work is complete.
BKW staff and external specialists carried out extensive preventive work and testing of components, fittings and systems. As planned, 36 of the 240 fuel rods were replaced.
During the maintenance work, KKM complied with other requirements of the Swiss Federal Nuclear Safety Inspectorate (ENSI) in a timely manner. The cooling water supply system that operates independently of the Aare was completed and connected to the SUSAN emergency system. This guarantees the supply of cooling water to KKM even in the event of very rare natural phenomena where the Aare is not available as a cooling source. For more information on the ENSI requirements, see: http://www.ensi.ch/de/2015/01/27/ensi-genehmigt-massnahmen-fuer-muehleberg-restlaufzeit-mit-auflagen/
Examinations of the core shroud produced results that were significantly below the two threshold values that KKM has to comply with to ensure safe operation. The cracks along a weld seam are stable. The cracks along a horizontal weld seam detected during a visual inspection last year were investigated using ultrasonic testing. The results revealed that the longest crack, measuring 99 mm in length, partly penetrates the wall. For more information (in German and French) on the core shroud and the results of the inspection, see: www.bkw.ch/kernmantel
During the process of restarting the plant, which always takes several days following annual maintenance work, scheduled start up tests caused the reactor to be shut down. The cause was identified in the turbine control system. KKM reported the incident to the ENSI and was granted a permit for the plant to be started up again.