Methodology and Results for the Safety Assessment for Low and Intermediate level Waste Repository (SFR) in Sweden

The Swedish low- and intermediate level waste repository, SFR, has been operating since 1988. When the nuclear power plants in Sweden will be decommissioned and dismantled additional repository capacity is required. Additional disposal capacity is also needed for operational waste from nuclear power units in operation since their operating life-times have been extended compared with what was originally planned. In December 2014, the Swedish Nuclear Fuel and Waste Management Company (SKB) submitted an application to the Swedish Radiation Safety Authority (SSM) to extend the existing repository for low- and intermediate level waste (SFR). SFR, the existing part and planned extension, is placed below the sea floor at 60-120 meter depth in Paleoproterozoic metagranite. For the application an evaluation of post-closure safety is required. This paper presents the safety assessment performed to evaluate if the repository complies with the Swedish Radiation Safety Authority's regulations concerning safety and protection of human health and the environment in the post-closure perspective. The results from the safety assessment are compared against the annual risk criterion specified in the regulations, 10^-6, which corresponds to 1% of the background radiation at the site. The time frame of the safety assessment is 100,000 years under which there is an evolution of both the repository and the external conditions (climate and surface systems). The extended SFR repository and the applied 10 step methodology for the safety assessment are described. Some steps of the methodology are discussed in more detail, e.g. the FEP-analysis and safety functions. Different scenarios that will contribute to the overall risk evaluation for the repository are generated from uncertainties in both external and internal processes. The understanding of the processes is based on extensive site investigations, research, and numerical modelling of the evolution of the repository and external conditions. Examples of major results for the dominating radionuclides (C-14, Mo-93 and Ni-59) are presented. The central conclusion of the safety assessment is that the extended SFR repository meets the regulatory criterion and is robust and safe in the post-closure perspective. (author)