Best Estimate Plus uncertainty (BEPU) approach for accident analysis

The Best Estimate Plus Uncertainty (BEPU) constitutes an approach or a procedure aimed at making feasible the application of nuclear thermal-hydraulics to the licensing and the safety evaluation processes of Nuclear Power Plants. The features of BEPU are such to make attractive the application to address any design and operational issue in NPP technology. Three main parts can be distinguished in the present paper: a) Introduction, bases and background for BEPU also creating the connection with other chapters of the book; b) Identification of the main elements of BEPU; c) Envisaged developments for the BEPU concepts. On the one hand the BEPU related one shall be considered as a mature technology within nuclear thermal-hydraulics; on the other hand there is wide room for expanding the role of the BEPU to the overall nuclear reactor safety assessment. Therefore, BEPU application results to cases of industrial interest are presented as well as envisaged developments involving either a deep role of Probabilistic Safety Assessment, or the shift of the current boundaries of BEPU applicability from the thermal-hydraulics of nuclear accidents to any area in nuclear reactor safety where analytical techniques are needed. The key achievement from the present paper is providing the reader with an idea of the meaning and the importance of BEPU: this implies a multiple-entry and a multiple-target roadmap which makes possible the exploitation of findings in nuclear thermal-hydraulics in nuclear reactor design and safety.