ABSTRACTThe use of computer simulations in the performance assessment for a
repository for spent nuclear fuel, are in many cases the only method to get
information on how the rock-repository system will work. One important
factor is the solubility of the elements released if the repository is
breached. This solubility may be determined experimentally or simulated.
Ifit is simulated, several factors such as thermodynamical uncertainties
will affect the reliability of the results. If these uncertainties are
assumed to be small, the composition of the water used in the calculations
may play a major part in the uncertainties in solubility. The water
composition, in tum, is either determined experimentally or calculated
through water-rock interactions. Thus, if the mineral composition of the
rock is known, it is possible to foresee the water composition. However, in
most cases a determination of the rock composition is made from drilling
cores and is thus quite uncertain. Therefore, if solubility calculations are
to be based on water properties calculated from rock-water interactions
another uncertainty is introduced. This paper is focused on uncertainty and
sensitivity analysis of rock-water interaction simulations and the
uncertainties thus obtained are propagated through a program making
uncertainty and sensitivity analysis of the solubility calculations. In both
cases the latin hypercube sampling technique have been used. The results
show that the solubilities are in most cases log normal distributed while
the different elements in the simulated groundwater in some cases diverge
significantly from such a distribution. The numerical results are comforting
in that the uncertainty intervals of the solubilities are rather small, i.e.
up to 30%.
Use of Replicated Latin Hypercube Sampling to Estimate Sampling Variance in Uncertainty and Sensitivity Analysis Results for the Geologic Disposal of Radioactive Waste