Slovenia will soon start building a repository for low- and and intermediate-level radioactive waste produced by its sole nuclear power plan. Construction will start in May with the facility slated to become operational in 2028.

A Slovenian consortium led by engineering company Riko has been picked to build the main facilities adjacent to the Krško nuclear power station and has already signed a contract with the Agency for Radioactive Waste Management (ARAO).

Partnering with Slovenian builders Kolektor, CGP and Kostak, Riko will build the repository for €93 million. The only other bid, by the South Korean companies Korea Hydro & Nuclear Power Co. and Daewoo E&C, was more expensive and incomplete.

The contract covers the construction of a silo some 60 metres deep and 27 metres wide that will have space for 990 containers of radioactive waste, in ten layers.

This is sufficient for half the waste the Krško nuclear power station generates during its lifespan and half the waste from the decommissioning. The other half will be handled by Croatia, which owns 50% of Krško.

The Riko-led consortium will also build several buildings on the surface, while the construction of a special elevator and lifting equipment will be tackled in a separate stage of the project.

At its inception the entire project was valued at €200 million. But due to surging prices of construction services in recent years, a re-evaluation is under way.

Multi-compartment concept

The silo will be the most demanding part of the project.

"It will be a multi-compartment repository concept, meaning that waste will be packed into barrels and barrels packed into concrete containers. These will then be lowered into the silo and enveloped in concrete," ARAO director Sandi Viršek said.

Once the silo is filled, it will be topped with a concrete lid and a 15-metre layer of clay.

As the silo starts operating, presumably in 2028, waste now temporarily stored at the Krško plant will be moved into it. The plant produces 90% of all radioactive waste generated in Slovenia.

Radioactive waste from medicine, industry and research, stored at a facility in Brinje, near Ljubljana, will also be moved to the new silo, which is located in Vrbina, only 300 metres from the Krško plant.

A 10- to 15-year dormant period will follow until around 2040, when decommissioning of the power plant is expected to begin. This will kick-off the second stage of operations, the storage of waste from decommissioning.

Solution for spent fuel still pending

The silo is to be sealed in 2059, after which a 50-year active monitoring phase is planned, to be followed by 250 years of passive monitoring. The surface above the silo will be available for use soon after the repository is sealed.

The silo is not planned to store waste from any new nuclear reactor Slovenia might choose to build. If the country decides to take this step, an additional silo will have to be built, said Viršek, adding that an environmental permit had been issued for two silos.

Slovenia still needs to find a solution for spent fuel, which is currently stored in a pool at the power plant. This type of storage is planned until 2103, after which the waste is to be stored more than 500 metres underground.