Instant Release Fraction (Source and Expert ranges) for SFC-1: UOX 50 and 60 GWd/tHM MOX 50 GWd/tHM. Status 2011

Belgium and elsewhere, it is necessary to have sufficient knowledge about the rate and mechanisms by which the spent fuel will release its radionuclide inventory into the environment. Most of the inventory will be released slowly on a geological time scale, but a certain fraction may be released at high rate shortly after contact with ground water. The fraction that is released fast for today’s fuels can be measured experimentally, and will be called ‘accessible fraction of inventory’ (AFI) in the terminology of SFC-1. The AFI values are thus purely experimental data. The estimation of the fast release at the time of the canister breaching builds further on the knowledge about the AFI of todays’s fuels, but also involves an evaluation of hypotheses about the further evolution of the fuel. The resulting values for the released fractions are intended for use in performance assessment calculations, and are called ‘instant release fraction’ (IRF). In literature, the distinction between experimental and extrapolated data is often unclear. For SFC-1, the distinction will be made more explicitly. This report summarizes related literature data, focussing on IRF data, while another report is devoted to the AFI [ER-0407].