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Science and Technology of Nuclear Installations
Volume 2009 (2009), Article ID 768947, 18 pages
Research Article

Application of REPAS Methodology to Assess the Reliability of Passive Safety Systems

Nuclear Research Group San Piero a Grado (GRNSPG), Department of Mechanics, Nuclear and Production Engineering, University of Pisa, via Diotisalvi, 2 56100 Pisa, Italy

Received 9 December 2008; Accepted 3 August 2009

Academic Editor: Xu Cheng

Copyright © 2009 Franco Pierro et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The paper deals with the presentation of the Reliability Evaluation of Passive Safety System (REPAS) methodology developed by University of Pisa. The general objective of the REPAS is to characterize in an analytical way the performance of a passive system in order to increase the confidence toward its operation and to compare the performances of active and passive systems and the performances of different passive systems. The REPAS can be used in the design of the passive safety systems to assess their goodness and to optimize their costs. It may also provide numerical values that can be used in more complex safety assessment studies and it can be seen as a support to Probabilistic Safety Analysis studies. With regard to this, some examples in the application of the methodology are reported in the paper. A best-estimate thermal-hydraulic code, RELAP5, has been used to support the analyses and to model the selected systems. Probability distributions have been assigned to the uncertain input parameters through engineering judgment. Monte Carlo method has been used to propagate uncertainties and Wilks' formula has been taken into account to select sample size. Failure criterions are defined in terms of nonfulfillment of the defined design targets.