Mechanisms governing the release of radionuclides from spent nuclear fuel in geological repository: Major outcomes of the European Project SFS

The aim of the research project "Spent Fuel Stability under repository conditions" (SFS) within the 5th FWP was to develop a common understanding of the radionuclide release from spent nuclear fuel in geological disposal and to build a RN release model in order to assess the fuel performance, focusing on an Instant Release Fraction (IRF) model and the Matrix Alteration Model (MAM). A new IRF model was developed based on the anticipated performances of the various fuel microstructures (gap, rim, grains boundaries) and the potential diffusion of RN before the canister breaching. To further develop the matrix alteration model, a large set of experimental data was acquired in order (i) to upgrade the current radiolytic kinetic scheme, (ii) to experimentally correlate the fuel alteration rate and the fuel alpha activity, (iii) to experimentally test the potential inhibitor effect of hydrogen on fuel dissolution. A new MAM was developed, which was calibrated using the experiments on inactive UO2 samples. This model was finally applied to representative granitic, salt and clayey environment to predict spent fuel long-term fuel performance.