Brunsbüttel nuclear power plant: Defective butterfly valve discovered

The Brunsbüttel nuclear power plant has not been in operation for more than ten years. During the dismantling of the plant, a defective butterfly valve was discovered. According to Vattenfall, the owner and operator of the nuclear power plant, the valve originates from the auxiliary cooling water system that carries water from the river Elbe.

The butterfly valve was removed and examined in a workshop. Vattenfall discovered that one of four support segments for the circumferential seal of the butterfly valve disc was missing, along with the associated fastening screws. The damper is a shut-off device that has to be closed for maintenance at the nuclear power plant. The cooling function of the line for refrigeration machines and the emergency diesel was not affected.

After her damage investigation, the authorised inspector consulted in accordance with the Atomic Energy Act determined that the reporting criteria according to the Nuclear Reporting Ordinance were fulfilled, since there was an indication of a systematic failure of a safety-relevant device. 

As a result, the reactor safety authority determined that a reporting obligation existed and requested the operating company to report the incident. Vattenfall assigned the event to category “N” (normal report). These are events that are below the International Nuclear Event Scale (INES) - i.e. that pose little or no danger.