REGULATORY ASSESSMENT OF A SPENT FUEL REPOSITORY AT THE FORSMARK SITE SWEDEN; EVOLUTION OF GROUNDWATER SITE CONDITIONS

摘要

On the 16 march 2011 the Swedish Nuclear Fuel and Waste Management Company submitted a license application for the construction of a KBS-3 spent fuel repository at the Forsmark site in Sweden, which is currently being reviewed by the Swedish Radiation Safety Authority. The application concerns the KBS-3 disposal method, which is based on containment of spent fuel in cast iron insert /copper canisters placed in deposition holes at about 450 m depth in granitic rock. Each canister is surrounded by a 30 cm thick buffer of bentonite clay. This paper provides an overview of scientific and regulatory issues related to SKB's modelling of hydrogeology and groundwater chemistry with the purpose of scrutinizing the basis for SKB 's corrosion failure analysis in the post-closure safety assessment. The corrosion failure analysis includes the advection corrosion case that involves chemical erosion of the buffer that may result from interaction with very dilute groundwater. The removal of buffer material through erosion may lead to enhanced corrosion of the copper canister shells by groundwater sulphide. The review findings presented in this paper mainly reflect the outcome of a number of external experts' reviews and from SSM's independent modelling of site hydrogeology. The assessment of the advection corrosion case in the licensing review has proven to be a challenging task due to its broad scope, complexity and multidisciplinary nature. Further, the compliance demonstration is based on spatial and temporal variability of both groundwater flow rates and groundwater composition in a deposition-hole scale, which both have a large impact on the modelling results. Regulatory scrutiny therefore needs to focus on the derivation of probability distribution functions for these variables.