Sweden expands underground rock caverns for radioactive waste storage

Sweden is moving ahead with a major underground expansion of the SFR final repository for short lived radioactive waste in Forsmark. The new contract covers the construction of six additional rock caverns for low and intermediate level radioactive waste from Swedish nuclear power plants and other sources.

The works form part of the wider expansion of the existing SFR facility, which has been in operation since 1988. The current repository can hold around 63,000 cubic metres of operational waste. The expansion will add approximately 117,000 cubic metres of new storage capacity, increasing the total facility capacity to about 180,000 cubic metres.

The new caverns will be around 240 m to 275 m long and built at a depth of 120 m to 140 m, broadly level with the lowest part of the existing repository. Construction is planned to begin in the third quarter of 2026, with the current contract expected to finish in late 2028. The complete expanded facility is expected to be ready for test operation in 2030 to 2031.

The SFR repository is located underground near Forsmark and is designed for short lived radioactive waste, mainly from nuclear power plant operation and decommissioning. Some waste from hospitals, research, industry and other technical activities is also handled within the system.

The new works include rock excavation, civil works, earthworks, water and sanitation works, and tunnel lining. This type of project requires careful control of rock mass stability, groundwater inflow, excavation sequencing, support installation and long term durability.

Deep rock caverns are not simply empty underground rooms. They are engineered containment spaces that must remain stable and accessible through construction, operation and closure. The behaviour of the surrounding rock, the quality of fractures, groundwater pathways and the interaction between lining, drainage and cavern geometry are all critical to performance.

The need for additional capacity is linked to future decommissioning waste from Swedish nuclear power plants. As reactors are dismantled, radioactive components, metals, concrete and other building materials must be managed safely and stored in a controlled final repository.

This creates a different challenge from normal tunnelling. The caverns must be constructed efficiently, but the design must also support long term safety, traceability and operational control. Excavation damage, water ingress, lining performance and access tunnel reliability all become part of the safety case.

The Forsmark expansion shows how underground construction is becoming central to nuclear infrastructure strategy. As countries deal with ageing nuclear assets and decommissioning programmes, the demand for engineered underground storage will continue to grow.