The reliability requirements of the XT-ADS and EFIT accelerator

An Accelerator Driven System (ADS) for transmutation of nuclear waste typically requires a 600 MeV - 1 GeV accelerator delivering a proton flux of a few mA for demonstrators (XT-ADS), and a few tens of mA for large industrial systems (EFIT). Such a machine belongs to the category of the high-power proton accelerators, with an additional requirement for exceptional 'reliability': because of the induced thermal stress to the subcritical core, the number of unwanted 'beam-trips' should not exceed a few per year, a specification that is far above usual performance. To reach such reliability levels, several guidelines have been followed during the conceptual design phase of the ADS accelerator, including in particular derating of components, redundancy for critical systems, and capability to sustain operation during most of the RF breakdowns ('fault tolerance'). Dedicated R and D is performed on this topic within the EUROTRANS programme, and the main results obtained so far will be briefly presented. (author)