As part of planned maintenance work, an emergency diesel generator unexpectedly started up in Block 2 of the decommissioned Philippsburg nuclear power plant due to problems when replacing an external power supply switch. There was no danger to people or the environment.
As part of planned maintenance, an external grid feeder switch was replaced in block two of the Philippsburg nuclear power plant. After the craftsmen had replaced the switch, the automatic switchover switched off the feeder switch for the main network and at the same time switched on the feeder switch for the external network. After the connection, however, the external grid feed switch opened again surprisingly. As a result, the associated auxiliary and emergency power rails became dead. As a result, the fuel pool cooling pump that was in operation switched off. The reactor protection then started the associated emergency diesel generator.
Safety-related importance is low
The safety-related effects of the specific event were minor. There was no danger to people or the environment. The operator then switched the power supply back to the mains connection and switched the pump for cooling the storage pool back on. The operator also replaced the affected switch.
Due to the erroneous opening of the switch, a pump for the storage pool cooling system failed for a short time. The other two strands of the storage tank cooling were available without restrictions. The affected pump could also be put back into operation after a very short time.
Due to the longer period of time since the final shutdown of the nuclear power plant and because some of the fuel elements have been brought to the Philippsburg interim fuel element storage facility since March 2022, the water in the fuel element storage pool is only heating up very slowly. Therefore, there was no measurable temperature increase.
The events that are significant for nuclear safety are to be reported to the nuclear supervisory authorities of the federal states according to the uniform federal criteria of the Nuclear Safety Officer and Reporting Ordinance - AtSMV. The aim of the reporting procedure is to monitor the safety level of the nuclear power plants, to prevent the occurrence of similar errors in other nuclear power plants and to incorporate the knowledge gained into technical safety improvements. The reportable events are assigned to different categories (explanations of the reporting criteria for reportable events):
Category S (immediate reporting): Events that must be reported to the supervisory authority immediately so that they can initiate checks or initiate measures as quickly as possible. This also includes incidents that indicate acute safety-related deficiencies.
Category E (reporting within 24 hours): Events that must be reported to the supervisory authority within 24 hours so that they can initiate checks or initiate measures within a short period of time. This also includes events whose cause must be clarified within a short period of time for safety reasons and, if necessary, remedied within a reasonable period of time. As a rule, these are events that are potentially but not immediately significant in terms of safety.
Category N (reporting by the fifth working day): Events that must be reported to the supervisory authority within five working days in order to be able to identify any security weaknesses at an early stage. As a rule, these are events of minor safety significance that go beyond routine operational individual events when the system is in proper condition and operation. Unavailabilities of components/systems that are temporarily caused intentionally by procedures specified in the operating manual do not have to be reported if this is also taken into account in the safety specification of the operating manual.
International rating scale INES
Due to an agreement between the operators of the nuclear power plants and the Federal Minister for the Environment, Nature Conservation and Nuclear Safety, reportable events in nuclear power plants are also classified according to the INES rating scale (International Nuclear and Radiological Event Scale) of the International Atomic Energy Agency (IAEA) and the organization's nuclear energy agency for economic cooperation and development . Its aim is to assess an event quickly and in a way that the public can understand.
The scale consists of seven levels:
Incident 2. Accident
3. Serious accident
4. Accident with local effects
5. Accident with wider effects
6. Serious accident
7. Catastrophic accident
Reportable events that are not to be assigned to the scale (1 to 7) according to the INES manual are assigned to "Level 0" according to national assessments, regardless of their safety-related significance.