Radwaste Management

Halfway to the Finnish

27 July 2009



Some 25 years after it began, Finland’s high-level waste disposal programme is on schedule. Posiva is preparing a construction licence application and if all goes well operation should be on track for 2020. By Timo Äikäs


Nuclear waste management was not an important issue in 1970s when the construction of Finnish nuclear power plants was commissioned. In government policy, final disposal was not considered an alternative; the main option was to ship the spent nuclear fuel abroad for reprocessing. Nothing was expected to come back. IVO, today known as Fortum Oyj, was successful in its efforts and had managed, in conjunction with the purchase of reactors, to negotiate the possibility to return spent fuel to the Soviet Union. This arrangement was in place until it was prohibited by amendment of the law in 1994.

TVO, which had bought reactors from Sweden, tried to seek possibilities for similar arrangements. This, however, appeared to be difficult since reprocessing companies wanted to return high-level waste (HLW) back to Finland. Largely for this reason TVO received the first operation licence for its two units at Olkiluoto for only five years. This was an important impetus for TVO to start to develop alternative ways to manage spent fuel. In preparing for the application for renewal of its operation licence, TVO studied the possibility of geological disposal in Finland and drafted a proposal for a long-term programme covering all necessary steps from site selection research to implementation.

At the same time TVO made a decision to build an interim storage facility for spent fuel with such capacity that the company would not be forced into a hurried solution. TVO did receive the new operation licence for Olkiluoto 1 and 2 for a longer period but government urged the company to pursue the export of spent fuel abroad permanently.

The power companies started to coordinate their waste management activities in 1977 to develop strategies for the management of low- and intermediate-level wastes (LLW and ILW). This work led to a conclusion that it would be more beneficial for both companies to build and operate their own repositories at their plant sites. The site characterisation work at Hästholmen in Loviisa and Olkiluoto in Eurajoki was commissioned in 1978.

Research and development work for LLW and ILW repositories was carried during the early 1980s and the repositories were excavated during late 1980s and early 1990s. The repositories at Olkiluoto and at Hästholmen have been operating successfully since 1992 and 1998, respectively.

Siting challenges

Government realised the difficulty of its export requirement and decided in 1983 that TVO could explore possibilities for geological disposal in Finland as an option, if export without return of HLW proved to be unfeasible. That being the case, it stipulated that a site should be selected by 2000 and disposal commissioned in 2020. The spent fuel would be cooled in the interim storage facility for 40 years and would then be suitable for disposal.

Siting a deep repository is not an easy task. But it had to be done since efforts to ship the spent fuel were not progressing for TVO. But where, and which location would be suitable?

The work carried out in Sweden did give some guidance on this. Namely, in Sweden a law was passed which stipulated that before a reactor can be commissioned, a safe method for disposal should be presented for nuclear waste. This method is known today as the KBS-method and consists of multiple barriers. It stood as a model for TVO’s research and development work. Also in Sweden, considerable characterisation of hard crystalline bedrock was conducted by the Swedish spent fuel and waste management organisation, SKB. This knowledge, together with the international Stripa-project in Sweden during the 1980’s, provided some valuable information for planning site selection research in Finland.

The site selection work was started in 1983 by screening potential candidate sites in the whole country. After the countrywide identification of potential sites and communication with local authorities, five candidate sites were selected for investigation in 1987. Each of the sites was subject to an extensive programme of surface-based investigations and modelling studies. At least ten deep boreholes (up to 1000m deep) were drilled at each site.

Finally in 1999 the Olkiluoto site was selected to host the deep repository. The site is located in the immediate vicinity of TVO’s power plant which is close to the town Rauma (population 39,000).

The selection was based on the scientific material accumulated from 15 years of site characterisation and evaluation, and on an environmental impact assessment (EIA) conducted in 1997–1999. An assessment on long-term safety, TILA-99, was produced to support the EIA. Its main conclusions were that the regulatory, operational and transportation safety requirements could be met irrespective of the site selected. Hence the social impact and infrastructure of the sites gained more weight. Social acceptance was highest in nuclear communities Eurajoki and Loviisa and markedly lower in Äänekoski and Kuhmo. It was found that the infrastructure of Olkiluoto provided the best support for a disposal facility and, in fact, most of the spent fuel accumulated is at Olkiluoto.

The selection was accepted by authorities, local community and government in 2000 and by parliament in 2001 in the decision making process (decision in principle). This decision is the first step for licensing a nuclear facility in Finlandand the overall good of the planned facility is judged on this basis.

The whole process from early studies to formal decision-making took 18 years, which indicates the thoroughness of work that comprised not only scientific studies but also public involvement and participation. During this period the world also changed. As the result of these changes, the disappearance of Soviet Union, for example, and Finland joining the EU, the nuclear energy act was amended by parliament and both the export and the import of nuclear waste prohibited. Since IVO lost the possibility to ship spent fuel to Russia in 1994, the company joined TVO’s programme for geological disposal in Finland. The responsibility for disposal was given to a new company, Posiva Oy, which power companies established jointly in 1995.

Preparation

The next step for Posiva is to prepare an application for a construction licence. The target for submitting the application to government is set in 2012. The licence includes a PSAR (preliminary safety assessment report), designs, system descriptions and a large number of topical reports. One of the main parts is the safety case, which is an assessment of long-term safety of the repository. All this material is scrutinised by the Finnish regulator, STUK.

The KBS-3 system is based on engineered barriers with crystalline bedrock as a natural barrier. Finland belongs to the Fennoscandian Shield area where the bedrock consists of hard, crystalline rock types that are between 2.5 and 3.4 billion years old. The main rock type of Olkiluoto is gneiss which is a metamorphic rock with a granitic composition.

The engineered barriers are the low solubility spent fuel (typically fuel assemblies are about 4m-long x 20cm x 20cm and contain 150–200 fuel rods), the copper-iron canister, where the copper works as a barrier against corrosion and a cast nodular graphite iron insert gives the required mechanical strength. The buffer between canister and the bedrock consists of highly compacted bentonite clay. Backfill in deposition tunnels is based on clay material with swelling capabilities.

Bentonite is a commercial name for clays which contain plenty of smectite mineral, the most common being montmorillonite. This clay has the ability to expand when it comes into contact with water so it will limit the movement of groundwater near the copper canister. The bentonite barrier also protects canisters against mechanical wear from possible movements in the bedrock. It buckles when necessary, but recovers its shape and can quickly to seal up any cracks that could occur while the rock moves.

Seals and massive backfill are needed along the access routes and central tunnels to prevent the excavated rooms becoming major conducting features.

Two variants of the KBS-3 concept are being considered. The reference concept is KBS-3V, in which the disposal canisters are emplaced vertically in individual deposition holes. The alternative concept is KBS-3H, in which the canisters are emplaced horizontally in long deposition drifts. The canister has been perfected to endure even extreme conditions, such as earthquakes, or the pressure inflicted by a continental glacier.

The canister designs are 1.05m wide, but their lengths vary according to the particular type of fuel assembly. There are three different fuel assembly types in Finnish nuclear power plants: one in Loviisa 1 and 2, another in Olkiluoto 1 and 2, and yet another in Olkiluoto 3.

The main safety function of the canister is to ensure a prolonged period of complete containment of spent fuel for least 100,000 years. This safety function rests first and foremost on the mechanical strength of the canister insert and the corrosion resistance of the copper surrounding it. The safety functions of the buffer include: protection of the canisters from external processes that could compromise containment, and limitation and retardation of radionuclide releases in the event of canister failure.

The safety functions of the host rock are to isolate the repository from the biosphere and normal human habitat, and to provide favourable and predictable mechanical, geochemical and hydrogeological conditions for the engineered barriers, protecting them from potentially detrimental processes taking place above and near the ground surface such that they contain the spent fuel. The rock also limits and retards inflow and release of harmful substances from the repository.

Other system components like backfill, plugs, structural and sealing components, have not been assigned safety functions. They are designed to be compatible with, and support the safety functions of the other barriers.

Underground

As part of site confirmation Posiva decided to construct an underground characterisation and research facility from ground surface to planned disposal depth. The purpose of this facility, called ONKALO, is to produce detailed information for the design and safety case which cannot be obtained from investigation on the surface. ONKALO also provides an opportunity to test and demonstrate processes for assessment of rock suitability, design of repository rooms and their excavation. The design work is ongoing and the layout is developing as we dig deeper and gain more knowledge from the rock.

ONKALO will later serve as an access to the repository. The access tunnel has been excavated by the conventional drill and blast method with an inclination of 1:10, which means that the length of the access tunnel will be more than 4km. Concurrently with the tunnel excavation, three bored vertical shafts are under construction for ventilation and personnel access. The construction methods and materials have been selected in order not to jeopardise the long-term safety of the repository site.

The excavation of the access tunnel was started in 2004 and it will reach the target depth early in 2010. The remaining auxiliary rooms and test galleries will be excavated in 2010 and 2011. STUK supervises the construction of ONKALO as if it were a nuclear facility under construction.

After receiving the construction licence Posiva will construct the encapsulation facility and first disposal tunnels at depth.

The final step is the application for an operation licence, which Posiva plans to submit to government in 2018. The disposal activities are scheduled to start in 2020 and disposal of the current inventory 5500tU (~2tU per canister) will take more than a hundred years. The thermal output of each canister is limited and spent fuel bundles must be cooled for 50 years. Since the reactors will be operated for at least 60 years, 100 years will be needed for disposal.

If the inventory increases to 12000tU, as is planned since Posiva’s owners are preparing for new reactors, the disposal period will be even longer.

Money

The state nuclear waste management fund is a reserve for future costs. The fund was introduced in the Nuclear Energy Act of 1987 and has been operating since 1988. It is not included in the state budget but is an external fund controlled by the Ministry of Employment and Economy. The fund fulfils the two globally accepted principles for such funds: the funds are collected in the cost of the nuclear electricity production and the funds are available when the related waste management operations are carried out. The nuclear operators are entitled to borrow back, at market interest rates, 75% of the capital against full securities. The state has the right to borrow the remaining 25% at the same interest rate.

Based on information from TVO and Fortum and an inventory of 5500tU, a 2006 estimate put the cost of the repository at EUR3 billion. There are a number of different parameters that could affect the costs, for example the price of raw materials and the burnup of spent fuel. If the price of copper increases by 1EUR/kg this would lead to a rise in costs of around EUR35 million. Similarly if the burnup of spent fuel were to increase by 5MWd/kgU this would mean an additional seven or eight year cooling time, costing around EUR10 million per year of additional operation.


Author Info:

Timo Äikäs is executive vice president, Posiva Oy, Olkiluoto, FI-27160 Eurajoki, Finland.

Related Articles
Methods for disposal of nuclear waste
Forsmark selected for Swedish repository
Two more nuclear reactors to be built in Finland
The copper controversy
EIA for new Loviisa unit launched
Olkiluoto 3 reactor building gets roof
Forsmark repository go-ahead
A new look inside cores of UK AGRs
Fortum's application for sixth Finnish unit

References

[1] Aikas T, (2001). "Everything is possible, even successful site selection." Proceedings of the BNES Conference UK Waste: Going Forward Dialogue and Decisions, London, UK.

[2] Posiva Oy, English Website, www.posiva.fi/en


[3] Patrakka E, Palmu J, Lehto K, (2008). "Assessment of Financial Provisions for Nuclear Waste Management Long-Term Perspective from Finnish Viewpoint" Proceedings of the Seventh European Commission Conference on the Management and Disposal of Radioactive Waste, Luxembourg.


[4] Aikas T, and Anttila P, (2008). "Repositories for low- and intermediate-level radioactive wastes in Finland, Reviews in Engineering Geology: Deep Geologic Repositories, Vol. XIX, p67-71.



Tables

Predicted spent fuel quanatities in Finland
Estimated cost of Finnish repository

Multiple Barrier Solution Multiple Barrier Solution
ONKALO ONKALO


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