Block II of the Neckarwestheim power plant has been reconnected to the grid following the completion of its inspection

• The safety of the power plant takes highest priority: The inspection period was extended for additional testing and maintenance work
• Diligent management of the power plant also guarantees its safe operation in the future

Neckarwestheim. Block II of the Neckarwestheim nuclear power plant (GKN II) has been reconnected to the grid since the early hours of this morning (8 November 2018) following the completion of its inspection. Over the past few weeks, testing and maintenance work was completed, fuel elements were replaced and a number of technical projects were implemented. As a result of some anomalies found in the steam generators at the power plant, EnBW extended the duration of the inspection (see press release from 14 September 2018). The specialists at EnBW carried out an in-depth assessment of the possible causes during this time and then completed the necessary maintenance work, which was agreed in advance with the Baden-Württemberg Ministry for the Environment as the supervisory authority, as well as with the independent auditors appointed by the Ministry. The power plant was restarted – as usual – after receiving approval from the Ministry.

Anomalies found during an inspection are always dealt with using the same procedure that is strictly oriented towards guaranteeing safety. “The safety of the power plant takes highest priority for us”, explains Christoph Heil, who as Managing Director of EnBW Kernkraft GmbH is responsible for the operation of GKN II. “The length of an inspection is also determined by this commitment to safety. We understand that the way a nuclear power plant functions and is operated is very complex. As questions concerning the findings in the steam generators have been raised, we want to once again clarify the facts here”, explains Christoph Heil.

The safe operation of the power plant was and is guaranteed

The four steam generators at GKN II are designed to transfer heat between the primary and secondary circuits of the power plant. Specially purified water flows through both the primary and secondary circuits and enables the heat transfer. The transfer of heat between the water from the primary circuit and the water from the secondary circuit is achieved via numerous heating pipes that are installed in the steam generators. However, the two circuits remain strictly separated from one another, i.e. the design of the steam generators ensures that only heat is transferred between the two circuits and not the contents of the circuits. Nevertheless, the integrity of the design is checked at regular intervals, while highly sensitive measuring equipment would immediately identify any leaks during operation. However, it can be verified that there were no leakages at GKN II.

All heating pipes in the steam generators were inspected – they were and remain leak-tight

Above and beyond the standard inspection regulations, EnBW subjected all four steam generators to a comprehensive inspection and used multiple technical procedures to precisely check all of the approximately 16,400 heating pipes during this process. During this inspection program, a weakness in the walls of some heating pipes was identified. Despite these findings, the thickness of the walls was still sufficient in the affected areas, i.e. all pipes were and remain leak-tight. The heating pipes are made out of a special, extremely tough alloy of iron, nickel and chrome. “This is why we can also say looking back that the safe operation of the power plant was guaranteed at all times. In simple terms, chemical processes that could be precisely understood had reduced the thickness of the walls in the affected areas”, explains Heil.

Responsible handling of the findings

EnBW presented its cause analysis to the supervisory authority and the independent auditors appointed by the supervisory authority and derived appropriate measures based upon it. These measures will help to minimise as far as possible the probability of other weaknesses like those identified from occurring. The company agreed a concept for the required maintenance work on the heating pipes in which the anomalies were found together with the supervisory authority and its auditors. During the inspection, the affected pipes were sealed with plugs of various lengths depending on the findings, i.e. the affected pipes were taken out of service, and – where necessary – additional stabilisation measures were used.

Alongside experienced specialists from EnBW, recognised experts appointed by the supervisory authority also worked on the issue. “GKN II was only reconnected to the grid after the experts and all other responsible parties were convinced that the safe operation of the power plant was guaranteed”, concludes Christoph Heil. The inspection work took place under the supervision of the Baden-Württemberg Ministry for the Environment and was accompanied by auditors from TÜV Süd (the technical inspection agency) appointed by the Ministry.