Preliminary use of RELAP5 Code with Internal Assessment of Uncertainty

The present work deals with the preliminary use of the RELAP5 code with the internal assessment of the uncertainty. The activity has been started as a follow up of the research leading to the proposal and applicability of UMAE (Uncertainty Methodology base on Accuracy Extrapolation) uncertainty methodology. The concept of hypercube to characterize the status of a LWR plant during any transient and the assumption of uncertainty connected with the hypercubes are adopted: the CIAU (Code with Internal Assessment of Uncertainty) method has been set up. In the frame of the activity of CIAU development, matrix and a vector for uncertainty have been obtained; three type of matrixes and vectors are utilized: 1. matrix and vector deriving from tests results qualified by UMAE conditions; 2. matrix and vector deriving from tests results obtained from several sources (UMAE et not UMAE qualified) 3. matrix and vector used only for testing purposes (not derived from a physical process) are derived to evaluate the uncertainty connected with a generic time trend calculated by the code. The present paper describes an application of matrix and vector at item 3. (author)