The Construction of Underground Rock Characterisation Facility Started 10 Years Ago
As the finishing touches are being applied to the building automation works in Posiva’s 10-year-old ONKALO, testing of deposition equipment prototypes is already underway in the ONKALO areaONKALO has seen over a decade of construction and research work. The construction of the ONKALO underground rock characterisation facility began with the initial blast on 29 June 2004, and the actual excavation work commenced during September 2004.
Research conducted at ONKALO has verified the suitability of the Olkiluoto bedrock for final disposal. In addition, it has led to the identification of feasible construction areas for the deposition tunnels.
In addition to bedrock research, ONKALO has provided an opportunity for innovation in the area of rock construction and to the further development of disposal technology under working conditions. ONKALO is the world’s first and currently only underground bedrock research facility which is located on the final disposal site.
Building automation works are currently being finalised at ONKALO. At the same time, personnel are preparing for the commencement of full-scale testing. Several research and testing projects are underway at ONKALO. The underground research facility’s vehicle access tunnel reaches a depth of 455 metres. In addition to the vehicle access tunnel, ONKALO is comprised of two ventilation shafts and a personnel shaft. The shafts were raise-bored to completion in spring 2014.
Construction and building automation work for the second phase of the hoist building that has been designed to complement ONKALO’s access arrangements began in early summer. The work will be completed in 2015. The addition of a personnel lift is included in the overall construction contract.
Deposition equipment prototype testing is underway in the ONKALO area
Posiva’s unique final disposal project required the designing of completely new types of machinery and equipment for uniquely specific purposes. Two large deposition equipment prototypes have arrived at Posiva’s ONKALO site: one is a buffer block transfer and installation device, and the other is a canister transfer and installation vehicle. Both of them were designed and constructed in Finland. The testing of deposition equipment prototypes at Olkiluoto will take place both above ground and under actual disposal conditions in ONKALO’s underground demonstration facilities. The equipment will be further developed as required on the basis of test results.
The buffer block transfer and installation device will be used to install buffer blocks made from compressed bentonite clay into the deposition hole. The installation device lifts the 2,000–3,500-kilogram buffer blocks via vacuum suction cups. The fully power-operated installation device will be transferred to the deposition tunnel using a terminal tractor and then positioned precisely on top of the deposition hole with the help of automatic laser measurement equipment. The equipment also comprises a bentonite block transfer device and transfer containers used to transfer the blocks to the installation device.
The canister transfer and installation vehicle prototype will be used to test the installation of disposal canisters in the deposition hole bored in the bedrock. Whilst the device may weigh no less than 103 tonnes when in the process of transferring canisters, its interior is filled with various types of finely tuned mechanics. The device’s multiple safety features are the result of careful design.
The purpose of the canister transfer and installation vehicle is to enable the disposal of spent nuclear fuel, enclosed in canisters, into special deposition holes bored in the Olkiluoto bedrock. According to the plan, the device will be used to transport canisters from the interim storage facility located more than 400 metres below the ground surface to the deposition tunnel. Additionally, the device will be used to place canisters in deposition holes lined with buffer blocks fabricated from bentonite clay to within an accuracy of 10 millimetres.
Additional information: Kanerva Kuisma, Deputy Communications Manager, Posiva, tel. +358 50 313 1167