From Site Data to Safety Assessment Analysis of P

Authors: Sten Berglund Emma Bosson Mona Sassner

Publish Date: 2013/04/26

Volume: 42, Issue: 4, Pages: 425-434

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Abstract

This paper presents an analysis of present and future hydrological conditions at the Forsmark site in Sweden which has been proposed as the site for a geological repository for spent nuclear fuel Forsmark is a coastal site that changes in response to shoreline displacement In the considered time frame until year 10 000 ad the hydrological system will be affected by landscape succession associated with shoreline displacement and changes in vegetation regolith stratigraphy and climate Based on extensive site investigations and modeling of present hydrological conditions the effects of different processes on future site hydrology are quantified As expected shoreline displacement has a strong effect on local hydrology eg groundwater flow in areas that change from sea to land The comparison between present and future land areas emphasizes the importance of climate variables relative to other factors for main hydrological features such as water balancesAnalyses of hydrological processes such as groundwater and surface water flow and water exchanges between atmosphere regolith and vegetation are often fundamental components in environmental assessments and geoscientific research studies Applications may be focused on the water itself eg for drinking water supply or consider cases where water primarily is of interest as a carrier of chemical substances eg in contaminant transport or as an environment where biogeochemical processes take place In applications like these hydrological models are often developed and used to predict or otherwise describe the future The time periods considered in most of these studies of future hydrology are relatively short on the order of a few decades up to say one hundred years However in recent years there has been an increasing interest in issues involving much longer time scales such as longterm climate change and risk assessments of longlived contaminants When considering these longer time perspectives also changes in the studied systems as such must be taken into account for example Rowland et al 2010 emphasize the need for integrating hydrological ecological geomorphological and geochemical processes in studies of changes in permafrost systemsThis paper presents modeling of present and future hydrological conditions at the Forsmark site in Sweden In 2009 Forsmark was selected by the Swedish Nuclear Fuel and Waste Management Company SKB as the intended site for the planned geological repository for spent fuel from the Swedish nuclear power plants and an application for constructing and operating the repository was submitted to the authorities in 2011 Kautsky et al 2013 As a basis for site selection and the application multidisciplinary site investigations of bedrock regolith and surface ecosystems were performed by SKB Site descriptive models SKB 2008 focusing on the present state of the site were developed and then used as a starting point for repository design environmental impact assessment and the assessment of longterm radiological safety SKB 2011 which were all important parts of the submitted applicationQuantification of hydrological processes was a central component in many parts of the safety assessment of the planned repository including the analysis of the conditions within the repository tunnels and deposition holes the quantification of radionuclide transport from the repository to the biosphere and the calculations of radiation doses in the biosphere Therefore a set of different hydrological/hydrogeological models focusing on different processes issues or parts of the hydrological system were developed during the site investigations and the safety assessment of the spent fuel repository Specifically surface hydrology/nearsurface hydrogeology models Johansson 2008 Bosson et al 2008 2010 were developed for the surface system/biosphere description and bedrock hydrogeology models Follin 2008 Selroos and Follin 2010 were developed for the geosphere/repository description Meteorological and hydrological data from the site investigations at Forsmark have been used also in a number of scientific studies addressing hydrological and solute transport issues not directly related to nuclear waste eg Jarsjö et al 2008 Juston et al 2009 Destouni et al 2010 These studies have contributed to the site understanding and provided support to the conceptual and numerical modeling performed by SKB Recently modeling studies of future hydrological conditions at Forsmark have been reported by Bosson et al 2012a bThe present study utilizes extends and analyses simulation results reported by Bosson et al 2008 2010 Compared with most other hydrological studies it considers a relatively long time period from today until 10 000 ad This means that some longterm processes that usually can be ignored in model development are potentially of importance in the hydrological modeling In particular the Forsmark site is situated on the Baltic Sea coast at a location where shoreline displacement takes place at a rate implying that this process needs to be taken into account within the time frame under consideration Lindborg 2010 Lindborg et al 2013 Available shoreline displacement modeling results see SKB 2010 for a discussion show that new land areas will be created outside the present coastline during the considered time period Lakes and streams are formed in depressions in the former sea bottom and will undergo the same succession from lakes to wetlands and possibly further to agricultural areas or forests as can be observed in the present land areas Lindborg et al 2013 In the model development presented here future shoreline locations and landscape succession are considered together with associated changes in regolith distribution and stratigraphy due to processes such as wave action and sedimentation climate and vegetationA main objective of this study is to present a methodology for sitespecific model development and application of model results in safety assessment calculations We also wish to analyze further some aspects of the modeling believed to be of particular importance and general interest Specifically the model calibration based on measured and modeled data for present conditions the development of models for future hydrological conditions and the application of hydrological model results in the compartment model used in radionuclide transport and radiation dose calculations are discussed in the paperCandidate and priority areas see text considered in the Forsmark site investigations and modeling for the planned spent fuel repository The main lakes eg Lake Bolundsfjärden and sea bays eg Asphällsfjärden are also indicated The graycolored area in the upper left corner is the Forsmark nuclear power plant and ‘SFR’ indicates the existing repository for shortlived radioactive waste

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