2014:29 Technical Note, Independent Modelling of Radionuclide Transport, Evaluation of Colloid Transport Modelling – Main Review Phase

SKB excludes consideration of colloids originating inside the canister in its performance assessment on the basis of the filtration capability of the buffer material.  In the canister failure by corrosion scenario (central corrosion case), the buffer material is assumed eroded, and the filtration argument is not entirely valid for excluding modelling in-canister colloids.  In this Technical Note, we evaluate the relevance of colloids to dose estimates, including the eroded buffer case. 

Modelling radionuclide attachment to clay colloids as reversible linear equilibrium sorption (i.e., using a Kd distribution factor approach) is reasonable and well supported.  Nonetheless, in this Technical Note we examine the effect of both reversible attachment and permanent attachment to colloids (radionuclides forming true colloids or with zero desorption rates from colloids).  We found that reversible attachment would be more influential to dose estimates in the central corrosion case, and colloids, in general, would have a minor effect on dose estimates in the canister failure by shear load scenario.