Finland's Onkalo Spent Fuel Disposal Facility Starts Drilling of First Disposal Hole

On the afternoon of August 26, 2026, Finland's Onkalo spent fuel final disposal facility commenced drilling of its first disposal hole deep in the bedrock at Olkiluoto. Posiva stated that the drilling operation is being carried out at a depth of more than 400 meters underground, with the drill bit beginning to cut into the approximately 1.9-billion-year-old Olkiluoto bedrock.

Kimmo Lehtola, Posiva's Operations Construction Manager, explained that a kick-off meeting had been held the day before the operation, focusing on reviewing safety matters, technical specifications, and the detailed drilling plan. On the morning and early afternoon of the drilling day, the team completed final adjustments to the equipment, after which the drilling rig began its work. He noted that the team had previously drilled several practice holes, and that preparation for the actual disposal hole construction had been ongoing for a considerable period.

The equipment used for this operation is a Disposal Hole Drilling Machine (DHBM), manufactured by Herrenknecht AG of Germany and delivered to the Onkalo site in June 2022. The drilling rig measures over 9 meters in length, 3 meters in width, and nearly 4 meters in height, weighing 78 tons; its accompanying power unit is 7 meters long and weighs 22 tons, while the drill pipe handling device is 4.1 meters high and weighs 18.5 tons. At the end of 2022, the supplier's team completed four test holes, after which Posiva's team, with assistance from the supplier, completed an additional four test holes.

The disposal holes will be drilled vertically into the floor of the excavated disposal tunnel, with a final depth of 8.4 meters and a diameter of 1.75 meters. As required, the deviation of the hole center point from the vertical centerline must not exceed 25 millimeters over the full depth of the hole. The first batch of disposal holes will be subject to stricter inspection, with at least the first three holes requiring immediate re-measurement upon completion to confirm quality before continuing with subsequent drilling. If the deviation exceeds the allowable range, the hole will not be permitted for use in final disposal.

Lehtola stated that under Onkalo conditions, drilling a disposal hole approximately 8 meters deep typically requires about 10 hours of effective drilling time. In addition to the drilling itself, equipment positioning, anchoring, removal, hole cleaning, and drying also require considerable time. Once drilling enters normal production flow, the target is to complete approximately two disposal holes within one working week.

The Onkalo disposal facility plans to encapsulate spent fuel and place it in bedrock at a depth of approximately 450 meters. The disposal system comprises sealed iron-copper canisters, a bentonite buffer surrounding the canisters, tunnel backfill material made of swelling clay, tunnel and facility sealing structures, and the host rock barrier. The first final disposal tunnel currently under construction is approximately 330 meters long and will accommodate about 30 disposal holes.

Posiva is jointly owned by Fortum and Teollisuuden Voima Oyj (TVO). The company has applied for an operating license for the Olkiluoto spent fuel encapsulation plant and final disposal facility, intended to dispose of spent fuel from TVO's Olkiluoto nuclear power plant and Fortum's Loviisa nuclear power plant units. The Radiation and Nuclear Safety Authority of Finland (STUK) stated earlier this month that the project has met the safety requirements for granting the operating license. Posiva's President and CEO Ilkka Poikolainen stated that the company's goal is to reach operational readiness for final disposal by the end of 2026.