Finland set the pace for spent fuel repository programmes after its government-approved construction at a disposal site at Onkalo in November. Posiva continues work at the underground cavern network and aims to start disposing of fuel in the 2020s as Corrina Thomson reports.
Finland’s Posiva Oy, set up in 1995 to manage nuclear waste disposal, is jointly owned by nuclear utilities Teollisuuden Voima Oyj (TVO) and Fortum Power and Heat Oy. It is leading the field in geological disposal of used nuclear fuel after the Finnish government approved a construction licence for its repository late last year. Contracts are in place and construction is set to begin shortly.
The country’s pragmatic, methodical approach to its nuclear waste legacy has led to this leading position evolving in one of the smaller countries of northern Europe. Alongside it has been cooperation with Sweden’s nuclear fuel and waste management company SKB on using the KBS- 3 disposal system.
In Finland, each nuclear power company must pay for decommissioning and each pays into the State nuclear waste management fund according to how much electricity they generate. Spent fuel from the two BWRs at Olkiluoto and two VVERs at Loviisa is lined up for disposal at Posiva’s repository site at Olkiluoto island, Eurajoki, which is situated in the Gulf of Bothnia.
As well as being responsible for Finland’s spent fuel disposal, Posiva also now provides product development and services commercially through a subsidiary business, Posiva Solutions, based on its established record in this sector. Posiva Solutions is offering models and services, based on local conditions, to organisations looking for nuclear waste management and spent fuel disposal expertise.
At the end of 2015, the total amount of spent nuclear fuel in interim storage at Olkiluoto and Loviisa was about 2100t. The spent nuclear fuel has to be cooled for several decades to bring heat generation down to the level required for final disposal, so disposal cannot begin until the early 2020s.
The construction licence granted in November 2015 makes it possible for Posiva to start construction of a fuel encapsulation plant at Olkiluoto as well as begin excavation of the repository. The Finnish government decision to approve the construction licence followed more than 40 years of work developing and researching the final disposal solution.
A key part of this work was carried out at the Onkalo underground rock characterisation facility at Olkiluoto, which reaches a depth of about 455m. This rock laboratory has provided geological, hydrogeological and geochemical data that inform Posiva’s repository plan.
Onkalo also provides a place where excavation and final disposal techniques can be investigated in realistic conditions, and where Posiva can investigate the impact of construction work on local conditions. The research helps to ensure the suitability of the Olkiluoto rock for the repository and assists in identifying the areas within the site where construction of final disposal tunnels will be most cost-effective.
Schedule
Posiva said the fuel used in Olkiluoto 1&2 and Loviisa 1&2 requires a cooling period of about 40 years before it can be disposed of, whereas the fuel in Olkiluoto 3 would need to be cooled for about 60 years. Apart from these cooling periods, another factor affecting the repository schedule is whether other plants, such as the proposed VVER at Hanhikivi, come to fruition and whether their fuel is disposed of at Onkalo or elsewhere.
Posiva Solutions provides final fuel disposal services to Fennovoima. These include ecological and geological research at two potential sites, Pyhäjoki, near the Hanhikivi site, and at Eurajoki, where the Onkalo final repository is being built by Posiva for TVO and Fortum.
In June this year the environmental impact assessment for disposal of used fuel from Hanhikivi 1, which is being built for Fennovoima by Russian state nuclear corporation Rosatom at Pyhäjokil, was submitted to the Finnish government.
Licence
Nuclear regulator STUK’s assessment of Posiva’s construction licence application, issued in February 2015, said that an incremental approach is reasonable in designing and ascertaining the safety of Posiva’s encapsulation plant and repository. STUK said the licence application did not need any further changes. However, it noted there were uncertainties and assumptions about the specific properties of the site and disposal system performance that should be verified or reduced based on information gained during construction and operation. Posiva’s 2015 annual report says that there are open points highlighted in STUK’s review that need to be resolved during construction of the encapsulation plant and the final repository. These resolutions are required prior to submission of the operating licence.
Posiva is preparing a safety case for the operating licence application through the TURVA-2020 (Safety-2020) project, which will also take account of the final disposal repository for low- and intermediate-level waste. It will give a sharper focus on the link between safety functions, performance goals and design requirements, and provide clearer justification for the analysed scenarios.
Ice ages and permafrost affect the conditions in a future repository and STUK pointed out the uncertainty of climate evolution analyses that extend far into the future.
In assembling to the safety case, studies have been carried out in Greenland and in Lake Saimaa, Finland, on the future climate. Research was carried out into the biosphere of the reference area, comprising studies of marshland, rivers, fauna and flora, as well as agricultural studies in the regions of Satakunta and Southwest Finland.
Meanwhile, Posiva and its Swedish counterpart SKB have conducted a review of the requirements that each applies
to the bedrock, canister, buffer, backfill and plugging to try to harmonise their requirements. If this were achieved, it would mean raw materials and components could be sourced from the same suppliers or production plants.
Building the cavern
Posiva finished phase two of the area works in 2015, including completion of a building contract that made it possible to acquire and install a personnel lift, fit out the building, and install the systems needed for operations. The procurement contract for the personnel lift to be installed in the lifting equipment building was awarded to KONE Hissit Oy in December 2015.
The lift descends to a depth of more than 400m and delivery included a lift for construction use, enabling the installation of the final shaft equipment.
The lift utilises KONE’s UltraRope technology, a technology that could break industry limits and enable future lift travel heights of 1km, which is twice the distance currently feasible. The UltraRope technology consists of a carbon fibre core and a high- friction coating. According to KONE, this removes the disadvantages of conventional steel rope.
The Onkalo construction lift is expected to be ready in early 2019. The passenger lift is due to be ready by the end of 2020 and will be used from the start of 2021.
In February this year, Posiva signed a contract with construction and services company YIT Rakennus Oy for the next excavation project at Onkalo. Excavation was scheduled to start in April with the contract comprising an access tunnel and a maintenance and parking garage at a depth of 430-440m. Sealing and reinforcement is also part of the contract, which is due to run for ten months and employ 30 people.
Onkalo work
Posiva has recently produced a summary of nuclear waste management operations at Olkiluoto and Loviisa for 2015. This document focuses on operations relating to final disposal of spent nuclear fuel in Olkiluoto and Posiva itself, rather than disposal of operational waste. The latter has been taking place at Olkiluoto and in Hästholmen in the town of Loviisa since the 1990s.
Posiva noted that the design work and tasks related to the Onkalo research tunnel were integrated into the design of the
final disposal facility in 2015. Any plans for facilities that were part of the original scope of Onkalo were finished in spring 2015. Building work carried out last year at Onkalo was primarily related to previously built structures and facilities.
The new report noted that several boreholes at Olkiluoto were plugged and the groundwater-monitoring network was extended by adding two new locations. Research work continued in the existing boreholes for both monitoring purposes and updating the site description. Multi- disciplinary work for the fifth version of the Olkiluoto site description continued during the year.
New boreholes for research or method testing applications were drilled, in one Onkalo investigation tunnel, and in the demonstration area and in the technical facilities.
Ongoing research at Onkalo included work on the physical, mechanical, electrical and thermal properties of rock, groundwater flow on different scales, the reduction of sulphate, and migration properties of the rock matrix. Studies into rock construction and host-rock- suitability classification continued at the demonstration facilities.
Copper canisters
A project was launched in cooperation with SKB in 2015 to add to the stress analyses on spent fuel canisters, with new structural analyses examining subjects such as the effect of canister insert defects on canister strength.
Developments focusing on fabrication of the copper canister and on friction-stir welding also continued. Fabrication work focused on optimising the forming of the bottom of the copper overpack to enhance the microstructure of copper. Grain size can be significantly reduced with the new technique, which brings strength advantages.
Work related to fabrication of the canisters’ cast iron insert for BWR fuel proceeded and two inserts were cast. A large study took place to analyse variations in the material properties of the BWR canister insert and their impact.
Buffer
Posiva is working on the construction plan for the repository buffer, with engineering work on analysing the effects of canister design changes on the buffer design. Thermal conductivities in the buffer were also studied, and the design and execution of the chamfer in the top part of the buffer. Development of expansion pressures in the buffer remained an area of research. The most important outcome of this research was establishing water content and expansion pressure values in a larger variety of conditions.
Work continues on issues such as: the erosion of buffer material by water under certain conditions; and decay of substances dissolved from cement, their migration in the rock fracture network, and interaction with other components of the final disposal system. There were also studies on the mechanical performance of the buffer in the event of rock movements.
For the main tunnel backfill, four materials were chosen and plans prepared for the final selection. Tests were carried out on directing leakage water uniformly into a wider area using geotextiles, as well as on the impact of fine fractions of pellet backfill on the storage capacity of water, and installation of a temporary drainpipe in the pellet backfill material. At Onkalo, installation tests of specific backfill components were continued through installation tests on the floor-levelling layer.
Posiva continued work on the POPLU project, which covers design, test and construction of the deposition tunnel
end plug. POPLU is related to a joint European programme, coordinated by Posiva, that focuses on closure solutions for final disposal tunnels. The work was a component-specific test and included work related to construction of the plug, installation of pressurisation equipment used for plug tests, and installation of instrumentation used for monitoring plug performance during pressurisation.
Posiva and SKB have continued to work on development of the KBS-3H horizontal disposal solution. In line with this, a draft report is being finalised on the Big Bertha 4 bentonite buffer performance test. The subsequent Big Bertha 5 test also began, which is a long-term test of expansion of the bentonite buffer through the perforated protective cylinder of the installation pack. The aim is to experience full saturation of the bentonite. The impact of rock movements on the horizontal solution was also studied in comparison with the vertical disposal solution.
Encapsulation plant
Also in 2015, updating and supplementary work was carried out on the facility plan for the encapsulation plant, and a prototype of the canister transfer trolley was produced and then tested. Manufacturing of a prototype remote-controlled mover for canister transfers proceeded and factory acceptance tests were carried out at the end of the year.
The facility project proceeded through two steps: the definition of design tasks phase and a competitive bidding process. Now it is in the implementation design phase. The latter has reached a point where the design of fuel handling cell systems and equipment has begun.
Construction and civil engineering design related to the encapsulation plant has started and Posiva anticipates it will
be possible to submit the building permit application to Eurajoki municipality this year. It was also agreed that the final repository project should encompass the scope of the Onkalo project that is not yet complete. This will be added to the next project plan for the final disposal repository.
For the encapsulation plant, the canister lift design has started and tests of the prototype canister transfer and installation vehicle continue in realistic conditions inside Onkalo. Also in the underground caverns, tests on the buffer block installation machine and the block transfer vehicle continue.
A prototype backfill installation machine has been built and installation tests have been carried out on the ground surface. Also, plans have been made for installation of the backfill pellets, with tests being carried out in above ground facilities.
In the last year, Posiva has continued significant detailed work towards the reality of building and operating a spent
fuel repository. STUK’s and the Finnish Government’s approval of the construction licence is a benchmark that shows Finland’s pragmatic approach to building a spent fuel repository is making significant, real progress in a global context.