TVO (Teollisuuden Voima Oyj) is the owner of Olkiluoto nuclear power plant. TVO disposes of the low and intermediate wastes arising from the power plant operation into its own repository located at the power plant site. The repository is located at the depth between 60 m and 100 m in the bedrock. In the future, decommissioning wastes from the three reactor units are planned to be disposed of in an extension of the current repository. Fortum has supported TVO by compiling a safety case for TVO's low and intermediate level waste repository, which was needed for periodic safety review 2021. The works were delivered between 2019-2021.
A safety case is a report portfolio demonstrating the long-term safety of a final repository. Fortum has developed safety case experience since 1990s to support the disposal of wastes from the Loviisa power plant in its own repository at the Loviisa site as well as to support external customers such as TVO in their disposal projects. Fortum has excellent knowledge of safety cases concerning low and intermediate level waste. The different safety cases and safety analyses have resulted in experience and know-how regarding e.g. groundwater flow modelling in the bedrock, concrete degradation modelling and radionuclide transport modelling in the repository, in the bedrock and in the surface environment as well as dose assessments both to humans and other biota.
Fortum has complied safety cases for TVO's low and intermediate level waste repository in 2006 (for operational waste) and 2008 (for decommissioning waste). In 2021, the safety case for TVO’s existing low and intermediate level waste repository and its planned extension for the decommissioning was updated and finalized in connection to the periodic safety review 2021.
Description of working methods used in project
The project was executed in good cooperation with TVO. During the whole delivery period 2019-2021 periodical management meetings with TVO were arranged to ensure the success of the project. TVO provided the necessary data regarding the waste and its activity inventory, repository data and the site investigations. Posiva´s final repository of the spent fuel is located near to the TVO’s low and intermediate level waste repository, so Posiva's data was also utilised, especially regarding climate and biosphere. TVO, with Posiva's support, reviewed all the safety case material produced.
The key modelling software utilized during the project were Comsol Multiphysics (groundwater flow modelling, gas transport modelling) and Ecolego (radionuclide transport modelling and dose calculations, concrete degradation modelling).