Within the Fifth Framework Programme of the European Union (EU), the PDS-XADS project is focused on Preliminary Design Studies of an Experimental Accelerator-driven Reactor System (ADS). Three basic designs are being studied in detail – two ADS design options, one with a lead-bismuth eutectic (LBE) cooled core (an 80 MWth unit and a smaller unit) and another (80 MWth) with a gas (helium) cooled core. One part of the PDS-XADS project involves the assessment of the safety of the two 80 MWth designs. The main objectives are as follows: develop an integrated safety approach common to both the LBE and the gas-cooled concepts; identify the main safety issues in an XADS with their phenomenology and develop an evaluation methodology for both alternatives; and perform transient analyses with the aim of producing safety analysis reports on the design features required to meet XADS safety objectives.