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The Finnish power companies TVO and FPH currently operate four nuclear reactors, two each at the Olkiluoto and Loviisa sites. Both companies are responsible for the safe management of nuclear wastes. The underground repository program for low- and intermediate-level waste was commissioned in the late 1970s. From the start, the design basis has been geological disposal, the safety of which rests on natural and engineered barriers. The disposal system should isolate the waste for a few hundred years. During this time, the radiotoxicity of the waste will decline significantly. The critical radionuclides are 14C, 239Pu/240Pu, 59Ni, 90Sr, and 137Cs. The Olkiluoto site consists mainly of micaceous gneiss intercalated with sparsely fractured tonalite. A tonalitic portion of the site was chosen for more detailed characterization. The Loviisa site consists entirely of Rapakivi granite, which is coarse grained and porphyritic. The repository layout was in both cases constrained by the local geology. At Olkiluoto, the shape of the tonalitic body bounded by fracture zones led to a vertical silo-type concept 60–100 m below the surface. At Loviisa, the subhorizontal fracture zones above the planned disposal depth favored horizontal drifts 120 m below the surface. Thorough safety assessments were conducted during the licensing process. The Olkiluoto repository was built between 1988 and 1992, and the Loviisa repository was built between 1993 and 1997. Operation of Olkiluoto was commissioned in 1992, and Loviisa was commissioned in 1998. In the future, the repositories will also be used for disposal of waste when the nuclear power plants are decommissioned.

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