Criticality Safety Assessment for a Conceptual High-Level-Waste Repository in Water-Saturated Geologic Media

An assessment for the criticality safety of a conceptual repository for vitrified high-level radioactive waste from reprocessed fuel of commercial light water reactors in a water-saturated granitic rock has been performed by quantitatively estimating the mass of fissile ²³⁵U existing in the entire far field as the performance measure. The uncertainties associated with the performance measure have been obtained by a statistical analysis with the Latin hypercube sampling method.

With the assumed probability distribution functions for the model parameters, the mass of ²³⁵U released from the repository and existing in the far field at 100 million years is estimated to be <40 kg with a 90% confidence level. This implies that all ²³⁵U existing in the entire far field at that time must accumulate in a single location for an overmoderated criticality event to occur in granitic rock.