Browsing by Author "Kupiainen, Pekka"

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    Growing oxide trilayers using pulsed laser deposition
    (2013-05-23) Kupiainen, Pekka; Van Dijken, Sebastiaan; Perustieteiden korkeakoulu; Van Dijken, Sebastiaan
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    Simplified concepts in modelling a multi-barrier radioactive waste disposal system and biosphere using probabilistic methods
    (2014-09-30) Kupiainen, Pekka; Nummi, Olli; Eurajoki, Tapani; Perustieteiden korkeakoulu; Tuomisto, Filip
    In Finland, the disposal system for spent nuclear fuel is based on a nested barrier system where barriers are designed to confine and limit possible radionuclide release rates into the biosphere. A postulated leak in a waste canister is used to assess the performance of the individual barriers. The radionuclide migration is depicted by using a simplified solute transport model that is an alternative approach compared to numerical modelling used largely in the performance assessments. An earlier simplified model is extended by introducing both a simplified biosphere analysis and a probabilistic simulation in order to estimate the radiological consequences of the disposal. In the simplified model, the radionuclide migration is calculated by using an analogy to a branching radioactive decay chain. The time constants of the model are solute half-times and delay times in the release barriers and biosphere compartments. A dose assessment is performed based on the resulting radionuclide inventories in the biosphere compartments. With a probabilistic simulation, initial data can be distributed and confidence levels for the release rates or dose rates can be determined. A simulation with seven nuclides (C-14, Cl-36, Se-79, Mo-93, Nb-94, Ag 108m, I-129) using the simplified model and chosen parameter distributions and correlations reveal that the distributions for results (time constants, dose rates, release rates) are roughly log-normal or log-uniform. The median total dose rate (50 % confidence level) and cautious 95 % confidence level have about two orders of magnitude difference at most during the 10 millennia time scope. The parameters with the largest uncertainty do not affect the final result if they are not related to the most significant barriers of the system (canister or buffer). The simplified model performs well for the geosphere transport but overestimates the results of the biosphere analysis compared to earlier results with similar parameters.