Sweden’s development and expansion of its Forsmark waste storage vaults has enjoyed significant progress over the last few decades, especially in the last 10 years. As a result, more excavations are beginning at the coastal site to expand an existing vault for short-lived radioactive waste. Far more tunnelling is also set to commence in the near future to create a deep geological repository.
The granitic rock mass north of Stockholm, offers large and separate zones to hold different types of waste storage, from low level waste to spent nuclear fuel.
The repository as planned will be a vast warren of tunnels, carefully and progressively opened up in the chosen bedrock. The deep geological repository has a time horizon of multiple millennia for safe storage of spent fuel. However, with decades of excavations and storage activities ahead, in terms of infrastructure construction at a normal human scale, the development of the high-level waste storage vault is a long-term project. The Forsmark site in Östhammar municipality has hosted a vault at shallower depths, for short-lived waste since the late 1980s. The vault is the final repository for radioactive waste from power plants as well as from research, industry and medical uses.
The Swedish Nuclear Fuel and Waste Management Co (SKB – Svensk Kärnbränslehantering) is now extending this waste vault to triple its capacity. Rock blasting for the extensive excavations began in late 2024. The full construction project is expected to take about six years to complete. Its excavations will be underway as those for the neighbouring deeper vault, for spent fuel, also get underway. A third storage system class is needed by SKB, for long-lived radioactive waste. It is still in planning and the site is yet to be selected. The last and smallest of the three vaults, it would store metallic materials such as core components, control rods, and reactor pressure vessels for example.
Deep Geological Repository – The journey begins
Forsmark was not, from the outset, the predetermined site to provide deep burial of high-level waste. It was competing against the bedrock characteristics of another keen candidate, the Laxemar site, in Oskarshamn municipality, in the south of Sweden.
Oskarshamn already hosts an interim storage facility for spent fuel (Clab) in water-filled concrete basins with steel linings 30m down in the bedrock. Operational since the mid-1980s, SKB is seeking to expand as existing capacity would be reached before the Forsmark deep repository is operational. Excellent bedrock is key to safe storage of spent fuel with strong and highly competent rock mass, along with favourable groundwater characteristics. While Laxemar initially looked able to host the storage vault at slightly deeper depths until new analysis of rock stresses showed that “these stresses have less impact on the repository depth” than had been assumed, according to SKB’s report ‘Site Investigation:
Forsmark (2002-2007)’. Forsmark could thus locate a vault deeper than first thought – and, at a depth of around 470m, comparable to that offered by Oskarshamn.
Additional aspects related to post-closure safety were decisive in choosing Forsmark as the site. By the time SKB made its choice in 2009 hundreds of scientific reports had been produced and 25 cored boreholes drilled. Of these, 19 were more than 500m depth and a further nine went to more than 1km depth.
In 2011, SKB filed an application to build and operate the high-level facility abnd government approval was granted in early 2022. A year ago, SKB was granted an environment permit to start construction and by mid-2025, it had signed a collaboration agreement with Implenia for the major initial tunnelling works required.
Preparing to excavate
Implenia is to plan and perform detailed design and then excavations for the 5km-long spiralling access tunnel to reach some 470m below the surface and the ‘central’ base area. In addition it will excavate the first of the local grid of large tunnels for various operational activities at the base of the shafts and access tunnel; and, also the initial transport tunnels that will open up the first repository storage zones.
Implenia is also to design and build three deep shafts down to the repository level. The shafts are for ventilation and a lift, also to serve and support the activities of the underground complex over the coming decades of its operational life. In Q3 of this year, the contractor began mobilising on site. Upon final safety approvals from the national radiation safety authority, StralSakerhetsMyndigheten, and after further preparatory works on the surface, the first excavations would then begin.
Excavation of the shaft, access tunnel and the initial repository-level tunnels are anticipated to take about eight years to complete. The full scale of the underground repository, though, is far more extensive. Current expectations are than the repository will have been fully extended in some 60 years’ time, by the 2080s. By then, it is anticipated that some 66 km of tunnels will have been excavated, within a grid network covering an area of 4km²,. Expectations are that around 2.7m m3 of rock will have been excavated to form the tunnels at the repository level, and also the access tunnel and shafts from the surface. The scale of excavation is greater than the 1.85m m3 that had been initially discussed before Forsmark was picked over Oskarshamn as favoured candidate to be the host site.
Disposal
SKB says that when the repository has finished excavating its first access, base, transport and storage tunnels then disposal of spent fuel can begin. The present timeline anticipates the disposal activities should be able to commence in the 2030s.
The deposition storage tunnels will terminate in dead-ends. Along each ‘deposition’ storage tunnel will be regularly spaced small silos carved into the rock, each to receive a single canister. The silos will then be backfilled with bentonite clay, the silo tunnels are then to plugged and sealed off as the area is filled. This is the ‘KBS-3’ storage concept.
The tunnels linking to the silo storage locations will also be sealed off, eventually, as will the entire vault, on its completion later this century. Only a few of these branch tunnels are to be in use at any one time.
Operational storage activities, therefore, will gradually back out of each deposition tunnel, eventually to be filled completely, back to the junction with the main transport tunnel. Ultimately, with all the branch deposition tunnels leading off a particular transport tunnel having been filled, then that main tunnel itself be filled.
The plan is for Forsmark to host approximately 12,000 tonnes of spent fuel to be held in 6000 canisters.
Other excavations at Forsmark
Excavations also started at Forsmark recently for the extension of the shallower-depth vault for short-lived radioactive waste. The existing vault is about 60m and more below the ground surface and has a storage capacity of about 63,000m3. Rock blasting for the new section began almost a year ago and is to add twice as much storage capacity as the original, at depths of about 120m-140m. The tunnelling works involve the creation of six 275m-long caverns. The new storage section will take the total capacity of this vault to about 180,000m3.
The expansion project received approval from environmental authorities in late 2022. Tunnelling work is being undertaken by contractor Skanska, which was appointed in mid-2023. With SKB obtaining approval for the works from the Swedish Radiation Safety Authority, in November 2024, first blasting began soon after. It is anticipated the construction work and fit-out will be completed around 2030.
In addition to holding radioactive waste from the healthcare and industry sectors, and research, the expanded vault is also to take waste from the decommissioning and dismantling of Swedish nuclear power plants. The power plant waste is to include reactor components and building materials.
Recently, the maintenance teams on the existing vault have borrowed lessons and experience from the neighbouring power plant teams to use the latest drone technology for remote surveys, to monitor key areas of the infrastructure. SKB says this helps with the accessibility, speed, frequency and cost of inspections of the existing underground storage facility.
In future, a vault for long-lived radioactive waste is also required and SKB has not yet selected the site. The vault is foreseen as requiring a storage capacity of approximately 16,000m3 and located at a depth of about 500m.
