On the uncertainty of a model or a method. From the viewpoint of core-monitoring

In case of any model of a physical process it is always a central question how close the model is to reality. A model usually provides a relatively large set of parameters and it can operate under a wide range of conditions. Unfortunately, there is neither a generally accepted methodology to estimate the model uncertainty nor an unambiguous mathematical definition of this uncertainty. One gets even more confused when a method combines information from measurements with data provided by a mathematical model. Unfortunately, in case of the on-line core-monitoring we face exactly this situation. The goal is to outline the ambiguity of the uncertainty and to provide some practical guidelines on how an uncertainty analysis can be carried out for a core-monitoring system. (author). 2 figs