Finland's Posiva starts drilling first deposition hole at Onkalo repository

en.Wedoany.com Reported - Finnish radioactive waste management company Posiva has started drilling the first actual deposition hole at the Onkalo deep geological repository for spent nuclear fuel at the Olkiluoto site. The hole is located in bedrock more than 400 meters deep, which formed 1.9 billion years ago. On Tuesday, Posiva held a kick-off meeting to re-verify safety matters, technical specifications, and the detailed construction plan for the drilling operation. On Wednesday afternoon, the deposition hole drilling machine (DHBM) officially began its work.

Kimmo Lehtola, Posiva's Operations Construction Manager, said that the equipment underwent final adjustments during the morning and early afternoon, after which the drill bit made contact with the rock. He noted that the team had previously practiced drilling several holes, and the preparation for drilling the actual deposition hole had been ongoing for a considerable time—drilling a hole that will be part of the final disposal process is something the team has long awaited.

The drilling machine was manufactured by German company Herrenknecht AG and arrived at the Onkalo site in June 2022. In the complete assembly, the deposition hole drilling machine itself is over 9 meters long, 3 meters wide, nearly 4 meters high, and weighs 78 tons; it also includes a 7-meter-long, 22-ton energy unit, and drilling handling equipment measuring 4.1 meters high and weighing 18.5 tons. At the end of 2022, the Herrenknecht team first completed four trial drillings, after which the Posiva team drilled four test holes with the supplier's assistance.

These deposition holes are drilled vertically downward from the floor of the already excavated final disposal tunnels. The designed hole depth is 8.4 meters, with a hole diameter of 1.75 meters. The construction quality requires that the center point of the deposition hole deviate no more than 25 millimeters from the vertical centerline over the entire hole length. The first drilled deposition holes will undergo stricter inspection than usual; at least the first three holes must be completed and confirmed acceptable through immediate re-measurement before proceeding to the next hole. If monitoring shows that the allowable deviation is exceeded, the hole will be deemed unsuitable for final disposal.

Lehtola stated that drilling an 8-meter-deep hole at Onkalo takes approximately 10 hours of effective drilling time. Rock hardness affects progress, but this empirical value is relatively stable under local geological conditions. Once drilling operations transition to normal production, the plan is to complete approximately two finished deposition holes per week.

This type of deep geological repository consists of a highly engineered network of underground chambers and tunnels, designed to permanently isolate high-activity radioactive waste so that harmful radiation does not reach the surface environment. Sweden, France, the United Kingdom, and the United States are also advancing similar solutions.

At Onkalo, spent nuclear fuel will be placed in bedrock at a depth of approximately 450 meters. The disposal system consists of sealed iron-copper canisters, a bentonite buffer surrounding the canisters, tunnel backfill material made of expandable clay, tunnel and site sealing structures, and the surrounding rock. The first final disposal tunnel currently under construction is approximately 330 meters long and is planned to accommodate about 30 drilled deposition holes.

Posiva's repository site is located in Eurajoki, near the Olkiluoto nuclear power plant. It was selected in 2000, and the following year the Finnish Parliament approved the project's principle decision. Posiva is jointly owned by Finnish nuclear power companies Fortum and Teollisuuden Voima Oyj (TVO). In December 2013, the company submitted a construction license application to the Ministry of Employment and the Economy, with related research conducted through the Olkiluoto rock investigation and the Onkalo underground laboratory, which was later expanded into the basis for the repository. The Finnish Government approved the construction license in November 2015, and construction of the repository began in 2016.

In July 2022, Posiva announced the completion of excavation of the first five actual disposal tunnels, which had been under construction since May 2021, with a total length of approximately 1,700 meters. According to estimates, a total of 100 disposal tunnels will be excavated over the 100-year operating period of the final disposal facility, with a total length of approximately 35 kilometers, a maximum individual tunnel length of 350 meters, and tunnel cross-sections approximately 4.5 meters high and 3.5 meters wide.

On December 30, 2021, Posiva submitted an operating license application to the Ministry of Economic Affairs and Employment for the Olkiluoto spent fuel encapsulation plant and final disposal facility, with the application period covering March 2024 to the end of 2070. These facilities are intended for the disposal of spent nuclear fuel generated by TVO's Olkiluoto units and Fortum's Loviisa units. The final decision on the operating license is made by the Finnish Government, subject to a positive opinion from the Radiation and Nuclear Safety Authority (STUK). STUK has been reviewing the application since May 2022 and announced earlier this month that the safety requirements for the world's first spent fuel disposal repository operating license have been met. The Ministry of Economic Affairs and Employment stated that a proposal for the operating license decision could be prepared in the autumn and submitted to the Government.

Ilkka Poikolainen, President and CEO of Posiva, stated that the company's goal is to have the operational conditions in place to begin final disposal by the end of 2026.