Production and maintenance

Independent of the weather and other influences, NEK generates low-carbon electrical energy from nuclear power 24 hours a day, every day of the year. Up to 35 MW power is used for plant’s own consumption and the remaining 696 MW is transmitted through the 400-kV network to the consumption centres in Slovenia and Croatia. Its annual generation of electrical energy covers approximately 20% of the electrical energy demand in Slovenia and 16% in Croatia.

The heat used to generate electrical energy is released during the nuclear fission of uranium fuel inside the reactor. Uranium 235 isotope serves as nuclear fuel and can account for up to 5% of the total nuclear fuel mass, whereas the remaining 95% of the mass consists of the Uranium 238 isotope which is not direct fuel; however, indirectly through nuclear reactions, the latter also gradually turns into fuel. The reactor consists of:

• 121 fuel assemblies,
• each fuel assembly contains 235 fuel rods,
• each fuel rod contains 360 uranium dioxide (UO₂) pellets.

The useful life of each individual fuel assembly is 3 years or 2 nuclear fuel cycles in the reactor core, after which it is replaced with a new fuel assembly.

Proper ageing management, maintenance, and modernisation ensure equipment operational readiness throughout the entire life-time of the plant. Current state evaluation is used as a basis for the implementation of preventive maintenance programs which ensure equipment functionality throughout the expected service life. Our equipment is modernized based on operating experience and this brings improved solutions and progress in operational safety and stability.

The plant’s equipment is managed through in-service oversight and maintenance.

Outage is the regular shutdown of the Krško Nuclear Power Plant scheduled every 18 months. That is when we implement the following:

• extensive equipment maintenance,
• modifications, upgrades,
• safety systems tests,
• we renew the energy potential by replacing approximately half of the 121 fuel assemblies forming the reactor core.

During the outage, all the fuel assemblies are moved to the spent fuel pool where they are additionally inspected and their suitability to be returned to the reactor core is comprehensively assessed. We belong to the group of nuclear power plants that employ their own operators to execute the unloading and loading of the fuel.