Sorption of radionuclides on host rocks is a key process in the safe geological disposal of radioactive waste. For performance assessment (PA) calculations, the magnitude of sorption, expressed normally by a distribution coefficient (Kd), needs to be determined taking into account the rock types and geochemical conditions and associated uncertainty. The Kd setting approach is needed to apply for various rock types and geochemical conditions, and to evolve from site-generic to site-specific

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... s by considering site-specific information obtained in forthcoming site investigation stage. Such comprehensive Kd setting approach applicable for various conditions and situations was developed based on international state of the art knowledge by integrating three different methods; i) direct use of measured Kd data extracted from the sorption database, ii) transferring procedures by scaling differences between experimental and PA conditions, and iii) thermodynamic sorption models. This integrated approach was tested for crystalline host rock (granitic rock) by comparing example derivation of Kd values and their uncertainties of Cs and Am by the three different methods. The results indicated that the integrated Kd setting approach is effective, and that Kd can be quantitatively evaluated by all approaches when adequate data and models are available. The Kd dataset for key safety-relevant 25 elements in PA calculation for generic granitic rocks was developed based on the direct use of measured data, and compared with the recent Kd dataset in European PA projects. This Kd setting approach allows to estimate the Kd values and their uncertainties for various rock types and geochemical conditions in accordance with the amount of site-specific information in a stepwise manner.