DIPE: Determination of input parameters uncertainties methodology applied to CATHARE V2.5-1

Since the revision of the 10 CFR50.46 in 1988, the best-estimate codes may be used in safety demonstration and licensing, provided that uncertainties are added to the relevant output parameters before comparing them with the acceptance criteria. The uncertainty of output parameters comes principally from the lack of knowledge of the input parameters (initial and boundary conditions of the calculated transient, empirical models of the code, etc.). The application of the best estimate plus uncertainty analysis can be made in three steps in a statistical evaluation: 1. The determination of the input parameters (IP) statistical characteristics. 2. The modelling and understanding of the output parameters. 3. The evaluation of the 95th percentile with a high degree of confidence. The first step is generally done manually according to expert judgments and comparing experimental data. The user effect is also very important in the determination of the statistical characteristics: range of variation and probability law. To reduce this user effect and to help the experts in their evaluation, IRSN has been developing a fully automated methodology and approach. This methodology is called DIPE: Determination of Input Parameters uncertaintiEs. This paper presents the advantages and limits of the application of DIPE for the physical models input parameters of CATHARE V2.5-1, a thermal-hydraulics code used in safety demonstration. DIPE will be applied to separate effect tests data used in the code qualification such as CANON and MARVIKEN. (author)