Borssele nuclear power plant restarted after maintenance shutdown

Replacement of fuel assemblies

The fuel for a nuclear reactor such as Borssele is contained in sealed rods several meters long. A bundle of these rods is called a fuel assembly. The nuclear fuel in an assembly lasts for approximately four years. For that reason, EPZ replaces about one-quarter of the fuel each year. 

During the refuelling outage, the reactor must be taken offline. This provides a good opportunity for scheduled maintenance and inspections at the plant. When the reactor is idle, personnel can work in areas that would otherwise be inaccessible or less accessible. By performing a lot of maintenance within a short period during the refuelling outage, the nuclear power plant can remain in operation as much as possible for the rest of the year. For this reason, the refuelling outage is always combined with the annual maintenance shutdown.

Delay due to additional maintenance

The 2026 maintenance shutdown was originally scheduled to last about three weeks. However, it was extended because additional maintenance proved necessary. This type of additional maintenance is common practice during a shutdown, as it is only then that all systems can undergo detailed inspection.

One example of the additional work was welding in the nuclear section of the facility. During inspections, the owner, EPZ, also identified an anomaly in the residual heat removal system. This system cools the fuel rods if the main cooling system fails. To carry out the repair, EPZ had to remove all fuel assemblies from the reactor, which would otherwise not have been necessary. As a result, other activities were delayed. 

Leaking fuel assembly replaced

In 2025 the Borssele nuclear power plant experienced to leaking fuel assemblies. This also happened in 2024. The leaks were small and well within the safety limits, but such leaks should not occur. EPZ is researching these events (Dutch webpage). The ANVS is monitoring this research closely. During the refuelling outage, we also paid attention to this topic together with EPZ.

Oversight by the ANVS

The ANVS oversees the nuclear safety of the Borssele nuclear power plant. We also supervised the refuelling outage and maintenance activities. For example, the maintenance plans were submitted to our inspectors for approval. ANVS inspectors were present at the plant almost daily. They conducted inspections focused on nuclear safety and radiation protection.

A major project during this maintenance outage was the ten-year leak-tightness test of the airtight containment structure housing the reactor and its nuclear fuel. This containment function ensures that radioactive material remains confined in the event of a potential incident within the structure. As this is a critical safety function, we paid close attention to it. The test was successfully completed.