2012:32 Technical Note, Groundwater Chemistry in SKB’s Safety Assessment SR-Site: Initial Review

This preliminary review of SR-Site is focused specifically on the treatment of groundwater chemistry in the description of the Forsmark site and in the long-term safety of a deep geological repository at Forsmark.  Data for the chemical and isotopic compositions of groundwaters have contributed to a site descriptive model (SDM) for Forsmark.  In that SDM, groundwater chemistry is interpreted for several purposes.  The main outputs are the description of present-day chemical conditions in rocks at the target depth for a repository and an interpretation of how the present-day groundwater system has evolved over the long-term due to the effects of environmental changes on groundwater movements.

Groundwater chemistry data and interpretations in the SDM have contributed to the development of the SR-Site assessment of long-term safety of a future repository.  That requires a reliable and adequate understanding of how near-field chemistry around the engineered barriers might change over time and what reactions with rock will moderate potential perturbations and natural changes.  For the case that radionuclides are released from the repository into the surrounding groundwaters, the compositions of groundwaters may also affect how radionuclides are transported through the bedrock.

SKB confidence about groundwater chemistry aspects of SR-Site is generally supported by the data, interpretations and models.  There are a number of issues about the data, interpretations and models that could mean that future groundwater chemistry conditions would possibly lie outside the parameter range that is described in SR-Site; whether these additional uncertainties are negligible or otherwise for the safety case is yet to be evaluated.