Following the choice of the phenomenon,, and of relevant experiment, a first step of the activity consisted in evaluating an experimental data base including comparisons among the hardware data and initial conditions of the facilities and tests involved. This essentially led to the identification of the relevant events and parameters of phenomenon considered. By adopting the methodology based on the extrapolation of the code accuracy ,uncertainty ranges were established that characterise the calculation of the considered CHF phenomenon in the plant. In order to achieve this, a special method was applied to identify and to group the different ways in which the CHF phenomena can occur. Accuracy is related to the comparison between calculated and experimental data, and is a measurement of the difference between experimental and calculated data.
Uncertainty is related to the prediction of incidental scenarios in the nuclear power plant.
It is an a indication of the error in the evaluation of the different parameters during the transient. Our methodology, aiming at the evaluation of uncertainty, is based on the extrapolation of accuracy. Both for the first and the second dry-out, the error of the code is included in the range predicted by the methodology. However, it must be note that the range predicted for uncertainty is quite large.