Hindawi Publishing Corporation Science and Technology of Nuclear Installations Volume 2012, Article ID 173637, 19 pages doi:10.1155/2012/173637 Research Article SPES3 Facility RELAP5 Sensitivity Analyses on the Containment System for Design Review Andrea Achilli, 1 Cinzia Congiu, 1 Roberta Ferri, 1 Fosco Bianchi, 2 Paride Meloni, 2 Davor Grgi´ c, 3 and Milorad Dzodzo 4 1 SIET S.p.A., UdP, Via Nino Bixio 27/c, 29121 Piacenza, Italy 2 ENEA, UTFISSM, Via Martiri di Monte Sole 4, 40129 Bologna, Italy 3 FER, University of Zagreb, Unska 3, 10000 Zagreb, Croatia 4 Research and Technology Unit, Westinghouse Electric Company LLC, Cranberry Township, PA 16066, USA Correspondence should be addressed to Roberta Ferri, ferri@siet.it Received 11 March 2011; Accepted 27 July 2011 Academic Editor: Alessandro Del Nevo Copyright © 2012 Andrea Achilli 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. An Italian MSE R&D programme on Nuclear Fission is funding, through ENEA, the design and testing of SPES3 facility at SIET, for IRIS reactor simulation. IRIS is a modular, medium size, advanced, integral PWR, developed by an international consortium of utilities, industries, research centres and universities. SPES3 simulates the primary, secondary and containment systems of IRIS, with 1:100 volume scale, full elevation and prototypical thermal-hydraulic conditions. The RELAP5 code was extensively used in support to the design of the facility to identify criticalities and weak points in the reactor simulation. FER, at Zagreb University, performed the IRIS reactor analyses with the RELAP5 and GOTHIC coupled codes. The comparison between IRIS and SPES3 simulation results led to a simulation-design feedback process with step-by-step modifications of the facility design, up to the final configuration. For this, a series of sensitivity cases was run to investigate specific aspects affecting the trend of the main parameters of the plant, as the containment pressure and EHRS removed power, to limit fuel clad temperature excursions during accidental transients. This paper summarizes the sensitivity analyses on the containment system that allowed to review the SPES3 facility design and confirm its capability to appropriately simulate the IRIS plant. 1. Introduction The IRIS reactor, with its integral design, is an advanced engineering solution of the latest LWR technology. Medium- sized, safe, modular, and economic, it provides a viable bridge to generation IV and satisfies the GNEP requirements for grid-appropriate NPPs [1–3]. In the frame of an R&D program on nuclear fission, funded by the Italian Ministry of Economic Development, ENEA, as member of the IRIS consortium, is supporting the design, construction, and testing of the SPES3 ITF at SIET laboratories [4–6]. The SPES3 design was carried out following the subse- quent steps: (a) definition of a preliminary facility design, based on specified system geometry; (b) setup of the RELAP5 facility model and DBA simulation; (c) comparison of SPES3 and IRIS results against the same transient; (d) identification of the main differences and understanding of related reasons; (e) FSA application to selected thermo- fluid-dynamic parameters in order to assess and quantify the discrepancies; (f) updating of the SPES3 design to match the IRIS behaviour; (g) final result comparison; (h) final FSA application and assessment of acceptability criteria for considering SPES3 correctly simulating IRIS. The above-mentioned process allowed to verify the SBLOCA PIRT objectives for the IRIS reactor, as defined by a group of international experts [7]. The Phenomena Iden- tification and Ranking Table put in evidence the thermal- hydraulic phenomena playing an important role in operation of IRIS safety systems. Two figures of merit were considered fundamental for the accident sequence control: containment pressure and reactor vessel mass inventory. Sufficient water in the vessel allows to remove stored energy, and decay heat without fuel clad temperature excursions and adequate heat