Long a dream to securely contain high-level nuclear waste deeply underground for millennia, no burial vault for the ages as yet exists. US politics kicked the proposed Yucca scheme in Nevada into the long-grass a few years ago, and only a few months past at the end of 2012, the UK heard that a favoured site for a proposed scheme in England had been rejected by the local county, Cumbria, that would have played host.

Bucking the international trend, though, Sweden and Finland have been making particular progress with the strategic challenge. If all goes to plan and schedule, they could have their first shipments of high-level nuclear waste being taken far underground for burial starting around the early 2020s – approximately a decade away, and possibly less.

The elected site in Sweden is at Forsmark, north east of Stockholm, and it had to compete for the right to be the candidate site; a rival community in the south of the country had wanted the honour; the not in my backyard problem, or at least lukewarm enthusiasm witnessed elsewhere, was not the issue in Sweden.

The Forsmark site is already a complex, home to a nuclear power plant and also an existing underground vault (SFR complex) for lower-level nuclear waste, which is being extended. After years of site investigation, the Swedish Nuclear Fuel and Waste Management Co (SKB) filed an application for the licence to construct and operate the high-level waste vault in 2011.

Finland filed its own constuction permit application a few months ago to build a vault at Olkiluoto, north of Turku, where nuclear power plants are located. The site is already under initial development by the national nuclear waste agency, Posiva, however, with the first major tunnel already excavated.

In an approach differing from that of Sweden and many other nations, Posiva – as required under legislation covering the waste storage, and in absence of its own local, existing, rock characterisation facility – has had to go underground to test the rock insitu by creating its own laboratory (called Onkalo), in effect.

Posiva has constructed what would be the vault’s spiral access tunnel, extending down to the depth of the main storage zones and, only slightly above, site investigation and other tests are being carried out. The main tunnelling work on the ramp was completed over 2011-12. Currently, Posiva anticipates that the initial sections of the Olkiluoto vault to be opened up and operational, able to take high-level waste, from 2022, potentially, and slightly earlier than SKB’s plans for Forsmark.

Forsmark
After about 20 years of studies and field research across Sweden, Forsmark won the race to be Sweden’s choice for the nuclear waste vault in 2009, overcoming competition from its last rival, Oskarshamn, to the south of the capital.

To securely and safely house high-level nuclear waste, distance is the vital barrier – in this case depth below ground, in excellent rock mass with acceptable groundwater characteristics. Every metre down adds vital points in calculations for protection, keeping waste away from the general environment. What began tipping the scales in the search in favour of Forsmark was SKB learning that the site could have a vault constructed far deeper than previously thought.

Site investigation data had revealed stresses in the granitic rock mass, which is part of the Fennoscandian Shield, to be less than expected; the stress profile did not rise with depth as quickly as had been estimated. Less stress meant more opportunity to excavate, and at deeper depths, to create storage vaults without detrimental stress release and negative effects on the quality of the rock mass.

The result was that a vault could be located about 470m below the surface at Forsmark, or almost the same depth as Oskarshamn. With the rivals on almost even scores for depth, there was little difference either in the total excavation volumes needed for shafts, access tunnels and the caverns that would hold technical rooms. What was left, then, and fell heavily in Forsmark’s favour, was that it only required 1,850,000m³ of excavation to create the required storage zone grid of tunnels, or twothirds the volume needed by the Oskarshamn option.

Forsmark had it. At Forsmark, the deep repository has been conceived to its KBS-3 storage concept, referring to a particular arrangement of holding the waste in copper canisters that are slotted and sealed into vertical boreholes in grouted, highly competent rock. With a tight fit, the canisters are packed all around with bentonite clay.

Around 40-45 vertical boreholes will be excavated at 6-6.8m distances apart along each of the 300m long placement, or deposition, tunnels which themselves will branch off main tunnels, running parallel at about 40m centres depending on thermal conductivity of the rock.

Multiple deposition tunnels would be open, taking canisters. As each canister is placed and sealed then that section of tunnel will be backfilled. Eventually, the entire deposition tunnel will be blocked off. It is expected that the operation life of a deposition tunnel will be no more than five years, says Rolf Christiansson, a senior rock engineer with SKB.

With this concept, only a small percentage of the tunnels in the grid of the repository masterplan would be available for access and holding of waste canisters at any time. This approach of incremental but consistent, highquality tunnelling, and then sealing off, should give the deep repository an operational life spanning decades.

Aspo Hard Rock Laboratory, located near Oskarshamn, has been used to test excavation quality research as well as examine different storage and sealing concepts for a high-level waste vault. Though far from Forsmark, the tunnels enable SKB to test underground for the storage project, whereas in Finland no such existing facility is available.

The Aspo facility has a maximum depth of 450m and has been expanded to create new test areas that will help with preparing for the tunnelling, and long-term performance, of the high-level waste vault at Forsmark.

Rolf Christiansson, a senior rock engineer with SKB, says a prototype system for digital photogrammetry has been developed for geological mapping, and which gives accurate documentation of the excavated tunnel geometry. Further test work will include investigating the use of electronic detonators.

"We hope to be able to give fast feedback to the contractor," says Christiansson. That way, constant adjustment can be made in each round of drill and blast to ensure the quality of perimeter control, and minimise the excavation damage zone.

He adds: "We have worked with both grout design and development of grouting materials." Saying that key parameters include there being no chemical components in the grout, no organics and also that the pH alkalinity should be less than 11 in leached water.

More recently, he says, SKB has added efforts to brief the Swedish tunnelling sector in preparation for the particular high-quality excavation needs of the large, long-term work coming up. The nuclear waste sector demands better performance to minimise disruption to rock quality; rock mass integrity is more imprtant that production speed.

Christiansson says drilling precision is one of the keys to delivering the careful blasting needed, and for effective charge distribution it will be vital to ensure ‘good control of the amounts of exploves put into the holes.’

A construction period of approximately seven years has been envisaged to get the vault’s shafts, ramps, tunnels and caverns of the initial storage zone operational.

The schedule was for construction and tunnelling to start around 2017.

However, to allow more flexibility around the licensing process, last November a buffer of about two years was approved by SKB’s board, putting the possible start of works back to about 2019-2020. That does not automatically also reset the initial operational date, however, says SKB, as ways would be sought and examined to help reduce the construction period, if possible.

If so, the originally antcipated date of around 2024 will be able to be held, otherwise it would stand to be about 2025-26, it is estimated.

SFR Expansion
SKB is planning to expand the existing SFR, low-to-medium level nuclear waste vault at Forsmark by adding far more storage volume, as mutiple caverns next to, but deeper than, the present repository depth of around 60m. The extension project would more than triple the total storage volume of the SFR complex to approximately 200,000m³.

Plans were revised late last year to place the new section of vault deeper than the existing caverns, at about 120m below the surface, or about twice the current storage depth, says SKB spokesman Jimmy Larsson-Hagberg. Consequently, these ‘rather big changes in the layout’ will mean the 140,000m³ extension will take longer to build, pushing back the start of operations in the new vault from the initial schedule of 2020 to around 2022-23, again ‘depending on the licensing process.’

The agency anticipates submitting its licensing application for the SFR expansion about late 2013. However, it says the final layout of the expansion vault has yet to be decided.

Under the 2020 schedule, it was anticipated that tunnelling might commence around 2016. As yet, no explicit change to the start of the construction schedule has been decided, only that the task will take longer to go deeper.

Therefore, it is possible that the tunnelling for the SFR expansion could be at least well advanced, and possibly even majority completed, by late in this decade when excavation for the high-level waste vault – to be built under a totally separate project – is getting underway, depending on its licensing progress, of course.

Olkiluoto
The Olkiluoto site, in Finland, is to have the deep repository constructed about 400-450m below the surface, almost as deep as at Forsmark, in Sweden. Work began nine years ago at the site, gradually excavating down the spiral ramp to the storage level, and excavation contractor Destia completing the majority of that initial tunnelling by 2011, and some further works undertaken into 2012-13.

However, the works doubled-up as the access route to create the Onkalo rock characterisation facility in the absence of there being one in Finland. Although it takes the scheme underground earlier in its development schedule, the need to excavate – to conduct tests for licensing approval for the project – has been major effort for Posiva.

The Onkalo research facility includes a series of tunnels: a central, 70m long access tunnel (8.5m wide by just over 6m high); 50m long Demonstration Tunnel One (3.5m wide and less than 5m high); and, 120m long Demonstration Tunnel Two. In each demonstration tunnel, following exploratory pilot holes, there are 1.75m diameter boreholes excavated to depths of almost 8m. The boreholes were excavated using Sandvik subsidiary Tunnel Raise Borers’ prototype Rhino 500HSP unit.

Rock test data confirmed the suitability of the bedrock to host the the deep repository and the construction application was filed in late December last year.

Pending award of the construction permit, Posiva expects that main tunnelling for the repository and construction of the associated facilities, such as the surface encapsulation plant, could commence in 2015, says Reijo Sundell, president of the agency (which is owned by TVO and Fortum).

Speaking in February, he added that should Posiva be able to submit an application for an operating licence by 2020 then first waste might be able to be taken at the Olkiluoto vault by 2022.

"We will keep testing the final disposal concept and gathering more information on the functionality of the associated equipment, systems and methods," said Sundell.

The engineered barriers of the disposal concept are similar to that for Forsmark – canisters capable of withstanding corrosion, then case in bentonite clay to decouple the container from the bedrock, and a progressive backfilling and plugging system.

Last year saw tests of borehole excavation for waste containment canisters. This year the site will see the arrival of the transfer and installation vehicle for the canisters, and also the benotonite block installation device.

The sealing-off technology for the repository will be tested full-scale as part of a larger, European development project – DOPAS.

The project is budgeted at EUR 15.7M (USD 20.8M) and runs from 2012-2016.

Future in the North
With their appications submitted for the respective nuclear waste storage projects, Sweden and Finland have a few years yet to go and much tunnelling to undertake before they know which will be first vault to come into operation.

It is not a race, and there is keen liaison between SKB and Posiva, and the authorities and engineers of both nations, but however it plays out the eyes of the international nuclear waste sector, politicians and, not least, tunnelling peers, will be watching keenly the developments in the far north