Overview of hydrogeological site-descriptive modeling conducted for the proposed high-level nuclear waste repository site at Forsmark, Sweden

Abstract

In an essay in a previous issue of Hydrogeology Journal, Selroos and Follin (2014) outlined the hydrogeological sitedescriptive modeling performed regarding the Forsmark site in Sweden in order to support an application for a future repository for high-level spent nuclear fuel. The essay was accompanied by three individual reports (Follin and Stigsson 2014; Follin et al. 2014; Follin and Hartley 2014) where more detail was given on various modeling aspects (e.g. parameterization of a deformation zone model, development of a discrete fracture network model, and model integration and confirmatory testing of the integrated model against various types of data). The aim of the site-descriptive hydrogeological modeling was to develop a hydrogeological account of the past and present conditions at the site by analyzing, assessing, and modeling the data obtained during the stage of surfacebased site characterization. Corresponding site-descriptive models for other earth science disciplines were also developed; the combination of these models constitutes an integrated site-descriptive model of the site and its regional setting, including the current state of the geosphere and the biosphere as well as natural processes affecting long-term evolution. The process and experiences of developing an inter-disciplinary site-descriptive model for the Forsmark site is discussed in detail in Andersson et al. (2013). In the current issue of Hydrogeology Journal, corresponding modeling performed as part of the safety assessment supporting the application is summarized. Whereas the site-descriptive modeling dealt with past and present conditions, the safety assessment deals with the long-term safety and, hence, future conditions. The objectives of the hydrogeological modelling performed as part of the safety assessment are outlined here. In addition, the individual modeling efforts are brought into a safety assessment context in order to exemplify and illustrate how the modelling supports the assessment end-point, i.e. to show regulatory compliance. The Swedish Nuclear Fuel and Waste Management Company (SKB) is responsible for the handling and final disposal of all nuclearwaste in Sweden. The concept developed for geological disposal is denoted ‘KBS-3’ and consists of copper canisters deposited in vertical deposition holes under the floor of deposition tunnels located at approximately 500 m depth in crystalline bedrock (SKB 1983; Banwart et al. 1997; Hedin et al. 2001; Thegerstrom and Olsson 2011). The canisters have a cast-iron insert to provide mechanical stability, and are surrounded by bentonite clay in the deposition hole. The tunnels are backfilled and pumping that has been draining the tunnels is stopped; thereafter, groundwater begins to resaturate the repository. The KBS-3 system is thus a multibarrier system where the three independent barriers are the copper canister, the bentonite buffer, and the bedrock. The safety assessment of which the present modeling is a part, is denoted ‘SR-Site’ (SKB 2011; Hedin et al. 2011) and was a major part of the application to obtain a permit to construct a repository for spent high-level nuclear fuel at Forsmark. The application was submitted to the relevant Swedish authorities inMarch 2011; if the present application is approved within the forecasted time horizon, repository construction could start in 2019. Further detailed characterization and monitoring will be performed in parallel with construction and will provide a basis for future safety assessments. After subsequent applications, based on the renewed safety assessments and approval of a licence, the repository could be in operation around 2030 and then be one of the first such operational repositories in the world. This essay serves as an introduction to three reports in this issue of Hydrogeology Journal (Joyce et al. 2014; Received: 29 August 2013 /Accepted: 18 June 2014 Published online: 12 July 2014