Safety case for TVO's low and intermediate level waste repository 2021

A long-term safety case for TVO’s existing low and intermediate level waste repository and its planned extension for the decommissioning was compiled during the project in connection to the periodic safety review. The safety case considered the evolution of the repository and surface environment from their initial state at the closure up to one million years. The identified key uncertainties in the repository performance were systematically combined into six scenarios. The radiological impacts within these scenarios were studied in the radionuclide release, transport and dose modelling both using deterministic and probabilistic methods. Both the deterministic results and the probabilistic results were used in comparison with the regulatory constraints to build confidence on the safety of the disposal. Altogether, the safety case portfolio consisted of six reports and over 1200 pages.

Case Description

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).

Loviisa nuclear radioactive waste repository

Project information

Customer: Teollisuuden Voima Oyj (TVO)

Project: Safety case for TVO's low and intermediate level waste repository 2021

Project start and end: 2019-2021

Country: Finland

Main contractor: Fortum Power and Heat Oy (Fortum)

Antti Ketolainen, Nuclear Services

Antti Ketolainen

Senior Manager
Decommissioning and Waste
Tel: +358 40 751 8956
Antti [dot] V [dot] Ketolainen [at] fortum [dot] com

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