SHAFTS & CAVERNS | TECHNICAL
REPOSITORIES MOVE AHEAD
FORSMARK
Sweden is advancing the development of its underground storage complex at Forsmark by starting to extend its vault for short-lived radioactive waste and preparing to undertake major excavations even deeper that will hold spent nuclear fuel. Report by Patrick Reynolds.
Sweden’s efforts to further develop underground storage vaults at Forsmark, to hold more radioactive waste and also create a vast vault for spent nuclear fuel, respectively, has enjoyed significant progress over the last 10 years or more. The granitic rock mass under the coastline, north of
Stockholm, offers extensive zones to hold quite different types of waste for the long-term, from radioactive materials now to, soon, spent nuclear fuel at deeper depths. Excavations have commenced to extend Forsmark’s
existing vault for short-lived radioactive waste. In addition, work began recently to prepare for the initial tunnelling to start creating a deep geological repository for spent fuel. The deep geological repository will take high-level
waste in sealed canisters and bury each vessel in its own silo, far below the ground surface. The repository is planned to be a vast warren of tunnels, carefully and progressively opened up in the chosen bedrock. The tunnels linking to the silo storage locations will also be sealed off, eventually, as will the entire vault, by its completion, due later this century. Opening up the rock mass to carve out the deep
repository will be done slowly, in stages, taking time. Decades. But the pattern is established. Along each
‘deposition’ storage tunnel will be small silos carved into the rock. They will be numerous but spaced, at regular intervals, each to receive a single canister. The process then has the backfilled, and sealed. When all the silo slots along a deposition tunnel are full then that tunnel itself will have been filled, finally, and then plugged and sealed off. Eventually, all of what has been excavated and
opened up to create the storage slots will be sealed off. The deep geological repository has a perspective of
millennia for safe storage of spent fuel, which makes the coming decades of excavations and storage activities seem relatively short. However, in terms of infrastructure construction at a normal human lifetime scale, the development of the high-level waste storage vault is a long project - to be carefully executed, by generations of engineers. For Forsmark, the journey of construction is only
starting in the life of its deep geological repository. But the site in Östhammar municipality - which
already hosts a nuclear power plant - is not new to underground storage of waste. At shallower depths, Forsmark hosted a vault for short-lived waste. Operating since the late 1980s, the vault is the final repository for radioactive waste from power plants in Sweden as well as from research, industry and medical uses.
Right:
Flow diagram of SKB’s radioactive and spent fuel management system ILLUSTRATIONS COURTESY OF SKB
October 2025
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