GEOLOGICAL DISPOSAL OF SPENT NUCLEAR FUEL: THE COMMISSIONING PHASE OF THE FINAL DISPOSAL FACILITY IN FINLAND

The final disposal facility being constructed and commissioned in Olkiluoto by Posiva Oy in the Southwest coast of Finland consist of an encapsulation plant above the surface and the underground disposal facility. The Finnish Government granted a construction license for these facilities in November 2015. Posiva Oy did submit the application for an operating license in the end of 2021 and the expectation is that the worlds first disposal facility starts its operations to dispose of spent nuclear fuel in the mid-2020s.

The over 40 years of design, research, and development together with construction of an underground rock characterisation facility, ONKALO® have been the basis for the licencing the repository. The work was summarised is PSAR (Preliminary Safety Assessment Report) and updated for FSAR (Final Safety Assessment Report) including the extensive Safety Case and System Descriptions and Environmental Impact Assessment (EIA) update. Simultaneously Posiva is preparing the production by testing the disposal concept in full-scale in the repository conditions. The full-scale in situ system test was implemented with prototype machinery and includes the monitoring phase to follow up the early behaviour of the disposal concept. Concept is a KBS-3V type engineered barrier system (EBS) consisting of copper-cast iron canister installed in vertical deposition hole surrounded by bentonite buffer. The tunnels hosting the holes are than backfilled with bentonite clay and plugged with reinforced concrete plug.

As part of the commissioning the facilities Posiva performs a final disposal system test, the so called Trial Run of Final Disposal (TRFD). The TRFD comprises the whole disposal process including the transport of dummy fuel assemblies from interim storage, the encapsulation and the operations in repository with final disposal systems and machinery. The construction of the deposition tunnel and holes for the TRFD has been completed in 2022 and the site is ready to install the KBS-3V concept.

Once the Finnish Government grants to Posiva the operating license, the final disposal facility will operate around 100 years prior the closure phase.