Waste packages often contain wastes forms of different types of spent fuels and of various operational history, whereas information about secondary reactor parameters may not be available. In this case the so-called characteristic fuel burn-up and cooling time are determined. These values are obtained from a correlations involving key-nuclides (easy-to-measure nuclides). Each correlation is associated with corresponding uncertainty bandwidth. The bandwidth strongly depends on secondary reactor parameters such as initial enrichment, temperature and density of the fuel and moderator, reactor‘s operational history. The purpose of our investigation is to understand the limitations of the scaling and correlations, to define and verify the range of validity, and to scrutinize the dependencies and propagation of uncertainties that affect the waste inventory declarations and their independent verification. This is accomplished by numerical assessment and simulation of the waste production processes using the widely accepted codes SCALE 6.0 and 6.1 to simulate the cooling time and burn-up of a spent fuel element
