Nuclear Engineering and Design 236 (2006) 2452–2473 Comparison of the transient behaviour of LBE-and gas-cooled experimental accelerator-driven systems K. Mikityuk a,∗ , P. Coddington a , E. Bubelis a , R. Chawla a,b a Laboratory for Reactor Physics and Systems Behaviour Paul Scherrer Institute, 5232 Villigen PSI, Switzerland b Ecole Polytechnique F´ ed´ erale de Lausanne (EPFL), 1015 Lausanne, Switzerland Received 22 November 2005; received in revised form 15 March 2006; accepted 16 March 2006 Abstract The paper presents a comparison of transient calculations for two 80-MWt MOX-fuelled experimental accelerator-driven systems (XADS), one cooled by lead-bismuth eutectic and the other by helium. The results for protected (with accelerator beam trip) and unprotected (without accelerator beam trip) transient overpower, spurious beam trip, loss of flow, loss of heat sink, and loss of coolant accidents, as well as the failure of heat exchanger tubes, are analysed for the two systems. The analysis was performed using TRAC/AAA, which is part of the PSI FAST code system. The advantages and shortcomings of the two designs from the viewpoint of their transient behaviour are discussed. © 2006 Elsevier B.V. All rights reserved. 1. Introduction Within the fifth Frame-Work Program of the E.U., the Pre- liminary Design Study of an eXperimental Accelerator-Driven System (PDS-XADS) project was focused on the study of three alternative systems: two 80 MWt design options, with (1) a lead bismuth eutectic (LBE)-cooled core (Cinotti and Gherardi, 2002) and (2) a gas (helium)-cooled core (Giraud, 2003), and the 50 MWt LBE-cooled MYRRHA concept (Abderrahim and D’Hondth, 2005). All three designs were considered to be driven by a neutron spallation source resulting from a 600 MeV proton accelerator beam impacting an LBE windowless target. One of the work packages of the PDS-XADS project was concerned with the assessment of the safety of the two 80 MWt designs (Coddington et al., 2004), with the following main objectives: • Develop an integrated safety approach common to both the LBE- and the gas-cooled concepts; • Identify the main XADS safety issues along with their phe- nomenology and develop an evaluation methodology for both alternatives; ∗ Corresponding author. Tel.: +41 56 3102385; fax: +41 56 3102327. E-mail address: konstantin.mikityuk@psi.ch (K. Mikityuk). • Perform transient analyses and produce safety analysis reports with identification of the design features required to meet the XADS safety objectives. A separate work package of the PDS-XADS project consid- ered the design and safety of the third XADS design, i.e. the 50 MWt LBE-cooled, MYRRHA concept. In this paper, representative results of the transient analyses performed at PSI, as a contribution to the PDS-XADS study for two 80 MWt XADS designs (Cinotti and Gherardi, 2002 and Giraud, 2003), are discussed. The list of transients considered includes transient overpower (TOP), spurious beam trip (BT), loss of flow (LOF), loss of heat sink (LOHS), and loss of coolant accidents (LOCA). In most cases, both protected (with acceler- ator beam trip) and unprotected (without accelerator beam trip) events have been simulated. The failure of the heat exchanger tubes (HXR), leading to secondary fluid penetration into the pri- mary system was also considered. The transients were simulated using the TRAC/AAA code (Spore et al., 2001), which is a part of the FAST code system (Mikityuk et al., 2005) being devel- oped at PSI for the comprehensive safety analysis of advanced fast-spectrum reactors. Benchmarking and assessment of the FAST code system for application to heavy liquid metal and gas cooled reactors is reported in (Mikityuk et al., 2005), which includes in par- ticular an assessment against the TALL facility (a small scale 0029-5493/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.nucengdes.2006.03.012