Excavation of the final disposal repository unit for spent nuclear fuel in Finland began as of May 5, Posiva Oy has announced.
The start comes after years of development activities on research and methodology for rock construction and tunneling. The Radiation and Nuclear Safety Authority of Finland (STUK) certified the process and said that pre-conditions for a construction start had been fulfilled, the company said.
The years of research and development of rock construction have produced procedures for the construction of a nuclear facility suited for the Finnish bedrock. The development of the methodology started with the construction of the ONKALO facility in 2004, says Posiva's Construction Manager Juha Riihimki.
The first five tunnels to be excavated during the next 18 months mark the beginning of an extensive building effort. It is estimated that one hundred deposition tunnels will be excavated during the 100-year operational period of the final disposal facility, totaling a length of about 35 kilometers. The maximum length of one tunnel is 350 meters. The tunnels are about 4.5 meters high and about 3.5 meters wide.
The excavation of the first five tunnels is part of Posiva's approximately 500 million-euro EKA project that covers all the final disposal facilities needed, including both their construction and the equipment, as well as the start of the final disposal operation in the first deposition tunnel. To pin down the EKA project, it means that Posiva is the first operator in the world to start geological final disposal of spent nuclear fuel.
The repository design allows about 30 canisters placed in one tunnel. Their number depends on how many deposition holes there are in the tunnel and that is determined by the volume of suitable rock based on the rock fractures. The thirty canisters placed in one tunnel can accommodate about 65 tons of spent nuclear fuel, Riihimäki said.
The encapsulation of spent nuclear fuel and the emplacement of the canisters in the deposition holes will start once the Finnish Government grants the operating license for the final disposal facility.
The current estimate is that the final disposal operation will start in the mid-2020s.
The excavation and reinforcement of the tunnels, which have now been started according to tight regulatory requirements, signify for Posiva a transfer to the execution of the most complex and exacting rock structure system in ONKALO.
Approximately dozens of subcontractors and 300 persons are currently working in the ONKALO project.
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